AMEREN CORP, 10-K filed on 2/28/2017
Annual Report
Document And Entity Information (USD $)
12 Months Ended
Dec. 31, 2016
Jan. 31, 2017
Jun. 30, 2016
Document Type
10-K 
 
 
Amendment Flag
false 
 
 
Document Period End Date
Dec. 31, 2016 
 
 
Document Fiscal Year Focus
2016 
 
 
Document Fiscal Period Focus
FY 
 
 
Trading Symbol
AEE 
 
 
Entity Registrant Name
AMEREN CORP 
 
 
Entity Central Index Key
0001002910 
 
 
Current Fiscal Year End Date
--12-31 
 
 
Entity Filer Category
Large Accelerated Filer 
 
 
Entity Common Stock, Shares Outstanding
 
242,634,798 
 
Entity Voluntary Filers
No 
 
 
Entity Current Reporting Status
Yes 
 
 
Entity Public Float
 
 
$ 13,000,372,477 
Entity Well-known Seasoned Issuer
Yes 
 
 
Union Electric Company
 
 
 
Document Type
10-K 
 
 
Amendment Flag
false 
 
 
Document Period End Date
Dec. 31, 2016 
 
 
Document Fiscal Year Focus
2016 
 
 
Document Fiscal Period Focus
FY 
 
 
Trading Symbol
AEE 
 
 
Entity Registrant Name
UNION ELECTRIC CO 
 
 
Entity Central Index Key
0000100826 
 
 
Current Fiscal Year End Date
--12-31 
 
 
Entity Filer Category
Non-accelerated Filer 
 
 
Entity Common Stock, Shares Outstanding
 
102,123,834 
 
Entity Voluntary Filers
No 
 
 
Entity Current Reporting Status
Yes 
 
 
Entity Well-known Seasoned Issuer
No 
 
 
Ameren Illinois Company
 
 
 
Document Type
10-K 
 
 
Amendment Flag
false 
 
 
Document Period End Date
Dec. 31, 2016 
 
 
Document Fiscal Year Focus
2016 
 
 
Document Fiscal Period Focus
FY 
 
 
Trading Symbol
AEE 
 
 
Entity Registrant Name
Ameren Illinois Co 
 
 
Entity Central Index Key
0000018654 
 
 
Current Fiscal Year End Date
--12-31 
 
 
Entity Filer Category
Non-accelerated Filer 
 
 
Entity Common Stock, Shares Outstanding
 
25,452,373 
 
Entity Voluntary Filers
No 
 
 
Entity Current Reporting Status
Yes 
 
 
Entity Well-known Seasoned Issuer
Yes 
 
 
Consolidated Statement Of Income (Loss) (USD $)
In Millions, except Per Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Operating Revenues:
 
 
 
Electric
$ 5,196 
$ 5,180 
$ 4,913 
Gas
880 
918 
1,140 
Total operating revenues
6,076 
6,098 
6,053 
Operating Expenses:
 
 
 
Fuel
745 
878 
826 
Purchased power
621 
514 
461 
Gas purchased for resale
341 
415 
615 
Other operations and maintenance
1,676 
1,694 
1,684 
Provision for Callaway construction and operating license
0 
69 
0 
Depreciation and amortization
845 
796 
745 
Taxes other than income taxes
467 
473 
468 
Total operating expenses
4,695 
4,839 
4,799 
Operating Income
1,381 
1,259 
1,254 
Other Income and Expenses:
 
 
 
Miscellaneous income
74 1
74 1
79 1
Miscellaneous expense
32 1
30 1
22 1
Total other income (expense)
42 
44 
57 
Interest charges
382 
355 
341 
Income Before Income Taxes
1,041 
948 
970 
Income taxes
382 
363 
377 
Income from Continuing Operations
659 
585 
593 
Income (Loss) from Discontinued Operations, Net of Tax
0 
51 
(1)
Net Income (Loss)
659 
636 
592 
Pension and other postretirement activity, net of income taxes (benefit)
(20)
6 
(12)
Comprehensive Income (Loss)
633 
636 
574 
Less: Net Income (Loss) Attributable to Noncontrolling Interests:
 
 
 
Continuing Operations
6 
6 
6 
Net Income (Loss):
 
 
 
Net income attributable to Ameren Corporation - continuing operations
653 
579 
587 
Discontinued Operations
0 
51 
(1)
Net income attributable to Ameren common shareholders
653 
630 
586 
Earnings (Loss) per Common Share – Basic:
 
 
 
Continuing Operations - Basic
$ 2.69 
$ 2.39 
$ 2.42 
Discontinued Operations - Basic
$ 0.00 
$ 0.21 
$ 0.00 
Earnings (Loss) per Common Share – Basic
$ 2.69 
$ 2.60 
$ 2.42 
Earnings (Loss) per Common Share – Diluted:
 
 
 
Continuing Operations - Diluted
$ 2.68 
$ 2.38 
$ 2.40 
Discontinued Operations - Diluted
$ 0.00 
$ 0.21 
$ 0.00 
Earnings (Loss) per Common Share – Diluted
$ 2.68 
$ 2.59 
$ 2.40 
Dividends per Common Share
$ 1.715 
$ 1.655 
$ 1.61 
Average Common Shares Outstanding - Basic
242.6 
242.6 
242.6 
Average Common Shares Outstanding - Diluted
243.4 
243.6 
244.4 
Union Electric Company
 
 
 
Operating Revenues:
 
 
 
Electric
3,394 
3,470 
3,388 
Gas
128 
137 
164 
Other
1 
2 
1 
Total operating revenues
3,523 
3,609 
3,553 
Operating Expenses:
 
 
 
Fuel
745 
878 
826 
Purchased power
252 
111 
126 
Gas purchased for resale
49 
57 
82 
Other operations and maintenance
893 
925 
939 
Provision for Callaway construction and operating license
0 
69 
0 
Depreciation and amortization
514 
492 
473 
Taxes other than income taxes
325 
335 
322 
Total operating expenses
2,778 
2,867 
2,768 
Operating Income
745 
742 
785 
Other Income and Expenses:
 
 
 
Miscellaneous income
52 
52 
60 
Miscellaneous expense
10 
11 
12 
Total other income (expense)
42 
41 
48 
Interest charges
211 
219 
211 
Income Before Income Taxes
576 
564 
622 
Income taxes
216 
209 
229 
Net Income (Loss)
360 
355 
393 
Other Comprehensive Income
0 
0 
0 
Comprehensive Income (Loss)
360 
355 
393 
Net Income (Loss):
 
 
 
Preferred Stock Dividends
3 
3 
3 
Net Income Available to Common Stockholder
357 
352 
390 
Ameren Illinois Company
 
 
 
Operating Revenues:
 
 
 
Electric
1,736 
1,683 
1,522 
Gas
754 
783 
976 
Total operating revenues
2,490 
2,466 
2,498 
Operating Expenses:
 
 
 
Purchased power
399 
420 
343 
Gas purchased for resale
292 
358 
533 
Other operations and maintenance
804 
797 
771 
Depreciation and amortization
319 
295 
263 
Taxes other than income taxes
132 
130 
138 
Total operating expenses
1,946 
2,000 
2,048 
Operating Income
544 
466 
450 
Other Income and Expenses:
 
 
 
Miscellaneous income
21 
21 
17 
Miscellaneous expense
12 
12 
8 
Total other income (expense)
9 
9 
9 
Interest charges
140 
131 
112 
Income Before Income Taxes
413 
344 
347 
Income taxes
158 
127 
143 
Net Income (Loss)
255 
217 
204 
Pension and other postretirement activity, net of income taxes (benefit)
(5)
(3)
(3)
Comprehensive Income (Loss)
250 
214 
201 
Net Income (Loss):
 
 
 
Preferred Stock Dividends
3 
3 
3 
Net Income Available to Common Stockholder
$ 252 
$ 214 
$ 201 
Consolidated Statement Of Income (Loss) (Parenthetical) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Pension and other postretirement activity, tax (benefit)
$ (7)
$ 3 
$ (7)
Ameren Illinois Company
 
 
 
Pension and other postretirement activity, tax (benefit)
$ (1)
$ (2)
$ (2)
Consolidated Statement Of Comprehensive Income (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Income from Continuing Operations
$ 659 
$ 585 
$ 593 
Pension and other postretirement activity, net of income taxes (benefit)
(20)
6 
(12)
Comprehensive Income (Loss) from Continuing Operations
639 
591 
581 
Less: Comprehensive Income from Continuing Operations Attributable to Noncontrolling Interests
6 
6 
6 
Comprehensive Income from Continuing Operations Attributable to Ameren Corporation
633 
585 
575 
Comprehensive Income (Loss) from Discontinued Operations Attributable to Ameren Common shareholders
0 
51 
(1)
Comprehensive Income (Loss)
$ 633 
$ 636 
$ 574 
Consolidated Statement Of Comprehensive Income (Parenthetical) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Pension and other postretirement activity, tax (benefit)
$ (7)
$ 3 
$ (7)
Consolidated Balance Sheet (USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Dec. 31, 2015
Current Assets:
 
 
Cash and cash equivalents
$ 9 
$ 292 
Accounts receivable - trade (less allowance for doubtful accounts)
437 
388 
Unbilled revenue
295 
239 
Miscellaneous accounts and notes receivable
63 
98 
Inventories
527 
538 
Current regulatory assets
149 
260 
Other current assets
98 
88 
Assets of discontinued operations (Note 1)
15 
14 
Total current assets
1,593 
1,917 
Property, Plant and Equipment, Net
20,113 1
18,799 1
Investments and Other Assets:
 
 
Nuclear decommissioning trust fund
607 
556 
Goodwill
411 
411 
Regulatory assets
1,437 
1,382 
Other assets
538 
575 
Total investments and other assets
2,993 
2,924 
TOTAL ASSETS
24,699 
23,640 
Current Liabilities:
 
 
Current maturities of long-term debt
681 
395 
Short-term debt
558 
301 
Accounts and wages payable
805 
777 
Taxes accrued
46 
43 
Interest accrued
93 
89 
Customer deposits
107 
100 
Current regulatory liabilities
110 
80 
Other current liabilities
248 
279 
Liabilities of discontinued operations (Note 1)
26 
29 
Total current liabilities
2,674 
2,093 
Long-term Debt, Net
6,595 
6,880 
Deferred Credits and Other Liabilities:
 
 
Accumulated deferred income taxes, net
4,264 
3,885 
Accumulated deferred investment tax credits
55 
60 
Regulatory liabilities
1,985 
1,905 
Asset retirement obligations
635 
618 
Pension and other postretirement benefits
769 
580 
Other deferred credits and liabilities
477 
531 
Total deferred credits and other liabilities
8,185 
7,579 
Commitments and Contingencies (Notes 2, 10, 14 and 15)
   
   
Stockholders' Equity:
 
 
Common stock
2 
2 
Other paid-in capital, principally premium on common stock
5,556 
5,616 
Retained earnings
1,568 
1,331 
Accumulated other comprehensive income (loss)
(23)
(3)
Total stockholders' equity
7,103 
6,946 
Noncontrolling Interests
142 
142 
Total equity
7,245 
7,088 
TOTAL LIABILITIES AND EQUITY
24,699 
23,640 
Union Electric Company
 
 
Current Assets:
 
 
Cash and cash equivalents
0 
199 
Advances to money pool
161 
36 
Accounts receivable - trade (less allowance for doubtful accounts)
187 
174 
Accounts receivable - affiliates
12 
54 
Unbilled revenue
154 
128 
Miscellaneous accounts and notes receivable
14 
78 
Inventories
392 
387 
Current regulatory assets
35 
89 
Other current assets
49 
41 
Total current assets
1,004 
1,186 
Property, Plant and Equipment, Net
11,478 1
11,183 1
Investments and Other Assets:
 
 
Nuclear decommissioning trust fund
607 
556 
Regulatory assets
619 
605 
Other assets
327 
321 
Total investments and other assets
1,553 
1,482 
TOTAL ASSETS
14,035 
13,851 
Current Liabilities:
 
 
Current maturities of long-term debt
431 
266 
Accounts and wages payable
444 
417 
Accounts payable - affiliates
68 
56 
Taxes accrued
30 
31 
Interest accrued
54 
59 
Current regulatory liabilities
12 
28 
Other current liabilities
123 
120 
Total current liabilities
1,162 
977 
Long-term Debt, Net
3,563 
3,844 
Deferred Credits and Other Liabilities:
 
 
Accumulated deferred income taxes, net
3,013 
2,844 
Accumulated deferred investment tax credits
53 
58 
Regulatory liabilities
1,215 
1,172 
Asset retirement obligations
629 
612 
Pension and other postretirement benefits
291 
234 
Other deferred credits and liabilities
19 
28 
Total deferred credits and other liabilities
5,220 
4,948 
Commitments and Contingencies (Notes 2, 10, 14 and 15)
   
   
Stockholders' Equity:
 
 
Common stock
511 
511 
Other paid-in capital, principally premium on common stock
1,828 
1,822 
Preferred stock not subject to mandatory redemption
80 
80 
Retained earnings
1,671 
1,669 
Total stockholders' equity
4,090 
4,082 
TOTAL LIABILITIES AND EQUITY
14,035 
13,851 
Ameren Illinois Company
 
 
Current Assets:
 
 
Cash and cash equivalents
0 
71 
Accounts receivable - trade (less allowance for doubtful accounts)
242 
204 
Accounts receivable - affiliates
10 
22 
Unbilled revenue
141 
111 
Miscellaneous accounts and notes receivable
22 
19 
Inventories
135 
151 
Current regulatory assets
108 
167 
Other current assets
25 
15 
Total current assets
683 
760 
Property, Plant and Equipment, Net
7,469 
6,848 
Investments and Other Assets:
 
 
Goodwill
411 
411 
Regulatory assets
816 
771 
Other assets
95 
113 
Total investments and other assets
1,322 
1,295 
TOTAL ASSETS
9,474 
8,903 
Current Liabilities:
 
 
Current maturities of long-term debt
250 
129 
Short-term debt
51 
0 
Accounts and wages payable
264 
249 
Accounts payable - affiliates
63 
66 
Taxes accrued
16 
13 
Interest accrued
33 
28 
Customer deposits
69 
69 
Mark-to-market derivative liabilities
15 
45 
Environmental remediation
38 
28 
Current regulatory liabilities
78 
39 
Other current liabilities
94 
86 
Total current liabilities
971 
752 
Long-term Debt, Net
2,338 
2,342 
Deferred Credits and Other Liabilities:
 
 
Accumulated deferred income taxes, net
1,631 
1,480 
Accumulated deferred investment tax credits
2 
2 
Regulatory liabilities
768 
732 
Pension and other postretirement benefits
346 
271 
Accrued Environmental Loss Contingencies, Noncurrent
162 
205 
Other deferred credits and liabilities
222 
222 
Total deferred credits and other liabilities
3,131 
2,912 
Commitments and Contingencies (Notes 2, 10, 14 and 15)
   
   
Stockholders' Equity:
 
 
Common stock
0 
0 
Other paid-in capital, principally premium on common stock
2,005 
2,005 
Preferred stock not subject to mandatory redemption
62 
62 
Retained earnings
967 
825 
Accumulated other comprehensive income (loss)
0 
5 
Total stockholders' equity
3,034 
2,897 
TOTAL LIABILITIES AND EQUITY
$ 9,474 
$ 8,903 
Consolidated Balance Sheet (Parenthetical) (USD $)
In Millions, except Share data, unless otherwise specified
Dec. 31, 2016
Dec. 31, 2015
Accounts receivable - trade, allowance for doubtful accounts
$ 19 
$ 19 
Common stock, par value
$ 0.01 
$ 0.01 
Common stock, shares authorized
400,000,000 
400,000,000 
Common stock, shares outstanding
242,600,000 
242,600,000 
Union Electric Company
 
 
Accounts receivable - trade, allowance for doubtful accounts
7 
7 
Common stock, par value
$ 5 
$ 5 
Common stock, shares authorized
150,000,000 
150,000,000 
Common stock, shares outstanding
102,100,000 
102,100,000 
Ameren Illinois Company
 
 
Accounts receivable - trade, allowance for doubtful accounts
$ 12 
$ 12 
Common Stock, No Par Value
$ 0 
$ 0 
Common stock, shares authorized
45,000,000 
45,000,000 
Common stock, shares outstanding
25,500,000 
25,500,000 
Consolidated Statement Of Cash Flows (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Cash Flows From Operating Activities:
 
 
 
Net income (loss)
$ 659 
$ 636 
$ 592 
(Income) Loss from discontinued operations, net of tax
0 
(51)
1 
Adjustments to reconcile net income to net cash provided by operating activities:
 
 
 
Provision for Callaway construction and operating license
0 
69 
0 
Depreciation and amortization
835 
777 
710 
Amortization of nuclear fuel
88 
97 
81 
Amortization of debt issuance costs and premium/discounts
22 
22 
22 
Deferred income taxes and investment tax credits, net
386 
369 
451 
Allowance for equity funds used during construction
(27)1
(30)1
(34)1
Share-based Compensation
17 
24 
25 
Other
4 
(10)
(24)
Changes in assets and liabilities:
 
 
 
Receivables
(71)
83 
31 
Inventories
11 
(14)
3 
Accounts and wages payable
19 
(2)
10 
Taxes accrued
13 
(22)
(44)
Regulatory assets and liabilities
215 
94 
(281)
Assets, other
(24)
53 
30 
Liabilities, other
(10)
(44)
(14)
Pension and other postretirement benefits
(16)
(9)
(10)
Counterparty collateral, net
3 
(7)
22 
Net cash provided by operating activities - continuing operations
2,124 
2,035 
1,571 
Net cash provided by operating activities - discontinued operations
(1)
(4)
(6)
Net cash provided by operating activities
2,123 
2,031 
1,565 
Cash Flows From Investing Activities:
 
 
 
Capital expenditures
(2,076)
(1,917)
(1,785)
Nuclear fuel expenditures
(55)
(52)
(74)
Purchases of securities - nuclear decommissioning trust fund
(392)
(363)
(405)
Sales and maturities of securities - nuclear decommissioning trust fund
377 
349 
391 
Proceeds from Collection of Notes Receivable
0 
20 
95 
Contributions to Note Receivable
0 
(8)
(89)
Other
5 
20 
11 
Net cash used in investing activities - continuing operations
(2,141)
(1,951)
(1,856)
Net cash used in investing activities - discontinued operations
0 
(25)
139 
Net cash used in investing activities
(2,141)
(1,976)
(1,717)
Cash Flows From Financing Activities:
 
 
 
Dividends on common stock
(416)
(402)
(390)
Dividends paid to noncontrolling interest holders
(6)
(6)
(6)
Short-term debt, net
257 
(413)
346 
Maturities, redemptions, and repurchases of long-term debt
(395)
(120)
(697)
Issuances of Long-term debt
389 
1,197 
898 
Capital issuance costs
(9)
(12)
(11)
Share-based payments
(83)
(12)
(14)
Other
(2)
0 
1 
Net cash provided by (used in) financing activities
(265)
232 
127 
Net change in cash and cash equivalents
(283)
287 
(25)
Cash and cash equivalents at beginning of year
292 
5 
30 
Cash and cash equivalents at end of year
9 
292 
5 
Cash Paid (Refunded) During the Year:
 
 
 
Interest net of capitalized
358 
335 
333 
Income taxes, net
(12)
(15)
(27)
Union Electric Company
 
 
 
Cash Flows From Operating Activities:
 
 
 
Net income (loss)
360 
355 
393 
Adjustments to reconcile net income to net cash provided by operating activities:
 
 
 
Provision for Callaway construction and operating license
0 
69 
0 
Depreciation and amortization
506 
476 
442 
Amortization of nuclear fuel
88 
97 
81 
Amortization of debt issuance costs and premium/discounts
6 
6 
7 
Deferred income taxes and investment tax credits, net
179 
82 
245 
Allowance for equity funds used during construction
(23)
(22)
(32)
Other
5 
2 
3 
Changes in assets and liabilities:
 
 
 
Receivables
5 
72 
(10)
Inventories
(4)
(39)
8 
Accounts and wages payable
(18)
3 
25 
Taxes accrued
11 
1 
(197)
Regulatory assets and liabilities
84 
117 
(68)
Assets, other
(25)
26 
52 
Liabilities, other
(1)
4 
0 
Pension and other postretirement benefits
(4)
(2)
1 
Net cash provided by operating activities
1,169 
1,247 
950 
Cash Flows From Investing Activities:
 
 
 
Capital expenditures
(738)
(622)
(747)
Nuclear fuel expenditures
(55)
(52)
(74)
Purchases of securities - nuclear decommissioning trust fund
(392)
(363)
(405)
Sales and maturities of securities - nuclear decommissioning trust fund
377 
349 
391 
Money pool advances, net
125 
36 
0 
Other
(1)
0 
(2)
Net cash used in investing activities
(934)
(724)
(837)
Cash Flows From Financing Activities:
 
 
 
Dividends on common stock
(355)
(575)
(340)
Return of capital to parent
0 
0 
(215)
Dividends on preferred stock
(3)
(3)
(3)
Short-term debt, net
0 
(97)
97 
Money pool borrowings, net
0 
0 
(105)
Maturities, redemptions, and repurchases of long-term debt
(266)
(120)
(109)
Issuances of Long-term debt
149 
249 
350 
Capital issuance costs
(3)
(3)
(3)
Capital contribution from parent
44 
224 
215 
Net cash provided by (used in) financing activities
(434)
(325)
(113)
Net change in cash and cash equivalents
(199)
198 
0 
Cash and cash equivalents at beginning of year
199 
1 
1 
Cash and cash equivalents at end of year
0 
199 
1 
Noncash Or Part Noncash Capital Contribution From Parent
0 
38 
9 
Cash Paid (Refunded) During the Year:
 
 
 
Interest net of capitalized
209 
212 
203 
Income taxes, net
27 
72 
215 
Ameren Illinois Company
 
 
 
Cash Flows From Operating Activities:
 
 
 
Net income (loss)
255 
217 
204 
Adjustments to reconcile net income to net cash provided by operating activities:
 
 
 
Depreciation and amortization
318 
292 
259 
Amortization of debt issuance costs and premium/discounts
14 
14 
13 
Deferred income taxes and investment tax credits, net
154 
221 
196 
Allowance for equity funds used during construction
(4)
(8)
(2)
Other
(1)
(14)
(19)
Changes in assets and liabilities:
 
 
 
Receivables
(72)
16 
(13)
Inventories
15 
25 
(4)
Accounts and wages payable
12 
37 
7 
Taxes accrued
1 
(2)
(7)
Regulatory assets and liabilities
120 
(26)
(215)
Assets, other
(3)
17 
15 
Liabilities, other
(5)
(27)
1 
Pension and other postretirement benefits
(8)
(4)
(6)
Counterparty collateral, net
3 
(3)
14 
Net cash provided by operating activities
803 
763 
445 
Cash Flows From Investing Activities:
 
 
 
Capital expenditures
(924)
(918)
(835)
Other
6 
5 
7 
Net cash used in investing activities
(918)
(913)
(828)
Cash Flows From Financing Activities:
 
 
 
Dividends on common stock
(110)
0 
0 
Dividends on preferred stock
(3)
(3)
(3)
Short-term debt, net
51 
(32)
32 
Money pool borrowings, net
0 
(15)
(41)
Maturities, redemptions, and repurchases of long-term debt
(129)
0 
(163)
Issuances of Long-term debt
240 
248 
548 
Capital issuance costs
(4)
(3)
(6)
Capital contribution from parent
0 
25 
15 
Other
(1)
0 
1 
Net cash provided by (used in) financing activities
44 
220 
383 
Net change in cash and cash equivalents
(71)
70 
0 
Cash and cash equivalents at beginning of year
71 
1 
1 
Cash and cash equivalents at end of year
0 
71 
1 
Cash Paid (Refunded) During the Year:
 
 
 
Interest net of capitalized
127 
120 
110 
Income taxes, net
$ 8 
$ (113)
$ (44)
Consolidated Statement Of Cash Flows (Parenthetical) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Interest Paid, Capitalized
$ 15 
$ 17 
$ 18 
Union Electric Company
 
 
 
Interest Paid, Capitalized
12 
12 
16 
Ameren Illinois Company
 
 
 
Interest Paid, Capitalized
$ 3 
$ 5 
$ 2 
Consolidated Statement Of Stockholders' Equity (USD $)
In Millions, unless otherwise specified
Total
Common Stock
Other Paid-In Capital
Retained Earnings
Deferred Retirement Benefit Costs
Accumulated Other Comprehensive Income (Loss)
Noncontrolling Interest
Total Ameren Corporation Stockholders' Equity
Union Electric Company
Union Electric Company
Common Stock
Union Electric Company
Other Paid-In Capital
Union Electric Company
Preferred Stock Not Subject To Mandatory Redemption
Union Electric Company
Retained Earnings
Ameren Illinois Company
Ameren Illinois Company
Common Stock
Ameren Illinois Company
Other Paid-In Capital
Ameren Illinois Company
Preferred Stock Not Subject To Mandatory Redemption
Ameren Illinois Company
Retained Earnings
Ameren Illinois Company
Deferred Retirement Benefit Costs
Ameren Illinois Company
Accumulated Other Comprehensive Income (Loss)
Beginning of year at Dec. 31, 2013
 
$ 2 
$ 5,632 
$ 907 
$ 3 
 
$ 142 
 
 
 
$ 1,560 
 
$ 1,842 
 
 
$ 1,965 
 
$ 410 
$ 11 
 
Increase (Decrease) in Stockholders' Equity [Roll Forward]
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Stock-based compensation activity
 
 
(15)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Net income attributable to Ameren common shareholders
586 
 
 
586 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Net income (loss)
592 
 
 
 
 
 
 
 
393 
 
 
 
393 
204 
 
 
 
204 
 
 
Common stock dividends
 
 
 
(390)
 
 
 
 
 
 
 
 
(340)
 
 
 
 
0 
 
 
Capital contribution from parent
 
 
 
 
 
 
 
 
215 
 
224 
 
 
15 
 
15 
 
 
 
 
Return of capital to parent
 
 
 
 
 
 
 
 
215 
 
(215)
 
 
 
 
 
 
 
 
 
Preferred stock dividends
 
 
 
 
 
 
 
 
 
 
 
 
(3)
 
 
 
 
(3)
 
 
Change in deferred retirement benefit costs
12 
 
 
 
(12)
 
 
 
 
 
 
 
 
3 
 
 
 
 
 
(3)
Net income attributable to noncontrolling interest holder
 
 
 
 
 
 
6 
 
 
 
 
 
 
 
 
 
 
 
 
 
Dividends paid to noncontrolling interest holders
 
 
 
 
 
 
(6)
 
 
 
 
 
 
 
 
 
 
 
 
 
Stockholders' equity, end of year at Dec. 31, 2014
 
 
 
 
 
 
 
6,713 
4,052 
 
 
 
 
2,661 
 
 
 
 
 
 
End of year at Dec. 31, 2014
6,855 
2 
5,617 
1,103 
(9)
(9)
142 
 
 
511 
1,569 
80 
1,892 
 
0 
1,980 
62 
611 
8 
8 
End of year (shares) at Dec. 31, 2014
242.6 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Increase (Decrease) in Stockholders' Equity [Roll Forward]
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Net income attributable to Ameren common shareholders
108 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Net income (loss)
110 
 
 
 
 
 
 
 
42 
 
 
 
 
54 
 
 
 
 
 
 
Stockholders' equity, end of year at Mar. 31, 2015
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Beginning of year at Dec. 31, 2014
6,855 
2 
5,617 
1,103 
(9)
(9)
142 
 
 
511 
1,569 
80 
1,892 
 
0 
1,980 
62 
611 
8 
8 
Beginning of year (shares) at Dec. 31, 2014
242.6 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Increase (Decrease) in Stockholders' Equity [Roll Forward]
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Stock-based compensation activity
 
 
(1)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Net income attributable to Ameren common shareholders
630 
 
 
630 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Net income (loss)
636 
 
 
 
 
 
 
 
355 
 
 
 
355 
217 
 
 
 
217 
 
 
Common stock dividends
 
 
 
(402)
 
 
 
 
 
 
 
 
(575)
 
 
 
 
0 
 
 
Capital contribution from parent
 
 
 
 
 
 
 
 
224 
 
253 
 
 
25 
 
25 
 
 
 
 
Return of capital to parent
 
 
 
 
 
 
 
 
0 
 
0 
 
 
 
 
 
 
 
 
 
Preferred stock dividends
 
 
 
 
 
 
 
 
 
 
 
 
(3)
 
 
 
 
(3)
 
 
Change in deferred retirement benefit costs
(6)
 
 
 
6 
 
 
 
 
 
 
 
 
3 
 
 
 
 
 
(3)
Net income attributable to noncontrolling interest holder
 
 
 
 
 
 
6 
 
 
 
 
 
 
 
 
 
 
 
 
 
Dividends paid to noncontrolling interest holders
 
 
 
 
 
 
(6)
 
 
 
 
 
 
 
 
 
 
 
 
 
Stockholders' equity, end of year at Dec. 31, 2015
6,946 
 
 
 
 
 
 
6,946 
4,082 
 
 
 
 
2,897 
 
 
 
 
 
 
End of year at Dec. 31, 2015
7,088 
2 
5,616 
1,331 
(3)
(3)
142 
 
 
511 
1,822 
80 
1,669 
 
0 
2,005 
62 
825 
5 
5 
End of year (shares) at Dec. 31, 2015
242.6 
 
 
 
 
 
 
 
102.1 
 
 
 
 
25.5 
 
 
 
 
 
 
Beginning of year at Sep. 30, 2015
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Increase (Decrease) in Stockholders' Equity [Roll Forward]
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Net income attributable to Ameren common shareholders
29 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Net income (loss)
30 
 
 
 
 
 
 
 
11 
 
 
 
 
33 
 
 
 
 
 
 
Stockholders' equity, end of year at Dec. 31, 2015
6,946 
 
 
 
 
 
 
6,946 
4,082 
 
 
 
 
2,897 
 
 
 
 
 
 
End of year at Dec. 31, 2015
7,088 
2 
 
 
 
(3)
 
 
 
511 
 
80 
 
 
0 
 
62 
 
5 
 
End of year (shares) at Dec. 31, 2015
242.6 
 
 
 
 
 
 
 
102.1 
 
 
 
 
25.5 
 
 
 
 
 
 
Increase (Decrease) in Stockholders' Equity [Roll Forward]
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Net income attributable to Ameren common shareholders
105 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Net income (loss)
107 
 
 
 
 
 
 
 
15 
 
 
 
 
60 
 
 
 
 
 
 
Stockholders' equity, end of year at Mar. 31, 2016
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Beginning of year at Dec. 31, 2015
7,088 
2 
5,616 
1,331 
(3)
(3)
142 
 
 
511 
1,822 
80 
1,669 
 
0 
 
62 
825 
5 
5 
Beginning of year (shares) at Dec. 31, 2015
242.6 
 
 
 
 
 
 
 
102.1 
 
 
 
 
25.5 
 
 
 
 
 
 
Increase (Decrease) in Stockholders' Equity [Roll Forward]
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Stock-based compensation activity
 
 
(60)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Net income attributable to Ameren common shareholders
653 
 
 
653 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Net income (loss)
659 
 
 
 
 
 
 
 
360 
 
 
 
360 
255 
 
 
 
255 
 
 
Common stock dividends
 
 
 
(416)
 
 
 
 
 
 
 
 
(355)
 
 
 
 
(110)
 
 
Capital contribution from parent
 
 
 
 
 
 
 
 
44 
 
6 
 
 
0 
 
 
 
 
 
 
Return of capital to parent
 
 
 
 
 
 
 
 
0 
 
0 
 
 
 
 
 
 
 
 
 
Preferred stock dividends
 
 
 
 
 
 
 
 
 
 
 
 
(3)
 
 
 
 
(3)
 
 
Change in deferred retirement benefit costs
20 
 
 
 
(20)
 
 
 
 
 
 
 
 
5 
 
 
 
 
 
(5)
Net income attributable to noncontrolling interest holder
 
 
 
 
 
 
6 
 
 
 
 
 
 
 
 
 
 
 
 
 
Dividends paid to noncontrolling interest holders
 
 
 
 
 
 
(6)
 
 
 
 
 
 
 
 
 
 
 
 
 
Stockholders' equity, end of year at Dec. 31, 2016
7,103 
 
 
 
 
 
 
7,103 
4,090 
 
 
 
 
3,034 
 
 
 
 
 
 
End of year at Dec. 31, 2016
7,245 
2 
5,556 
1,568 
(23)
(23)
142 
 
 
511 
1,828 
80 
1,671 
 
0 
2,005 
62 
967 
0 
0 
End of year (shares) at Dec. 31, 2016
242.6 
 
 
 
 
 
 
 
102.1 
 
 
 
 
25.5 
 
 
 
 
 
 
Beginning of year at Sep. 30, 2016
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Increase (Decrease) in Stockholders' Equity [Roll Forward]
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Net income attributable to Ameren common shareholders
32 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Net income (loss)
33 
 
 
 
 
 
 
 
10 
 
 
 
 
30 
 
 
 
 
 
 
Stockholders' equity, end of year at Dec. 31, 2016
7,103 
 
 
 
 
 
 
7,103 
4,090 
 
 
 
 
3,034 
 
 
 
 
 
 
End of year at Dec. 31, 2016
$ 7,245 
$ 2 
 
 
 
$ (23)
 
 
 
$ 511 
 
$ 80 
 
 
$ 0 
$ 2,005 
$ 62 
 
$ 0 
 
End of year (shares) at Dec. 31, 2016
242.6 
 
 
 
 
 
 
 
102.1 
 
 
 
 
25.5 
 
 
 
 
 
 
Summary Of Significant Accounting Policies
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
General
Ameren, headquartered in St. Louis, Missouri, is a public utility holding company under PUHCA 2005. Ameren’s primary assets are its equity interests in its subsidiaries, including Ameren Missouri, Ameren Illinois, and ATXI. Ameren’s subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. Dividends on Ameren’s common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren’s principal subsidiaries are listed below. Ameren also has various other subsidiaries that conduct other activities, such as the provision of shared services.
•
Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri. Ameren Missouri was incorporated in Missouri in 1922 and is successor to a number of companies, the oldest of which was organized in 1881. It is the largest electric utility in the state of Missouri. It supplies electric and natural gas service to a 24,000-square-mile area in central and eastern Missouri. This area has an estimated population of 2.8 million and includes the Greater St. Louis area. Ameren Missouri supplies electric service to 1.2 million customers and natural gas service to 0.1 million customers.
•
Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois. Ameren Illinois was incorporated in Illinois in 1923 and is the successor to a number of companies, the oldest of which was organized in 1902. Ameren Illinois supplies electric and natural gas utility service to portions of central and southern Illinois with an estimated population of 3.1 million in an area of 40,000 square miles. Ameren Illinois supplies electric service to 1.2 million customers and natural gas service to 0.8 million customers.
•
ATXI operates a FERC rate-regulated electric transmission business. ATXI is developing MISO-approved electric transmission projects, including the Illinois Rivers, Spoon River, and Mark Twain projects. ATXI is also evaluating competitive electric transmission investment opportunities outside of MISO as they arise.
Ameren's financial statements are prepared on a consolidated basis and therefore include the accounts of its majority-owned subsidiaries. All intercompany transactions have been eliminated. Ameren Missouri and Ameren Illinois have no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated. Unless otherwise stated, these notes to the financial statements exclude discontinued operations for all periods presented.
Our accounting policies conform to GAAP. Our financial statements reflect all adjustments (which include normal, recurring adjustments) that are necessary, in our opinion, for a fair presentation of our results. The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. Such estimates and assumptions affect reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of financial statements, and the reported amounts of revenues and expenses during the reported periods. Actual results could differ from those estimates.
Regulation
We are regulated by the MoPSC, the ICC, and the FERC. We defer certain costs as assets pursuant to actions of rate regulators or because of expectations that we will be able to recover such costs in future rates charged to customers. We also defer certain amounts as liabilities pursuant to actions of rate regulators or based on the expectation that such amounts will be returned to customers in future rates. Regulatory assets and liabilities are amortized consistent with the period of expected regulatory treatment. In addition to the cost recovery mechanisms discussed in the Purchased Gas, Power, and Fuel Rate-adjustment Mechanisms section below, Ameren Missouri and Ameren Illinois have approvals from rate regulators to use other cost recovery mechanisms. Ameren Missouri has a pension and postretirement benefit cost tracker, an uncertain tax positions tracker, a renewable energy standards cost tracker, a solar rebate program tracker, and the MEEIA energy efficiency rider. Ameren Illinois' and ATXI's electric transmission rates are determined pursuant to formula ratemaking. Additionally, Ameren Illinois' electric distribution business participates in the performance-based formula ratemaking process established pursuant to the IEIMA. Ameren Illinois also has environmental cost riders, an asbestos-related litigation rider, an energy efficiency rider, a QIP rider, a VBA rider, and a bad debt rider. See Note 2 – Rate and Regulatory Matters for additional information on regulatory assets and liabilities.

The Ameren Illinois asbestos-related litigation rider includes a trust fund that was established when Ameren acquired IP. At December 31, 2016 and 2015, the trust fund balance of $22 million was reflected in "Other assets" on Ameren's and Ameren Illinois' balance sheet. This balance is restricted only for the use of funding certain asbestos-related claims. The rider is subject to the following terms: 90% of the cash expenditures in excess of the amount included in base electric rates is to be recovered from the trust fund. If cash expenditures are less than the amount in base rates, Ameren Illinois will contribute 90% of the difference to the trust fund.
Cash and Cash Equivalents
Cash and cash equivalents include cash on hand and temporary investments purchased with an original maturity of three months or less.
Allowance for Doubtful Accounts Receivable
The allowance for doubtful accounts represents our estimate of existing accounts receivable that will ultimately be uncollectible. The allowance is calculated by applying estimated loss factors to various classes of outstanding receivables, including unbilled revenue. The loss factors used to estimate uncollectible accounts are based upon both historical collections experience and management’s estimate of future collections success given the existing and anticipated future collections environment. Ameren Illinois has a bad debt rider that adjusts rates for net write-offs of customer accounts receivable above or below those being collected in rates.
Inventories
Inventories are recorded at the lower of cost or market. Cost is determined by the average-cost method. Inventories are capitalized when purchased and then expensed as consumed or capitalized as plant assets when installed, as appropriate. The following table presents a breakdown of inventories for each of the Ameren Companies at December 31, 2016 and 2015:
 
 
Ameren Missouri
 
Ameren Illinois
 
Ameren
2016
 
 
 
 
 
 
Fuel(a)
 
$
172

 
$
—

 
$
172

Natural gas stored underground
 
9

 
73

 
82

Other inventories
 
211

 
62

 
273

Total inventories
 
$
392

 
$
135

 
$
527

2015
 
 
 
 
 
 
Fuel(a)
 
$
173

 
$
—

 
$
173

Natural gas stored underground
 
10

 
87

 
97

Other inventories
 
204

 
64

 
268

Total inventories
 
$
387

 
$
151

 
$
538

(a)
Consists of coal, oil, and propane.
Purchased Gas, Power and Fuel Rate-adjustment Mechanisms
Ameren Missouri and Ameren Illinois have various rate-adjustment mechanisms in place that provide for the recovery of purchased natural gas and electric fuel and purchased power costs without a traditional rate case proceeding. See Note 2 – Rate and Regulatory Matters for the regulatory assets and liabilities recorded at December 31, 2016 and 2015, related to the rate-adjustment mechanisms discussed below.
In Ameren Missouri’s and Ameren Illinois’ natural gas businesses, changes in natural gas costs are reflected in billings to their customers through PGA clauses. The difference between actual natural gas costs and costs billed to customers in a given period is deferred as a regulatory asset or liability. The deferred amount is either billed or refunded to customers in a subsequent period.
In Ameren Illinois’ electric distribution business, changes in purchased power and transmission service costs are reflected in billings to its customers through pass-through rate-adjustment clauses. The difference between actual purchased power and transmission service costs and costs billed to customers in a given period is deferred as a regulatory asset or liability. The deferred amount is either billed or refunded to customers in a subsequent period.
Ameren Missouri has a FAC that allows an adjustment of electric rates three times per year for a pass-through to customers of 95% of changes in fuel and purchased power costs, including transportation charges and revenues, net of off-system sales, greater or less than the amount set in base rates, subject to MoPSC prudence review. The difference between the actual amounts incurred for these items and the amounts recovered from Ameren Missouri customers' base rates is deferred as a regulatory asset or liability. The deferred amounts are either billed or refunded to electric customers in a subsequent period. Since May 30, 2015, transmission revenues and substantially all transmission charges are excluded from net energy costs as a result of the April 2015 MoPSC electric rate order.
Property, Plant, and Equipment, Net
We capitalize the cost of additions to and betterments of units of property, plant and equipment. The cost includes labor, material, applicable taxes, and overhead. An allowance for funds used during construction, as discussed below, is also capitalized as a cost of our rate-regulated assets. Maintenance expenditures, including nuclear refueling and maintenance outages, are expensed as incurred. When units of depreciable property are retired, the original costs, less salvage values, are charged to accumulated depreciation. If environmental expenditures are related to assets currently in use, as in the case of the installation of pollution control equipment, the cost is capitalized and depreciated over the expected life of the asset. See Asset Retirement Obligations below and Note 3 – Property, Plant, and Equipment, Net for additional information.
Depreciation
Depreciation is provided over the estimated lives of the various classes of depreciable property by applying composite rates on a straight-line basis to the cost basis of such property. The provision for depreciation for the Ameren Companies in 2016, 2015, and 2014 ranged from 3% to 4% of the average depreciable cost.
Allowance for Funds Used During Construction
We capitalize allowance for funds used during construction, or the cost of borrowed funds and the cost of equity funds (preferred and common shareholders’ equity) applicable to rate-regulated construction expenditures, in accordance with the utility industry's accounting practice. Allowance for funds used during construction does not represent a current source of cash funds. This accounting practice offsets the effect on earnings of the cost of financing during construction, and it treats such financing costs in the same manner as construction charges for labor and materials.
Under accepted ratemaking practice, cash recovery of allowance for funds used during construction and other construction costs occurs when completed projects are placed in service and reflected in customer rates. The following table presents the annual allowance for funds used during construction debt and equity blended rates that were applied to construction projects in 2016, 2015, and 2014:
 
2016
 
2015
 
2014
Ameren Missouri
7
%
 
7
%
 
7
%
Ameren Illinois
5
%
 
6
%
 
2
%

Goodwill
Goodwill represents the excess of the purchase price of an acquisition over the fair value of the net assets acquired. Ameren and Ameren Illinois evaluate goodwill for impairment in each of their reporting units as of October 31 each year, or more frequently if events and circumstances change that would more likely than not reduce the fair value of their reporting units below their carrying amounts. Ameren and Ameren Illinois had goodwill of $411 million at October 31, 2016 and October 31, 2015. To determine whether the fair value of a reporting unit is more likely than not greater than its carrying amount, Ameren and Ameren Illinois elect to perform either a qualitative assessment or to bypass the qualitative assessment and perform a two-step quantitative test, on an annual basis. On October 31, 2015, Ameren and Ameren Illinois performed a quantitative test and determined that the estimated fair value of the Ameren Illinois reporting unit significantly exceeded its carrying value as of that date. Based on these results, Ameren and Ameren Illinois elected to perform a qualitative assessment for their annual goodwill impairment test conducted as of October 31, 2016.
The results of Ameren’s and Ameren Illinois’ qualitative assessment indicated that it was more likely than not that the fair value of the Ameren Illinois reporting unit exceeded its carrying value as of October 31, 2016, resulting in no impairment of Ameren’s or Ameren Illinois’ goodwill. The following factors, among others, were considered by Ameren and Ameren Illinois when assessing whether it was more likely than not that the fair value of the Ameren Illinois reporting unit exceeded its carrying value for the October 31, 2016, test:
•
macroeconomic conditions, including those conditions within Ameren Illinois’ service territory;
•
pending rate case outcomes and projections of future rate case outcomes;
•
changes in laws and potential law changes;
•
observable industry market multiples;
•
achievement of IEIMA performance metrics and the yield of 30-year United States Treasury bonds;
•
an unexpected further reduction in the FERC-allowed return on equity related to transmission services; and
•
projected operating results and cash flows.
As of December 31, 2016, the Ameren Companies changed the manner in which they assess performance and allocate resources, driven by increasing investment in FERC rate-regulated electric transmission and Ameren Illinois electric distribution and natural gas distribution businesses as well as the unique regulatory environment for each jurisdiction. Ameren now has four reporting units: Ameren Missouri, Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Transmission. Ameren Illinois now has three reporting units: Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission. See Note 16 – Segment Information for additional information related to the change in Ameren’s and Ameren Illinois' segments.
As of the date of the segment change, December 31, 2016, Ameren and Ameren Illinois reassigned goodwill to the new reporting units using a relative fair value allocation approach. The Level 3 fair value hierarchy valuation approach used to reassign goodwill was based on a market participant view and used a weighted combination of a discounted cash flow analysis and a market multiples analysis. Key assumptions used in estimating the fair value of the reporting units included discount and growth rates, utility sector market performance and transactions, and projected operating results and cash flows. As a result of the goodwill reassignment, Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission had goodwill of $238 million, $80 million, and $93 million, respectively, at December 31, 2016. The Ameren Transmission reporting unit was reassigned the same $93 million of goodwill as the Ameren Illinois Transmission reporting unit.
In conjunction with the goodwill reassignment, Ameren and Ameren Illinois completed the first step of the quantitative test to determine whether the fair values of the new reporting units exceeded their carrying values as of December 31, 2016. Ameren and Ameren Illinois determined that the estimated fair values of the Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, Ameren Illinois Transmission, and Ameren Transmission reporting units each exceeded their respective carrying values by at least 40%, indicating no impairment of Ameren’s or Ameren Illinois’ goodwill. The Ameren and Ameren Illinois goodwill that was reassigned to the new reporting units on December 31, 2016, had no accumulated goodwill impairment losses.
Impairment of Long-lived Assets
We evaluate long-lived assets classified as held and used for impairment when events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. Whether an impairment has occurred is determined by comparing the estimated undiscounted cash flows attributable to the assets to the carrying value of the assets. If the carrying value exceeds the undiscounted cash flows, we recognize an impairment charge equal to the amount by which the carrying value exceeds the estimated fair value of the assets. In the period in which we determine an asset meets held for sale criteria, we record an impairment charge to the extent the book value exceeds its estimated fair value less cost to sell. We did not identify any events or changes in circumstances that indicated that the carrying value of long-lived assets may not be recoverable in 2016 and 2015.
Environmental Costs
Liabilities for environmental costs are recorded on an undiscounted basis when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated. Costs are expensed or deferred as a regulatory asset when it is expected that the costs will be recovered from customers in future rates.
Asset Retirement Obligations
We record the estimated fair value of legal obligations associated with the retirement of tangible long-lived assets in the period in which the liabilities are incurred and capitalize a corresponding amount as part of the book value of the related long-lived asset. In subsequent periods, we adjust AROs based on changes in the estimated fair values of the obligations with a corresponding increase or decrease in the asset book value. Asset book values, reflected within "Property, Plant, and Equipment, Net" on the balance sheet, are depreciated over the remaining useful life of the related asset. Due to regulatory recovery, that depreciation is recorded within a regulatory asset or liability balance related to AROs. Ameren and Ameren Missouri have a nuclear decommissioning trust fund for the decommissioning of the Callaway energy center. Net realized and unrealized gains and losses within the nuclear decommissioning trust fund are deferred and are currently recorded as a regulatory liability, along with the depreciation of the asset book values, discussed above, and the accretion of the AROs. The depreciation of the asset book values at Ameren Missouri was $31 million, $13 million, and $1 million for the years ended December 31, 2016, 2015, and 2014, respectively, which was recorded as a reduction to the regulatory liability. The depreciation recorded to the regulatory asset at Ameren Illinois was immaterial in each respective period. Uncertainties as to the probability, timing, or amount of cash expenditures associated with AROs affect our estimates of fair value. Ameren and Ameren Missouri have recorded AROs for retirement costs associated with Ameren Missouri’s Callaway energy center decommissioning, CCR facilities, and river structures. Also, Ameren, Ameren Missouri, and Ameren Illinois have recorded AROs for retirement costs associated with asbestos removal and the disposal of certain transformers. Asset removal costs that do not constitute legal obligations are classified as regulatory liabilities. See Note 2 – Rate and Regulatory Matters.
The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the years ended December 31, 2016 and 2015:
 
Ameren
Missouri
 
Ameren
Illinois
 
Ameren
 
Balance at December 31, 2014
$
389

 
$
7

 
$
396

 
Liabilities incurred
3

 
—

 
3

 
Liabilities settled
(1
)
 
(1
)
 
(2
)
 
Accretion in 2015(a)
23

 
(b)

 
23

 
Change in estimates(c)
203

 
(b)

 
203

 
Balance at December 31, 2015
$
617

(e) 
$
6

(d) 
$
623

(e) 
Liabilities incurred
3

 
—

 
3

 
Liabilities settled
(2
)
 
(b)

 
(2
)
 
Accretion in 2016(a)
25

 
(b)

 
25

 
Change in estimates
1

 
—

 
1

 
Balance at December 31, 2016
$
644

(e) 
$
6

(d) 
$
650

(e) 

(a)
Accretion expense was recorded as a decrease to regulatory liabilities.
(b)
Less than $1 million.
(c)
The ARO increase resulted in a corresponding increase recorded to "Property, Plant, and Equipment, Net." Ameren and Ameren Missouri increased their AROs related to the decommissioning of the Callaway energy center by $99 million to reflect the 2015 cost study and funding analysis filed with the MoPSC, the extension of the estimated operating life until 2044, and a reduction in the discount rate assumption. See Note 10 – Callaway Energy Center for additional information. In addition, as a result of new federal regulations, Ameren and Ameren Missouri recorded an increase of $100 million to their AROs associated with CCR storage facilities. See Note 15 – Commitments and Contingencies for additional information. Ameren and Ameren Missouri also increased their AROs by $4 million due to a change in the estimated retirement dates of the Meramec and Rush Island energy centers as a result of the MoPSC's April 2015 electric rate order.
(d)
Included in “Other deferred credits and liabilities” on the balance sheet.
(e)
Balance included $5 million and $15 million in "Other current liabilities" on the balance sheet as of December 31, 2015 and 2016, respectively.
See the Divestiture Transactions and Discontinued Operations section below for additional information on the AROs related to the abandoned Meredosia and Hutsonville energy centers, which are presented as discontinued operations and therefore not included in the table above.
Noncontrolling Interests
As of December 31, 2016 and 2015, Ameren’s noncontrolling interests included the preferred stock of Ameren Missouri and Ameren Illinois.
Operating Revenue
The Ameren Companies record operating revenue for electric or natural gas service when it is delivered to customers. We accrue an estimate of electric and natural gas revenues for service rendered but unbilled at the end of each accounting period.
Ameren Illinois participates in the performance-based formula ratemaking framework pursuant to the IEIMA. In addition, Ameren Illinois' and ATXI's electric transmission service operating revenues are regulated by the FERC. The provisions of the IEIMA and the FERC's electric transmission formula rate framework provide for annual reconciliations of the electric distribution and electric transmission service revenue requirements necessary to reflect the actual recoverable costs incurred in a given year with the revenue requirements in customer rates for that year, including an allowed return on equity. In each of those electric jurisdictions, if the current year's revenue requirement is greater than the revenue requirement reflected in that year's customer rates, an increase to electric operating revenues with an offset to a regulatory asset is recorded to reflect the expected recovery of those additional amounts from customers within two years. In each jurisdiction, if the current year's revenue requirement is less than the revenue requirement reflected in that year's customer rates, a reduction to electric operating revenues with an offset to a regulatory liability is recorded to reflect the expected refund to customers within two years. See Note 2 – Rate and Regulatory Matters for information regarding Ameren Illinois' revenue requirement reconciliation pursuant to the IEIMA.
Accounting for MISO Transactions
MISO-related purchase and sale transactions are recorded by Ameren, Ameren Missouri, and Ameren Illinois using settlement information provided by MISO. Ameren Missouri records these purchase and sale transactions on a net hourly position. Ameren Missouri records net purchases in a single hour in “Operating Expenses – Purchased power” and net sales in a single hour in “Operating Revenues – Electric” in its statement of income. Ameren Illinois records net purchases in “Operating Expenses – Purchased power” in its statement of income to reflect all of its MISO transactions relating to the procurement of power for its customers. On occasion, Ameren Missouri's and Ameren Illinois' prior-period transactions will be resettled outside the routine settlement process because of a change in MISO’s tariff or a material interpretation thereof. In these cases, Ameren Missouri and Ameren Illinois recognize expenses associated with resettlements once the resettlement is probable and the resettlement amount can be estimated. Revenues are recognized once the resettlement amount is received. There were no material MISO resettlements in 2016, 2015, or 2014.
Nuclear Fuel
Ameren Missouri’s cost of nuclear fuel is capitalized and then amortized to fuel expense on a unit-of-production basis. The cost is charged to "Operating Expenses – Fuel" in the statement of income.
Stock-based Compensation
Stock-based compensation cost is measured at the grant date based on the fair value of the award, net of an assumed forfeiture rate. Ameren recognizes as compensation expense the estimated fair value of stock-based compensation on a straight-line basis over the requisite service period. See Note 12 – Stock-based Compensation for additional information.
Excise Taxes
Ameren Missouri and Ameren Illinois collect from their customers certain excise taxes that are levied on the sale or distribution of natural gas and electricity. Excise taxes are levied on Ameren Missouri's electric and natural gas businesses and on Ameren Illinois' natural gas business. They are recorded gross in “Operating Revenues – Electric,” “Operating Revenues – Natural gas,” and “Operating Expenses – Taxes other than income taxes” on the statement of income or the statement of income and comprehensive income. Excise taxes for electric service in Illinois are levied on customers and are therefore not included in Ameren Illinois' revenues and expenses. The following table presents the excise taxes recorded in “Operating Revenues – Electric,” “Operating Revenues – Natural gas,” and “Operating Expenses – Taxes other than income taxes” for the years ended December 31, 2016, 2015, and 2014:
 
2016
 
2015
 
2014
Ameren Missouri
$
151

 
$
156

 
$
151

Ameren Illinois
57

 
57

 
64

Ameren
$
208

 
$
213

 
$
215


Unamortized Debt Discounts, Premiums, and Issuance Costs
Long-term debt discounts, premiums, and issuance costs are amortized over the lives of the related issuances. Credit agreement fees are amortized over the term of that agreement.
Income Taxes
Ameren uses an asset and liability approach for its financial accounting and reporting of income taxes. Deferred tax assets and liabilities are recognized for transactions that are treated differently for financial reporting and income tax return purposes. These deferred tax assets and liabilities are based on statutory tax rates.
We recognize that regulators will probably reduce future revenues for deferred tax liabilities that were initially recorded at rates in excess of the current statutory rate. Therefore, reductions in deferred tax liabilities that were recorded because of decreases in the statutory rate have been credited to a regulatory liability. A regulatory asset has been established to recognize the probable recovery through future customer rates of tax benefits related to the equity component of allowance for funds used during construction, as well as the effects of tax rate increases.
Investment tax credits used on tax returns for prior years have been deferred as a noncurrent liability. The credits are being amortized over the useful lives of the related investment. Deferred income taxes were recorded on the temporary difference represented by the deferred investment tax credits and a corresponding regulatory liability. This recognizes the expected reduction in rates for future lower income taxes associated with the amortization of the investment tax credits. See Note 13 – Income Taxes.
Ameren Missouri, Ameren Illinois, and all the other Ameren subsidiary companies are parties to a tax allocation agreement with Ameren (parent) that provides for the allocation of consolidated tax liabilities. The tax allocation agreement specifies that each party be allocated an amount of tax using a stand-alone calculation, which is similar to that which would be owed or refunded had the party been separately subject to tax considering the impact of consolidation. Any net benefit attributable to the parent is reallocated to the other parties. This reallocation is treated as a capital contribution to the party receiving the benefit.
Earnings per Share
Basic earnings per share is computed by dividing “Net Income Attributable to Ameren Common Shareholders” by the weighted-average number of common shares outstanding during the period. Earnings per diluted share is computed by dividing “Net Income Attributable to Ameren Common Shareholders” by the weighted-average number of diluted common shares outstanding during the period. Earnings per diluted share reflects the potential dilution that would occur if certain stock-based performance share units were settled. The number of performance share units assumed to be settled was 0.8 million, 1.0 million, and 1.8 million for the years ended December 31, 2016, 2015, and 2014, respectively. There were no potentially dilutive securities excluded from the diluted earnings per share calculations for the years ended December 31, 2016, 2015, and 2014.
Capital Contributions and Return of Capital
In 2016, Ameren Missouri received cash capital contributions of $44 million from Ameren (parent) as a result of the tax allocation agreement, which included the accrued capital contribution from 2015.
In 2015, Ameren Missouri received cash capital contributions of $224 million from Ameren (parent) as a result of the tax allocation agreement, which included the Ameren Missouri accrued capital contribution from 2014. Additionally, as of December 31, 2015, Ameren Missouri accrued a $38 million capital contribution related to the same agreement. In 2015, Ameren Illinois received cash capital contributions of $25 million from Ameren (parent).
In 2014, Ameren Missouri and Ameren Illinois received cash capital contributions of $215 million and $15 million, respectively, from Ameren (parent) as a result of the tax allocation agreement. Additionally, as of December 31, 2014, Ameren Missouri accrued a $9 million capital contribution related to the same agreement. Also in 2014, Ameren Missouri returned capital of $215 million to Ameren (parent).
Divestiture Transactions and Discontinued Operations
In December 2013, Ameren completed the divestiture of New AER to IPH. The transaction agreement with IPH provided that if the Elgin, Gibson City, and Grand Tower natural-gas-fired energy centers were subsequently sold by Medina Valley and Medina Valley received additional proceeds from such sale, Medina Valley would pay Genco any proceeds from such sale, net of taxes and other expenses, in excess of the $137.5 million previously paid to Genco. In January 2014, Medina Valley completed the sale of the Elgin, Gibson City, and Grand Tower natural-gas-fired energy centers to Rockland Capital for a total purchase price of $168 million. The agreement with Rockland Capital required a portion of the purchase price to be held in escrow until January 31, 2016, to fund certain indemnity obligations, if any, of Medina Valley. The Rockland Capital escrow balance of $14 million and the corresponding payable due to Genco was reflected on Ameren's December 31, 2015, consolidated balance sheet in "Other current assets" and in "Other current liabilities," respectively. In 2016, Medina Valley received the amount held in escrow from Rockland Capital and paid Genco its portion of the escrow.
All matters related to the final tax basis of New AER and the related tax benefit resulting from its divestiture were resolved with the completion of the IRS audit of 2013. During 2015, based on the completion of the IRS audit of 2013, Ameren removed a reserve for unrecognized tax benefits of $53 million recorded in 2013 and recognized a tax benefit from discontinued operations.
The components of the assets and liabilities of Ameren's discontinued operations at December 31, 2016 and 2015, consist primarily of AROs and the related deferred income tax assets associated with the abandoned Meredosia and Hutsonville energy centers.
Accounting Changes and Other Matters
The following is a summary of recently adopted authoritative accounting guidance, as well as guidance issued but not yet adopted, that could affect the Ameren Companies.
Revenue from Contracts with Customers
In May 2014, the FASB issued authoritative guidance that changes the criteria for recognizing revenue from a contract with a customer. The underlying principle of the guidance is that an entity will recognize revenue for the transfer of promised goods or services to customers at an amount that the entity expects to be entitled to in exchange for those goods or services. The guidance also requires additional disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. Entities can apply the guidance retrospectively to each reporting period presented, the full retrospective method, or retrospectively by recording a cumulative effect adjustment to retained earnings in the period of initial adoption, the modified retrospective method. The utility industry continues to assess the impacts on accounting for contributions in aid of construction and similar arrangements, and collectibility, among other issues. The outcome of these assessments could have a significant impact on our results of operations and financial position. We plan to complete our assessment of the impacts of this guidance on our results of operations, financial position, presentation and disclosures, and transition method, in the next several months prior to our adoption in the first quarter of 2018.
Amendments to the Consolidation Analysis
In February 2015, the FASB issued authoritative guidance that amends the consolidation analysis for variable interest entities and voting interest entities. The new guidance affects (1) limited partnerships, similar legal entities, and certain investment funds, (2) the evaluation of fees paid to a decision maker or service provider as a variable interest, (3) how fee arrangements impact the primary beneficiary determination, and (4) the evaluation of related party relationships on the primary beneficiary determination. The adoption of this guidance in 2016 did not impact the Ameren Companies' results of operations, financial position, cash flows, or disclosures.
Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share
In May 2015, to address diversity in practice, the FASB issued authoritative guidance that removes the requirement to categorize within the fair value hierarchy all investments for which fair value is measured using the NAV practical expedient. The Ameren Companies have investments measured using the NAV practical expedient within the pension plan and postretirement benefit plan assets. We adopted this guidance on January 1, 2016 and retrospectively updated the presentation of these assets in the fair value hierarchy tables included in Note 11 - Retirement Benefits. The adoption of this guidance did not impact our results of operations, financial position or cash flows.
Financial Instruments - Recognition and Measurement, and Credit Losses
In January 2016, the FASB issued authoritative guidance that addressed certain aspects of recognition, measurement, presentation and disclosure of financial instruments. This guidance requires an entity to measure equity investments, other than those accounted for under the equity method of accounting, at fair value with changes in fair value recognized in net income. The recognition and measurement guidance will be effective for the Ameren Companies in the first quarter of 2018, and requires changes to be applied retrospectively with a cumulative effect adjustment to retained earnings as of the adoption date. Also, in June 2016, the FASB issued authoritative guidance that requires an entity to recognize an allowance for financial instruments that reflects its current estimate of credit losses expected to be incurred over the life of the financial instruments. The guidance requires an entity to measure expected credit losses based on relevant information about past events, current conditions, and reasonable and supportable forecasts that affect the collectibility of the reported amount. The credit loss guidance will be effective for the Ameren Companies in the first quarter of 2020, and requires changes to be applied retrospectively with a cumulative effect adjustment to retained earnings as of the adoption date. We are currently assessing the impacts of the new financial instruments guidance on our results of operations, financial position, and disclosures.
Leases
In February 2016, the FASB issued authoritative guidance that requires an entity to recognize assets and liabilities arising from all leases with a term greater than one year. Consistent with current GAAP, the recognition, measurement, and presentation of expenses and cash flows arising from a lease will depend on its classification as a finance or operating lease. The guidance also requires additional disclosures to enable users of financial statements to understand the amount, timing, and uncertainty of cash flows arising from leases. This guidance will affect the Ameren Companies' financial position by increasing the assets and liabilities recorded relating to their operating leases, which will be recognized and measured at the beginning of the earliest period presented. We are currently assessing the impacts of this guidance for other effects on our results of operations, cash flows and disclosures. We expect to adopt this guidance in the first quarter of 2019. See Note 15 – Commitments and Contingencies for additional information on our leases.
Improvements to Employee Share-Based Payment Accounting
In March 2016, the FASB issued authoritative guidance that simplifies the accounting for share-based payment transactions, including the income tax consequences, the calculation of diluted earnings per share, the treatment of forfeitures, the classification of awards as either equity or liabilities, and the classification on the statement of cash flows. Ameren determines for each performance share unit award whether the difference between the deduction for tax purposes and the compensation cost recognized for financial reporting purposes results in either an excess tax benefit or an excess tax deficit. Previously, excess tax benefits were recognized in "Other paid-in capital" on Ameren’s consolidated balance sheet, and in certain cases, excess tax deficits were recognized in “Income taxes” on Ameren’s consolidated income statement. The new guidance increases income statement volatility by requiring all excess tax benefits and deficits to be recognized in “Income taxes,” and treated as discrete items in the period in which they occur. Ameren adopted this guidance in 2016 and prospectively applied the amendment in this guidance requiring recognition of excess tax benefits and deficits in the income statement, which resulted in recognition of a $21 million income tax benefit and a corresponding $21 million increase in income from continuing operations and net income (9 cents per diluted share) during the period. Also as a result of the adoption of this guidance, Ameren made an accounting policy election to continue to estimate the number of forfeitures expected to occur. The amendments in the guidance that require application using a modified retrospective transition method did not impact Ameren. Therefore, there was no cumulative-effect adjustment to retained earnings recognized as of January 1, 2016. Ameren applied the amendments in this guidance relating to classification on the statement of cash flows retrospectively. For the year ended December 31, 2015, Ameren reclassified $2 million of excess tax benefits on the statement of cash flows from financing to operating activity. Also, for the years ended December 31, 2015 and December 31, 2014, Ameren reclassified $12 million and $14 million, respectively, of employee payroll taxes related to share-based payments from operating to financing activity.
Restricted Cash
In November 2016, the FASB issued authoritative guidance that requires restricted cash and restricted cash equivalents to be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. We are currently assessing the impacts of this guidance on our statements of cash flows and disclosures. The guidance will be effective for the Ameren Companies in the first quarter of 2018, and requires changes to be applied retrospectively to each period presented.
Rate And Regulatory Matters
RATE AND REGULATORY MATTERS
RATE AND REGULATORY MATTERS
Below is a summary of significant regulatory proceedings and related lawsuits. We are unable to predict the ultimate outcome of these matters, the timing of final decisions of the various agencies and courts, or the effect on our results of operations, financial position, or liquidity.
Missouri
February 2017 Unanimous Stipulation and Agreement
In July 2016, Ameren Missouri filed a request with the MoPSC seeking approval to increase its annual revenues for electric service. Relating to that request, in February 2017, Ameren Missouri, the MoPSC staff, the MoOPC, and all intervenors filed a unanimous stipulation and agreement with the MoPSC. The stipulation and agreement, which is subject to MoPSC approval, would result in a $3.4 billion revenue requirement, which is a $92 million increase in Ameren Missouri’s annual revenue requirement for electric service compared to its prior revenue requirement established in the MoPSC's April 2015 electric rate order. The stipulation and agreement did not specify the common equity percentage, the rate base, or the allowed return on common equity. The new revenue requirement reflects the current actual sales volumes of the New Madrid Smelter, whose operations remain suspended, as well as other agreed upon sales volumes.
The stipulation and agreement includes the continued use of the FAC and the regulatory tracking mechanisms for pension and postretirement benefits, uncertain income tax positions, and renewable energy standards that the MoPSC previously authorized in earlier electric rate orders. These regulatory tracking mechanisms provide for a base level of expense to be reflected in Ameren Missouri’s base electric rates with differences in the actual expenses incurred recorded as a regulatory asset or liability. Excluding cost reductions associated with reduced sales volumes, the base level of net energy costs under the stipulation and agreement would decrease by $54 million from the base level established in the MoPSC's April 2015 electric rate order. Changes in amortizations and the base level of expenses for the other regulatory tracking mechanisms, including extending the amortization period of certain regulatory assets, would reduce expenses by $26 million from the base levels established in the MoPSC's April 2015 electric rate order.
The stipulation and agreement contemplates that new rates will become effective on or before March 20, 2017. Ameren Missouri cannot predict whether the MoPSC will approve the stipulation and agreement or, if approved, whether any application for rehearing or appeal will be filed or the outcome if so filed.
Noranda and New Madrid Smelter
In the first quarter of 2016, Noranda, which was historically Ameren Missouri's largest customer, suspended operations at the New Madrid Smelter and filed voluntary petitions for a court-supervised restructuring process under Chapter 11 of the United States Bankruptcy Code. In October 2016, Noranda sold the New Madrid Smelter to ARG International AG. Operations at the New Madrid Smelter remain suspended and Ameren Missouri is uncertain of future sales to the smelter. As a result, Ameren Missouri will not fully recover its revenue requirement until rates are adjusted prospectively by the MoPSC to accurately reflect the actual sales volumes to the New Madrid Smelter. As of December 31, 2016, Ameren Missouri has been paid in full for all previous electric service amounts, and expects to continue to be paid in full for the minimal amount of electric service it is currently providing to the New Madrid Smelter.
MEEIA
In November 2016, the MoPSC approved a $28 million MEEIA 2013 performance incentive based on a stipulation and agreement between Ameren Missouri, the MoPSC staff, and the MoOPC. Ameren Missouri will collect the performance incentive over a two-year period that began in February 2017.
In November 2015, the MoPSC issued an order regarding the determination of an input used to calculate the performance incentive. Ameren Missouri filed an appeal of the order with the Missouri Court of Appeals, Western District. In December 2016, the Missouri Court of Appeals, Western District, upheld the November 2015 MoPSC order. Ameren Missouri has appealed the decision to uphold the MoPSC order to the Missouri Supreme Court.
ATXI’s Mark Twain Project
The Mark Twain project is a MISO-approved 95-mile transmission line to be located in northeast Missouri. In April 2016, the MoPSC granted ATXI a certificate of convenience and necessity for the Mark Twain project. Before starting construction, ATXI must obtain assents for road crossings from the five counties where the line will be constructed. None of the five county commissions have approved ATXI’s requests for the assents. In October 2016, ATXI filed suit in each of the five county circuit courts to obtain the assents. A decision in each of the five lawsuits is expected in 2017. ATXI plans to complete the project in 2019; however, further delays in obtaining the assents could delay the completion date.
Illinois
IEIMA
Under the provisions of the IEIMA's performance-based formula rate-making framework, which currently extends through 2022, Ameren Illinois’ electric distribution service rates are subject to an annual revenue requirement reconciliation to its actual recoverable costs. Each year, Ameren Illinois records a regulatory asset or a regulatory liability and a corresponding increase or decrease to operating revenues for any differences between the revenue requirement reflected in customer rates for that year and its estimate of the probable increase or decrease in the revenue requirement expected to ultimately be approved by the ICC based on that year's actual recoverable costs incurred. As of December 31, 2016, Ameren Illinois had recorded regulatory assets of $23 million and $68 million, including interest, to reflect its expected 2016 and the 2015 approved revenue requirement reconciliation adjustments, respectively. As of December 31, 2015, Ameren Illinois had recorded a $103 million regulatory asset to reflect its approved 2014 revenue requirement reconciliation adjustment, which was collected, with interest, from customers during 2016.
In December 2016, the ICC issued an order in Ameren Illinois’ annual update filing approving a $14 million decrease in Ameren Illinois’ electric delivery service revenue requirement beginning in January 2017. This update reflects an increase to the annual formula rate based on 2015 actual recoverable costs and expected net plant additions for 2016, an increase to include the 2015 revenue requirement reconciliation adjustment, which was initially recorded as a regulatory asset in 2015, and a decrease for the conclusion of the 2014 revenue requirement reconciliation adjustment, which was fully collected from customers in 2016.
FEJA
The FEJA revised certain portions of the IEIMA, including extending the IEIMA formula ratemaking process through 2022 and clarifying that a common equity ratio of up to and including 50% is prudent. Also, beginning in 2017, the FEJA decouples electric distribution revenues established in a rate proceeding from actual sales volumes by providing that any revenue changes driven by actual electric distribution sales volumes differing from sales volumes reflected in that year's rates will be collected from or refunded to customers within two years. This portion of the law extends beyond the end of the IEIMA in 2022. Through 2022, revenue differences will be included in the annual IEIMA revenue requirement reconciliation. Additionally, this law creates a customer surcharge relating to certain nuclear energy centers located in Illinois that, like the cost of power purchased by Ameren Illinois on behalf of its customers, will be passed through to electric distribution customers with no effect on Ameren Illinois' earnings.
Beginning as early as June 2017, the FEJA will allow Ameren Illinois to earn a return on its electric energy efficiency program investments. Ameren Illinois electric energy efficiency investments will be deferred as a regulatory asset and will earn a return at the company’s weighted average cost of capital, with the equity return based on the monthly average yield of the 30-year United States Treasury bonds plus 580 basis points. The equity portion of Ameren Illinois’ return on electric energy efficiency investments can also be increased or decreased by 200 basis points based on the achievement of annual energy savings goals. The FEJA increased the level of electric energy efficiency saving targets through 2030. Based on a formula provided in the act, Ameren Illinois estimates it can annually invest up to $100 million from 2018 through 2021, up to $107 million annually from 2022 through 2025, and up to $114 million annually from 2026 through 2030. The ICC has the ability to lower the electric energy efficiency saving goals if there are insufficient cost effective measures available. The electric energy efficiency program investments and the return on those investments will be recovered through a rider, and will not be included in the IEIMA formula rate process.
Federal
FERC Complaint Cases
In November 2013, a customer group filed a complaint case with the FERC seeking a reduction in the allowed base return on common equity for FERC-regulated transmission rate base under the MISO tariff from 12.38% to 9.15%. In September 2016, the FERC issued a final order in the November 2013 complaint case which lowered the allowed base return on common equity to 10.32%, or a 10.82% total return on common equity with the inclusion of the 50 basis point incentive adder for participation in an RTO. The order was consistent with the initial decision an administrative law judge issued in December 2015, and requires customer refunds, with interest, to be issued for the 15-month period ended February 2015. In addition, the new allowed return on common equity is reflected in rates prospectively from the September 2016 effective date of the order. Refunds for the November 2013 complaint case are expected to be issued in the first half of 2017.
As the maximum FERC-allowed refund period for the November 2013 complaint case ended in February 2015, another customer complaint case was filed in February 2015. The February 2015 complaint case seeks a reduction in the allowed base return on common equity for the FERC-regulated transmission rate base under the MISO tariff to 8.67%. In June 2016, an administrative law judge issued an initial decision in the February 2015 complaint case, which if approved by FERC, would lower the allowed base return on common equity to 9.70%, or a 10.20% total return on equity with the inclusion of the 50 basis point incentive adder for participation in an RTO. It would also require the issuance of customer refunds, with interest, for the 15-month period ended May 2016. The FERC is expected to issue a final order in the February 2015 complaint case in the second quarter of 2017. That final order will determine the allowed return on common equity for the 15-month period ended May 2016. That final order will also establish the allowed return on common equity that will apply prospectively from its expected second quarter 2017 effective date, replacing the current 10.82% total return on common equity, which became effective in September 2016. The 12.38% allowed return on common equity was effective for the period that began at the conclusion of the 15-month period for the February 2015 complaint case in May 2016 through the September 2016 effective date of the final order in the November 2013 complaint case.
Beginning with the January 2015 effective date, the RTO participation incentive adder reduces any refund to customers relating to a reduction of the allowed base return on common equity from the complaint cases discussed above and has been applied prospectively from the effective date of the September 2016 FERC order, resulting in a current allowed return on common equity of 10.82%.
As of December 31, 2016, Ameren and Ameren Illinois recorded current regulatory liabilities of $62 million and $42 million, respectively, to reflect the expected refunds, including interest, associated with the reduced allowed returns on common equity in the September 2016 FERC order and the initial decision in the February 2015 complaint case. Ameren Missouri does not expect that a reduction in the FERC-allowed base return on common equity would be material to its results of operations, financial position, or liquidity.
Combined Construction and Operating License
In 2008, Ameren Missouri filed an application with the NRC for a COL for a second nuclear unit at Ameren Missouri's existing Callaway County, Missouri, energy center site. In 2009, Ameren Missouri suspended its efforts to build a second nuclear unit at its existing Callaway site, and the NRC suspended review of the COL application. Prior to suspending its efforts, Ameren Missouri had capitalized $69 million related to the project. Primarily because of changes in vendor support for licensing efforts at the NRC, Ameren Missouri’s assessment of long-term capacity needs, declining costs of alternative generation technologies, and the regulatory framework in Missouri, Ameren Missouri discontinued its efforts to license and build a second nuclear unit at its existing Callaway site. As a result of this decision, in 2015, Ameren and Ameren Missouri recognized a $69 million noncash pretax provision for all of the previously capitalized COL costs. Ameren Missouri has withdrawn its COL application with the NRC.
Regulatory Assets and Liabilities
In accordance with authoritative accounting guidance regarding accounting for the effects of certain types of regulation, we defer certain costs as regulatory assets pursuant to actions of regulators or because we expect to recover such costs in rates charged to customers. We may also defer certain amounts as regulatory liabilities because of actions of regulators or because we expect that such amounts will be returned to customers in future rates. The following table presents our regulatory assets and regulatory liabilities at December 31, 2016 and 2015:
 
 
2016
 
2015
 
 
Ameren
Missouri
 
Ameren
Illinois
 
Ameren
 
 
Ameren
Missouri
 
Ameren
Illinois
 
Ameren
Current regulatory assets:
 
 
 
 
 
 
 
 
 
 
 
 
 
Under-recovered FAC(a)(b)
 
$
21

 
$
—

 
$
21

 
 
$
37

 
$
—

 
$
37

Under-recovered Illinois electric power costs(c)
 
—

 
3

 
3

 
 
—

 
3

 
3

Under-recovered PGA(c)
 
—

 
4

 
4

 
 
—

 
8

 
8

MTM derivative losses(d)
 
9


15

 
24

 
 
29

 
45

 
74

Energy efficiency riders(e)
 
5

 
—

 
5

 
 
23

 
—

 
23

IEIMA revenue requirement reconciliation adjustment(a)(f)
 
—

 
68

 
68

 
 
—

 
103

 
103

FERC revenue requirement reconciliation adjustment(a)(g)
 
—

 
7

 
13

 
 
—

 
8

 
12

VBA rider(a)(h)
 
—

 
11

 
11

 
 
—

 
—

 
—

Total current regulatory assets
 
$
35

 
$
108

 
$
149

 
 
$
89

 
$
167

 
$
260

Noncurrent regulatory assets:
 
 
 
 
 
 
 
 
 
 
 
 
 
Pension and postretirement benefit costs(i)
 
$
175

 
$
319

 
$
494

 
 
$
95

 
$
202

 
$
297

Income taxes(j)
 
229

 
1

 
230

 
 
247

 
4

 
251

Uncertain tax positions tracker(a)(k)
 
7

 
—

 
7

 
 
7

 
—

 
7

ARO(l)
 
—

 
3

 
3

 
 
—

 
4

 
4

Callaway costs(a)(m)
 
29

 
—

 
29

 
 
32

 
—

 
32

Unamortized loss on reacquired debt(a)(n)
 
65

 
59

 
124

 
 
69

 
69

 
138

Environmental cost riders(o)
 
—

 
196

 
196

 
 
—

 
230

 
230

MTM derivative losses(d)
 
9


178

 
187



15

 
175

 
190

Storm costs(a)(p)
 
—

 
15

 
15

 
 
—

 
9

 
9

Demand-side costs before the MEEIA implementation(a)(q)
 
18

 
—

 
18

 
 
31

 
—

 
31

Workers’ compensation claims(r)
 
6

 
7

 
13

 
 
6

 
7

 
13

Credit facilities fees(s)
 
4

 
—

 
4

 
 
4

 
—

 
4

Construction accounting for pollution control equipment(a)(t)
 
19

 
—

 
19

 
 
20

 
—

 
20

Solar rebate program(a)(u)
 
49

 
—

 
49

 
 
74

 
—

 
74

IEIMA revenue requirement reconciliation adjustment(a)(f)
 
—

 
23

 
23

 
 
—

 
62

 
62

FERC revenue requirement reconciliation adjustment(a)(g)
 
—

 
8

 
10

 
 
—

 
5

 
11

Other
 
9

 
7

 
16

 
 
5

 
4

 
9

Total noncurrent regulatory assets
 
$
619

 
$
816

 
$
1,437

 
 
$
605

 
$
771

 
$
1,382

Current regulatory liabilities:
 
 
 
 
 
 
 
 
 
 
 
 
 
Over-recovered FAC(b)
 
$
—

 
$
—

 
$
—

 
 
$
9

 
$
—

 
$
9

Over-recovered Illinois electric power costs(c)
 
—

 
25

 
25

 
 
—

 
6

 
6

Over-recovered PGA(c)
 
—

 
—

 
—

 
 
3

 
—

 
3

MTM derivative gains(d)
 
12

 
11

 
23


 
16

 
1

 
17

Estimated refund for FERC complaint cases(v)
 
—

 
42

 
62

 
 
—

 
32

 
45

Total current regulatory liabilities
 
$
12

 
$
78

 
$
110

 
 
$
28

 
$
39

 
$
80

Noncurrent regulatory liabilities:
 
 
 
 
 
 
 
 
 
 
 
 
 
Income taxes(w)
 
$
33

 
$
4

 
$
37

 
 
$
36

 
$
6

 
$
42

Uncertain tax positions tracker(k)
 
3

 
—

 
3

 
 
6

 
—

 
6

Asset removal costs(x)
 
970

 
697

 
1,669

 
 
933

 
671

 
1,605

ARO(l)
 
162

 
—

 
162

 
 
167

 
—

 
167

Bad debt rider(y)
 
—

 
3

 
3

 
 
—

 
6

 
6

Pension and postretirement benefit costs tracker(z)
 
35

 
—

 
35

 
 
19

 
—

 
19

Energy efficiency riders(e)
 
—

 
45

 
45

 
 
—

 
36

 
36

Renewable energy credits(aa)
 
—

 
15

 
15

 
 
—

 
12

 
12

Storm tracker(ab)
 
7

 
—

 
7

 
 
9

 
—

 
9

Other
 
5

 
4

 
9

 
 
2

 
1

 
3

Total noncurrent regulatory liabilities
 
$
1,215

 
$
768

 
$
1,985

 
 
$
1,172

 
$
732

 
$
1,905

(a)
These assets earn a return.
(b)
Under-recovered or over-recovered fuel costs to be recovered or refunded through the FAC. Specific accumulation periods aggregate the under-recovered or over-recovered costs over four months, any related adjustments that occur over the following four months, and the recovery from or refund to customers that occurs over the next eight months.
(c)
Under-recovered or over-recovered costs from utility customers. Amounts will be recovered from or refunded to customers within one year of the deferral.
(d)
Deferral of commodity-related derivative MTM losses or gains. See Note 7 – Derivative Financial Instruments for additional information.
(e)
The Ameren Missouri balance relates to the MEEIA. The MEEIA rider allows Ameren Missouri to collect from or refund to customers any annual difference in the actual amounts incurred and the amounts collected from customers for the MEEIA program costs, net shared benefits, and the throughput disincentive. Under the MEEIA rider, collections from or refunds to customers occur one year after the program costs, net shared benefits, and the throughput disincentive are incurred. The Ameren Illinois balance relates to a regulatory tracking mechanism to recover its electric and natural gas costs associated with developing, implementing, and evaluating customer energy efficiency and demand response programs. Any under-recovery or over-recovery will be collected from or refunded to customers over the year following the plan year.
(f)
The difference between Ameren Illinois' annual revenue requirement calculated under the IEIMA's performance-based formula ratemaking framework and the revenue requirement included in customer rates for that year. The under-recovery will be recovered from or refunded to customers with interest within two years.
(g)
Ameren Illinois' and ATXI's annual revenue requirement reconciliation calculated pursuant to the FERC's electric transmission formula ratemaking framework. The under-recovery or over-recovery will be recovered from or refunded to customers within two years.
(h)
Under-recovered natural gas sales volumes, including deviations from normal weather conditions. Each year's amount will be recovered from or refunded to customers from April through December of the following year.
(i)
These costs are being amortized in proportion to the recognition of prior service costs (credits) and actuarial losses (gains) attributable to Ameren’s pension plan and postretirement benefit plans. See Note 11 – Retirement Benefits for additional information.
(j)
Tax benefits related to the equity component of allowance for funds used during construction, as well as the effects of tax rate changes. This amount will be recovered over the expected life of the related assets.
(k)
The tracker is amortized over three years, beginning from the date the amounts are included in rates. See Note 13 – Income Taxes for additional information.
(l)
Recoverable or refundable removal costs for AROs, including net realized and unrealized gains and losses related to the nuclear decommissioning trust fund investments. See Note 1 – Summary of Significant Accounting Policies – Asset Retirement Obligations.
(m)
Ameren Missouri’s Callaway energy center operations and maintenance expenses, property taxes, and carrying costs incurred between the plant in-service date and the date the plant was reflected in rates. These costs are being amortized over the remaining life of the energy center's original operating license through 2024.
(n)
Losses related to reacquired debt. These amounts are being amortized over the lives of the related new debt issuances or the original lives of the old debt issuances if no new debt was issued.
(o)
The recoverable portion of accrued environmental site liabilities that will be collected from electric and natural gas customers through ICC-approved cost recovery riders. The period of recovery will depend on the timing of remediation expenditures. See Note 15 – Commitments and Contingencies for additional information.
(p)
Storm costs from 2013, 2015, and 2016 deferred in accordance with the IEIMA. These costs are being amortized over five-year periods beginning in the year the storm occurred.
(q)
Demand-side costs incurred prior to implementation of the MEEIA in 2013, including the costs of developing, implementing, and evaluating customer energy efficiency and demand response programs. Costs incurred from May 2008 through September 2008 are being amortized over a 10-year period that began in March 2009. Costs incurred from October 2008 through December 2009 are being amortized until May 2017. Costs incurred from January 2010 through February 2011 are being amortized over a six-year period that began in August 2011. Costs incurred from March 2011 through July 2012 are being amortized over a six-year period that began in January 2013. Costs incurred from August 2012 through December 2012 are being amortized over a six-year period that began in June 2015. The February 2017 stipulation and agreement, if approved, would modify these amortization periods.
(r)
The period of recovery will depend on the timing of actual expenditures.
(s)
Ameren Missouri’s costs incurred to enter into and maintain the Missouri Credit Agreement. These costs are being amortized over the life of the credit facility to construction work in progress, which will be depreciated when assets are placed into service. Additional costs were incurred in December 2016 to amend and restate the Missouri Credit Agreement.
(t)
The MoPSC’s May 2010 electric rate order allowed Ameren Missouri to record an allowance for funds used during construction for pollution control equipment at its Sioux energy center until the cost of that equipment was included in customer rates beginning in 2011. These costs are being amortized over the expected life of the Sioux energy center, currently through 2033.
(u)
Costs associated with Ameren Missouri's solar rebate program to fulfill its renewable energy portfolio requirement. These costs are being amortized over a three-year period that began in June 2015. The February 2017 stipulation and agreement, if approved, would modify this amortization period.
(v)
Estimated refunds to transmission customers related to FERC orders. See FERC Complaint Cases above.
(w)
Unamortized portion of investment tax credits and reductions to deferred tax liabilities recorded at rates in excess of current statutory rates. The unamortized portion of investment tax credits and the reduction to deferred tax liabilities are being amortized over the expected life of the underlying assets.
(x)
Estimated funds collected for the eventual dismantling and removal of plant retired from service, net of salvage value.
(y)
A regulatory tracking mechanism for the difference between the level of bad debt incurred by Ameren Illinois under GAAP and the level of such costs included in electric and natural gas rates. The over-recovery relating to 2014 was refunded to customers from June 2015 through May 2016. The over-recovery relating to 2015 is being refunded to customers from June 2016 through May 2017. The over-recovery relating to 2016 will be refunded to customers from June 2017 through May 2018.
(z)
A regulatory tracking mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates. For periods prior to December 2014, the MoPSC's April 2015 electric rate order directed the amortization to occur over three to five years, beginning in June 2015. For periods after December 2014, the amortization period will be determined in the July 2016 electric rate case. The February 2017 stipulation and agreement, if approved, would modify these amortization periods.
(aa)
Funds collected from customers for the purchase of renewable energy credits through IPA procurements for distributed generation. The balance will be amortized as renewable energy credits are purchased.
(ab)
A regulatory tracking mechanism at Ameren Missouri for the difference between the level of storm costs incurred in a particular year and the level of such costs included in rates. For periods prior to December 2014, the MoPSC's April 2015 electric rate order directed the amortization to occur over a five-year period that began in June 2015. For periods after December 2014, the amortization period will be determined in the July 2016 electric rate case. The April 2015 MoPSC order did not approve the continued use of the storm cost regulatory tracking mechanism. The February 2017 stipulation and agreement, if approved, would modify these amortization periods.
Ameren, Ameren Missouri, and Ameren Illinois continually assess the recoverability of their regulatory assets. Regulatory assets are charged to earnings when it is no longer probable that such amounts will be recovered through future revenues. To the extent that payments of regulatory liabilities are no longer probable, the amounts are credited to earnings.
Property And Plant, Net
PROPERTY AND PLANT, NET
PROPERTY, PLANT, AND EQUIPMENT, NET
The following table presents property, plant, and equipment, net, for each of the Ameren Companies at December 31, 2016 and 2015:
 
 
Ameren
Missouri(a)
 
Ameren
Illinois
 
Other
 
Ameren(a)
2016
 
 
 
 
 
 
 
 
Property, plant, and equipment at original cost:(b)
 
 
 
 
 
 
 
 
Electric generation
 
$
10,911

 
$
—

 
$
—

 
$
10,911

Electric distribution
 
5,563

 
5,287

 
—

 
10,850

Electric transmission
 
1,151

 
2,016

 
712

 
3,879

Natural gas
 
455

 
2,186

 
—

 
2,641

Other(c)
 
879

 
719

 
239

 
1,837

 
 
18,959

 
10,208

 
951

 
30,118

Less: Accumulated depreciation and amortization
 
7,880

 
2,850

 
231

 
10,961

 
 
11,079

 
7,358

 
720

 
19,157

Construction work in progress:
 
 
 
 
 
 
 
 
Nuclear fuel in process
 
206

 
—

 
—

 
206

Other
 
193

 
111

 
446

 
750

Property and plant, net
 
$
11,478

 
$
7,469

 
$
1,166

 
$
20,113

2015
 
 
 
 
 
 
 
 
Property, plant, and equipment at original cost:(b)
 
 
 
 
 
 
 
 
Electric generation
 
$
10,431

 
$
—

 
$
—

 
$
10,431

Electric distribution
 
5,303

 
4,952

 
—

 
10,255

Electric transmission
 
979

 
1,674

 
121

 
2,774

Natural gas
 
445

 
1,997

 
—

 
2,442

Other(c)
 
808

 
627

 
266

 
1,701

 
 
17,966

 
9,250

 
387

 
27,603

Less: Accumulated depreciation and amortization
 
7,460

 
2,632

 
255

 
10,347

 
 
10,506

 
6,618

 
132

 
17,256

Construction work in progress:
 
 
 
 
 
 
 
 
Nuclear fuel in process
 
275

 
—

 
—

 
275

Other
 
402

 
230

 
636

 
1,268

Property, plant, and equipment, net
 
$
11,183

 
$
6,848

 
$
768

 
$
18,799


(a)
Amounts in Ameren and Ameren Missouri include two CTs under separate capital lease agreements. The gross cumulative asset value of those agreements was $232 million and $233 million at December 31, 2016 and 2015, respectively. The total accumulated depreciation associated with the two CTs was $77 million and $72 million at December 31, 2016 and 2015, respectively. In addition, Ameren Missouri has investments in debt securities, classified as held-to-maturity and recorded in "Other assets" that are related to the two CTs from the city of Bowling Green and Audrain County. As of December 31, 2016 and 2015, the carrying value of these debt securities was $282 million and $288 million, respectively.
(b)
The estimated lives for each asset group are as follows: 5 to 100 years for electric generation, excluding Ameren Missouri's hydro generating assets which have useful lives of up to 150 years, 18 to 75 years for electric distribution, 50 to 75 years for electric transmission, 20 to 80 years for natural gas, and 5 to 55 years for other.
(c)
Other property, plant, and equipment includes assets used to support multiple utility services.
The following table provides accrued capital and nuclear fuel expenditures at December 31, 2016, 2015, and 2014, which represent noncash investing activity excluded from the accompanying statements of cash flows:
 
Ameren(a)
 
Ameren
Missouri
 
Ameren
Illinois
Accrued capital expenditures:
 
 
 
 
 
2016
$
251

 
$
116

 
$
87

2015
235

 
85

 
92

2014
181

 
72

 
59

Accrued nuclear fuel expenditures:
 
 
 
 
 
2016
20

 
20

 
(b)

2015
16

 
16

 
(b)

2014
13

 
13

 
(b)


(a)
Includes amounts for Ameren registrant and nonregistrant subsidiaries.
(b)
Not applicable.
Short-Term Debt And Liquidity
SHORT-TERM DEBT AND LIQUIDITY
SHORT-TERM DEBT AND LIQUIDITY
The liquidity needs of the Ameren Companies are typically supported through the use of available cash, drawings under committed credit agreements, commercial paper issuances, or in the case of Ameren Missouri and Ameren Illinois, short-term intercompany borrowings.
Credit Agreements
In December 2016, the Credit Agreements were amended and restated. The amended and restated agreements, among other things, extended the maturity dates of the Credit Agreements and provide $2.1 billion of credit through the extended maturity date. The Credit Agreements, which were previously scheduled to mature in December 2019, are now scheduled to mature in December 2021. The maturity date may be extended for two additional one-year periods upon mutual consent of the borrowers and lenders. Credit available under the agreements is provided by 22 international, national, and regional lenders, with no single lender providing more than $118 million of credit in aggregate.

The obligations of each borrower under the respective Credit Agreements to which it is a party are several and not joint. Except under limited circumstances relating to expenses and indemnities, the obligations of Ameren Missouri and Ameren Illinois under the respective Credit Agreements are not guaranteed by Ameren or any other subsidiary of Ameren. The following table presents the maximum aggregate amount available to each borrower under each facility (the amount being each borrower's "Borrowing Sublimit"):
 
 
Missouri Credit Agreement
Illinois
Credit Agreement
Ameren
 
$
700

$
500

Ameren Missouri
 
800

(a)

Ameren Illinois
 
  (a)

800

(a)
Not applicable.
The borrowers have the option to seek additional commitments from existing or new lenders to increase the total facility size of the Credit Agreements to a maximum of $1.2 billion for the Missouri Credit Agreement and $1.3 billion for the Illinois Credit Agreement. Ameren borrowings are due and payable no later than the maturity date of the Credit Agreement. Ameren Missouri and Ameren Illinois borrowings under the applicable Credit Agreement are due and payable no later than the earlier of the maturity date or 364 days after the originating date of the borrowing.
The obligations of the borrowers under the Credit Agreements are unsecured. Loans are available on a revolving basis under each of the Credit Agreements. Funds borrowed may be repaid and, subject to satisfaction of the conditions to borrowing, reborrowed from time to time. At the election of each borrower, the interest rates on such loans will be the alternate base rate plus the margin applicable to the particular borrower and/or the eurodollar rate plus the margin applicable to the particular borrower. The applicable margins will be determined by the borrower's long-term unsecured credit ratings or, if no such ratings are in effect, the borrower's corporate/issuer ratings then in effect. The borrowers have received commitments from the lenders to issue letters of credit up to $100 million under each of the Credit Agreements. In addition, the issuance of letters of credit is subject to the $2.1 billion overall combined facility borrowing limitations of the Credit Agreements.
The borrowers will use the proceeds from any borrowings under the Credit Agreements for general corporate purposes, including working capital, commercial paper liquidity support, issuance of letters of credit, loan funding under the Ameren money pool arrangements, and other short-term intercompany loan arrangements. Both of the Credit Agreements are available to Ameren to support issuances under Ameren's commercial paper program, subject to borrowing sublimits. The Missouri Credit Agreement and the Illinois Credit Agreement are available to support issuances under Ameren (parent)'s, Ameren Missouri's and Ameren Illinois' commercial paper programs, respectively. As of December 31, 2016, based on commercial paper outstanding and letters of credit issued under the Credit Agreements, the aggregate amount of credit capacity available to Ameren (parent), Ameren Missouri, and Ameren Illinois, collectively, was $1.5 billion.
Ameren, Ameren Missouri, and Ameren Illinois did not borrow under the Credit Agreements for the years ended December 31, 2016 and 2015.
Commercial Paper
The following table summarizes the borrowing activity and relevant interest rates under Ameren (parent)'s, Ameren Missouri's and Ameren Illinois' commercial paper programs for the years ended December 31, 2016 and 2015:
 
 
Ameren (parent)
Ameren Missouri
Ameren Illinois
Ameren Consolidated
2016
 
 
 
 
 
 
Average daily commercial paper outstanding
 
$
440

 
$
60

$
52

$
552

Outstanding borrowings at period-end
 
507

 
—

51

558

Weighted-average interest rate
 
0.82
%
 
0.74
%
0.69
%
0.80
%
Peak outstanding commercial paper during period(a)
 
$
574

 
$
208

$
195

$
839

Peak interest rate
 
1.05
%
 
0.85
%
0.90
%
1.05
%
2015
 
 
 
 
 
 
Average daily commercial paper outstanding
 
$
721

 
$
42

$
4

$
767

Outstanding borrowings at period-end
 
301

 
—

—

301

Weighted-average interest rate
 
0.57
%
 
0.50
%
0.44
%
0.55
%
Peak outstanding commercial paper during period(a)
 
$
874

 
$
294

$
48

$
1,108

Peak interest rate
 
0.91
%
 
0.60
%
0.60
%
0.91
%
(a)
The timing of peak outstanding commercial paper issuances varies by company. Therefore, the sum of the peak amounts presented by company might not equal the Ameren Consolidated peak amount for the period.
Indebtedness Provisions and Other Covenants
The information below is a summary of the Ameren Companies’ compliance with indebtedness provisions and other covenants.
The Credit Agreements contain conditions for borrowings and issuances of letters of credit. These conditions include the absence of default or unmatured default, material accuracy of representations and warranties (excluding any representation after the closing date as to the absence of material adverse change and material litigation, and the absence of any notice of violation, liability, or requirement under any environmental laws that could have a material adverse effect), and obtainment of required regulatory authorizations. In addition, it is a condition for any Ameren Illinois borrowing that, at the time of and after giving effect to such borrowing, Ameren Illinois not be in violation of any limitation on its ability to incur unsecured indebtedness contained in its articles of incorporation.
The Credit Agreements also contain nonfinancial covenants, including restrictions on the ability to incur certain liens, to transact with affiliates, to dispose of assets, to make investments in or transfer assets to its affiliates, and to merge with other entities. The Credit Agreements require each of Ameren, Ameren Missouri, and Ameren Illinois to maintain consolidated indebtedness of not more than 65% of its consolidated total capitalization pursuant to a defined calculation set forth in the agreements. As of December 31, 2016, the ratios of consolidated indebtedness to total consolidated capitalization, calculated in accordance with the provisions of the Credit Agreements, were 51%, 48%, and 47%, for Ameren, Ameren Missouri, and Ameren Illinois, respectively.
The Credit Agreements contain default provisions that apply separately to each borrower. However, a default of Ameren Missouri or Ameren Illinois under the applicable Credit Agreement is also deemed to constitute a default of Ameren under such agreement. Defaults include a cross-default resulting from a default of such borrower under any other agreement covering outstanding indebtedness of such borrower and certain subsidiaries (other than project finance subsidiaries and nonmaterial subsidiaries) in excess of $100 million in the aggregate (including under the other Credit Agreement). However, under the default provisions of the Credit Agreements, any default of Ameren under any Credit Agreement that results solely from a default of Ameren Missouri or Ameren Illinois does not result in a cross-default of Ameren under the other Credit Agreement. Further, the Credit Agreement default provisions provide that an Ameren default under any of the Credit Agreements does not constitute a default by Ameren Missouri or Ameren Illinois.
None of the Ameren Companies' credit agreements or financing agreements contain credit rating triggers that would cause a default or acceleration of repayment of outstanding balances. The Ameren Companies were in compliance with the provisions and covenants of their credit agreements at December 31, 2016.
Money Pools
Ameren has money pool agreements with and among its subsidiaries to coordinate and provide for certain short-term cash and working capital requirements.
Ameren Missouri, Ameren Illinois, and ATXI may participate in the utility money pool as both lenders and borrowers. Ameren and Ameren Services may participate in the utility money pool only as lenders. Surplus internal funds are contributed to the money pool from participants. The primary sources of external funds for the utility money pool are the Credit Agreements and the commercial paper programs. The total amount available to the pool participants from the utility money pool at any given time is reduced by the amount of borrowings made by participants, but is increased to the extent that the pool participants advance surplus funds to the utility money pool or remit funds from other external sources. The availability of funds is also determined by funding requirement limits established by regulatory authorizations. Participants receiving a loan under the money pool agreement must repay the principal amount of such loan, together with accrued interest. The rate of interest depends on the composition of internal and external funds in the utility money pool. The average interest rate for borrowing under the money pool for the year ended December 31, 2016 was 0.52% (2015 – 0.11%).
See Note 14 – Related Party Transactions for the amount of interest income and expense from the money pool arrangements recorded by the Ameren Companies for the years ended December 31, 2016, 2015, and 2014.
Long-Term Debt And Equity Financings
LONG-TERM DEBT AND EQUITY FINANCINGS
LONG-TERM DEBT AND EQUITY FINANCINGS
The following table presents long-term debt outstanding, including maturities due within one year, for the Ameren Companies as of December 31, 2016 and 2015:
 
2016
 
2015
Ameren (Parent):
 
 
 
2.70% Senior unsecured notes due 2020
$
350

 
$
350

3.65% Senior unsecured notes due 2026
350

 
350

Total long-term debt, gross
700

 
700

Less: Unamortized debt issuance costs
(6
)
 
(6
)
Long-term debt, net
$
694

 
$
694

Ameren Missouri:
 
 
 
Senior secured notes:(a)
 
 
 
5.40% Senior secured notes due 2016
—

 
260

6.40% Senior secured notes due 2017
425

 
425

6.00% Senior secured notes due 2018(b)
179

 
179

5.10% Senior secured notes due 2018
199

 
199

6.70% Senior secured notes due 2019(b)
329

 
329

5.10% Senior secured notes due 2019
244

 
244

5.00% Senior secured notes due 2020
85

 
85

3.50% Senior secured notes due 2024
350

 
350

5.50% Senior secured notes due 2034
184

 
184

5.30% Senior secured notes due 2037
300

 
300

8.45% Senior secured notes due 2039(b)
350

 
350

3.90% Senior secured notes due 2042(b)
485

 
485

3.65% Senior secured notes due 2045
400

 
250

Environmental improvement and pollution control revenue bonds:
 
 
 
1992 Series due 2022(c)(d)
47

 
47

1993 5.45% Series due 2028(e)
(e)

 
(e)

1998 Series A due 2033(c)(d)
60

 
60

1998 Series B due 2033(c)(d)
50

 
50

1998 Series C due 2033(c)(d)
50

 
50

Capital lease obligations:
 
 
 
City of Bowling Green capital lease (Peno Creek CT) due 2022
42

 
48

Audrain County capital lease (Audrain County CT) due 2023
240

 
240

Total long-term debt, gross
4,019

 
4,135

Less: Unamortized discount and premium
(6
)
 
(6
)
Less: Unamortized debt issuance costs
(19
)
 
(19
)
Less: Maturities due within one year
(431
)
 
(266
)
Long-term debt, net
$
3,563

 
$
3,844

 
2016
 
2015
Ameren Illinois:
 
 
 
Senior secured notes:
 
 
 
6.20% Senior secured notes due 2016
$
—

 
$
54

6.25% Senior secured notes due 2016
—

 
75

6.125% Senior secured notes due 2017(g)(h)
250

 
250

6.25% Senior secured notes due 2018(g)(h)
144

 
144

9.75% Senior secured notes due 2018(g)(h)
313

 
313

2.70% Senior secured notes due 2022(g)(h)
400

 
400

3.25% Senior secured notes due 2025(g)
300

 
300

6.125% Senior secured notes due 2028(g)
60

 
60

6.70% Senior secured notes due 2036(g)
61

 
61

6.70% Senior secured notes due 2036(f)
42

 
42

4.80% Senior secured notes due 2043(g)
280

 
280

4.30% Senior secured notes due 2044(g)
250

 
250

4.15% Senior secured notes due 2046(g)
490

 
250

Environmental improvement and pollution control revenue bonds:
 
 
 
5.90% Series 1993 due 2023(i)
(i)

 
(i)

5.70% 1994A Series due 2024(j)
(j)

 
(j)

1993 Series B-1 due 2028(d)(k)
17

 
17

Total long-term debt, gross
2,607

 
2,496

Less: Unamortized discount and premium
—

 
(7
)
Less: Unamortized debt issuance costs
(19
)
 
(18
)
Less: Maturities due within one year
(250
)
 
(129
)
Long-term debt, net
$
2,338

 
$
2,342

Ameren consolidated long-term debt, net
$
6,595

 
$
6,880


(a)
These notes are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any first mortgage bonds issued under the Ameren Missouri mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Missouri senior secured notes currently outstanding, we do not expect the first mortgage bond lien protection associated with these notes to fall away before 2042.
(b)
Ameren Missouri has agreed that so long as any of the 3.90% senior secured notes due 2042 are outstanding, Ameren Missouri will not permit a release date to occur, and so long as any of the 6.70% senior secured notes due 2019, 6.00% senior secured notes due 2018, and 8.45% senior secured notes due 2039 are outstanding, Ameren Missouri will not optionally redeem, purchase, or otherwise retire in full the outstanding first mortgage bonds not subject to release provisions.
(c)
These bonds are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture and have a fall-away lien provision similar to that of Ameren Missouri's senior secured notes. The bonds are also backed by an insurance guarantee policy.
(d)
The interest rates and the periods during which such rates apply vary depending on our selection of defined rate modes. Maximum interest rates could reach 18%, depending on the series of bonds. The bonds are callable at 100% of par value. The average interest rates for 2016 and 2015 were as follows:
    
 
2016
 
2015
Ameren Missouri 1992 Series due 2022
0.66%
 
0.06%
Ameren Missouri 1998 Series A due 2033
0.91%
 
0.24%
Ameren Missouri 1998 Series B due 2033
0.92%
 
0.24%
Ameren Missouri 1998 Series C due 2033
0.97%
 
0.24%
Ameren Illinois 1993 Series B-1 due 2028
0.70%
 
0.49%

(e)
These bonds are first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage bond indenture and are secured by substantially all Ameren Missouri property and franchises. The bonds are callable at 100% of par value. Less than $1 million principal amount of the bonds remain outstanding.
(f)
These notes are collaterally secured by first mortgage bonds issued by Ameren Illinois under its 1933 mortgage indenture. The notes have a fall-away lien provision, and Ameren Illinois could cause these notes to become unsecured at any time by redeeming the pollution control bonds 5.90% Series 1993 due 2023 (of which less than $1 million remains outstanding).
(g)
These notes are collaterally secured by mortgage bonds issued by Ameren Illinois under its 1992 mortgage indenture. They are secured by substantially all property of the former IP and CIPS. The notes have a fall-away lien provision and will remain secured only as long as any series of first mortgage bonds issued under its 1992 mortgage indenture remain outstanding. Redemption, purchase, or maturity of all mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Illinois senior secured notes currently outstanding, we do not expect the mortgage bond lien protection associated with these notes to fall away before 2022.
(h)
Ameren Illinois has agreed that so long as any of the 2.70% senior secured notes due 2022 are outstanding, Ameren Illinois will not permit a release date to occur, and so long as any of the 9.75% senior secured notes due 2018, 6.25% senior secured notes due 2018, and 6.125% senior secured notes due 2017 are outstanding, Ameren Illinois will not optionally redeem, purchase or otherwise retire in full the outstanding first mortgage bonds not subject to release provisions; therefore, a release date will not occur so long as any of these notes remain outstanding.
(i)
These bonds are first mortgage bonds issued by Ameren Illinois under its 1933 mortgage indenture. They are secured by substantially all property of the former CILCO. The bonds are callable at 100% of par value. Less than $1 million principal amount of the bonds remain outstanding.
(j)
These bonds are mortgage bonds issued by Ameren Illinois under its 1992 mortgage indenture. They are secured by substantially all property of the former IP and CIPS. The bonds are callable at 100% of par value. The bonds are also backed by an insurance guarantee policy. Less than $1 million principal amount of the bonds remains outstanding.
(k)
The bonds are callable at 100% of par value.
The following table presents the aggregate maturities of long-term debt, including current maturities, for the Ameren Companies at December 31, 2016:
 
Ameren
(parent)(a)
 
 Ameren
Missouri(a)
 
 Ameren
Illinois(a)
 
Ameren
Consolidated
2017
$
—

 
$
431

 
$
250

 
$
681

2018
—

 
383

 
457

 
840

2019
—

 
581

 
—

 
581

2020
350

 
92

 
—

 
442

2021
—

 
8

 
—

 
8

Thereafter
350

 
2,524

 
1,900

 
4,774

Total
$
700

 
$
4,019

 
$
2,607

 
$
7,326

(a)
Excludes unamortized discount and premium and debt issuance costs of $6 million, $25 million, and $19 million at Ameren (parent), Ameren Missouri, and Ameren Illinois, respectively.
All classes of Ameren Missouri’s and Ameren Illinois’ preferred stock are entitled to cumulative dividends, have voting rights, and are not subject to mandatory redemption. The preferred stock of Ameren's subsidiaries was included in "Noncontrolling Interests" on Ameren's consolidated balance sheet. The following table presents the outstanding preferred stock of Ameren Missouri and Ameren Illinois, which is redeemable, at the option of the issuer, at the prices shown below as of December 31, 2016 and 2015:
 
 
 
Redemption Price(per share)
 
2016
 
2015
Ameren Missouri:
 
 
 
 
 
 
 
Without par value and stated value of $100 per share, 25 million shares authorized
 
 
 
 
 
 
$3.50 Series
130,000 shares
 
$
110.00

 
$
13

 
$
13

$3.70 Series
40,000 shares
 
104.75

 
4

 
4

$4.00 Series
150,000 shares
 
105.625

 
15

 
15

$4.30 Series
40,000 shares
 
105.00

 
4

 
4

$4.50 Series
213,595 shares
 
110.00

(a) 
21

 
21

$4.56 Series
200,000 shares
 
102.47

 
20

 
20

$4.75 Series
20,000 shares
 
102.176

 
2

 
2

$5.50 Series A
14,000 shares
 
110.00

 
1

 
1

Total
 
 
 
$
80

 
$
80

Ameren Illinois:
 
 
 
 
 
 
 
With par value of $100 per share, 2 million shares authorized
 
 
 
 
 
 
4.00% Series
144,275 shares
 
$
101.00

 
$
14

 
$
14

4.08% Series
45,224 shares
 
103.00

 
5

 
5

4.20% Series
23,655 shares
 
104.00

 
2

 
2

4.25% Series
50,000 shares
 
102.00

 
5

 
5

4.26% Series
16,621 shares
 
103.00

 
2

 
2

4.42% Series
16,190 shares
 
103.00

 
2

 
2

4.70% Series
18,429 shares
 
103.00

 
2

 
2

4.90% Series
73,825 shares
 
102.00

 
7

 
7

4.92% Series
49,289 shares
 
103.50

 
5

 
5

5.16% Series
50,000 shares
 
102.00

 
5

 
5

6.625% Series
124,274 shares
 
100.00

 
12

 
12

7.75% Series
4,542 shares
 
100.00

 
1

 
1

Total
 
 
 
$
62

 
$
62

Total Ameren
 
 
 
$
142

 
$
142

(a)
In the event of voluntary liquidation, $105.50.
Ameren has 100 million shares of $0.01 par value preferred stock authorized, with no such shares outstanding. Ameren Missouri has 7.5 million shares of $1 par value preference stock authorized, with no such shares outstanding. Ameren Illinois has 2.6 million shares of no par value preferred stock authorized, with no such shares outstanding.
Ameren
In November 2015, Ameren (parent) issued $350 million of 2.70% senior unsecured notes due in November 2020, with interest payable semiannually in May and November of each year, beginning in May 2016. Ameren (parent) received proceeds of $348 million, which were used to repay a portion of its short-term debt.
In November 2015, Ameren (parent) issued $350 million of 3.65% senior unsecured notes due in February 2026, with interest payable semiannually in February and August of each year, beginning in February 2016. Ameren (parent) received proceeds of $347 million, which were used to repay a portion of its short-term debt.
In 2015, Ameren, Ameren Missouri, and Ameren Illinois filed a Form S-3 shelf registration statement registering the issuance of an indeterminate amount of certain types of securities. The registration statement became effective immediately upon filing and will expire in June 2018.
Ameren filed a Form S-3 registration statement with the SEC in 2014, authorizing the offering of 8.6 million additional shares of its common stock under DRPlus, which expires in May 2017. Shares of common stock sold under DRPlus are, at Ameren’s option, newly issued shares, treasury shares, or shares purchased in the open market or in privately negotiated transactions. As of December 31, 2016 and 2015, DRPlus participant funds of $8 million were reflected on Ameren's consolidated balance sheets in "Other current assets."
In 2013, Ameren filed a Form S-8 registration statement with the SEC, authorizing the offering of 4 million additional shares of its common stock under its 401(k) plan. Shares of common stock sold under the 401(k) plan are, at Ameren’s option, newly issued shares, treasury shares, or shares purchased in the open market or in privately negotiated transactions.
From 2014 through 2016, Ameren shares for its DRPlus and its 401(k) plans were purchased in the open market.
Ameren Missouri
In February 2016, $260 million principal amount of Ameren Missouri's 5.40% senior secured notes matured and were repaid with cash on hand and commercial paper borrowings.
In June 2016 and April 2015, Ameren Missouri issued $150 million and $250 million, respectively, of 3.65% senior secured notes due in April 2045, with interest payable semiannually in April and October of each year, beginning in October 2016 and 2015, respectively. Ameren Missouri received proceeds of $148 million from the June 2016 issuance and $247 million from the April 2015 issuance, which were both used to repay outstanding short-term debt, including short-term debt that Ameren Missouri incurred in connection with the repayment of $114 million of its 4.75% senior secured notes that matured in April 2015.
For information on Ameren Missouri's capital contributions and return of capital, refer to Capital Contributions and Return of Capital in Note 1 – Summary of Significant Accounting Policies.
Ameren Illinois
In June 2016, Ameren Illinois’ $54 million principal amount of 6.20% senior secured notes and $75 million principal amount of 6.25% senior secured notes matured and were repaid with commercial paper borrowings.
In December 2016 and 2015, Ameren Illinois issued $240 million and $250 million, respectively, of 4.15% senior secured notes due in March 2046, with interest payable semiannually in March and September, beginning in March 2017 and 2016, respectively. Ameren Illinois received proceeds of $245 million from each issuance, which were both used to repay a portion of its short-term debt.
For information on Ameren Illinois' capital contributions, refer to Capital Contributions and Return of Capital in Note 1 – Summary of Significant Accounting Policies.
Indenture Provisions and Other Covenants
Ameren Missouri’s and Ameren Illinois’ indentures and articles of incorporation include covenants and provisions related to issuances of first mortgage bonds and preferred stock. Ameren Missouri and Ameren Illinois are required to meet certain ratios to issue additional first mortgage bonds and preferred stock. A failure to achieve these ratios would not result in a default under these covenants and provisions but would restrict the companies’ ability to issue bonds or preferred stock. The following table summarizes the required and actual interest coverage ratios for interest charges, dividend coverage ratios, and bonds and preferred stock issuable as of December 31, 2016, at an assumed interest rate of 5% and dividend rate of 6%.
 
Required Interest
Coverage Ratio(a)
Actual Interest
Coverage Ratio
Bonds Issuable(b)
 
Required Dividend
Coverage Ratio(c)
Actual Dividend
Coverage Ratio
Preferred Stock
Issuable
 
Ameren Missouri
>2.0
4.6

$
4,077

  
>2.5
105.3

$
2,344

 
Ameren Illinois
>2.0
6.9

3,819

(d) 
>1.5
2.8

203

(e) 
(a)
Coverage required on the annual interest charges on first mortgage bonds outstanding and to be issued. Coverage is not required in certain cases when additional first mortgage bonds are issued on the basis of retired bonds.
(b)
Amount of bonds issuable based either on required coverage ratios or unfunded property additions, whichever is more restrictive. The amounts shown also include bonds issuable based on retired bond capacity of $1,206 million and $279 million at Ameren Missouri and Ameren Illinois, respectively.
(c)
Coverage required on the annual dividend on preferred stock outstanding and to be issued, as required in the respective company’s articles of incorporation.
(d)
Amount of bonds issuable by Ameren Illinois based on unfunded property additions and retired bonds solely under its 1992 mortgage indenture.
(e)
Preferred stock issuable is restricted by the amount of preferred stock that is currently authorized by Ameren Illinois' articles of incorporation.

Ameren's indenture does not require Ameren to comply with any quantitative financial covenants. The indenture does, however, include certain cross-default provisions. Specifically, either (1) the failure by Ameren to pay when due and upon expiration of any applicable grace period any portion of any Ameren indebtedness in excess of $25 million, or (2) the acceleration upon default of the maturity of any Ameren indebtedness in excess of $25 million under any indebtedness agreement, including borrowings under the Credit Agreements or the Ameren commercial paper program, constitutes a default under the indenture, unless such past due or accelerated debt is discharged or the acceleration is rescinded or annulled within a specified period.

Ameren Missouri and Ameren Illinois and certain other nonregistrant Ameren subsidiaries are subject to Section 305(a) of the Federal Power Act, which makes it unlawful for any officer or director of a public utility, as defined in the Federal Power Act, to participate in the making or paying of any dividend from any funds “properly included in capital account.” The FERC has consistently interpreted the provision to allow dividends to be paid as long as (1) the source of the dividends is clearly disclosed, (2) the dividends are not excessive, and (3) there is no self-dealing on the part of corporate officials. At a minimum, Ameren believes that dividends can be paid by its subsidiaries that are public utilities from net income and retained earnings. In addition, under Illinois law, Ameren Illinois may not pay any dividend on its stock unless, among other things, its earnings and earned surplus are sufficient to declare and pay a dividend after provision is made for reasonable and proper reserves, or unless Ameren Illinois has specific authorization from the ICC.
Ameren Illinois’ articles of incorporation require dividend payments on its common stock to be based on ratios of common stock to total capitalization and other provisions related to certain operating expenses and accumulations of earned surplus. Ameren Illinois has made a commitment to the FERC to maintain a minimum 30% ratio of common stock equity to total capitalization. As of December 31, 2016, using the FERC-agreed upon calculation method, Ameren Illinois’ ratio of common stock equity to total capitalization was 51%.
In order for the Ameren Companies to issue securities in the future, they will have to comply with all applicable requirements in effect at the time of any such issuances.
Off-Balance-Sheet Arrangements
At December 31, 2016, none of the Ameren Companies had off-balance-sheet financing arrangements, other than operating leases entered into in the ordinary course of business, letters of credit, and Ameren parent guarantee arrangements on behalf of its subsidiaries. None of the Ameren Companies expect to engage in any significant off-balance-sheet financing arrangements in the near future.
Other Income And Expenses
OTHER INCOME AND EXPENSES
OTHER INCOME AND EXPENSES
The following table presents the components of "Other Income and Expenses" in the Ameren Companies’ statements of income (loss) for the years ended December 31, 2016, 2015, and 2014:
 
2016
 
2015
 
2014
 
Ameren:(a)
 
 
 
 
 
 
Miscellaneous income:
 
 
 
 
 
 
Allowance for equity funds used during construction
$
27

 
$
30

 
$
34

 
Interest income on industrial development revenue bonds
27

 
27

 
27

 
Interest income (b)
13

  
14

  
10

 
Other
7

 
3

 
8

(c) 
Total miscellaneous income
$
74

 
$
74

 
$
79

 
Miscellaneous expense:
 
 
 
 
 
 
Donations
$
16

 
$
15

 
$
10

 
Other
16

 
15

 
12

 
Total miscellaneous expense
$
32

 
$
30

 
$
22

 
Ameren Missouri:
 
 
 
 
 
 
Miscellaneous income:
 
 
 
 
 
 
Allowance for equity funds used during construction
$
23

 
$
22

 
$
32

 
Interest income on industrial development revenue bonds
27

 
27

 
27

 
Interest income
1

 
1

 
1

 
Other
1

 
2

 
—

 
Total miscellaneous income
$
52

 
$
52

 
$
60

 
Miscellaneous expense:
 
 
 
 
 
 
Donations
$
4

 
$
5

 
$
6

 
Other
6

 
6

 
6

 
Total miscellaneous expense
$
10

 
$
11

 
$
12

 
Ameren Illinois:
 
 
 
 
 
 
Miscellaneous income:
 
 
 
 
 
 
Allowance for equity funds used during construction
$
4

 
$
8

 
$
2

 
Interest income (b)
12

  
12

  
7

 
Other
5

 
1

 
8

(c) 
Total miscellaneous income
$
21

 
$
21

 
$
17

 
Miscellaneous expense:
 
 
 
 
 
 
Donations
$
6

 
$
5

 
$
4

 
Other
6

 
7

 
4

 
Total miscellaneous expense
$
12

 
$
12

 
$
8

 
(a)
Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
(b)
Includes Ameren Illinois' interest income on the IEIMA revenue requirement reconciliation adjustment regulatory assets.
(c)
Includes Ameren Illinois' income earned in 2014 from customer-requested construction.
Derivative Financial Instruments
DERIVATIVE FINANCIAL INSTRUMENTS
DERIVATIVE FINANCIAL INSTRUMENTS
We use derivatives to manage the risk of changes in market prices for natural gas, power, and uranium, as well as the risk of changes in rail transportation surcharges through fuel oil hedges. Such price fluctuations may cause the following:
•
an unrealized appreciation or depreciation of our contracted commitments to purchase or sell when purchase or sale prices under the commitments are compared with current commodity prices;
•
market values of natural gas and uranium inventories that differ from the cost of those commodities in inventory; and
•
actual cash outlays for the purchase of these commodities that differ from anticipated cash outlays.
The derivatives that we use to hedge these risks are governed by our risk management policies for forward contracts, futures, options, and swaps. Our net positions are continually assessed within our structured hedging programs to determine whether new or offsetting transactions are required. The goal of the hedging program is generally to mitigate financial risks while ensuring that sufficient volumes are available to meet our requirements. Contracts we enter into as part of our risk management program may be settled financially, settled by physical delivery, or net settled with the counterparty.
The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of December 31, 2016 and 2015. As of December 31, 2016, these contracts extended through October 2019, March 2021, May 2032, and February 2020 for fuel oils, natural gas, power, and uranium, respectively.
  
Quantity (in millions, except as indicated)
 
2016
2015
Commodity
Ameren Missouri
Ameren Illinois
Ameren
Ameren Missouri
Ameren Illinois
Ameren
Fuel oils (in gallons)(a)
30
(b)
30
35
(b)
35
Natural gas (in mmbtu)
25
129
154
30
151
181
Power (in megawatthours)
1
9
10
1
10
11
Uranium (pounds in thousands)
345
(b)
345
494
(b)
494

(a)
Consists of ultra-low-sulfur diesel products.
(b)
Not applicable.
All contracts considered to be derivative instruments are required to be recorded on the balance sheet at their fair values, unless the NPNS exception applies. See Note 8 – Fair Value Measurements for discussion of our methods of assessing the fair value of derivative instruments. Many of our physical contracts, such as our purchased power contracts, qualify for the NPNS exception to derivative accounting rules. The revenue or expense on NPNS contracts is recognized at the contract price upon physical delivery.
If we determine that a contract meets the definition of a derivative and is not eligible for the NPNS exception, we review the contract to determine whether the resulting gains or losses qualify for regulatory deferral. Derivative contracts that qualify for regulatory deferral are recorded at fair value, with changes in fair value recorded as regulatory assets or liabilities in the period in which the change occurs. We believe derivative losses and gains deferred as regulatory assets and liabilities are probable of recovery, or refund, through future rates charged to customers. Regulatory assets and liabilities are amortized to operating income as related losses and gains are reflected in rates charged to customers. Therefore, gains and losses on these derivatives have no effect on operating income. As of December 31, 2016 and 2015, all contracts that met the definition of a derivative and were not eligible for the NPNS exception received regulatory deferral.

The following table presents the carrying value and balance sheet location of all derivative commodity contracts, none of which were designated as hedging instruments, as of December 31, 2016 and 2015:
 
Balance Sheet Location
 
Ameren
Missouri
 
Ameren
Illinois
 
Ameren
2016
 
 
 
 
 
 
 
Fuel oils
Other current assets
$
2

$
—

$
2

 
Other assets
 
1

 
—

 
1

Natural gas
Other current assets
 
1

 
11

 
12

 
Other assets
 
1

 
2

 
3

Power
Other current assets
 
9

 
—

 
9

 
Total assets (a)
$
14

$
13

$
27

Fuel oils
Other current liabilities
$
5

$
—

$
5

Natural gas
MTM derivative liabilities
 
(b)

 
3

 
(b)

 
Other current liabilities
 
1

 
—

 
4

 
Other deferred credits and liabilities
 
5

 
5

 
10

Power
MTM derivative liabilities
 
(b)

 
12

 
(b)

 
Other current liabilities
 
3

 
—

 
15

 
Other deferred credits and liabilities
 
—

 
173

 
173

Uranium
Other deferred credits and liabilities
 
4

 
—

 
4

 
Total liabilities (c)
$
18

$
193

$
211

2015
 
 
 
 
 
 
 
Natural gas
Other current assets
$
—

 
1

$
1

 
Other assets
 
1

 
—

 
1

Power
Other current assets
 
16

 
—

 
16

 
Total assets (a)
$
17

$
1

$
18

Fuel oils
Other current liabilities
$
22

$
—

$
22

 
Other deferred credits and liabilities
 
7

 
—

 
7

Natural gas
MTM derivative liabilities
 
(b)

 
32

 
(b)

 
Other current liabilities
 
6

 
—

 
38

 
Other deferred credits and liabilities
 
8

 
18

 
26

Power
MTM derivative liabilities
 
(b)

 
13

 
(b)

 
Other current liabilities
 
—

 
—

 
13

 
Other deferred credits and liabilities
 
—

 
157

 
157

Uranium
Other current liabilities
 
1

 
—

 
1

 
Total liabilities (c)
$
44

$
220

$
264

(a)
The cumulative amount of pretax net gains on all derivative instruments is deferred as a regulatory liability.
(b)
Balance sheet line item not applicable to registrant.
(c)
The cumulative amount of pretax net losses on all derivative instruments is deferred as a regulatory asset.
Derivative instruments are subject to various credit-related losses in the event of nonperformance by counterparties to the transaction. Exchange-traded contracts are supported by the financial and credit quality of the clearing members of the respective exchanges; these contracts have nominal credit risk. In all other transactions, we are exposed to credit risk. Our credit risk management program involves establishing credit limits and collateral requirements for counterparties, using master netting arrangements or similar agreements, and reporting daily exposure to senior management. As of December 31, 2016 and 2015, Ameren Missouri's balance sheet reflected $12 million and $11 million, respectively, of cash collateral posted within "Other Assets." As of December 31, 2015, Ameren Illinois' balance sheet reflected $3 million of cash collateral posted within "Other Assets."
We believe that entering into master netting arrangements or similar agreements mitigates the level of financial loss that could result from default by allowing net settlement of derivative assets and liabilities. These master netting arrangements allow the counterparties to net settle sale and purchase transactions. Further, collateral requirements are calculated at the master netting arrangement or similar agreement level by counterparty.
The Ameren Companies elect to present the fair value amounts of derivative assets and derivative liabilities subject to an enforceable master netting arrangement or similar agreement gross on the balance sheet. However, if the gross amounts recognized on the balance sheet were netted with derivative instruments and cash collateral received or posted, the net amounts would not be materially different from the gross amounts at December 31, 2016 and 2015.
Concentrations of Credit Risk
In determining our concentrations of credit risk related to derivative instruments, we review our individual counterparties and categorize each counterparty into groupings according to the primary business in which each engages. We calculate maximum exposures based on the gross fair value of financial instruments, including NPNS and other accrual contracts. These exposures are presented on a gross basis, which include affiliate exposure not eliminated at the consolidated Ameren level. As of December 31, 2016, if counterparty groups were to fail completely to perform on contracts, the Ameren Companies' maximum exposure would have been immaterial with or without consideration of the application of master netting arrangements or similar agreements and collateral held.
Derivative Instruments with Credit Risk-Related Contingent Features
Our commodity contracts contain collateral provisions tied to the Ameren Companies’ credit ratings. If our credit ratings were downgraded, or if a counterparty with reasonable grounds for uncertainty regarding our ability to satisfy an obligation requested adequate assurance of performance, additional collateral postings might be required. The following table presents, as of December 31, 2016, the aggregate fair value of all derivative instruments with credit risk-related contingent features in a gross liability position, the cash collateral posted, and the aggregate amount of additional collateral that counterparties could require. The additional collateral required is the net liability position allowed under the master netting arrangements or similar agreements, assuming (1) the credit risk-related contingent features underlying these arrangements were triggered on December 31, 2016, and (2) those counterparties with rights to do so requested collateral.
 
Aggregate Fair Value of
Derivative Liabilities(a)
 
Cash
Collateral Posted
 
Potential Aggregate Amount of
Additional Collateral Required(b)
2016
 
 
 
 
 
Ameren Missouri
$
64

 
$
3

 
$
54

Ameren Illinois
33

 
—

 
26

Ameren
$
97

 
$
3

 
$
80

(a)
Before consideration of master netting arrangements or similar agreements and including NPNS and other accrual contract exposures.
(b)
As collateral requirements with certain counterparties are based on master netting arrangements or similar agreements, the aggregate amount of additional collateral required to be posted is determined after consideration of the effects of such arrangements.
Fair Value Measurements
FAIR VALUE MEASUREMENTS
FAIR VALUE MEASUREMENTS
Fair value is defined as the price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. We use various methods to determine fair value, including market, income, and cost approaches. With these approaches, we adopt certain assumptions that market participants would use in pricing the asset or liability, including assumptions about market risk or the risks inherent in the inputs to the valuation. Inputs to valuation can be readily observable, market-corroborated, or unobservable. We use valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs. Authoritative accounting guidance established a fair value hierarchy that prioritizes the inputs used to measure fair value. All financial assets and liabilities carried at fair value are classified and disclosed in one of the following three hierarchy levels:
Level 1: Inputs based on quoted prices in active markets for identical assets or liabilities. Level 1 assets and liabilities are primarily exchange-traded derivatives and assets, including cash and cash equivalents and listed equity securities, such as those held in Ameren Missouri’s nuclear decommissioning trust fund.
The market approach is used to measure the fair value of equity securities held in Ameren Missouri's nuclear decommissioning trust fund. Equity securities in this fund are representative of the S&P 500 index, excluding securities of Ameren Corporation, owners and/or operators of nuclear power plants, and the trustee and investment managers. The S&P 500 index comprises stocks of large-capitalization companies.
Level 2: Market-based inputs corroborated by third-party brokers or exchanges based on transacted market data. Level 2 assets and liabilities include certain assets held in Ameren Missouri’s nuclear decommissioning trust fund, including corporate bonds and other fixed-income securities, United States Treasury and agency securities, and certain over-the-counter derivative instruments, including natural gas and financial power transactions.
Fixed income securities are valued by using prices from independent industry-recognized data vendors who provide values that are either exchange-based or matrix-based. The fair value measurements of fixed-income securities classified as Level 2 are based on inputs other than quoted prices that are observable for the asset or liability. Examples are matrix pricing, market corroborated pricing, and inputs such as yield curves and indices. Level 2 fixed income securities in the nuclear decommissioning trust fund are primarily corporate bonds, asset-backed securities, and United States agency bonds.
Derivative instruments classified as Level 2 are valued by corroborated observable inputs, such as pricing services or prices from similar instruments that trade in liquid markets. Our development and corroboration process entails obtaining multiple quotes or prices from outside sources. To derive our forward view to price our derivative instruments at fair value, we average the bid/ask spreads to the midpoints. To validate forward prices obtained from outside parties, we compare the pricing to recently settled market transactions. Additionally, a review of all sources is performed to identify any anomalies or potential errors. Further, we consider the volume of transactions on certain trading platforms in our reasonableness assessment of the averaged midpoints. The value of natural gas derivative contracts is based upon exchange closing prices without significant unobservable adjustments. The value of power derivatives contracts is based upon the use of multiple forward prices provided by third parties. The prices are averaged and shaped to a monthly profile when needed without significant unobservable adjustments.
Level 3: Unobservable inputs that are not corroborated by market data. Level 3 assets and liabilities are valued by internally developed models and assumptions or methodologies that use significant unobservable inputs. Level 3 assets and liabilities include derivative instruments that trade in less liquid markets, where pricing is largely unobservable. We value Level 3 instruments by using pricing models with inputs that are often unobservable in the market, such as certain internal assumptions, quotes or prices from outside sources not supported by a liquid market, or escalation rates. Our development and corroboration process entails reasonableness reviews and an evaluation of all sources to identify any anomalies or potential errors.
We perform an analysis each quarter to determine the appropriate hierarchy level of the assets and liabilities subject to fair value measurements. Financial assets and liabilities are classified in their entirety according to the lowest level of input that is significant to the fair value measurement. All assets and liabilities whose fair value measurement is based on significant unobservable inputs are classified as Level 3.
The following table describes the valuation techniques and unobservable inputs utilized by the Ameren Companies for the fair value of financial assets and liabilities classified as Level 3 in the fair value hierarchy for the periods ended December 31, 2016 and 2015:
 
 
Fair Value
 
 
 
 
Weighted
 
 
Assets
Liabilities
 
Valuation Technique(s)
Unobservable Input
Range
Average
Level 3 Derivative asset and liability – commodity contracts(a):
 
 
 
2016
 
 
 
 
 
 
 
 
 
Fuel oils
$
1

$
—

 
Option model
Volatilities(%)(b)
24 – 66
28
 
 
 
 
 
Discounted cash flow
Counterparty credit risk(%)(c)(d)
0.13 – 0.22
0.15
 
 
 
 
 
 
Ameren Missouri credit risk(%)(c)(d)
0.38
(e)
 
 
 
 
 
 
Escalation rate(%)(b)(f)
(2) – 2
0
 
Natural Gas
1

(1
)
 
Option model
Volatilities(%)(b)
31 – 66
36
 



 

Nodal basis($/mmbtu)(b)
(0.40) – (0.10)
(0.20)
 



 
Discounted cash flow
Nodal basis($/mmbtu)(b)
(0.80) – 0
(0.50)
 



 

Counterparty credit risk(%)(c)(d)
0.13 – 8
1
 



 

Ameren Illinois credit risk(%)(c)(d)
0.38
(e)
 
Power(g)
9

(187
)
 
Discounted cash flow
Average forward peak and off-peak pricing – forwards/swaps($/MWh)(h)
26 – 44
29
 
 
 
 
 
 
Estimated auction price for FTRs($/MW)(b)
(71) – 5,270
125
 
 
 
 
 
 
Nodal basis($/MWh)(h)
(6) – 0
(2)
 
 
 
 
 
 
Ameren Illinois credit risk(%)(c)(d)
0.38
(e)
 
 
 
 
 
Fundamental energy production model
Estimated future natural gas prices($/mmbtu)(b)
3 – 4
3
 
 
 
 
 
 
Escalation rate(%)(b)(i)
5
(e)
 
 
 
 
 
Contract price allocation
Estimated renewable energy credit costs($/credit)(b)
5 – 7
6
 
Uranium
—

(4
)
 
Option model
Volatilities(%)(b)
24
(e)
 
 
 
 
 
Discounted cash flow
Average forward uranium pricing($/pound)(b)
22 – 24
22
 
 
 
 
 
 
Ameren Missouri credit risk(%)(c)(d)
0.38
(e)
2015
 
 
 
 
 
 
 
 
 
Natural Gas
$
1

$
(1
)
 
Option model
Volatilities(%)(b)
35 – 55
45
 
 
 
 
 
 
Nodal basis($/mmbtu)(c)
(0.30) – 0
(0.20)
 
 
 
 
 
Discounted cash flow
Nodal basis($/mmbtu)(b)
(0.10) – 0
(0.10)
 
 
 
 
 
 
Counterparty credit risk(%)(c)(d)
0.40 – 12
7
 
 
 
 
 
 
Ameren Missouri credit risk(%)(c)(d)
0.40
(e)
 
Power(g)
16

(170
)
 
Discounted cash flow
Average forward peak and off-peak pricing – forwards/swaps($/MWh)(h)
22 – 39
29
 
 
 
 
 
 
Estimated auction price for FTRs($/MW)(b)
(270) – 2,057
211
 
 
 
 
 
 
Nodal basis($/MWh)(h)
(10) – (1)
(3)
 
 
Fair Value
 
 
 
 
Weighted
 
 
Assets
Liabilities
 
Valuation Technique(s)
Unobservable Input
Range
Average
 
 
 
 
 
 
Counterparty credit risk(%)(c)(d)
0.86
(e)
 
 
 
 
 
 
Ameren Illinois credit risk(%)(c)(d)
0.40
(e)
 
 
 
 
 
Fundamental energy production model
Estimated future natural gas prices($/mmbtu)(b)
3 – 4
4
 
 
 
 
 
 
Escalation rate(%)(b)(i)
3
(e)
 
 
 
 
 
Contract price allocation
Estimated renewable energy credit costs($/credit)(b)
5 – 7
6
 
Uranium
—

(1
)
 
Option model
Volatilities(%)(b)
20
(e)
 
 
 
 
 
Discounted cash flow
Average forward uranium pricing($/pound)(b)
35 – 42
37
 
 
 
 
 
 
Ameren Missouri credit risk(%)(c)(d)
0.40
(e)
(a)
The derivative asset and liability balances are presented net of counterparty credit considerations.
(b)
Generally, significant increases (decreases) in this input in isolation would result in a significantly higher (lower) fair value measurement.
(c)
Generally, significant increases (decreases) in this input in isolation would result in a significantly lower (higher) fair value measurement.
(d)
Counterparty credit risk is applied only to counterparties with derivative asset balances. Ameren Missouri and Ameren Illinois credit risk is applied only to counterparties with derivative liability balances.
(e)
Not applicable.
(f)
Escalation rate applies to fuel oil prices 2019 and beyond.
(g)
Power valuations use visible third-party pricing evaluated by month for peak and off-peak demand through 2020. Valuations beyond 2020 use fundamentally modeled pricing by month for peak and off-peak demand.
(h)
The balance at Ameren is comprised of Ameren Missouri and Ameren Illinois power contracts, which respond differently to unobservable input changes because of their opposing positions.
(i)
Escalation rate applies to power prices in 2031 and beyond for December 31, 2016, and to power prices in 2026 and beyond for December 31, 2015.
We consider nonperformance risk in our valuation of derivative instruments by analyzing the credit standing of our counterparties and considering any counterparty credit enhancements (e.g., collateral). The guidance also requires that the fair value measurement of liabilities reflect the nonperformance risk of the reporting entity, as applicable. Therefore, we have factored the impact of our credit standing, as well as any potential credit enhancements, into the fair value measurement of both derivative assets and derivative liabilities. Included in our valuation, and based on current market conditions, is a valuation adjustment for counterparty default derived from market data such as the price of credit default swaps, bond yields, and credit ratings. No gains or losses related to valuation adjustments for counterparty default risk were recorded at Ameren, Ameren Missouri, or Ameren Illinois in 2016, 2015 or 2014. At December 31, 2016 and 2015, the counterparty default risk valuation adjustment related to derivative contracts was immaterial for Ameren, Ameren Missouri, and Ameren Illinois.
The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of December 31, 2016:
 
 
 
Quoted Prices in
Active Markets for
Identical Assets
or Liabilities
(Level 1)
 
Significant Other
Observable
Inputs
(Level 2)
 
Significant Other
Unobservable
Inputs
(Level 3)
 
Total
 
Assets:
 
 
 
 
 
 
 
 
 
 
Ameren
Derivative assets – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Fuel oils
 
$
2

 
$
—

 
$
1

 
$
3

 
 
Natural gas
 
2

 
12

 
1

 
15

 
 
Power
 
—

 
—

 
9

 
9

 
 
Total derivative assets – commodity contracts
 
$
4

 
$
12

 
$
11

 
$
27

 
 
Nuclear decommissioning trust fund:
 
 
 
 
 
 
 
 
 
 
Cash and cash equivalents
 
$
1

 
$
—

 
$
—

 
$
1

 
 
Equity securities:
 
 
 
 
 
 
 
 
 
 
U.S. large capitalization
 
408

 
—

 
—

 
408

 
 
Debt securities:
 
 
 
 
 
 
 
 
 
 
U.S. Treasury and agency securities
 
—

 
112

 
—

 
112

 
 
Corporate bonds
 
—

 
67

 
—

 
67

 
 
Other
 
—

 
17

 
—

 
17

 
 
Total nuclear decommissioning trust fund
 
$
409

 
$
196

 
$
—

 
$
605

(b) 
 
Total Ameren
 
$
413

 
$
208

 
$
11

 
$
632

 
Ameren Missouri
Derivative assets – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
 
 
Quoted Prices in
Active Markets for
Identical Assets
or Liabilities
(Level 1)
 
Significant Other
Observable
Inputs
(Level 2)
 
Significant Other
Unobservable
Inputs
(Level 3)
 
Total
 
 
Fuel oils
 
$
2

 
$
—

 
$
1

 
$
3

 
 
Natural gas
 
—

 
1

 
1

 
2

 
 
Power
 
—

 
—

 
9

 
9

 
 
Total derivative assets – commodity contracts
 
$
2

 
$
1

 
$
11

 
$
14

 
 
Nuclear decommissioning trust fund:
 
 
 
 
 
 
 
 
 
 
Cash and cash equivalents
 
$
1

 
$
—

 
$
—

 
$
1

 
 
Equity securities:
 
 
 
 
 
 
 
 
 
 
U.S. large capitalization
 
408

 
—

 
—

 
408

 
 
Debt securities:
 
 
 
 
 
 
 
 
 
 
U.S. Treasury and agency securities
 
—

 
112

 
—

 
112

 
 
Corporate bonds
 
—

 
67

 
—

 
67

 
 
Other
 
—

 
17

 
—

 
17

 
 
Total nuclear decommissioning trust fund
 
$
409

 
$
196

 
$
—

 
$
605

(b) 
 
Total Ameren Missouri
 
$
411

 
$
197

 
$
11

 
$
619

 
Ameren Illinois
Derivative assets – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Natural gas
 
$
2

 
$
11

 
$
—

 
$
13

 
Liabilities:
 
 
 
 
 
 
 
 
 
 
Ameren
Derivative liabilities – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Fuel oils
 
$
5

 
$
—

 
$
—

 
$
5

 
 
Natural gas
 
—

 
13

 
1

 
14

 
 
Power
 
—

 
1

 
187

 
188

 
 
Uranium
 
—

 
—

 
4

 
4

 
 
Total Ameren
 
$
5

 
$
14

 
$
192

 
$
211

 
Ameren Missouri
Derivative liabilities – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Fuel oils
 
$
5

 
$
—

 
$
—

 
$
5

 
 
Natural gas
 
—

 
6

 
—

 
6

 
 
Power
 
—

 
1

 
2

 
3

 
 
Uranium
 
—

 
—

 
4

 
4

 
 
Total Ameren Missouri
 
$
5

 
$
7

 
$
6

 
$
18

 
Ameren Illinois
Derivative liabilities – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Natural gas
 
$
—

 
$
7

 
$
1

 
$
8

 
 
Power
 
—

 
—

 
185

 
185

 
 
Total Ameren Illinois
 
$
—

 
$
7

 
$
186

 
$
193

 
(a)
The derivative asset and liability balances are presented net of counterparty credit considerations.
(b)
Balance excludes $2 million of receivables, payables, and accrued income, net.
The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of December 31, 2015:
 
 
 
Quoted Prices in
Active Markets for
Identical Assets
or Liabilities
(Level 1)
 
Significant Other
Observable
Inputs
(Level 2)
 
Significant Other
Unobservable
Inputs
(Level 3)
 
Total
 
Assets:
 
 
 
 
 
 
 
 
 
 
Ameren
Derivative assets – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Natural gas
 
$
—

 
$
1

 
$
1

 
$
2

 
 
Power
 
—

 
—

 
16

 
16

 
 
Total derivative assets – commodity contracts
 
$
—

 
$
1

 
$
17

 
$
18

 
 
 
 
Quoted Prices in
Active Markets for
Identical Assets
or Liabilities
(Level 1)
 
Significant Other
Observable
Inputs
(Level 2)
 
Significant Other
Unobservable
Inputs
(Level 3)
 
Total
 
 
Nuclear decommissioning trust fund:
 
 
 
 
 
 
 
 
 
 
Cash and cash equivalents
 
$
4

 
$
—

 
$
—

 
$
4

 
 
Equity securities:
 
 
 
 
 
 
 
 
 
 
U.S. large capitalization
 
364

 
—

 
—

 
364

 
 
Debt securities:
 
 
 
 
 
 
 
 
 
 
U.S. Treasury and agency securities
 
—

 
109

 
—

 
109

 
 
Corporate bonds
 
—

 
58

 
—

 
58

 
 
Other
 
—

 
22

 
—

 
22

 
 
Total nuclear decommissioning trust fund
 
$
368

 
$
189

 
$
—

 
$
557

(b) 
 
Total Ameren
 
$
368

 
$
190

 
$
17

 
$
575

 
Ameren Missouri
Derivative assets – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Natural gas
 
$
—

 
$
—

 
$
1

 
$
1

 
 
Power
 
—

 
—

 
16

 
16

 
 
Total derivative assets – commodity contracts
 
$
—

 
$
—

 
$
17

 
$
17

 
 
Nuclear decommissioning trust fund:
 
 
 
 
 
 
 
 
 
 
Cash and cash equivalents
 
$
4

 
$
—

 
$
—

 
$
4

 
 
Equity securities:
 
 
 
 
 
 
 
 
 
 
U.S. large capitalization
 
364

 
—

 
—

 
364

 
 
Debt securities:
 
 
 
 
 
 
 
 
 
 
U.S. Treasury and agency securities
 
—

 
109

 
—

 
109

 
 
Corporate bonds
 
—

 
58

 
—

 
58

 
 
Other
 
—

 
22

 
—

 
22

 
 
Total nuclear decommissioning trust fund
 
$
368

 
$
189

 
$
—

 
$
557

(b) 
 
Total Ameren Missouri
 
$
368

 
$
189

 
$
17

 
$
574

 
Ameren Illinois
Derivative assets – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Natural gas
 
$
—

 
$
1

 
$
—

 
$
1

 
Liabilities:
 
 
 
 
 
 
 
 
 
 
Ameren
Derivative liabilities – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Fuel oils
 
$
29

 
$
—

 
$
—

 
$
29

 
 
Natural gas
 
1

 
62

 
1

 
64

 
 
Power
 
—

 
—

 
170

 
170

 
 
Uranium
 
—

 
—

 
1

 
1

 
 
Total Ameren
 
$
30

 
$
62

 
$
172

 
$
264

 
Ameren Missouri
Derivative liabilities – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Fuel oils
 
$
29

 
$
—

 
$
—

 
$
29

 
 
Natural gas
 
—

 
13

 
1

 
14

 
 
Uranium
 
—

 
—

 
1

 
1

 
 
Total Ameren Missouri
 
$
29

 
$
13

 
$
2

 
$
44

 
Ameren Illinois
Derivative liabilities – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Natural gas
 
$
1

 
$
49

 
$
—

 
$
50

 
 
Power
 
—

 
—

 
170

 
170

 
 
Total Ameren Illinois
 
$
1

 
$
49

 
$
170

 
$
220

 
(a)
The derivative asset and liability balances are presented net of counterparty credit considerations.
(b)
Balance excludes $(1) million of receivables, payables, and accrued income, net.
All costs related to financial assets and liabilities, including those classified as Level 3 in the fair value hierarchy are expected to be recoverable through customer rates; therefore, there is no impact to net income resulting from changes in the fair value of these instruments. For the years ended December 31, 2016 and 2015, the balances and changes in the fair value of Level 3 financial assets and liabilities associated with fuel oils, natural gas, and uranium were immaterial.
The following table summarizes the changes in the fair value of power financial assets and liabilities classified as Level 3 in the fair value hierarchy:
 
 
Net Derivative Commodity Contracts
 
 
Ameren
Missouri
 
Ameren
Illinois
 
Ameren
For the year ended December 31, 2015
 
 
 
 
 
 
Beginning balance at January 1, 2015
$
9

$
(142
)
$
(133
)
Realized and unrealized gains (losses) included in regulatory assets/liabilities:
 
2

 
(41
)
 
(39
)
Purchases
 
29

 
—

 
29

Settlements
 
(23
)
 
13

 
(10
)
Transfers out of Level 3
 
(1
)
 
—

 
(1
)
Ending balance at December 31, 2015
$
16

$
(170
)
$
(154
)
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2015
$
—

$
(39
)
$
(39
)
For the year ended December 31, 2016
 
 
 
 
 
 
Beginning balance at January 1, 2016
$
16

$
(170
)
$
(154
)
Realized and unrealized gains (losses) included in regulatory assets/liabilities:
 
(1
)
 
(29
)
 
(30
)
Purchases
 
13

 
—

 
13

Settlements
 
(21
)
 
14

 
(7
)
Ending balance at December 31, 2016
$
7

$
(185
)
$
(178
)
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2016
$
—

$
(27
)
$
(27
)

Transfers into or out of Level 3 represent either (1) existing assets and liabilities that were previously categorized as a higher level, but were recategorized to Level 3 because the inputs to the model became unobservable during the period, or (2) existing assets and liabilities that were previously classified as Level 3, but were recategorized to a higher level because the lowest significant input became observable during the period. For the years ended December 31, 2016 and 2015, there were no material transfers between Level 1 and Level 2, Level 1 and Level 3, or Level 2 and Level 3 related to derivative commodity contracts.
See Note 11 – Retirement Benefits for the fair value hierarchy tables detailing Ameren’s pension and postretirement plan assets as of December 31, 2016, as well as a table summarizing the changes in Level 3 plan assets during 2016.
The Ameren Companies’ carrying amounts of cash and cash equivalents approximate fair value because of the short-term nature of these instruments. They are considered to be Level 1 in the fair value hierarchy. The Ameren Companies' short-term borrowings also approximate fair value because of their short-term nature. Short-term borrowings are considered to be Level 2 in the fair value hierarchy as they are valued based on market rates for similar market transactions. The estimated fair value of long-term debt and preferred stock is based on the quoted market prices for same or similar issuances for companies with similar credit profiles or on the current rates offered to the Ameren Companies for similar financial instruments, which fair value measurement is considered Level 2 in the fair value hierarchy.
The following table presents the carrying amounts and estimated fair values of our long-term debt, capital lease obligations, and preferred stock at December 31, 2016 and 2015:
 
2016
 
2015
 
Carrying Amount
 
Fair Value
 
Carrying Amount
 
Fair Value
Ameren:(a)
 
 
 
 
 
 
 
Long-term debt and capital lease obligations (including current portion)
$
7,276

 
$
7,772

 
$
7,275

 
$
7,814

Preferred stock
142

 
131

 
142

 
125

Ameren Missouri:
 
 
 
 
 
 
 
Long-term debt and capital lease obligations (including current portion)
$
3,994

 
$
4,304

 
$
4,110

 
$
4,449

Preferred stock
80

 
79

 
80

 
75

Ameren Illinois:
 
 
 
 
 
 
 
Long-term debt (including current portion)
$
2,588

 
$
2,765

 
$
2,471

 
$
2,665

Preferred stock
62

 
52

 
62

 
50

(a)
Preferred stock is recorded in "Noncontrolling Interests" on the consolidated balance sheet.
Nuclear Decommissioning Trust Fund Investments
NUCLEAR DECOMMISSIONING TRUST FUND INVESTMENTS
NUCLEAR DECOMMISSIONING TRUST FUND INVESTMENTS
Ameren Missouri has investments in debt and equity securities that are held in a trust fund for the purpose of funding the decommissioning of its Callaway energy center. We have classified these investments as available for sale, and we have recorded all such investments at their fair market value at December 31, 2016, and 2015. See Note 10 – Callaway Energy Center for additional information.
Investments in the nuclear decommissioning trust fund have a target allocation of 60% to 70% in equity securities, with the balance invested in debt securities.
The following table presents proceeds from the sale and maturities of investments in Ameren Missouri’s nuclear decommissioning trust fund and the gross realized gains and losses resulting from those sales for the years ended December 31, 2016, 2015, and 2014:
 
2016
 
2015
 
2014
Proceeds from sales and maturities
$
377

 
$
349

 
$
391

Gross realized gains
7

 
8

 
7

Gross realized losses
4

 
2

 
2


Net realized and unrealized gains and losses are deferred and are currently recorded as a regulatory liability related to AROs on Ameren’s and Ameren Missouri’s balance sheets. This reporting is consistent with the method used to account for the decommissioning costs recovered in rates. Gains or losses associated with assets in the trust fund could result in lower or higher funding requirements for decommissioning costs, which are expected to be reflected in electric rates paid by Ameren Missouri’s customers. See Note 2 – Rate and Regulatory Matters.
The following table presents the costs and fair values of investments in debt and equity securities in Ameren's and Ameren Missouri’s nuclear decommissioning trust fund at December 31, 2016 and 2015:
Security Type
Cost
 
Gross Unrealized Gain
 
Gross Unrealized Loss
 
Fair Value
2016
 
 
 
 
 
 
 
Debt securities
$
197

 
$
3

$
4

 
$
196

Equity securities
161

 
253

 
6

 
408

Cash
1

 
—

 
—

 
1

Other(a)
2

 
—

 
—

 
2

Total
$
361

 
$
256

$
10

 
$
607

2015
 
 
 
 
 
 
 
Debt securities
$
191

 
$
2

$
4

 
$
189

Equity securities
147

 
224

 
7

 
364

Cash
4

 
—

 
—

 
4

Other(a)
(1
)
 
—

 
—

 
(1
)
Total
$
341

 
$
226

$
11

 
$
556


(a)
Represents net receivables and payables relating to pending security sales, interest, and security purchases.
The following table presents the costs and fair values of investments in debt securities in Ameren's and Ameren Missouri’s nuclear decommissioning trust fund according to their contractual maturities at December 31, 2016:
 
Cost
 
Fair Value
Less than 5 years
$
105

 
$
104

5 years to 10 years
47

 
47

Due after 10 years
45

 
45

Total
$
197

 
$
196


We have unrealized losses relating to certain available-for-sale investments included in our nuclear decommissioning trust fund, recorded as a regulatory asset as discussed above. Decommissioning will not occur until our nuclear energy center is retired. The Callaway energy center’s current operating license expires in 2044.
Callaway Energy Center
CALLAWAY ENERGY CENTER
CALLAWAY ENERGY CENTER
Under the NWPA, the DOE is responsible for disposing of spent nuclear fuel from the Callaway energy center and other commercial nuclear energy centers. Under the NWPA, Ameren and other utilities that own and operate those energy centers are responsible for paying the disposal costs. The NWPA established the fee that these utilities pay the federal government for disposing of the spent nuclear fuel at one mill, or one-tenth of one cent, for each kilowatthour generated and sold by those plants. The NWPA also requires the DOE to review the nuclear waste fee annually against the cost of the nuclear waste disposal program and to propose to the United States Congress any fee adjustment necessary to offset the costs of the program. As required by the NWPA, Ameren Missouri and other utilities have entered into standard contracts with the DOE. Consistent with the NWPA and its standard contract, which stated that the DOE would begin to dispose of spent nuclear fuel by 1998, Ameren Missouri had historically collected one mill from its electric customers for each kilowatthour of electricity that it generated and sold from its Callaway energy center. Because the federal government is not meeting its disposal obligation, the collection of this fee was suspended in May 2014. The DOE's delay in carrying out its obligation to dispose of spent nuclear fuel from the Callaway energy center is not expected to adversely affect the continued operations of the energy center.
As a result of the DOE's failure to fulfill its contractual obligations, Ameren Missouri and other nuclear energy center owners sued the DOE to recover costs incurred for ongoing storage of their spent fuel. The lawsuit resulted in a settlement agreement that provides for annual reimbursement of additional spent fuel storage and related costs. Ameren Missouri received reimbursements from the DOE of $24 million, $14 million, and $15 million in 2016, 2015, and 2014, respectively. Ameren Missouri will continue to apply for reimbursement from the DOE for allowable costs associated with the ongoing storage of spent fuel.
Electric utility rates charged to customers provide for the recovery of the Callaway energy center's decommissioning costs, which include decontamination, dismantling, and site restoration costs, over the expected life of the nuclear energy center. Amounts collected from customers are deposited into the external nuclear decommissioning trust fund to provide for the Callaway energy center’s decommissioning. It is assumed that the Callaway energy center site will be decommissioned through the immediate dismantlement method and removed from service. Ameren and Ameren Missouri have recorded an ARO for the Callaway energy center decommissioning costs at fair value, which represents the present value of estimated future cash outflows. Annual decommissioning costs of $7 million are included in the costs used to establish electric rates for Ameren Missouri's customers. Every three years, the MoPSC requires Ameren Missouri to file an updated cost study and funding analysis for decommissioning its Callaway energy center. In April 2016, the MoPSC approved no change in electric service rates for decommissioning costs.
The fair value of the trust fund for Ameren Missouri's Callaway energy center is reported as "Nuclear decommissioning trust fund" in Ameren's and Ameren Missouri's balance sheets. This amount is legally restricted and may be used only to fund the costs of nuclear decommissioning. Changes in the fair value of the trust fund are recorded as an increase or decrease to the nuclear decommissioning trust fund, with an offsetting adjustment to the related regulatory liability. If the assumed return on trust assets is not earned, Ameren Missouri believes that it is probable that any such earnings deficiency will be recovered in rates.
See Note 2 – Rate and Regulatory Matters and Note 9 – Nuclear Decommissioning Trust Fund Investments for additional information related to the Callaway energy center.
Retirement Benefits
RETIREMENT BENEFITS
RETIREMENT BENEFITS
The primary objective of the Ameren pension and postretirement benefit plans is to provide eligible employees with pension and postretirement health care and life insurance benefits. Ameren has defined benefit pension and postretirement benefit plans covering substantially all of its union employees. Ameren has defined benefit pension plans covering substantially all of its non-union employees and postretirement benefit plans covering non-union employees hired before October 2015. Ameren uses a measurement date of December 31 for its pension and postretirement benefit plans. Ameren Missouri and Ameren Illinois each participate in Ameren’s single-employer pension and other postretirement plans. Ameren’s qualified pension plan is the Ameren Retirement Plan. Ameren also has an unfunded nonqualified pension plan, the Ameren Supplemental Retirement Plan, which is available to provide certain management employees and retirees with a supplemental benefit when their qualified pension plan benefits are capped in compliance with Internal Revenue Code limitations. Ameren’s other postretirement plan is the Ameren Retiree Welfare Benefit Plan. Effective December 31, 2016, the applicable assets and liabilities of the Ameren Group Life Insurance Plan were merged with the Ameren Retiree Welfare Benefit Plan. Only Ameren subsidiaries participate in the plans listed above.
Ameren’s unfunded obligation under its pension and other postretirement benefit plans was $774 million and $567 million as of December 31, 2016, and December 31, 2015, respectively. These net liabilities are recorded in "Other current liabilities," "Pension and other postretirement benefits," and "Other assets" on Ameren's consolidated balance sheet. The primary factor contributing to the increase in the unfunded obligation during 2016 was a 50 basis point decrease in the pension and other postretirement benefit plan discount rates used to determine the present value of the obligation. The increase in the unfunded obligation also resulted in an increase to "Regulatory assets" on Ameren's, Ameren Missouri's, and Ameren Illinois' consolidated balance sheet.
The following table presents the net benefit liability recorded on the balance sheets of each of the Ameren Companies as of December 31, 2016 and 2015:
 
2016

2015

Ameren(a)
$
774

$
567

Ameren Missouri
293

236

Ameren Illinois
315

219

(a)
Includes amounts for Ameren registrant and nonregistrant subsidiaries.
Ameren recognizes the underfunded status of its pension and postretirement plans as a liability on its consolidated balance sheet, with offsetting entries to accumulated OCI and regulatory assets. The following table presents the funded status of Ameren's pension and postretirement benefit plans as of December 31, 2016 and 2015. It also provides the amounts included in regulatory assets and accumulated OCI at December 31, 2016 and 2015, that have not been recognized in net periodic benefit costs.
  
2016
 
2015
  
Pension Benefits(a)
 
Postretirement
Benefits(a)
 
Pension Benefits(a)
 
Postretirement
Benefits(a)
Accumulated benefit obligation at end of year
$
4,288

$
(b)

 
$
3,995

$
(b)

Change in benefit obligation:
 
 
 
 
 
 
 
Net benefit obligation at beginning of year
$
4,197

$
1,094

 
$
4,410

$
1,203

Service cost
81

 
19

 
92

 
24

Interest cost
185

 
50

 
174

 
48

Participant contributions
—

 
8

 
—

 
8

Actuarial (gain) loss
265

 
52

 
(256
)
 
(133
)
Settlement
—

 
—

 
(2
)
 
—

Benefits paid
(210
)
 
(54
)
 
(221
)
 
(56
)
Federal subsidy on benefits paid
(b)

 
1

 
(b)

 
—

Net benefit obligation at end of year
4,518

 
1,170

 
4,197

 
1,094

Change in plan assets:
 
 
 
 
 
 
 
Fair value of plan assets at beginning of year
3,653

 
1,071

 
3,794

 
1,109

Actual return on plan assets
313

 
73

 
(29
)
 
(8
)
Employer contributions
57

 
2

 
111

 
18

Federal subsidy on benefits paid
(b)

 
1

 
(b)

 
—

Participant contributions
—

 
8

 
—

 
8

Settlements
—

 
—

 
(2
)
 
—

Benefits paid
(210
)
 
(54
)
 
(221
)
 
(56
)
Fair value of plan assets at end of year
3,813

 
1,101

 
3,653

 
1,071

Funded status – deficiency
705

 
69

 
544

 
23

Accrued benefit cost at December 31
$
705

$
69

 
$
544

$
23

Amounts recognized in the balance sheet consist of:
 
 
 
 
 
 
 
Noncurrent asset(c)
$
—

$
—

 
$
—

$
(18
)
Current liability(d)
3

 
2

 
3

 
2

Noncurrent liability
702

 
67

 
541

 
39

Net liability recognized
$
705

$
69

 
$
544

$
23

Amounts recognized in regulatory assets consist of:
 
 
 
 
 
 
 
Net actuarial (gain) loss
$
535

$
(29
)
 
$
395

$
(82
)
Prior service cost (credit)
(4
)
 
(8
)
 
(5
)
 
(11
)
Amounts (pretax) recognized in accumulated OCI consist of:
 
 
 
 
 
 
 
Net actuarial (gain) loss
43

 
—

 
17

 
(3
)
Prior service cost (credit)
—

 
(1
)
 
—

 
—

Total
$
574

$
(38
)
 
$
407

$
(96
)
(a)
Includes amounts for Ameren registrant and nonregistrant subsidiaries.
(b)
Not applicable.
(c)
Included in "Other assets" on Ameren's consolidated balance sheet.
(d)
Included in "Other current liabilities" on Ameren's consolidated balance sheet.
The following table presents the assumptions used to determine our benefit obligations at December 31, 2016 and 2015:
  
Pension Benefits
 
Postretirement Benefits
  
2016
 
2015
 
2016
 
2015
Discount rate at measurement date
4.00
%
 
4.50
%
 
4.00
%
 
4.50
%
Increase in future compensation
3.50

 
3.50

 
3.50

 
3.50

Medical cost trend rate (initial)
(a)

 
(a)

 
5.00

 
5.00

Medical cost trend rate (ultimate)
(a)

 
(a)

 
5.00

 
5.00


(a)
Not applicable
Ameren determines discount rate assumptions by identifying a theoretical settlement portfolio of high-quality corporate bonds sufficient to provide for a plan's projected benefit payments. The settlement portfolio of bonds is selected from a pool of more than 700 high-quality corporate bonds. A single discount rate is then determined; that rate results in a discounted value of the plan's benefit payments that equates to the market value of the selected bonds. In addition, during 2016, Ameren adopted the Society of Actuaries 2016 Mortality Tables Report and Mortality Improvement Scale. The updated mortality tables assume a lower rate of mortality improvement as compared to the 2015 Mortality Tables Report and Mortality Improvement Scale that Ameren adopted in 2015. The 2016 tables lowered projected improvements in life expectancies for our employees and retirees, resulting in a decrease to our pension and other postretirement benefit obligations.
Funding
Pension benefits are based on the employees’ years of service, age, and compensation. Ameren’s pension plans are funded in compliance with income tax regulations, federal funding, and other regulatory requirements. As a result, Ameren expects to fund its pension plan at a level equal to the greater of the pension cost or the legally required minimum contribution. Considering its assumptions at December 31, 2016, its investment performance in 2016, and its pension funding policy, Ameren expects to make annual contributions of $50 million to $70 million in each of the next five years, with aggregate estimated contributions of $290 million. We expect Ameren Missouri’s and Ameren Illinois’ portion of the future funding requirements to be 35% and 55%, respectively. These amounts are estimates. They may change based on actual investment performance, changes in interest rates, changes in our assumptions, changes in government regulations, and any voluntary contributions. Our funding policy for postretirement benefits is primarily to fund the Voluntary Employee Beneficiary Association (VEBA) trusts to match the annual postretirement expense.
The following table presents the cash contributions made to our defined benefit retirement plan and to our postretirement plans during 2016, 2015, and 2014:
  
Pension Benefits
 
Postretirement Benefits
  
2016
 
2015
 
2014
 
2016
 
2015
 
2014
Ameren Missouri
$
21

 
$
47

 
$
41

 
$
1

 
$
8

 
$
3

Ameren Illinois
30

 
45

 
39

 
1

 
8

 
2

Other
6

 
19

 
19

 
—

 
2

 
1

Ameren
57

 
111

 
99

 
2

 
18

 
6

Investment Strategy and Policies
Ameren manages plan assets in accordance with the “prudent investor” guidelines contained in ERISA. The investment committee, which includes members of senior management, approves and implements investment strategy and asset allocation guidelines for the plan assets. The investment committee’s goals are twofold: first, to ensure that sufficient funds are available to provide the benefits at the time they are payable; and second, to maximize total return on plan assets and to minimize expense volatility consistent with its tolerance for risk. Ameren delegates the task of investment management to specialists in each asset class. As appropriate, Ameren provides each investment manager with guidelines that specify allowable and prohibited investment types. The investment committee regularly monitors manager performance and compliance with investment guidelines.
The expected return on plan assets assumption is based on historical and projected rates of return for current and planned asset classes in the investment portfolio. Projected rates of return for each asset class were estimated after an analysis of historical experience, future expectations, and the volatility of the various asset classes. After considering the target asset allocation for each asset class, we adjusted the overall expected rate of return for the portfolio for historical and expected experience of active portfolio management results compared with benchmark returns and for the effect of expenses paid from plan assets. Ameren will use an expected return on plan assets for its pension and postretirement plan assets of 7.00% in 2017. No plan assets are expected to be returned to Ameren during 2017.
Ameren’s investment committee strives to assemble a portfolio of diversified assets that does not create a significant concentration of risks. The investment committee develops asset allocation guidelines between asset classes, and it creates diversification through investments in assets that differ by type (equity, debt, real estate, private equity), duration, market capitalization, country, style (growth or value), and industry, among other factors. The diversification of assets is displayed in the target allocation table below. The investment committee also routinely rebalances the plan assets to adhere to the diversification goals. The investment committee’s strategy reduces the concentration of investment risk; however, Ameren is still subject to overall market risk. The following table presents our target allocations for 2017 and our pension and postretirement plans’ asset categories as of December 31, 2016 and 2015:
Asset
Category
Target Allocation
2017
 
Percentage of Plan Assets at December  31,
2016
 
2015
Pension Plan:
 
 
 
 
 
Cash and cash equivalents
0% – 5%
 
1
%
 
1
%
Equity securities:
 
 
 
 
 
U.S. large-capitalization
29% – 39%
 
34
%
 
34
%
U.S. small- and mid-capitalization
3% – 13%
 
9
%
 
7
%
International and emerging markets
9% – 19%
 
14
%
 
13
%
Total equity
51% – 61%
 
57
%
 
54
%
Debt securities
35% – 45%
 
37
%
 
40
%
Real estate
0% –  9%  
 
5
%
 
5
%
Private equity
0% –  5%  
 
(a)

 
(a)

Total
 
 
100
%
 
100
%
Postretirement Plans:
 
 
 
 
 
Cash and cash equivalents
0% – 7%
 
3
%
 
4
%
Equity securities:
 
 
 
 
 
U.S. large-capitalization
34% – 44%
 
40
%
 
39
%
U.S. small- and mid-capitalization
2% – 12%
 
7
%
 
7
%
International
9% – 19%
 
14
%
 
13
%
Total equity
55% – 65%
 
61
%
 
59
%
Debt securities
33% – 43%
 
36
%
 
37
%
Total
 
 
100
%
 
100
%

(a)
Less than 1% of plan assets.
In general, the United States large-capitalization equity investments are passively managed or indexed, whereas the international, emerging markets, United States small-capitalization, and United States mid-capitalization equity investments are actively managed by investment managers. Debt securities include a broad range of fixed-income vehicles. Debt security investments in high-yield securities, emerging market securities, and non-United-States-dollar-denominated securities are owned by the plans, but in limited quantities to reduce risk. Most of the debt security investments are under active management by investment managers. Real estate investments include private real estate vehicles; however, Ameren does not, by policy, hold direct investments in real estate property. Additionally, Ameren’s investment committee allows investment managers to use derivatives, such as index futures, exchange traded funds, foreign exchange futures, and options, in certain situations, to increase or to reduce market exposure in an efficient and timely manner.
Fair Value Measurements of Plan Assets
Investments in the pension and postretirement benefit plans were stated at fair value as of December 31, 2016. The fair value of an asset is the amount that would be received upon its sale in an orderly transaction between market participants at the measurement date. Cash and cash equivalents have initial maturities of three months or less and are recorded at cost plus accrued interest. The carrying amounts of cash and cash equivalents approximate fair value because of the short-term nature of these instruments. Investments traded in active markets on national or international securities exchanges are valued at closing prices on the last business day on or before the measurement date. Securities traded in over-the-counter markets are valued based on quoted market prices, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency. Investments measured under NAV as a practical expedient are based on the fair values of the underlying assets provided by the funds and their administrators. The fair value of real estate investments are based on NAV determined by annual appraisal reports prepared by an independent real estate appraiser. Investments measured at NAV often provide for daily, monthly, or quarterly redemptions with 60 or less days of notice depending on the fund. For some funds, redemption may also require approval from the fund's board of directors. Derivative contracts are valued at fair value, as determined by the investment managers (or independent third parties on behalf of the investment managers), who use proprietary models and take into consideration exchange quotations on underlying instruments, dealer quotations, and other market information.
The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the pension plan assets measured at fair value as of December 31, 2016:
 
Quoted Prices in
Active Markets for
Identified Assets
(Level 1)
 
Significant Other
Observable
Inputs
(Level 2)
 
Significant Other
Unobservable
Inputs
(Level 3)
 
Measured at NAV(a)
 
Total
Cash and cash equivalents
$
—

 
$
—

 
$
—

 
$
33

 
$
33

Equity securities:
 
 
 
 
 
 
 
 
 
U.S. large-capitalization
—

 
—

 
—

 
1,352

 
1,352

U.S. small- and mid-capitalization
361

 
—

 
—

 
—

 
361

International and emerging markets
133

 
—

 
—

 
389

 
522

Debt securities:
 
 
 
 
 
 
 
 
 
Corporate bonds
—

 
617

 
—

 
13

 
630

Municipal bonds
—

 
95

 
—

 
—

 
95

U.S. Treasury and agency securities
—

 
701

 
—

 
—

 
701

Other
—

 
21

 
—

 
—

 
21

Real estate
—

 
—

 
—

 
202

 
202

Private equity
—

 
—

 
—

 
6

 
6

Total
$
494

 
$
1,434

 
$
—

 
$
1,995

 
$
3,923

Less: Medical benefit assets at December 31(b)
 
 
 
 
 
 
 
 
(132
)
Plus: Net receivables at December 31(c)
 
 
 
 
 
 
 
 
22

Fair value of pension plans assets at year end
 
 
 
 
 
 
 
 
$
3,813

(a)
Reflects the adoption of the new authoritative accounting guidance related to investments measured at the NAV practical expedient. See Note 1 - Summary of Significant Accounting Policies for additional information.
(b)
Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation.
(c)
Receivables related to pending security sales, offset by payables related to pending security purchases.
The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the pension plan assets measured at fair value as of December 31, 2015:
 
Quoted Prices in
Active Markets for
Identified Assets or Liabilities
(Level 1)
 
Significant Other
Observable
Inputs
(Level 2)
 
Significant Other
Unobservable
Inputs
(Level 3)
 
Measured at NAV(a)
 
Total
Cash and cash equivalents
$
—

 
$
—

 
$
—

 
$
20

 
$
20

Equity securities:
 
 
 
 
 
 
 
 
 
U.S. large-capitalization
—

 
—

 
—

 
1,296

 
1,296

U.S. small- and mid-capitalization
268

 
—

 
—

 
—

 
268

International and emerging markets
122

 
126

 
—

 
243

 
491

Debt securities:
 
 
 
 
 
 
 
 
 
Corporate bonds
—

 
617

 
—

 
14

 
631

Municipal bonds
—

 
104

 
—

 
—

 
104

U.S. Treasury and agency securities
6

 
751

 
—

 
—

 
757

Other
—

 
5

 
—

 
—

 
5

Real estate
—

 
—

 
—

 
168

 
168

Private equity
—

 
—

 
—

 
8

 
8

Total
$
396

 
$
1,603

 
$
—

 
$
1,749

 
$
3,748

Less: Medical benefit assets at December 31(b)
 
 
 
 
 
 
 
 
(123
)
Plus: Net receivables at December 31(c)
 
 
 
 
 
 
 
 
28

Fair value of pension plans assets at year end
 
 
 
 
 
 
 
 
$
3,653

(a)
Reflects the adoption of the new authoritative accounting guidance related to investments measured at the NAV practical expedient. See Note 1 - Summary of Significant Accounting Policies for additional information.
(b)
Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation.
(c)
Receivables related to pending security sales, offset by payables related to pending security purchases.
The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the postretirement benefit plans assets measured at fair value as of December 31, 2016:
 
Quoted Prices in
Active Markets for
Identified Assets
(Level 1)
 
Significant Other
Observable
Inputs
(Level 2)
 
Significant Other
Unobservable
Inputs
(Level 3)
 
Measured at NAV(a)
 
Total
Cash and cash equivalents
$
53

 
$
—

 
$
—

 
$
—

 
$
53

Equity securities:
 
 
 
 
 
 
 
 
 
U.S. large-capitalization
291

 
—

 
—

 
101

 
392

U.S. small- and mid-capitalization
72

 
—

 
—

 
—

 
72

International
40

 
—

 
—

 
92

 
132

Other
—

 
7

 
—

 
—

 
7

Debt securities:
 
 
 
 
 
 
 
 
 
Corporate bonds
—

 
141

 
—

 
—

 
141

Municipal bonds
—

 
110

 
—

 
—

 
110

U.S. Treasury and agency securities
—

 
68

 
—

 
—

 
68

Other
—

 
—

 
—

 
19

 
19

Total
$
456

 
$
326

 
$
—

 
$
212

 
$
994

Plus: Medical benefit assets at December 31(b)
 
 
 
 
 
 
 
 
132

Less: Net payables at December 31(c)
 
 
 
 
 
 
 
 
(25
)
Fair value of postretirement benefit plans assets at year end
 
 
 
 
 
 
 
 
$
1,101

(a)
Reflects the adoption of the new authoritative accounting guidance related to investments measured at the NAV practical expedient. See Note 1 - Summary of Significant Accounting Policies for additional information.
(b)
Medical benefit (health and welfare) component for 401(h) accounts to fund a portion of the postretirement obligation. These 401(h) assets are included in the pension plan assets shown above.
(c)
Payables related to pending security purchases, offset by interest receivables and receivables related to pending security sales.
The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the postretirement benefit plans assets measured at fair value as of December 31, 2015:
 
Quoted Prices in
Active Markets for
Identified Assets
(Level 1)
 
Significant Other
Observable
Inputs
(Level 2)
 
Significant Other
Unobservable
Inputs
(Level 3)
 
Measured at NAV(a)
 
Total
Cash and cash equivalents
$
61

 
$
—

 
$
—

 
$
—

 
$
61

Equity securities:
 
 
 
 
 
 
 
 
 
U.S. large-capitalization
272

 
—

 
—

 
98

 
370

U.S. small- and mid-capitalization
65

 
—

 
—

 
—

 
65

International
33

 
38

 
—

 
55

 
126

Other
—

 
7

 
—

 
—

 
7

Debt securities:
 
 
 
 
 
 
 
 
 
Corporate bonds
—

 
138

 
—

 
—

 
138

Municipal bonds
—

 
114

 
—

 
—

 
114

U.S. Treasury and agency securities
—

 
55

 
—

 
—

 
55

Other
—

 
4

 
—

 
36

 
40

Total
$
431

 
$
356

 
$
—

 
$
189

 
$
976

Plus: Medical benefit assets at December 31(a)
 
 
 
 
 
 
 
 
123

Less: Net payables at December 31(b)
 
 
 
 
 
 
 
 
(28
)
Fair value of postretirement benefit plans assets at year end
 
 
 
 
 
 
 
 
$
1,071

(a)
Reflects the adoption of the new authoritative accounting guidance related to investments measured at the NAV practical expedient. See Note 1 - Summary of Significant Accounting Policies for additional information.
(b)
Medical benefit (health and welfare) component for 401(h) accounts to fund a portion of the postretirement obligation. These 401(h) assets are included in the pension plan assets shown above.
(c)
Payables related to pending security purchases, offset by Medicare, interest receivables, and receivables related to pending security sales.
Net Periodic Benefit Cost
The following table presents the components of the net periodic benefit cost of Ameren's pension and postretirement benefit plans during 2016, 2015, and 2014:
 
Pension Benefits
 
Postretirement Benefits
2016
 
 
 
Service cost
$
81

 
$
19

Interest cost
185

 
50

Expected return on plan assets
(253
)
 
(72
)
Amortization of:
 
 
 
Prior service credit
(1
)
 
(5
)
Actuarial (gain) loss
32

 
(11
)
Net periodic benefit cost (benefit)
$
44

 
$
(19
)
2015
 
 
 
Service cost
$
92

 
$
24

Interest cost
174

 
48

Expected return on plan assets
(248
)
 
(68
)
Amortization of:
 
 
 
Prior service credit
(1
)
 
(5
)
Actuarial loss
74

 
5

Settlement loss
1

 
—

Net periodic benefit cost (benefit)
$
92

 
$
4

2014
 
 
 
Service cost
$
79

 
$
19

Interest cost
183

 
50

Expected return on plan assets
(229
)
 
(65
)
Amortization of:
 
 
 
Prior service credit
(1
)
 
(5
)
Actuarial (gain) loss
49

 
(7
)
Net periodic benefit cost (benefit)
$
81

 
$
(8
)

The estimated amounts that will be amortized from regulatory assets and accumulated OCI into Ameren's net periodic benefit cost in 2017 are as follows:
  
Pension Benefits(a)
 
Postretirement Benefits(a)
Regulatory assets:
 
 
 
Prior service credit
$
(1
)
 
$
(5
)
Net actuarial (gain) loss
50

 
(7
)
Accumulated OCI:
 
 
 
Net actuarial loss
4

 
—

Total
$
53

 
$
(12
)
(a)
Includes amounts for Ameren registrant and nonregistrant subsidiaries.
Prior service cost is amortized on a straight-line basis over the average future service of active participants benefiting under the plan amendment. Net actuarial gains or losses subject to amortization are amortized on a straight-line basis over 10 years.
The Ameren Companies are responsible for their share of the pension and postretirement benefit costs. The following table presents the pension costs and the postretirement benefit costs incurred and included in continuing operations for the years ended December 31, 2016, 2015, and 2014:
  
Pension Costs
 
Postretirement Costs
  
2016
 
2015
 
2014
 
2016
 
2015
 
2014
Ameren Missouri(a)
$
26

 
$
54

 
$
50

 
$
(5
)
 
$
8

 
$
3

Ameren Illinois
22

 
38

 
30

 
(13
)
 
(3
)
 
(9
)
Other
(4
)
 
—

 
1

 
(1
)
 
(1
)
 
(2
)
Ameren
44

 
92

 
81

 
(19
)
 
4

 
(8
)
(a)
Does not include the impact of the regulatory tracking mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates.
The expected pension and postretirement benefit payments from qualified trust and company funds, which reflect expected future service, as of December 31, 2016, are as follows:
  
Pension Benefits
 
Postretirement Benefits
  
Paid from
Qualified
Trust Funds
 
        Paid from
         Company
      Funds
 
        Paid from
         Qualified
      Trust Funds
 
        Paid from
         Company
      Funds
2017
$
248

 
$
3

 
$
54

 
$
2

2018
254

 
3

 
57

 
2

2019
261

 
3

 
59

 
2

2020
265

 
3

 
61

 
2

2021
273

 
3

 
63

 
2

2022 – 2026
1,405

 
13

 
331

 
12


The following table presents the assumptions used to determine net periodic benefit cost for our pension and postretirement benefit plans for the years ended December 31, 2016, 2015, and 2014:
  
Pension Benefits
 
Postretirement Benefits
  
2016
 
2015
 
2014
 
2016
 
2015
 
2014
Discount rate at measurement date
4.50
%
 
4.00
%
 
4.75
%
 
4.50
%
 
4.00
%
 
4.75
%
Expected return on plan assets
7.00

 
7.25

 
7.25

 
7.00

 
7.00

 
7.00

Increase in future compensation
3.50

 
3.50

 
3.50

 
3.50

 
3.50

 
3.50

Medical cost trend rate (initial)
(a)

 
(a)

 
(a)

 
5.00

 
5.00

 
5.00

Medical cost trend rate (ultimate)
(a)

 
(a)

 
(a)

 
5.00

 
5.00

 
5.00


(a)
Not applicable
The table below reflects the sensitivity of Ameren’s plans to potential changes in key assumptions:
  
Pension Benefits
 
Postretirement Benefits
  
Service Cost
and Interest
Cost
 
    Projected
    Benefit
     Obligation
 
    Service Cost
    and Interest
    Cost
 
    Postretirement
      Benefit
       Obligation
0.25% decrease in discount rate
$
(1
)
 
$
142

 
$
—

 
$
38

0.25% increase in salary scale
2

 
16

 
—

 
—

1.00% increase in annual medical trend
—

 
—

 
3

 
54

1.00% decrease in annual medical trend
—

 
—

 
(3
)
 
(54
)

Other
Ameren sponsors a 401(k) plan for eligible employees. The Ameren 401(k) plan covered all eligible employees at December 31, 2016. The plan allows employees to contribute a portion of their compensation in accordance with specific guidelines. Ameren matches a percentage of the employee contributions up to certain limits. The following table presents the portion of the matching contribution to the Ameren 401(k) plan attributable to the continuing operations for each of the Ameren Companies for the years ended December 31, 2016, 2015, and 2014:
 
2016
 
2015
 
2014
Ameren Missouri
$
16

 
$
16

 
$
16

Ameren Illinois
12

 
12

 
11

Other
1

 
1

 
1

Ameren
29

 
29

 
28

Stock-Based Compensation
STOCK-BASED COMPENSATION
STOCK-BASED COMPENSATION
The 2014 Incentive Plan is Ameren’s long-term stock compensation plan for eligible employees and directors. The 2006 Incentive Plan was replaced prospectively for new grants beginning in April 2014. The 2014 Incentive Plan provides for a maximum of 8 million common shares to be available for grant to eligible employees and directors. At December 31, 2016, there were 5.8 million common shares remaining for grant under the 2014 Incentive Plan. The 2014 Incentive Plan awards may be stock options, stock appreciation rights, restricted stock, restricted stock units, performance shares, performance share units, cash-based awards, and other stock-based awards.
Performance Share Units
A share unit vests and entitles an employee to receive shares of Ameren common stock (plus accumulated dividends) if, at the end of the three-year performance period, certain specified performance or market conditions have been met and if the individual remains employed by Ameren through the required vesting period. The exact number of shares issued pursuant to a share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the performance goals. The vesting period for share units awarded in 2015 and 2016 extended beyond the three-year performance period to the payout date, while the vesting period for share units awarded in 2014 matched the three-year performance period and vested on December 31, 2016.
A summary of nonvested performance share units at December 31, 2016, and changes during the year ended December 31, 2016, under the 2006 Incentive Plan and the 2014 Incentive Plan are presented below:
  
Performance Share Units
  
Share
Units
 
Weighted-average
Fair Value per Share Unit
Nonvested at January 1, 2016
1,024,870

 
$
46.08

Granted(a)
588,615

 
44.13

Forfeitures
(15,949
)
 
45.07

Earned and vested(b)
(537,897
)
 
40.12

Nonvested at December 31, 2016
1,059,639

 
$
48.04

(a)
Includes performance share units (share units) granted to certain executive and nonexecutive officers and other eligible employees in 2016 under the 2014 Incentive Plan.
(b)
Includes share units granted in 2014 that vested as of December 31, 2016 and were earned pursuant to the terms of the award grants. Also includes share units that vested due to attainment of retirement eligibility by certain employees. Actual shares issued for retirement-eligible employees will vary depending on actual performance over the three-year measurement period.
The following table presents the stock-based compensation expense for the years ended December 31, 2016, 2015 and 2014:
 
2016
 
2015
 
2014
Ameren Missouri
$
4

 
$
5

 
$
5

Ameren Illinois
2

 
3

 
2

Other(a)
11

 
11

 
12

Ameren
17

 
19

 
19

Less income tax benefit
6

 
7

 
7

Stock-based compensation expense, net
$
11

 
$
12

 
$
12

(a)
Represents compensation expense of employees of Ameren Services. These amounts are not included in the Ameren Missouri and Ameren Illinois amounts above.
Ameren settled performance share units of $83 million, $27 million, and $33 million for the years ended December 31, 2016, 2015, and 2014. There were no significant compensation costs capitalized related to the performance share units during the years ended December 31, 2016, 2015, and 2014. As of December 31, 2016, total compensation cost of $25 million related to nonvested awards not yet recognized is expected to be recognized over a weighted-average period of 22 months.
The fair value of each share unit awarded in 2016 under the 2014 Incentive Plan was determined to be $44.13, which was based on Ameren's closing common share price of $43.23 at December 31, 2015, and lattice simulations. Lattice simulations are used to estimate expected share payout based on Ameren's total shareholder return for a three-year performance period relative to the designated peer group beginning January 1, 2016. The simulations can produce a greater fair value for the share unit than the applicable closing common share price because they include the weighted payout scenarios in which an increase in the share price has occurred. The significant assumptions used to calculate fair value also included a three-year risk-free rate of 1.31%, volatility of 15% to 20% for the peer group, and Ameren's attainment of a three-year average earnings per share threshold during the performance period.
The fair value of each share unit awarded in 2015 under the 2014 Incentive Plan was determined to be $52.88, which was based on Ameren’s closing common share price of $46.13 at December 31, 2014, and lattice simulations. The lattice simulations reflected the three-year performance period relative to the designated peer group beginning January 1, 2015. The significant assumptions used to calculate fair value also included a three-year risk-free rate of 1.10%, volatility of 12% to 18% for the peer group, and Ameren’s attainment of a three-year average earnings per share threshold during the performance period.
The fair value of each share unit awarded in 2014, excluding the grants issued in April 2014 for certain executive officers, under the 2006 Incentive Plan and the 2014 Incentive Plan was determined to be $38.90, which was based on Ameren’s closing common share price of $36.16 at December 31, 2013, and lattice simulations. The lattice simulations reflected the three-year performance period relative to the designated peer group beginning January 1, 2014. The significant assumptions used to calculate fair value also included a three-year risk-free rate of 0.78%, volatility of 12% to 18% for the peer group, and Ameren’s attainment of a three-year average earnings per share threshold during the performance period.
Income Taxes
INCOME TAXES
INCOME TAXES
The following table presents the principal reasons for the difference between the effective income tax rate and the statutory federal income tax rate for the years ended December 31, 2016, 2015, and 2014:
 
Ameren Missouri
 
Ameren Illinois
 
Ameren
2016
 
 
 
 
 
Statutory federal income tax rate:
35
 %
 
35
 %
 
35
 %
Increases (decreases) from:
 
 
 
 
 
Depreciation differences
1

 
—

 
—

Amortization of deferred investment tax credit
(1
)
 
—

 
—

State tax
3

 
5

 
4

Stock-based compensation(a)
—

 
—

 
(2
)
Valuation allowance
—

 
—

 
1

Other permanent items
—

 
(2
)
 
(1
)
Effective income tax rate
38
 %
 
38
 %
 
37
 %
2015
 
 
 
 
 
Statutory federal income tax rate:
35
 %
 
35
 %
 
35
 %
Increases (decreases) from:
 
 
 
 
 
Depreciation differences
—

 
(2
)
 
(1
)
Amortization of deferred investment tax credit
(1
)
 
—

 
(1
)
State tax
3

 
5

 
5

Other permanent items
—

 
(1
)
 
—

Effective income tax rate
37
 %
 
37
 %
 
38
 %
2014
 
 
 
 
 
Statutory federal income tax rate:
35
 %
 
35
 %
 
35
 %
Increases (decreases) from:
 
 
 
 
 
Amortization of deferred investment tax credit
(1
)
 
—

 
(1
)
State tax
3

 
6

 
4

Other permanent items
—

 
—

 
1

Effective income tax rate
37
 %
 
41
 %
 
39
 %

(a)
Reflects the adoption of new authoritative accounting guidance related to share-based compensation. See Note 1 – Summary of Significant Accounting Policies for more information.

The following table presents the components of income tax expense (benefit) for the years ended December 31, 2016, 2015, and 2014:
 
Ameren Missouri
 
Ameren Illinois
 
Other
 
Ameren
2016
 
 
 
 
 
 
 
Current taxes:
 
 
 
 
 
 
 
Federal
$
31

 
$
(8
)
 
$
(24
)
 
$
(1
)
State
6

 
12

 
(21
)
 
(3
)
Deferred taxes:
 
 
 
 
 
 
 
Federal
161

 
117

 
21

 
299

State
23

 
37

 
32

 
92

Amortization of deferred investment tax credits
(5
)
 
—

 
—

 
(5
)
Total income tax expense
$
216

 
$
158

 
$
8

 
$
382

2015
 
 
 
 
 
 
 
Current taxes:
 
 
 
 
 
 
 
Federal
$
110

 
$
(83
)
 
$
(29
)
 
$
(2
)
State
17

 
(11
)
 
(10
)
 
(4
)
Deferred taxes:
 
 
 
 
 
 
 
Federal
71

 
193

 
35

 
299

State
16

 
29

 
31

 
76

Amortization of deferred investment tax credits
(5
)
 
(1
)
 
—

 
(6
)
Total income tax expense
$
209

 
$
127

 
$
27

 
$
363

2014
 
 
 
 
 
 
 
Current taxes:
 
 
 
 
 
 
 
Federal
$
(13
)
 
$
(51
)
 
$
27

 
$
(37
)
State
(3
)
 
(2
)
 
(32
)
 
(37
)
Deferred taxes:
 
 
 
 
 
 
 
Federal
222

 
159

 
(12
)
 
369

State
28

 
38

 
22

 
88

Amortization of deferred investment tax credits
(5
)
 
(1
)
 
—

 
(6
)
Total income tax expense (benefit)
$
229

 
$
143

 
$
5

 
$
377


The Illinois corporate income tax rate was 9.5% in 2014. The tax rate decreased to 7.75% on January 1, 2015, and is scheduled to decrease to 7.3% on January 1, 2025.
The following table presents the deferred tax assets and deferred tax liabilities recorded as a result of temporary differences at December 31, 2016 and 2015:
 
Ameren Missouri
 
Ameren Illinois
 
Other
 
Ameren
2016
 
 
 
 
 
 
 
Accumulated deferred income taxes, net liability (asset):
 
 
 
 
 
 
 
Plant related
$
3,103

 
$
1,769

 
$
147

 
$
5,019

Regulatory assets, net
75

 
(1
)
 
—

 
74

Deferred employee benefit costs
(76
)
 
(38
)
 
(97
)
 
(211
)
Revenue requirement reconciliation adjustments
—

 
34

 
—

 
34

Tax carryforwards
(66
)
 
(138
)
 
(472
)
 
(676
)
Other
(23
)
 
5

 
42

 
24

Total net accumulated deferred income tax liabilities (assets)
$
3,013

 
$
1,631

 
$
(380
)
 
$
4,264

2015
 
 
 
 
 
 
 
Accumulated deferred income taxes, net liability (asset):
 
 
 
 
 
 
 
Plant related
$
2,931

 
$
1,587

 
$
37

 
$
4,555

Regulatory assets, net
81

 
(1
)
 
—

 
80

Deferred employee benefit costs
(76
)
 
(40
)
 
(91
)
 
(207
)
Revenue requirement reconciliation adjustments
—

 
66

 
—

 
66

Tax carryforwards
(65
)
 
(133
)
 
(405
)
 
(603
)
Other
(27
)
 
1

 
20

 
(6
)
Total net accumulated deferred income tax liabilities (assets)
$
2,844

 
$
1,480

 
$
(439
)
 
$
3,885


The following table presents the components of deferred tax assets relating to net operating loss carryforwards, tax credit carryforwards, and charitable contribution carryforwards at December 31, 2016 and 2015:
 
Ameren Missouri
 
Ameren Illinois
 
Other
 
Ameren
2016
 
 
 
 
 
 
 
Net operating loss carryforwards:
 
 
 
 
 
 
 
Federal(a)
$
33

 
$
137

 
$
324

 
$
494

State(a)
4

 
—

 
41

 
45

Total net operating loss carryforwards
$
37

 
$
137

 
$
365

 
$
539

Tax credit carryforwards:
 
 
 
 
 
 
 
Federal(a)
$
29

 
$
1

 
$
79

 
$
109

State(b)
—

 
—

 
21

 
21

Total tax credit carryforwards
$
29

 
$
1

 
$
100

 
$
130

Charitable contribution carryforwards(b)
$
—

 
$
—

 
$
18

 
$
18

Valuation allowance(c)
—

 
—

 
(11
)
 
(11
)
Total charitable contribution carryforwards
$
—

 
$
—

 
$
7

 
$
7

2015
 
 
 
 
 
 
 
Net operating loss carryforwards:
 
 
 
 
 
 
 
Federal
$
35

 
$
127

 
$
245

 
$
407

State
4

 
4

 
38

 
46

Total net operating loss carryforwards
$
39

 
$
131

 
$
283

 
$
453

Tax credit carryforwards:
 
 
 
 
 
 
 
Federal
$
26

 
$
1

 
$
78

 
$
105

State
—

 
1

 
40

 
41

State valuation allowance
—

 
—

 
(2
)
 
(2
)
Total tax credit carryforwards
$
26

 
$
2

 
$
116

 
$
144

Charitable contribution carryforwards
$
—

 
$
—

 
$
10

 
$
10

Valuation allowance
—

 
—

 
(4
)
 
(4
)
Total charitable contribution carryforwards
$
—

 
$
—

 
$
6

 
$
6


(a)
Will expire between 2029 and 2036.
(b)
Will expire between 2017 and 2021.
(c)
See Schedule II under Part IV, Item 15, in this report for information on changes in the valuation allowance.
Uncertain Tax Positions
As of December 31, 2016 and 2015, the Ameren Companies did not record any uncertain tax positions. The settlements discussed below resolved previously recorded uncertain tax positions.
In 2015, final settlements for tax years 2012 and 2013 were reached with the IRS. The 2015 settlement of the 2013 tax year impacted discontinued operations. See Note 1 – Summary of Significant Accounting Policies for additional information.

In 2014, final settlements for tax years 2007 through 2011 were reached with the IRS. These settlements, which resolved the uncertain tax positions associated with the timing of research tax deductions for these years, resulted in a decrease in Ameren’s and Ameren Missouri’s unrecognized tax benefits of $20 million, and $13 million, respectively. In addition, the settlement for tax years 2007 through 2011 provided certainty for the previously uncertain tax positions associated with the timing of research tax deductions for the remaining open tax years of 2012, 2013, and 2014. The certainty provided from the settlement resulted in an $18 million decrease in both Ameren’s and Ameren Missouri’s unrecognized tax benefits. The settlement also resulted in a $2 million increase to Ameren’s state unrecognized tax benefits. The net reduction in unrecognized tax benefits in 2014 did not materially affect income tax expense for the Ameren Companies.
State income tax returns are generally subject to examination for a period of three years after filing. The state impact of any federal changes remains subject to examination by various states for up to one year after formal notification to the states. The Ameren Companies currently do not have material state income tax issues under examination, administrative appeals, or litigation.
Ameren Missouri has an uncertain tax position tracker. Under Missouri's regulatory framework, uncertain tax positions do not reduce Ameren Missouri's electric rate base. When an uncertain income tax position liability is resolved, the MoPSC requires, through the uncertain tax position tracker, the creation of a regulatory asset or regulatory liability to reflect the time value, using the weighted-average cost of capital included in each of the electric rate orders in effect before the tax position was resolved, of the difference between the uncertain tax position liability that was excluded from rate base and the final tax liability. The resulting regulatory asset or liability will affect earnings in the year it is created and then will be amortized over three years, beginning on the effective date of new rates established in the next electric rate case.
Related Party Transactions
RELATED PARTY TRANSACTIONS
In the normal course of business, the Ameren Companies have engaged in, and may in the future engage in, affiliate transactions. These transactions primarily consist of natural gas and power purchases and sales, services received or rendered, and borrowings and lendings. Transactions between affiliates are reported as intercompany transactions on their financial statements, but are eliminated in consolidation for Ameren’s financial statements. Below are the material related party agreements.
Electric Power Supply Agreements
Ameren Illinois must acquire capacity and energy sufficient to meet its obligations to customers. Ameren Illinois uses periodic RFP processes, administered by the IPA and approved by the ICC, to contract capacity and energy on behalf of its customers. Ameren Missouri participates in the RFP process and has been a winning supplier for certain periods.
Capacity Supply Agreements
In a procurement event in 2012, Ameren Missouri contracted to supply a portion of Ameren Illinois' capacity requirements for $1 million and $3 million for the 12 months ended May 31, 2014, and 2015, respectively. In a procurement event in 2015, Ameren Missouri contracted to supply a portion of Ameren Illinois' capacity requirements for $15 million for the 12 months ending May 31, 2017. 
Energy Swaps and Energy Products
Based on the outcome of IPA administered procurement events, Ameren Missouri and Ameren Illinois have entered into energy product agreements by which Ameren Missouri agreed to sell, and Ameren Illinois agreed to purchase, a set amount of megawatthours at a predetermined price over a specified period of time. The following table presents the agreements the companies have entered into, as well as the specified time period, price, and amount of megawatthours included in each agreement:
IPA
 Procurement Event
Time Period
MWh
 
Average Price per MWh
May 2014
January 2015 – February 2017
168,400

$
51
April 2015
June 2015 – June 2017
667,000

 
36
September 2015
November 2015 – May 2018
339,000

 
38
April 2016
June 2017 – September 2018
375,200

 
35
September 2016
May 2017 – September 2018
82,800

 
34

Collateral Postings
Under the terms of the Illinois energy product agreements entered into through RFP processes administered by the IPA, suppliers must post collateral under certain market conditions to protect Ameren Illinois in the event of nonperformance. The collateral postings are unilateral, which means that only the suppliers can be required to post collateral. Therefore, Ameren Missouri, as a winning supplier in the RFP process, may be required to post collateral. As of December 31, 2016 and 2015, there were no collateral postings required of Ameren Missouri related to the Illinois energy product agreements.
Interconnection and Transmission Agreements
Ameren Missouri and Ameren Illinois are parties to an interconnection agreement for the use of their respective transmission lines and other facilities for the distribution of power. These agreements have no contractual expiration date, but may be terminated by either party with three years’ notice.
Support Services Agreements
Ameren Services provides support services to its affiliates. The costs of support services, including wages, employee benefits, professional services, and other expenses, are based on, or are an allocation of, actual costs incurred. The support services agreement can be terminated at any time by the mutual agreement of Ameren Services and that affiliate or by either party with 60 days' notice before the end of a calendar year.
In addition, Ameren Missouri and Ameren Illinois provide affiliates, primarily Ameren Services, with access to their facilities for administrative purposes. The costs of the rent and facility services are based on, or are an allocation of, actual costs incurred.
Separately, Ameren Missouri and Ameren Illinois provide storm-related and miscellaneous support services to each other on an as-needed basis. 
Transmission Services
Ameren Illinois receives transmission services from ATXI for its retail load in the AMIL pricing zone.
Money Pool
See Note 4 – Short-term Debt and Liquidity and Note 5 – Long-term Debt and Equity Financings for a discussion of affiliate borrowing arrangements.
Tax Allocation Agreement
See Note 1 – Summary of Significant Accounting Policies for a discussion of the tax allocation agreement and the related capital contributions and return of capital.
The following table presents the impact on Ameren Missouri and Ameren Illinois of related party transactions for the years ended December 31, 2016, 2015, and 2014. It is based primarily on the agreements discussed above and the money pool arrangements discussed in Note 4 – Short-term Debt and Liquidity.
Agreement
Income Statement Line Item                    
 
  
 
Ameren
Missouri
 
Ameren
Illinois
Ameren Missouri power supply agreements
Operating Revenues
 
2016
$
28

$
(a)

with Ameren Illinois
 
 
2015
 
15

 
(a)

 
 
 
2014
 
5

 
(a)

Ameren Missouri and Ameren Illinois
Operating Revenues
 
2016
 
25

 
5

rent and facility services
 
 
2015
 
25

 
4

 
 
 
2014
 
21

 
2

Ameren Missouri and Ameren Illinois
Operating Revenues
 
2016
 
1

 
(b)

miscellaneous support services
 
 
2015
 
2

 
(b)

 
 
 
2014
 
1

 
(b)

Total Operating Revenues
 
 
2016
$
54

$
5

 
 
 
2015
 
42

 
4

 
 
 
2014
 
27

 
2

Ameren Illinois power supply
Purchased Power
 
2016
$
(a)

$
28

agreements with Ameren Missouri
 
 
2015
 
(a)

 
15

 
 
 
2014
 
(a)

 
5

Ameren Illinois transmission
Purchased Power
 
2016
 
(a)

 
2

services from ATXI
 
 
2015
 
(a)

 
2

 
 
 
2014
 
(a)

 
2

Total Purchased Power
 
 
2016
$
(a)

$
30

 
 
 
2015
 
(a)

 
17

 
 
 
2014
 
(a)

 
7

Ameren Services support services
Other Operations and
 
2016
$
129

$
123

agreement
Maintenance
 
2015
 
131

 
119

 
 
 
2014
 
124

 
109

Money pool borrowings (advances)
Interest (Charges)
 
2016
$
(b)

$
(b)

 
Income
 
2015
 
(b)

 
(b)

 
 
 
2014
 
(b)

 
(b)

(a)
Not applicable.
(b)
Amount less than $1 million.
Commitments And Contingencies
COMMITMENTS AND CONTINGENCIES
COMMITMENTS AND CONTINGENCIES
We are involved in legal, tax, and regulatory proceedings before various courts, regulatory commissions, authorities, and governmental agencies with respect to matters that arise in the ordinary course of business, some of which involve substantial amounts of money. We believe that the final disposition of these proceedings, except as otherwise disclosed in these notes to our financial statements, will not have a material adverse effect on our results of operations, financial position, or liquidity.
See also Note 1 – Summary of Significant Accounting Policies, Note 2 – Rate and Regulatory Matters, Note 10 – Callaway Energy Center, and Note 14 – Related Party Transactions in this report.
Callaway Energy Center
The following table presents insurance coverage at Ameren Missouri’s Callaway energy center at December 31, 2016. The property coverage and the nuclear liability coverage renewal dates are April 1 and January 1, respectively, of each year.
Type and Source of Coverage
Maximum Coverages
 
Maximum Assessments
 
Public liability and nuclear worker liability:
 
 
 
 
American Nuclear Insurers
$
375

(a) 
$
—

 
Pool participation
12,986

(b)  
127

(c)  
 
$
13,361

(d)  
$
127

 
Property damage:
 
 
 
 
Nuclear Electric Insurance Limited
$
2,710

(e)  
$
30

(f)  
European Mutual Association for Nuclear Insurance
450

(g)  
—

 
 
$
3,160

 
$
30

 
Replacement power:
 
 
 
 
Nuclear Electric Insurance Limited
$
490

(h)  
$
7

(f)  

(a)
Effective January 1, 2017, limit was increased to $450 million.
(b)
Provided through mandatory participation in an industrywide retrospective premium assessment program.
(c)
Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $375 million in the event of an incident at any licensed United States commercial reactor, payable at $19 million per year.
(d)
Limit of liability for each incident under the Price-Anderson liability provisions of the Atomic Energy Act of 1954, as amended. A company could be assessed up to $127 million per incident for each licensed reactor it operates, with a maximum of $19 million per incident to be paid in a calendar year for each reactor. This limit is subject to change to account for the effects of inflation and changes in the number of licensed reactors.
(e)
NEIL provides $2.71 billion in property damage, decontamination, and premature decommissioning insurance for radiation events. NEIL provides $2.3 billion in property damage for nonradiation events.
(f)
All NEIL-insured plants could be subject to assessments should losses exceed the accumulated funds from NEIL.
(g)
European Mutual Association for Nuclear Insurance provides $450 million in excess of the $2.71 billion and $2.3 billion property coverage for radiation and nonradiation events, respectively, provided by NEIL.
(h)
Provides replacement power cost insurance in the event of a prolonged accidental outage. Weekly indemnity is up to $4.5 million for 52 weeks, which commences after the first 12 weeks of an outage, plus up to $3.6 million per week for a minimum of 71 weeks thereafter, for a total not exceeding the policy limit of $490 million. Nonradiation events are sub-limited to $328 million.
The Price-Anderson Act is a federal law that limits the liability for claims from an incident involving any licensed United States commercial nuclear energy center. The limit is based on the number of licensed reactors. The limit of liability and the maximum potential annual payments are adjusted at least every five years for inflation to reflect changes in the Consumer Price Index. The most recent five-year inflationary adjustment became effective in September 2013. Owners of a nuclear reactor cover this exposure through a combination of private insurance and mandatory participation in a financial protection pool, as established by the Price-Anderson Act.
Losses resulting from terrorist attacks on nuclear facilities are covered under NEIL’s insurance policies, subject to an industrywide aggregate policy coverage limit of $3.24 billion within a 12-month period, or $1.83 billion for events not involving radiation contamination.
If losses from a nuclear incident at the Callaway energy center exceed the limits of or are not covered by insurance, or if insurance coverage is unavailable, Ameren Missouri is at risk for any uninsured losses. If a serious nuclear incident were to occur, it could have a material adverse effect on Ameren’s and Ameren Missouri’s results of operations, financial position, and liquidity.
Leases
We lease various facilities, office equipment, plant equipment, and rail cars under capital and operating leases. The following table presents our lease obligations at December 31, 2016:
 
2017
 
2018
 
2019
 
2020
 
2021
 
After 5 Years
 
Total
Ameren:(a)
 
 
 
 
 
 
 
 
 
 
 
 
 
Minimum capital lease payments(b)
$
33

 
$
32

 
$
32

 
$
32

 
$
32

 
$
297

 
$
458

Less amount representing interest
27

 
26

 
25

 
25

 
25

 
48

 
176

Present value of minimum capital lease payments
$
6

 
$
6

 
$
7

 
$
7

 
$
7

 
$
249

 
$
282

Operating leases(c)
13

 
12

 
12

 
11

 
10

 
23

 
81

Total lease obligations
$
19

 
$
18

 
$
19

 
$
18

 
$
17

 
$
272

 
$
363

Ameren Missouri:
 
 
 
 
 
 
 
 
 
 
 
 
 
Minimum capital lease payments(b)
$
33

 
$
32

 
$
32

 
$
32

 
$
32

 
$
297

 
$
458

Less amount representing interest
27

 
26

 
25

 
25

 
25

 
48

 
176

Present value of minimum capital lease payments
$
6

 
$
6

 
$
7

 
$
7

 
$
7

 
$
249

 
$
282

Operating leases(c)
11

 
11

 
11

 
10

 
9

 
21

 
73

Total lease obligations
$
17

 
$
17

 
$
18

 
$
17

 
$
16

 
$
270

 
$
355

Ameren Illinois:
 
 
 
 
 
 
 
 
 
 
 
 
 
Operating leases(c)
$
1

 
$
1

 
$
1

 
$
1

 
$
1

 
$
1

 
$
6

(a)
Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
(b)
See Properties under Part I, Item 2, and Note 3 – Property, Plant, and Equipment, Net, of this report for additional information.
(c)
Amounts related to certain land-related leases have indefinite payment periods. The annual obligations of $3 million, $2 million, and $1 million for Ameren, Ameren Missouri, and Ameren Illinois for these items are included in the 2017 through 2021 columns, respectively.
The following table presents total rental expense included in operating expenses for the years ended December 31, 2016, 2015, and 2014:
 
2016
 
2015
 
2014
Ameren(a)
$
38

 
$
36

 
$
37

Ameren Missouri
34

 
34

 
32

Ameren Illinois
30

 
28

 
25

(a)
Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
Other Obligations
To supply a portion of the fuel requirements of our energy centers, we have entered into various long-term commitments for the procurement of coal, natural gas, nuclear fuel, and methane gas. We also have entered into various long-term commitments for purchased power and natural gas for distribution. The table below presents our estimated fuel, purchased power, and other commitments for fuel at December 31, 2016. Ameren’s and Ameren Missouri’s purchased power commitments include a 102-megawatt power purchase agreement with a wind farm operator, which expires in 2024. Ameren’s and Ameren Illinois’ purchased power commitments include the Ameren Illinois power purchase agreements entered into as part of the IPA-administered power procurement process. Included in the Other column are minimum purchase commitments under contracts for equipment, design and construction, and meter reading services at December 31, 2016.
 
Coal
 
Natural
Gas(a)
 
Nuclear
Fuel
 
Purchased
Power(b)
 
Methane
Gas
 
Other
 
Total
Ameren:(c)
 
 
 
 
 
 
 
 
 
 
 
 
 
2017
$
599

 
$
238

 
$
45

 
$
255

 
$
3

 
$
118

 
$
1,258

2018
371

 
167

 
70

 
156

 
4

 
60

 
828

2019
311

 
99

 
27

 
79

 
4

 
60

 
580

2020
27

 
45

 
38

 
58

 
5

 
56

 
229

2021
—

 
12

 
44

 
58

 
5

 
29

 
148

Thereafter
—

 
43

 
45

 
478

 
65

 
198

 
829

Total
$
1,308

 
$
604

 
$
269

 
$
1,084

 
$
86

 
$
521

 
$
3,872

Ameren Missouri:
 
 
 
 
 
 
 
 
 
 
 
 
 
2017
$
599

 
$
43

 
$
45

 
$
22

 
$
3

 
$
39

 
$
751

2018
371

 
29

 
70

 
22

 
4

 
29

 
525

2019
311

 
15

 
27

 
22

 
4

 
29

 
408

2020
27

 
10

 
38

 
22

 
5

 
29

 
131

2021
—

 
5

 
44

 
22

 
5

 
28

 
104

Thereafter
—

 
18

 
45

 
59

 
65

 
183

 
370

Total
$
1,308

 
$
120

 
$
269

 
$
169

 
$
86

 
$
337

 
$
2,289

Ameren Illinois:
 
 
 
 
 
 
 
 
 
 
 
 
 
2017
$
—

 
$
195

 
$
—

 
$
233

 
$
—

 
$
36

 
$
464

2018
—

 
138

 
—

 
134

 
—

 
24

 
296

2019
—

 
83

 
—

 
57

 
—

 
27

 
167

2020
—

 
35

 
—

 
36

 
—

 
27

 
98

2021
—

 
8

 
—

 
36

 
—

 
—

 
44

Thereafter
—

 
25

 
—

 
419

 
—

 
—

 
444

Total
$
—

 
$
484

 
$
—

 
$
915

 
$
—

 
$
114

 
$
1,513

(a)
Includes amounts for generation and for distribution.
(b)
The purchased power amounts for Ameren and Ameren Illinois include agreements through 2032 for renewable energy credits with various renewable energy suppliers. The agreements contain a provision that allows Ameren Illinois to reduce the quantity purchased in the event that Ameren Illinois would not be able to recover the costs associated with the renewable energy credits.
(c)
Includes amounts for Ameren registrant and nonregistrant subsidiaries.
Environmental Matters
We are subject to various environmental laws and regulations enforced by federal, state, and local authorities. The development and operation of electric generation, transmission, and distribution facilities and natural gas storage, transmission, and distribution facilities, can trigger compliance with diverse environmental laws and regulations. These laws and regulations address emissions, discharges to water, water usage, impacts to air, land, and water, and chemical and waste handling. Complex and lengthy processes are required to obtain and renew approvals, permits, and licenses for new, existing or modified facilities. Additionally, the use and handling of various chemicals or hazardous materials require release prevention plans and emergency response procedures.
The EPA has promulgated environmental regulations that have a significant impact on the electric utility industry. Over time, compliance with these regulations could be costly for Ameren Missouri, which operates coal-fired power plants. As of December 31, 2016, Ameren Missouri’s fossil-fueled energy centers represented 18% and 34% of Ameren’s and Ameren Missouri’s rate base, respectively. Regulations impacting the electric utility industry include the regulation of CO2 emissions from existing power plants through the Clean Power Plan and from new power plants through the revised NSPS; the CSAPR, which requires further reductions of SO2 emissions and NOx emissions from power plants; a regulation governing management and storage of CCR; the MATS, which requires reduction of emissions of mercury, toxic metals, and acid gases from power plants; revised NSPS for particulate matter, SO2, and NOx emissions from new sources; effluent standards applicable to wastewater discharges from power plants; and regulations under the Clean Water Act that could require significant capital expenditures, such as modifications to water intake structures at Ameren Missouri’s energy centers. The EPA also periodically reviews and revises national ambient air quality standards, including those standards associated with emissions from power plants, such as particulate matter, ozone, SO2 and NOx. Certain of these regulations are being or are likely to be challenged through litigation, so their ultimate implementation, as well as the timing of any such implementation, is uncertain. Although many details of future regulations are unknown, the individual or combined effects of recent environmental regulations could result in significant capital expenditures and increased operating costs for Ameren and Ameren Missouri. Compliance with these environmental laws and regulations could be prohibitively expensive, result in the closure or alteration of the operation of some of Ameren Missouri’s energy centers, or require further capital investment. Ameren and Ameren Missouri expect that these costs would be recoverable through rates, subject to MoPSC prudence review, but the nature and timing of costs and their recovery could result in regulatory lag.
Ameren Missouri's current plan for compliance with existing environmental regulations for air emissions includes burning ultra-low-sulfur coal and installing new or optimizing existing pollution control equipment. Ameren and Ameren Missouri estimate that they will need to make capital expenditures of $425 million to $525 million in the aggregate from 2017 through 2021 in order to comply with existing environmental regulations. Ameren Missouri may be required to install additional air emissions controls beyond 2021. This estimate of capital expenditures includes expenditures required for the CCR regulations, the Clean Water Act rule applicable to cooling water intake structures at existing power plants, and the Clean Water Act effluent limitation guidelines applicable to steam electric generating units, all of which are discussed below. This estimate does not include the potential impacts of the Clean Power Plan discussed below. The actual amount of capital expenditures required to comply with existing environmental regulations may vary substantially from the above estimate because of uncertainty as to the precise compliance strategies that will be used and their ultimate cost, among other things.
The following sections describe the more significant recent environmental laws and rules and environmental enforcement and remediation matters that affect or could affect our operations.
Clean Air Act
Federal and state laws require significant reductions in SO2 and NOx through either emission source reductions or the use and retirement of emission allowances. The first phase of the CSAPR emission reduction requirements became effective in 2015. The second phase of emission reduction requirements, which were revised by the EPA in 2016, will become effective in 2017; additional emission reduction requirements may apply in subsequent years. To achieve compliance with the CSAPR, Ameren Missouri burns ultra-low-sulfur coal, operates two scrubbers at its Sioux energy center, and optimizes other existing pollution control equipment. Ameren Missouri does not expect to make additional capital investments to comply with the 2017 CSAPR requirements. However, Ameren Missouri expects to incur additional costs to lower its emissions at one or more of its energy centers to comply with the CSAPR in future years. These higher costs are expected to be recovered from customers through the FAC or higher base rates.
CO2 Emissions Standards
In 2015, the EPA issued final regulations that set CO2 emissions standards for new power plants. These new standards establish separate emissions limits for new natural-gas-fired combined cycle plants and new coal-fired plants.The Clean Power Plan sets forth CO2 emissions standards applicable to existing power plants. The rule was stayed by the United States Supreme Court in February 2016, pending the outcome of various legal challenges.
If upheld and implemented, the Clean Power Plan would require Missouri and Illinois to reduce CO2 emissions from power plants within their states significantly below 2005 levels by 2030. The rule contains interim compliance periods commencing in 2022 that would require each state to demonstrate progress in achieving its CO2 emissions reduction target. Ameren continues to evaluate the Clean Power Plan's potential impacts to its operations, including those related to electric system reliability, and to its level of investment in customer energy efficiency programs, renewable energy, and other forms of generation. Significant uncertainty exists regarding the impact of the Clean Power Plan as its implementation will depend upon plans to be developed by the states. Numerous legal challenges are pending, which could result in the rule being declared invalid or the nature and timing of CO2 emissions reductions being revised. All implementation requirements are deferred until such time as these legal challenges are concluded. A decision by the District of Columbia Circuit Court of Appeals is expected to be issued in 2017, and subsequent appeals to the United States Supreme Court are likely. We cannot predict the outcome of such legal challenges or their impact on our results of operations, financial position, or liquidity. If the rule is ultimately upheld and not rescinded or altered significantly by the new federal administration, compliance measures could result in the closure or alteration of the operation of some of Ameren Missouri’s coal and natural-gas-fired energy centers, which could in turn result in increased operating costs and require Ameren Missouri to make unplanned or accelerated capital expenditures. Ameren Missouri expects substantially all of these increased costs to be recoverable, subject to MoPSC prudence review, through higher rates to customers, which could be significant.
Federal and state legislation or regulations that mandate limits on the emission of CO2 may result in significant increases in capital expenditures and operating costs, which could lead to increased liquidity needs and higher financing costs. Mandatory limits on the emission of CO2 could increase costs for Ameren Missouri’s customers or have a material adverse effect on Ameren's and Ameren Missouri's results of operations, financial position, and liquidity if regulators delay or deny recovery in rates of these compliance costs. The cost of Ameren Illinois’ purchased power and natural gas purchased for resale could increase. However, Ameren Illinois expects these costs would be recovered from customers with no material adverse effect on its results of operations, financial position, or liquidity. Ameren's and Ameren Missouri's earnings might benefit from increased investment to comply with CO2 emission limitations to the extent that the investments are reflected and recovered on a timely basis in rates charged to customers.
NSR and Clean Air Litigation
In January 2011, the Department of Justice, on behalf of the EPA, filed a complaint against Ameren Missouri in the United States District Court for the Eastern District of Missouri. The complaint, as amended in October 2013, alleged that in performing projects at its Rush Island coal-fired energy center in 2007 and 2010, Ameren Missouri violated provisions of the Clean Air Act and Missouri law. The litigation has been divided into two phases: liability and remedy. In January 2017, the district court issued a liability ruling that the projects violated provisions of the Clean Air Act and Missouri law. The case will now proceed to the second phase to determine the actions required to remedy the violations found in the liability phase of the litigation. The EPA previously withdrew all claims for penalties and fines. At the conclusion of both phases of the litigation, Ameren Missouri intends to appeal the liability ruling to the United States Circuit Court of Appeals for the Eighth Circuit. A decision by the district court regarding the remedy phase of the litigation could occur in 2018.
The ultimate resolution of this matter could have a material adverse effect on the results of operations, financial position, and liquidity of Ameren and Ameren Missouri. Among other things and subject to economic and regulatory considerations, resolution of this matter could result in increased capital expenditures for the installation of pollution control equipment, as well as increased operations and maintenance expenses. We are unable to predict the ultimate resolution of this matter or the costs that might be incurred.
Clean Water Act
In 2014, the EPA issued its final rule applicable to cooling water intake structures at existing power plants. The rule requires a case-by-case evaluation and plan for reducing aquatic organisms impinged on the facility’s intake screens or entrained through the plant's cooling water system. Additionally, in 2015, the EPA issued its final rule to revise the effluent limitation guidelines applicable to steam electric generating units. Effluent limitation guidelines are national standards for water discharges that are based on the effectiveness of available control technology. The EPA's 2015 rule prohibits effluent discharges of certain waste streams and imposes more stringent limitations on certain components in water discharges from power plants. All of Ameren Missouri’s coal-fired and nuclear energy centers are subject to the cooling water intake structures rule. All of Ameren Missouri’s coal-fired energy centers are subject to the effluent limitations rule. Implementation of both rules will occur during the renewal process of each energy center’s water discharge permit, which will occur between 2018 and 2023. The rules could have an adverse effect on Ameren’s and Ameren Missouri’s results of operations, financial position, and liquidity if their implementation requires extensive modifications to the cooling water systems and water discharge systems at Ameren Missouri’s energy centers and if those investments are not recovered on a timely basis in electric rates charged to Ameren Missouri’s customers.
Ash Management
In 2015, the EPA issued regulations regarding the management and disposal of CCR from coal fired energy centers. These regulations affect CCR disposal and handling costs at Ameren Missouri's energy centers. They require closure of impoundments if performance criteria relating to groundwater impacts and location restrictions are not achieved. During 2015, Ameren and Ameren Missouri recorded an increase to their AROs associated with CCR storage facilities and accelerated the closure of certain CCR storage facilities at its energy centers as a result of the new regulations. Ameren plans to close these CCR storage facilities between 2018 and 2023. See Note 1 – Summary of Significant Accounting Policies in this report for additional information.
Ameren Missouri's capital expenditure plan includes the cost of constructing landfills as part of its environmental compliance plan.
Remediation
The Ameren Companies are involved in a number of remediation actions to clean up sites affected by the use or disposal of materials containing hazardous substances. Federal and state laws can require responsible parties to fund remediation actions regardless of their degree of fault, the legality of original disposal, or the ownership of a disposal site. Ameren Missouri and Ameren Illinois have each been identified by federal or state governments as a potentially responsible party at several contaminated sites.
As of December 31, 2016, Ameren Illinois owned or was otherwise responsible for 44 former MGP sites in Illinois, which are in various stages of investigation, evaluation, remediation, and closure. Ameren Illinois estimates it could substantially conclude remediation efforts by 2023. The ICC allows Ameren Illinois to recover remediation and litigation costs associated with its former MGP sites from its electric and natural gas utility customers through environmental cost riders. Costs are subject to annual prudence review by the ICC. As of December 31, 2016, Ameren Illinois estimated the obligation related to these former MGP sites at $200 million to $268 million. Ameren and Ameren Illinois recorded a liability of $200 million to represent the estimated minimum obligation for these sites, as no other amount within the range was a better estimate.
The scope of the remediation activities at these former MGP sites may increase as remediation efforts continue. Considerable uncertainty remains in these estimates because many site-specific factors can influence the ultimate actual costs, including unanticipated underground structures, the degree to which groundwater is encountered, regulatory changes, local ordinances, and site accessibility. The actual costs may vary substantially from these estimates.
Ameren Missouri participated in the investigation of various sites known as Sauget Area 2 located in Sauget, Illinois. In 2000, the EPA notified Ameren Missouri and numerous other companies that former landfills and lagoons at those sites may contain soil and groundwater contamination. From about 1926 until 1976, Ameren Missouri operated an energy center adjacent to Sauget Area 2. Ameren Missouri currently owns a parcel of property at Sauget Area 2 that was once used by others as a landfill.
In December 2013, the EPA issued its record of decision for Sauget Area 2 approving the investigation and the remediation actions recommended by the potentially responsible parties. Further negotiation among the potentially responsible parties will determine how to fund the implementation of the EPA-approved cleanup remedies. As of December 31, 2016, and December 31, 2015, Ameren Missouri estimated its obligation related to Sauget Area 2 at $1 million to $2.5 million. Ameren Missouri recorded a liability of $1 million to represent its estimated minimum obligation, as no other amount within the range was a better estimate.
Our operations or those of our predecessor companies involve the use of, disposal of, and in appropriate circumstances, the cleanup of substances regulated under environmental laws. We are unable to determine whether such practices will result in future environmental commitments or will affect our results of operations, financial position, or liquidity.
Ameren Missouri Municipal Taxes
The cities of Creve Coeur and Winchester, Missouri, on behalf of themselves and other municipalities in Ameren Missouri’s service area, filed a class action lawsuit in November 2011 against Ameren Missouri in the Circuit Court of St. Louis County, Missouri. The lawsuit alleges that Ameren Missouri failed to collect and pay gross receipts taxes or license fees on certain revenues, including revenues from wholesale power and interchange sales. Ameren and Ameren Missouri recorded immaterial liabilities on their respective balance sheets as of December 31, 2016, and December 31, 2015, representing their estimate of the probable loss due as a result of this lawsuit. Ameren and Ameren Missouri believe there is a remote possibility that a liability relating to this lawsuit could be material to Ameren's and Ameren Missouri’s results of operations, financial position, and liquidity. Ameren Missouri believes its defenses are meritorious and is defending itself vigorously. However, there can be no assurances that Ameren Missouri will be successful in its efforts.
Segment Information
SEGMENT INFORMATION
SEGMENT INFORMATION
During the fourth quarter of 2016, the Ameren Companies changed the manner in which performance is assessed and resources are allocated, driven by increasing investment in FERC-regulated electric transmission and Ameren Illinois electric distribution and natural gas distribution businesses, as well as the unique regulatory environment for each jurisdiction. Ameren now has four segments: Ameren Missouri, Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Transmission. The Ameren Missouri segment includes all of the operations of Ameren Missouri. Ameren Illinois Electric Distribution consists of the electric distribution business of Ameren Illinois. Ameren Illinois Natural Gas consists of the natural gas business of Ameren Illinois. Ameren Transmission is primarily composed of the aggregated electric transmission businesses of Ameren Illinois and ATXI and associated Ameren (parent) interest charges. The category called Other primarily includes Ameren parent company activities and Ameren Services.
Ameren Missouri has one segment. Ameren Illinois has three segments: Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission. See Note 1 – Summary of Significant Accounting Policies for additional information regarding the operations of Ameren Missouri and Ameren Illinois.
Segment operating revenue and a majority of operating expenses are directly assigned by Ameren Illinois to each Ameren Illinois segment. Common operating expenses, miscellaneous income and expense, interest charges, and income tax expense are allocated by Ameren Illinois to each Ameren Illinois segment based on certain factors, which primarily relate to the nature of the cost. Additionally, Ameren Illinois Transmission earns revenue from transmission service provided to Ameren Illinois Electric Distribution. The transmission expense for Illinois customers who have elected to purchase their power from Ameren Illinois is recovered through a cost recovery mechanism with no net effect on Ameren Illinois Electric Distribution earnings, as costs are offset by corresponding revenues. Transmission revenues from these transactions are reflected at Ameren Transmission and Ameren Illinois Transmission. An intersegment elimination at Ameren and Ameren Illinois occurs to eliminate these transmission revenues and expenses.
Prior to the fourth quarter of 2016, Ameren had two segments: Ameren Missouri and Ameren Illinois, which comprised the operations of the respective subsidiaries. The category called Other primarily included Ameren parent company activities, Ameren Services, and ATXI. Prior-period presentation has been adjusted for comparative purposes to reflect the 2016 change in segments.
The following tables present information about the reported revenues and specified items reflected in net income attributable to common shareholders from continuing operations and capital expenditures at Ameren and Ameren Illinois for the years ended December 31, 2016, 2015, and 2014. Ameren, Ameren Missouri, and Ameren Illinois management review segment capital expenditure information rather than any individual or total asset amount.
Ameren
 
Ameren Missouri
 
Ameren Illinois Electric Distribution
 
Ameren Illinois Natural Gas
 
Ameren Transmission
 
Other
 
Intersegment
Eliminations
 
Consolidated
2016
 
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
$
3,469

 
$
1,545

 
$
753

 
$
309

 
$
—

 
$
—

 
$
6,076

Intersegment revenues
54

 
4

 
1

 
46

(a) 
—

 
(105
)
 
—

Depreciation and amortization
514

 
226

 
55

 
43

 
7

 
—

 
845

Interest income
28

 
11

 
—

 
1

 
11

 
(11
)
 
40

Interest charges
211

 
72

 
34

 
58

 
18

 
(11
)
 
382

Income taxes
216

 
78

 
39

 
74

 
(25
)
 
—

 
382

Net income (loss) attributable to Ameren common shareholders from continuing operations
357

 
126

 
59

 
117

 
(6
)
 
—

 
653

Capital expenditures
738

 
470

 
181

 
689

 
4

(b) 
(6
)
 
2,076

2015
 
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
$
3,566

 
$
1,529

 
$
782

 
$
219

 
$
2

 
$
—

 
$
6,098

Intersegment revenues
43

 
3

 
1

 
40

(a) 
—

 
(87
)
 
—

Depreciation and amortization
492

 
212

 
52

 
33

 
7

 
—

 
796

Interest income
28

 
12

 
—

 
—

 
7

 
(6
)
 
41

Interest charges
219

 
71

 
35

 
35

 
1

 
(6
)
 
355

Income taxes
209

 
71

 
24

 
51

 
8

 
—

 
363

Net income (loss) attributable to Ameren common shareholders from continuing operations
352

 
123

 
37

 
83

 
(16
)
 
—

 
579

Capital expenditures
622

 
491

 
133

 
669

 
2

(b) 
—

 
1,917

2014
 
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
$
3,526

 
$
1,401

 
$
976

 
$
150

 
$
—

 
$
—

 
$
6,053

Intersegment revenues
27

 
2

 
—

 
37

(a) 
—

 
(66
)
 
—

Depreciation and amortization
473

 
197

 
41

 
26

 
8

 
—

 
745

Interest income
28

 
7

 
—

 
—

 
5

 
(3
)
 
37

Interest charges
211

 
63

 
28

 
26

 
16

 
(3
)
 
341

Income taxes
229

 
75

 
39

 
38

 
(4
)
 
—

 
377

Net income (loss) attributable to Ameren common shareholders from continuing operations
390

 
113

 
50

 
51

 
(17
)
 
—

 
587

Capital expenditures
747

 
403

 
137

 
491

 
7

(b) 
—

 
1,785


(a)
Ameren Illinois Transmission earns revenue from transmission service provided to Ameren Illinois Electric Distribution. See discussion of transactions above.
(b)
Includes the elimination of intercompany transfers.    


Ameren Illinois
 
Ameren Illinois Electric Distribution
 
Ameren Illinois Natural Gas
 
Ameren Illinois Transmission
 
Intersegment
Eliminations
 
Consolidated
 
2016
 
 
 
 
 
 
 
 
 
 
External revenues
$
1,549

 
$
754

 
$
187

 
$
—

 
$
2,490

 
Intersegment revenues
—

 
—

 
45

(a) 
(45
)
 
—

 
Depreciation and amortization
226

 
55

 
38

 
—

 
319

 
Interest income
11

 
—

 
1

 
—

 
12

 
Interest charges
72

 
34

 
34

 
—

 
140

 
Income taxes
78

 
39

 
41

 
—

 
158

 
Net income available to common shareholder
126

 
59

 
67

 
—

 
252

 
Capital expenditures
470

 
181

 
273

 
—

 
924

 
2015
 
 
 
 
 
 
 
 
 
 
External revenues
$
1,532

 
$
783

 
$
151

 
$
—

 
$
2,466

 
Intersegment revenues
—

 
—

 
38

(a) 
(38
)
 
—

 
Depreciation and amortization
212

 
52

 
31

 
—

 
295

 
Interest income
12

 
—

 
—

 
—

 
12

 
Interest charges
71

 
35

 
25

 
—

 
131

 
Income taxes
71

 
24

 
32

 
—

 
127

 
Net income available to common shareholder
123

 
37

 
54

 
—

 
214

 
Capital expenditures
491

 
133

 
294

 
—

 
918

 
2014
 
 
 
 
 
 
 
 
 
 
External revenues
$
1,403

 
$
976

 
$
119

 
$
—

 
$
2,498

 
Intersegment revenues
—

 
—

 
35

(a) 
(35
)
 
—

 
Depreciation and amortization
197

 
41

 
25

 
—

 
263

 
Interest income
7

 
—

 
—

 
—

 
7

 
Interest charges
63

 
28

 
21

 
—

 
112

 
Income taxes
75

 
39

 
29

 
—

 
143

 
Net income available to common shareholder
113

 
50

 
38

 
—

 
201

 
Capital expenditures
403

 
137

 
295

 
—

 
835

 
(a)
Ameren Illinois Transmission earns revenue from transmission service provided to Ameren Illinois Electric Distribution. See discussion of transactions above.
Selected Quarterly Information
SELECTED QUARTERLY INFORMATION
Ameren
2016
 
 
2015
Quarter ended
March 31
 
June 30
 
September 30
 
December 31
 
 
March 31
 
June 30
 
September 30
 
December 31
Operating revenues
$
1,434

 
$
1,427

 
$
1,859

 
$
1,356

 
 
$
1,556

 
$
1,401

 
$
1,833

 
$
1,308

Operating income
220

 
325

 
691

 
145

 
 
256

 
237

 
626

 
140

Net income
107

 
148

 
371

 
33

 
 
110

 
151

 
345

 
30

Net income attributable to Ameren common shareholders – continuing operations
$
105

 
$
147

 
$
369

 
$
32

 
 
$
108

 
$
98

 
$
343

 
$
30

Net income (loss) attributable to Ameren common shareholders – discontinued operations
—

 
—

 
—

 
—

 
 
—

 
52

 
—

 
(1
)
Net income attributable to Ameren common shareholders
$
105

 
$
147

 
$
369

 
$
32

 
 
$
108

 
$
150

 
$
343

 
$
29

Earnings per common share – basic – continuing operations
$
0.43

 
$
0.61

 
$
1.52

 
$
0.13

 
 
$
0.45

 
$
0.40

 
$
1.42

 
$
0.12

Earnings per common share – basic – discontinued operations
—

 
—

 
—

 
—

 
 
—

 
0.21

 
—

 
—

Earnings per common share – basic
$
0.43

 
$
0.61

 
$
1.52

 
$
0.13

 
 
$
0.45

 
$
0.61

 
$
1.42

 
$
0.12

Earnings per common share – diluted – continuing operations(a)
$
0.43

 
$
0.61

 
$
1.52

 
$
0.13

 
 
$
0.45

 
$
0.40

 
$
1.41

 
$
0.12

Earnings per common share – diluted – discontinued operations
—

 
—

 
—

 
—

 
 
—

 
0.21

 
—

 
—

Earnings per common share – diluted(a)
$
0.43

 
$
0.61

 
$
1.52

 
$
0.13

 
 
$
0.45

 
$
0.61

 
$
1.41

 
$
0.12

(a)
The sum of quarterly amounts, including per share amounts, may not equal amounts reported for year-to-date periods. This is because of the effects of rounding and the changes in the number of weighted-average diluted shares outstanding each period.
Ameren Missouri Quarter ended
 
Operating
Revenues
 
Operating
Income
 
Net Income
 
Net Income
Available
to Common
Shareholder
March 31, 2016
 
$
741

 
$
63

 
$
15

 
$
14

March 31, 2015
 
800

 
115

 
42

 
41

June 30, 2016
 
867

 
197

 
93

 
92

June 30, 2015
 
884

 
146

 
62

 
61

September 30, 2016
 
1,165

 
431

 
242

 
241

September 30, 2015
 
1,171

 
423

 
240

 
239

December 31, 2016
 
750

 
54

 
10

 
10

December 31, 2015
 
754

 
58

 
11

 
11


Ameren Illinois Quarter ended
 
Operating
Revenues
 
Operating
Income
 
Net Income
 
Net Income
Available
to Common
Shareholder
March 31, 2016
 
$
677

 
$
133

 
$
60

 
$
59

March 31, 2015
 
745

 
120

 
54

 
53

June 30, 2016
 
542

 
107

 
46

 
45

June 30, 2015
 
513

 
83

 
32

 
31

September 30, 2016
 
676

 
230

 
119

 
119

September 30, 2015
 
655

 
189

 
98

 
98

December 31, 2016
 
595

 
74

 
30

 
29

December 31, 2015
 
553

 
74

 
33

 
32

Schedule I - Condensed Financial Information Of Parent
Condensed Financial Information Of Parent
SCHEDULE I – CONDENSED FINANCIAL INFORMATION OF PARENT
AMEREN CORPORATION
CONDENSED STATEMENT OF INCOME AND COMPREHENSIVE INCOME
For the Years Ended December 31, 2016, 2015, and 2014
(In millions)
2016
 
2015
 
2014
Operating revenues
$
—

 
$
—

 
$
—

Operating expenses
14

 
14

 
11

Operating loss
(14
)
 
(14
)
 
(11
)
Equity in earnings of subsidiaries
663

 
600

 
607

Interest income from affiliates
10

 
6

 
3

Total other income (expense), net
(5
)
 
(5
)
 
2

Interest charges
28

 
3

 
16

Income tax (benefit)
(27
)
 
5

 
(2
)
Net Income Attributable to Ameren Common Shareholders – Continuing Operations
653

 
579

 
587

Net Income (Loss) Attributable to Ameren Common Shareholders
 – Discontinued Operations
—

 
51

 
(1
)
Net Income Attributable to Ameren Common Shareholders
$
653

 
$
630

 
$
586

 
 
 
 
 
 
Net Income Attributable to Ameren Common Shareholders – Continuing Operations
$
653

 
$
579

 
$
587

Other Comprehensive Income, Net of Taxes:
 
 
 
 
 
Pension and other postretirement benefit plan activity, net of income taxes (benefit) of $(7), $3, and $(7), respectively
(20
)
 
6

 
(12
)
Comprehensive Income from Continuing Operations Attributable to Ameren Common Shareholders
633

 
585

 
575

Comprehensive Income (Loss) from Discontinued Operations Attributable to Ameren Common Shareholders
—

 
51

 
(1
)
Comprehensive Income Attributable to Ameren Common Shareholders
$
633

 
$
636

 
$
574

SCHEDULE I – CONDENSED FINANCIAL INFORMATION OF PARENT
AMEREN CORPORATION
CONDENSED BALANCE SHEET
(In millions)
December 31, 2016
 
December 31, 2015
Assets:
 
 
 
Cash and cash equivalents
$
1

 
$
—

Advances to money pool
27

 
—

Accounts receivable – affiliates
31

 
53

Miscellaneous accounts and notes receivable
26

 
3

Other current assets
8

 
9

Total current assets
93

 
65

Investments in subsidiaries
7,498

 
7,227

Note receivable – ATXI
350

 
290

Accumulated deferred income taxes, net
419

 
426

Other assets
135

 
158

          Total assets
$
8,495

 
$
8,166

Liabilities and Shareholders’ Equity:
 
 
 
Short-term debt
507

 
301

Borrowings from money pool
33

 
14

Accounts payable – affiliates
13

 
75

Other current liabilities
17

 
22

Total current liabilities
570

 
412

Long-term debt
694

 
694

Pension and other postretirement benefits
45

 
33

Other deferred credits and liabilities
83

 
81

Total liabilities
1,392

 
1,220

Commitments and Contingencies (Notes 4 and 5)
 
 
 
Shareholders’ Equity:
 
 
 
Common stock, $.01 par value, 400.0 shares authorized – shares outstanding of 242.6
2

 
2

Other paid-in capital, principally premium on common stock
5,556

 
5,616

Retained earnings
1,568

 
1,331

Accumulated other comprehensive loss
(23
)
 
(3
)
Total shareholders’ equity
7,103

 
6,946

Total liabilities and shareholders’ equity
$
8,495

 
$
8,166

SCHEDULE I – CONDENSED FINANCIAL INFORMATION OF PARENT
AMEREN CORPORATION
CONDENSED STATEMENT OF CASH FLOWS
For the Years Ended December 31, 2016, 2015, and 2014
(In millions)
 
2016
 
2015
 
2014
Net cash flows provided by operating activities
 
$
483

 
$
551

 
$
528

Cash flows from investing activities:
 
 
 
 
 
 
Money pool advances, net
 
(27
)
 
55

 
279

Notes receivable – affiliates, net
 
(60
)
 
(96
)
 
(134
)
Investments in subsidiaries
 
(123
)
 
(509
)
 
(280
)
Distributions from subsidiaries
 
—

 
—

 
215

Proceeds from note receivable – Marketing Company
 
—

 
20

 
95

Contributions to note receivable – Marketing Company
 
—

 
(8
)
 
(89
)
Other
 
2

 
(24
)
 
(12
)
Net cash flows provided by (used in) investing activities
 
(208
)
 
(562
)
 
74

Cash flows from financing activities:
 
 
 
 
 
 
Dividends on common stock
 
(416
)
 
(402
)
 
(390
)
Short-term debt, net
 
206

 
(284
)
 
217

Money pool borrowings, net
 
19

 
14

 
—

Maturities of long-term debt
 
—

 
—

 
(425
)
Issuances of long-term debt
 
—

 
700

 
—

Capital issuance costs
 
—

 
(6
)
 
—

Share-based payments
 
(83
)
 
(12
)
 
(14
)
Net cash flows provided by (used in) financing activities
 
(274
)
 
10

 
(612
)
Net change in cash and cash equivalents
 
$
1

 
$
(1
)
 
$
(10
)
Cash and cash equivalents at beginning of year
 
—

 
1

 
11

Cash and cash equivalents at end of year
 
$
1

 
$
—

 
$
1

 
 
 
 
 
 
 
Cash dividends received from consolidated subsidiaries
 
$
465

 
$
575

 
$
340

 
 
 
 
 
 
 
Noncash investing activity – investments in subsidiaries
 
—

 
(38
)
 
(19
)
AMEREN CORPORATION (parent company only)
NOTES TO CONDENSED FINANCIAL STATEMENTS
December 31, 2016
NOTE 1 – BASIS OF PRESENTATION
Ameren Corporation (parent company only) is a public utility holding company that conducts substantially all of its business operations through its subsidiaries. Ameren Corporation (parent company only) has accounted for its subsidiaries using the equity method. These financial statements are presented on a condensed basis.
See Note 1 – Summary of Significant Accounting Policies under Part II, Item 8, of this report for additional information. See Note 14 – Related Party Transactions under Part II, Item 8, of this report for information on the tax allocation agreement between Ameren Corporation (parent company only) and its subsidiaries.
NOTE 2 – SHORT-TERM DEBT AND LIQUIDITY
Ameren, Ameren Services, and other non-state-regulated Ameren subsidiaries have the ability, subject to Ameren parent company and applicable regulatory short-term borrowing authorizations, to access funding from the Credit Agreements and the commercial paper programs through a non-state-regulated subsidiary money pool agreement. All participants may borrow from or lend to the non-state-regulated money pool. The total amount available to pool participants from the non-state-regulated subsidiary money pool at any given time is reduced by the amount of borrowings made by participants, but is increased to the extent that the pool participants advance surplus funds to the non-state-regulated subsidiary money pool or remit funds from other external sources. The non-state-regulated subsidiary money pool was established to coordinate and to provide short-term cash and working capital for the participants. Participants receiving a loan under the non-state-regulated subsidiary money pool agreement must repay the principal amount of such loan, together with accrued interest. The rate of interest depends on the composition of internal and external funds in the non-state-regulated subsidiary money pool. Interest revenues and interest charges related to non-state-regulated money pool advances and borrowings were immaterial in 2014, 2015 and 2016.
Ameren Corporation (parent company only) had a total of $51 million in guarantees outstanding, primarily for ATXI, that were not recorded on its December 31, 2016 balance sheet. The ATXI guarantees were issued to local governments as assurance for potential remediation of damage caused by ATXI construction.
See Note 4 – Short-term Debt and Liquidity under Part II, Item 8, of this report for a description and details of short-term debt and liquidity needs of Ameren Corporation (parent company only).
NOTE 3 – LONG-TERM OBLIGATIONS
See Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, of this report for additional information on Ameren Corporation's (parent company only) long-term debt, indenture provisions, and restricted cash balance.
NOTE 4 – COMMITMENTS AND CONTINGENCIES
See Note 15 – Commitments and Contingencies under Part II, Item 8, of this report for a description of all material contingencies of Ameren Corporation (parent company only).
NOTE 5 – DIVESTITURE TRANSACTIONS AND DISCONTINUED OPERATIONS
See Note 1 – Summary of Significant Accounting Policies under Part II, Item 8, of this report for information regarding the divestiture transactions and discontinued operations.
Schedule II - Valuation And Qualifying Accounts
Valuation And Qualifying Accounts
SCHEDULE II – VALUATION AND QUALIFYING ACCOUNTS
FOR THE YEARS ENDED DECEMBER 31, 2016, 2015, AND 2014
(in millions)
 
 
 
 
 
 
 
 
 
Column A
Column B
 
Column C
 
Column D
 
Column E
Description
Balance at
Beginning
of Period
 
(1)
Charged to Costs
and Expenses
 
(2)
Charged to Other
Accounts(a)
 
Deductions(b)
 
Balance at End
of Period
Ameren:
 
 
 
 
 
 
 
 
 
Deducted from assets – allowance for doubtful accounts:
 
 
 
 
 
 
 
 
 
2016
$
19

 
$
32

 
$
3

 
$
35

 
$
19

2015
21

 
33

 
5

 
40

 
19

2014
18

 
36

 
4

 
37

 
21

Deferred tax valuation allowance:
 
 
 
 
 
 
 
 
 
2016
$
6

 
$
7

 
$
(2
)
 
$
—

 
$
11

2015
10

 
4

 
(8
)
 
—

 
6

2014
7

 
3

 
—

 
—

 
10

Ameren Missouri:
 
 
 
 
 
 
 
 
 
Deducted from assets – allowance for doubtful accounts:
 
 
 
 
 
 
 
 
 
2016
$
7

 
$
10

 
$
—

 
$
10

 
$
7

2015
8

 
13

 
—

 
14

 
7

2014
5

 
16

 
—

 
13

 
8

Deferred tax valuation allowance:
 
 
 
 
 
 
 
 
 
2016
$
—

 
$
—

 
$
—

 
$
—

 
$
—

2015
1

 
—

 
(1
)
 
—

 
—

2014
1

 
—

 
—

 
—

 
1

Ameren Illinois:
 
 
 
 
 
 
 
 
 
Deducted from assets – allowance for doubtful accounts:
 
 
 
 
 
 
 
 
 
2016
$
12

 
$
22

 
$
3

 
$
25

 
$
12

2015
13

 
20

 
5

 
26

 
12

2014
13

 
20

 
4

 
24

 
13

Deferred tax valuation allowance:
 
 
 
 
 
 
 
 
 
2016
$
—

 
$
—

 
$
—

 
$
—

 
$
—

2015
1

 
—

 
(1
)
 
—

 
—

2014
1

 
—

 
—

 
—

 
1

(a)
Amounts associated with the allowance for doubtful accounts relate to the uncollectible account reserve associated with receivables purchased by Ameren Illinois from alternative retail electric suppliers, as required by the Illinois Public Utilities Act. The amounts relating to the deferred tax valuation allowance are for items that have expired and were removed from both the underlying accumulated deferred income tax account as well as the offsetting valuation account.
(b)
Uncollectible accounts charged off, less recoveries.
Summary Of Significant Accounting Policies (Policy)
General 
Ameren’s primary assets are its equity interests in its subsidiaries, including Ameren Missouri, Ameren Illinois, and ATXI. Ameren’s subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. Dividends on Ameren’s common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren’s principal subsidiaries are listed below. Ameren also has various other subsidiaries that conduct other activities, such as the provision of shared services.
•
Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri. Ameren Missouri was incorporated in Missouri in 1922 and is successor to a number of companies, the oldest of which was organized in 1881. It is the largest electric utility in the state of Missouri. It supplies electric and natural gas service to a 24,000-square-mile area in central and eastern Missouri. This area has an estimated population of 2.8 million and includes the Greater St. Louis area. Ameren Missouri supplies electric service to 1.2 million customers and natural gas service to 0.1 million customers.
•
Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois. Ameren Illinois was incorporated in Illinois in 1923 and is the successor to a number of companies, the oldest of which was organized in 1902. Ameren Illinois supplies electric and natural gas utility service to portions of central and southern Illinois with an estimated population of 3.1 million in an area of 40,000 square miles. Ameren Illinois supplies electric service to 1.2 million customers and natural gas service to 0.8 million customers.
•
ATXI operates a FERC rate-regulated electric transmission business. ATXI is developing MISO-approved electric transmission projects, including the Illinois Rivers, Spoon River, and Mark Twain projects. ATXI is also evaluating competitive electric transmission investment opportunities outside of MISO as they arise.
Ameren's financial statements are prepared on a consolidated basis and therefore include the accounts of its majority-owned subsidiaries. All intercompany transactions have been eliminated. Ameren Missouri and Ameren Illinois have no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated.
Consolidation 
Unless otherwise stated, these notes to the financial statements exclude discontinued operations for all periods presented.
Our accounting policies conform to GAAP. Our financial statements reflect all adjustments (which include normal, recurring adjustments) that are necessary, in our opinion, for a fair presentation of our results. The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. Such estimates and assumptions affect reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of financial statements, and the reported amounts of revenues and expenses during the reported periods. Actual results could differ from those estimates.
Public Utilities 
Purchased Gas, Power and Fuel Rate-adjustment Mechanisms
Ameren Missouri and Ameren Illinois have various rate-adjustment mechanisms in place that provide for the recovery of purchased natural gas and electric fuel and purchased power costs without a traditional rate case proceeding. See Note 2 – Rate and Regulatory Matters for the regulatory assets and liabilities recorded at December 31, 2016 and 2015, related to the rate-adjustment mechanisms discussed below.
In Ameren Missouri’s and Ameren Illinois’ natural gas businesses, changes in natural gas costs are reflected in billings to their customers through PGA clauses. The difference between actual natural gas costs and costs billed to customers in a given period is deferred as a regulatory asset or liability. The deferred amount is either billed or refunded to customers in a subsequent period.
In Ameren Illinois’ electric distribution business, changes in purchased power and transmission service costs are reflected in billings to its customers through pass-through rate-adjustment clauses. The difference between actual purchased power and transmission service costs and costs billed to customers in a given period is deferred as a regulatory asset or liability. The deferred amount is either billed or refunded to customers in a subsequent period.
Ameren Missouri has a FAC that allows an adjustment of electric rates three times per year for a pass-through to customers of 95% of changes in fuel and purchased power costs, including transportation charges and revenues, net of off-system sales, greater or less than the amount set in base rates, subject to MoPSC prudence review. The difference between the actual amounts incurred for these items and the amounts recovered from Ameren Missouri customers' base rates is deferred as a regulatory asset or liability. The deferred amounts are either billed or refunded to electric customers in a subsequent period. Since May 30, 2015, transmission revenues and substantially all transmission charges are excluded from net energy costs as a result of the April 2015 MoPSC electric rate order.
Environmental Costs
Liabilities for environmental costs are recorded on an undiscounted basis when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated. Costs are expensed or deferred as a regulatory asset when it is expected that the costs will be recovered from customers in future rates.
Regulation
We are regulated by the MoPSC, the ICC, and the FERC. We defer certain costs as assets pursuant to actions of rate regulators or because of expectations that we will be able to recover such costs in future rates charged to customers. We also defer certain amounts as liabilities pursuant to actions of rate regulators or based on the expectation that such amounts will be returned to customers in future rates. Regulatory assets and liabilities are amortized consistent with the period of expected regulatory treatment. In addition to the cost recovery mechanisms discussed in the Purchased Gas, Power, and Fuel Rate-adjustment Mechanisms section below, Ameren Missouri and Ameren Illinois have approvals from rate regulators to use other cost recovery mechanisms. Ameren Missouri has a pension and postretirement benefit cost tracker, an uncertain tax positions tracker, a renewable energy standards cost tracker, a solar rebate program tracker, and the MEEIA energy efficiency rider. Ameren Illinois' and ATXI's electric transmission rates are determined pursuant to formula ratemaking. Additionally, Ameren Illinois' electric distribution business participates in the performance-based formula ratemaking process established pursuant to the IEIMA. Ameren Illinois also has environmental cost riders, an asbestos-related litigation rider, an energy efficiency rider, a QIP rider, a VBA rider, and a bad debt rider. See Note 2 – Rate and Regulatory Matters for additional information on regulatory assets and liabilities.
Cash and Cash Equivalents 
Cash and Cash Equivalents
Cash and cash equivalents include cash on hand and temporary investments purchased with an original maturity of three months or less.
Allowance for Doubtful Accounts Receivable 
Allowance for Doubtful Accounts Receivable
The allowance for doubtful accounts represents our estimate of existing accounts receivable that will ultimately be uncollectible. The allowance is calculated by applying estimated loss factors to various classes of outstanding receivables, including unbilled revenue. The loss factors used to estimate uncollectible accounts are based upon both historical collections experience and management’s estimate of future collections success given the existing and anticipated future collections environment. Ameren Illinois has a bad debt rider that adjusts rates for net write-offs of customer accounts receivable above or below those being collected in rates.
Materials and Supplies 
recorded at the lower of cost or market. Cost is determined by the average-cost method. Inventories are capitalized when purchased and then expensed as consumed or capitalized as plant assets when installed, as appropriate.
Property and Plant 
Property, Plant, and Equipment, Net
We capitalize the cost of additions to and betterments of units of property, plant and equipment. The cost includes labor, material, applicable taxes, and overhead. An allowance for funds used during construction, as discussed below, is also capitalized as a cost of our rate-regulated assets. Maintenance expenditures, including nuclear refueling and maintenance outages, are expensed as incurred. When units of depreciable property are retired, the original costs, less salvage values, are charged to accumulated depreciation. If environmental expenditures are related to assets currently in use, as in the case of the installation of pollution control equipment, the cost is capitalized and depreciated over the expected life of the asset. See Asset Retirement Obligations below and Note 3 – Property, Plant, and Equipment, Net for additional information.
Depreciation
Depreciation is provided over the estimated lives of the various classes of depreciable property by applying composite rates on a straight-line basis to the cost basis of such property. The provision for depreciation for the Ameren Companies in 2016, 2015, and 2014 ranged from 3% to 4% of the average depreciable cost.
Allowance for Funds Used During Construction 
Allowance for Funds Used During Construction
We capitalize allowance for funds used during construction, or the cost of borrowed funds and the cost of equity funds (preferred and common shareholders’ equity) applicable to rate-regulated construction expenditures, in accordance with the utility industry's accounting practice. Allowance for funds used during construction does not represent a current source of cash funds. This accounting practice offsets the effect on earnings of the cost of financing during construction, and it treats such financing costs in the same manner as construction charges for labor and materials.
Under accepted ratemaking practice, cash recovery of allowance for funds used during construction and other construction costs occurs when completed projects are placed in service and reflected in customer rates.
Goodwill 
$411 million at October 31, 2016 and October 31, 2015. To determine whether the fair value of a reporting unit is more likely than not greater than its carrying amount, Ameren and Ameren Illinois elect to perform either a qualitative assessment or to bypass the qualitative assessment and perform a two-step quantitative test, on an annual basis. On October 31, 2015, Ameren and Ameren Illinois performed a quantitative test and determined that the estimated fair value of the Ameren Illinois reporting unit significantly exceeded its carrying value as of that date. Based on these results, Ameren and Ameren Illinois elected to perform a qualitative assessment for their annual goodwill impairment test conducted as of October 31, 2016.
The results of Ameren’s and Ameren Illinois’ qualitative assessment indicated that it was more likely than not that the fair value of the Ameren Illinois reporting unit exceeded its carrying value as of October 31, 2016, resulting in no impairment of Ameren’s or Ameren Illinois’ goodwill. The following factors, among others, were considered by Ameren and Ameren Illinois when assessing whether it was more likely than not that the fair value of the Ameren Illinois reporting unit exceeded its carrying value for the October 31, 2016, test:
•
macroeconomic conditions, including those conditions within Ameren Illinois’ service territory;
•
pending rate case outcomes and projections of future rate case outcomes;
•
changes in laws and potential law changes;
•
observable industry market multiples;
•
achievement of IEIMA performance metrics and the yield of 30-year United States Treasury bonds;
•
an unexpected further reduction in the FERC-allowed return on equity related to transmission services; and
•
projected operating results and cash flows.
As of December 31, 2016, the Ameren Companies changed the manner in which they assess performance and allocate resources, driven by increasing investment in FERC rate-regulated electric transmission and Ameren Illinois electric distribution and natural gas distribution businesses as well as the unique regulatory environment for each jurisdiction. Ameren now has four reporting units: Ameren Missouri, Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Transmission. Ameren Illinois now has three reporting units: Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission. See Note 16 – Segment Information for additional information related to the change in Ameren’s and Ameren Illinois' segments.
As of the date of the segment change, December 31, 2016, Ameren and Ameren Illinois reassigned goodwill to the new reporting units using a relative fair value allocation approach. The Level 3 fair value hierarchy valuation approach used to reassign goodwill was based on a market participant view and used a weighted combination of a discounted cash flow analysis and a market multiples analysis. Key assumptions used in estimating the fair value of the reporting units included discount and growth rates, utility sector market performance and transactions, and projected operating results and cash flows. As a result of the goodwill reassignment, Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission had goodwill of $238 million, $80 million, and $93 million, respectively, at December 31, 2016. The Ameren Transmission reporting unit was reassigned the same $93 million of goodwill as the Ameren Illinois Transmission reporting unit.
In conjunction with the goodwill reassignment, Ameren and Ameren Illinois completed the first step of the quantitative test to determine whether the fair values of the new reporting units exceeded their carrying values as of December 31, 2016. Ameren and Ameren Illinois determined that the estimated fair values of the Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, Ameren Illinois Transmission, and Ameren Transmission reporting units each exceeded their respective carrying values by at least 40%, indicating no impairment of Ameren’s or Ameren Illinois’ goodwill. The Ameren and Ameren Illinois goodwill that was reassigned to the new reporting units on December 31, 2016, had no accumulated goodwill impairment losses.
Impairment of Long-lived Assets 
We evaluate long-lived assets classified as held and used for impairment when events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. Whether an impairment has occurred is determined by comparing the estimated undiscounted cash flows attributable to the assets to the carrying value of the assets. If the carrying value exceeds the undiscounted cash flows, we recognize an impairment charge equal to the amount by which the carrying value exceeds the estimated fair value of the assets. In the period in which we determine an asset meets held for sale criteria, we record an impairment charge to the extent the book value exceeds its estimated fair value less cost to sell. We did not identify any events or changes in circumstances that indicated that the carrying value of long-lived assets may not be recoverable in 2016 and 2015.
Asset Retirement Obligations 
Asset Retirement Obligations
We record the estimated fair value of legal obligations associated with the retirement of tangible long-lived assets in the period in which the liabilities are incurred and capitalize a corresponding amount as part of the book value of the related long-lived asset. In subsequent periods, we adjust AROs based on changes in the estimated fair values of the obligations with a corresponding increase or decrease in the asset book value. Asset book values, reflected within "Property, Plant, and Equipment, Net" on the balance sheet, are depreciated over the remaining useful life of the related asset. Due to regulatory recovery, that depreciation is recorded within a regulatory asset or liability balance related to AROs. Ameren and Ameren Missouri have a nuclear decommissioning trust fund for the decommissioning of the Callaway energy center. Net realized and unrealized gains and losses within the nuclear decommissioning trust fund are deferred and are currently recorded as a regulatory liability, along with the depreciation of the asset book values, discussed above, and the accretion of the AROs. The depreciation of the asset book values at Ameren Missouri was $31 million, $13 million, and $1 million for the years ended December 31, 2016, 2015, and 2014, respectively, which was recorded as a reduction to the regulatory liability. The depreciation recorded to the regulatory asset at Ameren Illinois was immaterial in each respective period. Uncertainties as to the probability, timing, or amount of cash expenditures associated with AROs affect our estimates of fair value. Ameren and Ameren Missouri have recorded AROs for retirement costs associated with Ameren Missouri’s Callaway energy center decommissioning, CCR facilities, and river structures. Also, Ameren, Ameren Missouri, and Ameren Illinois have recorded AROs for retirement costs associated with asbestos removal and the disposal of certain transformers. Asset removal costs that do not constitute legal obligations are classified as regulatory liabilities. See Note 2 – Rate and Regulatory Matters.
Noncontrolling Interest 
Noncontrolling Interests
As of December 31, 2016 and 2015, Ameren’s noncontrolling interests included the preferred stock of Ameren Missouri and Ameren Illinois.
Revenue 
Operating Revenue
The Ameren Companies record operating revenue for electric or natural gas service when it is delivered to customers. We accrue an estimate of electric and natural gas revenues for service rendered but unbilled at the end of each accounting period.
Ameren Illinois participates in the performance-based formula ratemaking framework pursuant to the IEIMA. In addition, Ameren Illinois' and ATXI's electric transmission service operating revenues are regulated by the FERC. The provisions of the IEIMA and the FERC's electric transmission formula rate framework provide for annual reconciliations of the electric distribution and electric transmission service revenue requirements necessary to reflect the actual recoverable costs incurred in a given year with the revenue requirements in customer rates for that year, including an allowed return on equity. In each of those electric jurisdictions, if the current year's revenue requirement is greater than the revenue requirement reflected in that year's customer rates, an increase to electric operating revenues with an offset to a regulatory asset is recorded to reflect the expected recovery of those additional amounts from customers within two years. In each jurisdiction, if the current year's revenue requirement is less than the revenue requirement reflected in that year's customer rates, a reduction to electric operating revenues with an offset to a regulatory liability is recorded to reflect the expected refund to customers within two years. See Note 2 – Rate and Regulatory Matters for information regarding Ameren Illinois' revenue requirement reconciliation pursuant to the IEIMA.
Cost Of Sales 
Nuclear Fuel
Ameren Missouri’s cost of nuclear fuel is capitalized and then amortized to fuel expense on a unit-of-production basis. The cost is charged to "Operating Expenses – Fuel" in the statement of income.
Accounting for MISO Transactions
MISO-related purchase and sale transactions are recorded by Ameren, Ameren Missouri, and Ameren Illinois using settlement information provided by MISO. Ameren Missouri records these purchase and sale transactions on a net hourly position. Ameren Missouri records net purchases in a single hour in “Operating Expenses – Purchased power” and net sales in a single hour in “Operating Revenues – Electric” in its statement of income. Ameren Illinois records net purchases in “Operating Expenses – Purchased power” in its statement of income to reflect all of its MISO transactions relating to the procurement of power for its customers. On occasion, Ameren Missouri's and Ameren Illinois' prior-period transactions will be resettled outside the routine settlement process because of a change in MISO’s tariff or a material interpretation thereof. In these cases, Ameren Missouri and Ameren Illinois recognize expenses associated with resettlements once the resettlement is probable and the resettlement amount can be estimated. Revenues are recognized once the resettlement amount is received.
Stock-Based Compensation 
Stock-based Compensation
Stock-based compensation cost is measured at the grant date based on the fair value of the award, net of an assumed forfeiture rate. Ameren recognizes as compensation expense the estimated fair value of stock-based compensation on a straight-line basis over the requisite service period.
Excise Taxes 
Excise Taxes
Ameren Missouri and Ameren Illinois collect from their customers certain excise taxes that are levied on the sale or distribution of natural gas and electricity. Excise taxes are levied on Ameren Missouri's electric and natural gas businesses and on Ameren Illinois' natural gas business. They are recorded gross in “Operating Revenues – Electric,” “Operating Revenues – Natural gas,” and “Operating Expenses – Taxes other than income taxes” on the statement of income or the statement of income and comprehensive income. Excise taxes for electric service in Illinois are levied on customers and are therefore not included in Ameren Illinois' revenues and expenses.
Unamortized Debt Discount, Premium, And Expense 
Unamortized Debt Discounts, Premiums, and Issuance Costs
Long-term debt discounts, premiums, and issuance costs are amortized over the lives of the related issuances. Credit agreement fees are amortized over the term of that agreement.
Income Taxes 
Income Taxes
Ameren uses an asset and liability approach for its financial accounting and reporting of income taxes. Deferred tax assets and liabilities are recognized for transactions that are treated differently for financial reporting and income tax return purposes. These deferred tax assets and liabilities are based on statutory tax rates.
We recognize that regulators will probably reduce future revenues for deferred tax liabilities that were initially recorded at rates in excess of the current statutory rate. Therefore, reductions in deferred tax liabilities that were recorded because of decreases in the statutory rate have been credited to a regulatory liability. A regulatory asset has been established to recognize the probable recovery through future customer rates of tax benefits related to the equity component of allowance for funds used during construction, as well as the effects of tax rate increases.
Investment tax credits used on tax returns for prior years have been deferred as a noncurrent liability. The credits are being amortized over the useful lives of the related investment. Deferred income taxes were recorded on the temporary difference represented by the deferred investment tax credits and a corresponding regulatory liability. This recognizes the expected reduction in rates for future lower income taxes associated with the amortization of the investment tax credits. See Note 13 – Income Taxes.
Ameren Missouri, Ameren Illinois, and all the other Ameren subsidiary companies are parties to a tax allocation agreement with Ameren (parent) that provides for the allocation of consolidated tax liabilities. The tax allocation agreement specifies that each party be allocated an amount of tax using a stand-alone calculation, which is similar to that which would be owed or refunded had the party been separately subject to tax considering the impact of consolidation. Any net benefit attributable to the parent is reallocated to the other parties. This reallocation is treated as a capital contribution to the party receiving the benefit.
Earnings Per Share 
Earnings per Share
Basic earnings per share is computed by dividing “Net Income Attributable to Ameren Common Shareholders” by the weighted-average number of common shares outstanding during the period. Earnings per diluted share is computed by dividing “Net Income Attributable to Ameren Common Shareholders” by the weighted-average number of diluted common shares outstanding during the period. Earnings per diluted share reflects the potential dilution that would occur if certain stock-based performance share units were settled. The number of performance share units assumed to be settled was 0.8 million, 1.0 million, and 1.8 million for the years ended December 31, 2016, 2015, and 2014, respectively. There were no potentially dilutive securities excluded from the diluted earnings per share calculations for the years ended December 31, 2016, 2015, and 2014.
Accounting Changes and Other Matters 
Accounting Changes and Other Matters
The following is a summary of recently adopted authoritative accounting guidance, as well as guidance issued but not yet adopted, that could affect the Ameren Companies.
Revenue from Contracts with Customers
In May 2014, the FASB issued authoritative guidance that changes the criteria for recognizing revenue from a contract with a customer. The underlying principle of the guidance is that an entity will recognize revenue for the transfer of promised goods or services to customers at an amount that the entity expects to be entitled to in exchange for those goods or services. The guidance also requires additional disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. Entities can apply the guidance retrospectively to each reporting period presented, the full retrospective method, or retrospectively by recording a cumulative effect adjustment to retained earnings in the period of initial adoption, the modified retrospective method. The utility industry continues to assess the impacts on accounting for contributions in aid of construction and similar arrangements, and collectibility, among other issues. The outcome of these assessments could have a significant impact on our results of operations and financial position. We plan to complete our assessment of the impacts of this guidance on our results of operations, financial position, presentation and disclosures, and transition method, in the next several months prior to our adoption in the first quarter of 2018.
Amendments to the Consolidation Analysis
In February 2015, the FASB issued authoritative guidance that amends the consolidation analysis for variable interest entities and voting interest entities. The new guidance affects (1) limited partnerships, similar legal entities, and certain investment funds, (2) the evaluation of fees paid to a decision maker or service provider as a variable interest, (3) how fee arrangements impact the primary beneficiary determination, and (4) the evaluation of related party relationships on the primary beneficiary determination. The adoption of this guidance in 2016 did not impact the Ameren Companies' results of operations, financial position, cash flows, or disclosures.
Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share
In May 2015, to address diversity in practice, the FASB issued authoritative guidance that removes the requirement to categorize within the fair value hierarchy all investments for which fair value is measured using the NAV practical expedient. The Ameren Companies have investments measured using the NAV practical expedient within the pension plan and postretirement benefit plan assets. We adopted this guidance on January 1, 2016 and retrospectively updated the presentation of these assets in the fair value hierarchy tables included in Note 11 - Retirement Benefits. The adoption of this guidance did not impact our results of operations, financial position or cash flows.
Financial Instruments - Recognition and Measurement, and Credit Losses
In January 2016, the FASB issued authoritative guidance that addressed certain aspects of recognition, measurement, presentation and disclosure of financial instruments. This guidance requires an entity to measure equity investments, other than those accounted for under the equity method of accounting, at fair value with changes in fair value recognized in net income. The recognition and measurement guidance will be effective for the Ameren Companies in the first quarter of 2018, and requires changes to be applied retrospectively with a cumulative effect adjustment to retained earnings as of the adoption date. Also, in June 2016, the FASB issued authoritative guidance that requires an entity to recognize an allowance for financial instruments that reflects its current estimate of credit losses expected to be incurred over the life of the financial instruments. The guidance requires an entity to measure expected credit losses based on relevant information about past events, current conditions, and reasonable and supportable forecasts that affect the collectibility of the reported amount. The credit loss guidance will be effective for the Ameren Companies in the first quarter of 2020, and requires changes to be applied retrospectively with a cumulative effect adjustment to retained earnings as of the adoption date. We are currently assessing the impacts of the new financial instruments guidance on our results of operations, financial position, and disclosures.
Leases
In February 2016, the FASB issued authoritative guidance that requires an entity to recognize assets and liabilities arising from all leases with a term greater than one year. Consistent with current GAAP, the recognition, measurement, and presentation of expenses and cash flows arising from a lease will depend on its classification as a finance or operating lease. The guidance also requires additional disclosures to enable users of financial statements to understand the amount, timing, and uncertainty of cash flows arising from leases. This guidance will affect the Ameren Companies' financial position by increasing the assets and liabilities recorded relating to their operating leases, which will be recognized and measured at the beginning of the earliest period presented. We are currently assessing the impacts of this guidance for other effects on our results of operations, cash flows and disclosures. We expect to adopt this guidance in the first quarter of 2019. See Note 15 – Commitments and Contingencies for additional information on our leases.
Improvements to Employee Share-Based Payment Accounting
In March 2016, the FASB issued authoritative guidance that simplifies the accounting for share-based payment transactions, including the income tax consequences, the calculation of diluted earnings per share, the treatment of forfeitures, the classification of awards as either equity or liabilities, and the classification on the statement of cash flows. Ameren determines for each performance share unit award whether the difference between the deduction for tax purposes and the compensation cost recognized for financial reporting purposes results in either an excess tax benefit or an excess tax deficit. Previously, excess tax benefits were recognized in "Other paid-in capital" on Ameren’s consolidated balance sheet, and in certain cases, excess tax deficits were recognized in “Income taxes” on Ameren’s consolidated income statement. The new guidance increases income statement volatility by requiring all excess tax benefits and deficits to be recognized in “Income taxes,” and treated as discrete items in the period in which they occur. Ameren adopted this guidance in 2016 and prospectively applied the amendment in this guidance requiring recognition of excess tax benefits and deficits in the income statement, which resulted in recognition of a $21 million income tax benefit and a corresponding $21 million increase in income from continuing operations and net income (9 cents per diluted share) during the period. Also as a result of the adoption of this guidance, Ameren made an accounting policy election to continue to estimate the number of forfeitures expected to occur. The amendments in the guidance that require application using a modified retrospective transition method did not impact Ameren. Therefore, there was no cumulative-effect adjustment to retained earnings recognized as of January 1, 2016. Ameren applied the amendments in this guidance relating to classification on the statement of cash flows retrospectively. For the year ended December 31, 2015, Ameren reclassified $2 million of excess tax benefits on the statement of cash flows from financing to operating activity. Also, for the years ended December 31, 2015 and December 31, 2014, Ameren reclassified $12 million and $14 million, respectively, of employee payroll taxes related to share-based payments from operating to financing activity.
Restricted Cash
In November 2016, the FASB issued authoritative guidance that requires restricted cash and restricted cash equivalents to be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. We are currently assessing the impacts of this guidance on our statements of cash flows and disclosures. The guidance will be effective for the Ameren Companies in the first quarter of 2018, and requires changes to be applied retrospectively to each period presented.
Derivative Financial Instruments Derivative Financial Instruments (Policies)
Derivatives, Policy [Policy Text Block]
The Ameren Companies elect to present the fair value amounts of derivative assets and derivative liabilities subject to an enforceable master netting arrangement or similar agreement gross on the balance sheet.
an unrealized appreciation or depreciation of our contracted commitments to purchase or sell when purchase or sale prices under the commitments are compared with current commodity prices;
•
market values of natural gas and uranium inventories that differ from the cost of those commodities in inventory; and
•
actual cash outlays for the purchase of these commodities that differ from anticipated cash outlays.
The derivatives that we use to hedge these risks are governed by our risk management policies for forward contracts, futures, options, and swaps. Our net positions are continually assessed within our structured hedging programs to determine whether new or offsetting transactions are required. The goal of the hedging program is generally to mitigate financial risks while ensuring that sufficient volumes are available to meet our requirements. Contracts we enter into as part of our risk management program may be settled financially, settled by physical delivery, or net settled with the counterparty.
Summary Of Significant Accounting Policies (Tables)
Schedule Of Inventories 
The following table presents a breakdown of inventories for each of the Ameren Companies at December 31, 2016 and 2015:
 
 
Ameren Missouri
 
Ameren Illinois
 
Ameren
2016
 
 
 
 
 
 
Fuel(a)
 
$
172

 
$
—

 
$
172

Natural gas stored underground
 
9

 
73

 
82

Other inventories
 
211

 
62

 
273

Total inventories
 
$
392

 
$
135

 
$
527

2015
 
 
 
 
 
 
Fuel(a)
 
$
173

 
$
—

 
$
173

Natural gas stored underground
 
10

 
87

 
97

Other inventories
 
204

 
64

 
268

Total inventories
 
$
387

 
$
151

 
$
538

(a)
Consists of coal, oil, and propane.
Schedule Of Rates Used For Allowance For Funds Used During Construction 
The following table presents the annual allowance for funds used during construction debt and equity blended rates that were applied to construction projects in 2016, 2015, and 2014:
 
2016
 
2015
 
2014
Ameren Missouri
7
%
 
7
%
 
7
%
Ameren Illinois
5
%
 
6
%
 
2
%
Schedule Of Asset Retirement Obligations 
The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the years ended December 31, 2016 and 2015:
 
Ameren
Missouri
 
Ameren
Illinois
 
Ameren
 
Balance at December 31, 2014
$
389

 
$
7

 
$
396

 
Liabilities incurred
3

 
—

 
3

 
Liabilities settled
(1
)
 
(1
)
 
(2
)
 
Accretion in 2015(a)
23

 
(b)

 
23

 
Change in estimates(c)
203

 
(b)

 
203

 
Balance at December 31, 2015
$
617

(e) 
$
6

(d) 
$
623

(e) 
Liabilities incurred
3

 
—

 
3

 
Liabilities settled
(2
)
 
(b)

 
(2
)
 
Accretion in 2016(a)
25

 
(b)

 
25

 
Change in estimates
1

 
—

 
1

 
Balance at December 31, 2016
$
644

(e) 
$
6

(d) 
$
650

(e) 

(a)
Accretion expense was recorded as a decrease to regulatory liabilities.
(b)
Less than $1 million.
(c)
The ARO increase resulted in a corresponding increase recorded to "Property, Plant, and Equipment, Net." Ameren and Ameren Missouri increased their AROs related to the decommissioning of the Callaway energy center by $99 million to reflect the 2015 cost study and funding analysis filed with the MoPSC, the extension of the estimated operating life until 2044, and a reduction in the discount rate assumption. See Note 10 – Callaway Energy Center for additional information. In addition, as a result of new federal regulations, Ameren and Ameren Missouri recorded an increase of $100 million to their AROs associated with CCR storage facilities. See Note 15 – Commitments and Contingencies for additional information. Ameren and Ameren Missouri also increased their AROs by $4 million due to a change in the estimated retirement dates of the Meramec and Rush Island energy centers as a result of the MoPSC's April 2015 electric rate order.
(d)
Included in “Other deferred credits and liabilities” on the balance sheet.
(e)
Balance included $5 million and $15 million in "Other current liabilities" on the balance sheet as of December 31, 2015 and 2016, respectively.
Schedule Of Excise Taxes 
The following table presents the excise taxes recorded in “Operating Revenues – Electric,” “Operating Revenues – Natural gas,” and “Operating Expenses – Taxes other than income taxes” for the years ended December 31, 2016, 2015, and 2014:
 
2016
 
2015
 
2014
Ameren Missouri
$
151

 
$
156

 
$
151

Ameren Illinois
57

 
57

 
64

Ameren
$
208

 
$
213

 
$
215

Rate And Regulatory Matters (Tables)
Schedule Of Regulatory Assets And Liabilities
The following table presents our regulatory assets and regulatory liabilities at December 31, 2016 and 2015:
 
 
2016
 
2015
 
 
Ameren
Missouri
 
Ameren
Illinois
 
Ameren
 
 
Ameren
Missouri
 
Ameren
Illinois
 
Ameren
Current regulatory assets:
 
 
 
 
 
 
 
 
 
 
 
 
 
Under-recovered FAC(a)(b)
 
$
21

 
$
—

 
$
21

 
 
$
37

 
$
—

 
$
37

Under-recovered Illinois electric power costs(c)
 
—

 
3

 
3

 
 
—

 
3

 
3

Under-recovered PGA(c)
 
—

 
4

 
4

 
 
—

 
8

 
8

MTM derivative losses(d)
 
9


15

 
24

 
 
29

 
45

 
74

Energy efficiency riders(e)
 
5

 
—

 
5

 
 
23

 
—

 
23

IEIMA revenue requirement reconciliation adjustment(a)(f)
 
—

 
68

 
68

 
 
—

 
103

 
103

FERC revenue requirement reconciliation adjustment(a)(g)
 
—

 
7

 
13

 
 
—

 
8

 
12

VBA rider(a)(h)
 
—

 
11

 
11

 
 
—

 
—

 
—

Total current regulatory assets
 
$
35

 
$
108

 
$
149

 
 
$
89

 
$
167

 
$
260

Noncurrent regulatory assets:
 
 
 
 
 
 
 
 
 
 
 
 
 
Pension and postretirement benefit costs(i)
 
$
175

 
$
319

 
$
494

 
 
$
95

 
$
202

 
$
297

Income taxes(j)
 
229

 
1

 
230

 
 
247

 
4

 
251

Uncertain tax positions tracker(a)(k)
 
7

 
—

 
7

 
 
7

 
—

 
7

ARO(l)
 
—

 
3

 
3

 
 
—

 
4

 
4

Callaway costs(a)(m)
 
29

 
—

 
29

 
 
32

 
—

 
32

Unamortized loss on reacquired debt(a)(n)
 
65

 
59

 
124

 
 
69

 
69

 
138

Environmental cost riders(o)
 
—

 
196

 
196

 
 
—

 
230

 
230

MTM derivative losses(d)
 
9


178

 
187



15

 
175

 
190

Storm costs(a)(p)
 
—

 
15

 
15

 
 
—

 
9

 
9

Demand-side costs before the MEEIA implementation(a)(q)
 
18

 
—

 
18

 
 
31

 
—

 
31

Workers’ compensation claims(r)
 
6

 
7

 
13

 
 
6

 
7

 
13

Credit facilities fees(s)
 
4

 
—

 
4

 
 
4

 
—

 
4

Construction accounting for pollution control equipment(a)(t)
 
19

 
—

 
19

 
 
20

 
—

 
20

Solar rebate program(a)(u)
 
49

 
—

 
49

 
 
74

 
—

 
74

IEIMA revenue requirement reconciliation adjustment(a)(f)
 
—

 
23

 
23

 
 
—

 
62

 
62

FERC revenue requirement reconciliation adjustment(a)(g)
 
—

 
8

 
10

 
 
—

 
5

 
11

Other
 
9

 
7

 
16

 
 
5

 
4

 
9

Total noncurrent regulatory assets
 
$
619

 
$
816

 
$
1,437

 
 
$
605

 
$
771

 
$
1,382

Current regulatory liabilities:
 
 
 
 
 
 
 
 
 
 
 
 
 
Over-recovered FAC(b)
 
$
—

 
$
—

 
$
—

 
 
$
9

 
$
—

 
$
9

Over-recovered Illinois electric power costs(c)
 
—

 
25

 
25

 
 
—

 
6

 
6

Over-recovered PGA(c)
 
—

 
—

 
—

 
 
3

 
—

 
3

MTM derivative gains(d)
 
12

 
11

 
23


 
16

 
1

 
17

Estimated refund for FERC complaint cases(v)
 
—

 
42

 
62

 
 
—

 
32

 
45

Total current regulatory liabilities
 
$
12

 
$
78

 
$
110

 
 
$
28

 
$
39

 
$
80

Noncurrent regulatory liabilities:
 
 
 
 
 
 
 
 
 
 
 
 
 
Income taxes(w)
 
$
33

 
$
4

 
$
37

 
 
$
36

 
$
6

 
$
42

Uncertain tax positions tracker(k)
 
3

 
—

 
3

 
 
6

 
—

 
6

Asset removal costs(x)
 
970

 
697

 
1,669

 
 
933

 
671

 
1,605

ARO(l)
 
162

 
—

 
162

 
 
167

 
—

 
167

Bad debt rider(y)
 
—

 
3

 
3

 
 
—

 
6

 
6

Pension and postretirement benefit costs tracker(z)
 
35

 
—

 
35

 
 
19

 
—

 
19

Energy efficiency riders(e)
 
—

 
45

 
45

 
 
—

 
36

 
36

Renewable energy credits(aa)
 
—

 
15

 
15

 
 
—

 
12

 
12

Storm tracker(ab)
 
7

 
—

 
7

 
 
9

 
—

 
9

Other
 
5

 
4

 
9

 
 
2

 
1

 
3

Total noncurrent regulatory liabilities
 
$
1,215

 
$
768

 
$
1,985

 
 
$
1,172

 
$
732

 
$
1,905

(a)
These assets earn a return.
(b)
Under-recovered or over-recovered fuel costs to be recovered or refunded through the FAC. Specific accumulation periods aggregate the under-recovered or over-recovered costs over four months, any related adjustments that occur over the following four months, and the recovery from or refund to customers that occurs over the next eight months.
(c)
Under-recovered or over-recovered costs from utility customers. Amounts will be recovered from or refunded to customers within one year of the deferral.
(d)
Deferral of commodity-related derivative MTM losses or gains. See Note 7 – Derivative Financial Instruments for additional information.
(e)
The Ameren Missouri balance relates to the MEEIA. The MEEIA rider allows Ameren Missouri to collect from or refund to customers any annual difference in the actual amounts incurred and the amounts collected from customers for the MEEIA program costs, net shared benefits, and the throughput disincentive. Under the MEEIA rider, collections from or refunds to customers occur one year after the program costs, net shared benefits, and the throughput disincentive are incurred. The Ameren Illinois balance relates to a regulatory tracking mechanism to recover its electric and natural gas costs associated with developing, implementing, and evaluating customer energy efficiency and demand response programs. Any under-recovery or over-recovery will be collected from or refunded to customers over the year following the plan year.
(f)
The difference between Ameren Illinois' annual revenue requirement calculated under the IEIMA's performance-based formula ratemaking framework and the revenue requirement included in customer rates for that year. The under-recovery will be recovered from or refunded to customers with interest within two years.
(g)
Ameren Illinois' and ATXI's annual revenue requirement reconciliation calculated pursuant to the FERC's electric transmission formula ratemaking framework. The under-recovery or over-recovery will be recovered from or refunded to customers within two years.
(h)
Under-recovered natural gas sales volumes, including deviations from normal weather conditions. Each year's amount will be recovered from or refunded to customers from April through December of the following year.
(i)
These costs are being amortized in proportion to the recognition of prior service costs (credits) and actuarial losses (gains) attributable to Ameren’s pension plan and postretirement benefit plans. See Note 11 – Retirement Benefits for additional information.
(j)
Tax benefits related to the equity component of allowance for funds used during construction, as well as the effects of tax rate changes. This amount will be recovered over the expected life of the related assets.
(k)
The tracker is amortized over three years, beginning from the date the amounts are included in rates. See Note 13 – Income Taxes for additional information.
(l)
Recoverable or refundable removal costs for AROs, including net realized and unrealized gains and losses related to the nuclear decommissioning trust fund investments. See Note 1 – Summary of Significant Accounting Policies – Asset Retirement Obligations.
(m)
Ameren Missouri’s Callaway energy center operations and maintenance expenses, property taxes, and carrying costs incurred between the plant in-service date and the date the plant was reflected in rates. These costs are being amortized over the remaining life of the energy center's original operating license through 2024.
(n)
Losses related to reacquired debt. These amounts are being amortized over the lives of the related new debt issuances or the original lives of the old debt issuances if no new debt was issued.
(o)
The recoverable portion of accrued environmental site liabilities that will be collected from electric and natural gas customers through ICC-approved cost recovery riders. The period of recovery will depend on the timing of remediation expenditures. See Note 15 – Commitments and Contingencies for additional information.
(p)
Storm costs from 2013, 2015, and 2016 deferred in accordance with the IEIMA. These costs are being amortized over five-year periods beginning in the year the storm occurred.
(q)
Demand-side costs incurred prior to implementation of the MEEIA in 2013, including the costs of developing, implementing, and evaluating customer energy efficiency and demand response programs. Costs incurred from May 2008 through September 2008 are being amortized over a 10-year period that began in March 2009. Costs incurred from October 2008 through December 2009 are being amortized until May 2017. Costs incurred from January 2010 through February 2011 are being amortized over a six-year period that began in August 2011. Costs incurred from March 2011 through July 2012 are being amortized over a six-year period that began in January 2013. Costs incurred from August 2012 through December 2012 are being amortized over a six-year period that began in June 2015. The February 2017 stipulation and agreement, if approved, would modify these amortization periods.
(r)
The period of recovery will depend on the timing of actual expenditures.
(s)
Ameren Missouri’s costs incurred to enter into and maintain the Missouri Credit Agreement. These costs are being amortized over the life of the credit facility to construction work in progress, which will be depreciated when assets are placed into service. Additional costs were incurred in December 2016 to amend and restate the Missouri Credit Agreement.
(t)
The MoPSC’s May 2010 electric rate order allowed Ameren Missouri to record an allowance for funds used during construction for pollution control equipment at its Sioux energy center until the cost of that equipment was included in customer rates beginning in 2011. These costs are being amortized over the expected life of the Sioux energy center, currently through 2033.
(u)
Costs associated with Ameren Missouri's solar rebate program to fulfill its renewable energy portfolio requirement. These costs are being amortized over a three-year period that began in June 2015. The February 2017 stipulation and agreement, if approved, would modify this amortization period.
(v)
Estimated refunds to transmission customers related to FERC orders. See FERC Complaint Cases above.
(w)
Unamortized portion of investment tax credits and reductions to deferred tax liabilities recorded at rates in excess of current statutory rates. The unamortized portion of investment tax credits and the reduction to deferred tax liabilities are being amortized over the expected life of the underlying assets.
(x)
Estimated funds collected for the eventual dismantling and removal of plant retired from service, net of salvage value.
(y)
A regulatory tracking mechanism for the difference between the level of bad debt incurred by Ameren Illinois under GAAP and the level of such costs included in electric and natural gas rates. The over-recovery relating to 2014 was refunded to customers from June 2015 through May 2016. The over-recovery relating to 2015 is being refunded to customers from June 2016 through May 2017. The over-recovery relating to 2016 will be refunded to customers from June 2017 through May 2018.
(z)
A regulatory tracking mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates. For periods prior to December 2014, the MoPSC's April 2015 electric rate order directed the amortization to occur over three to five years, beginning in June 2015. For periods after December 2014, the amortization period will be determined in the July 2016 electric rate case. The February 2017 stipulation and agreement, if approved, would modify these amortization periods.
(aa)
Funds collected from customers for the purchase of renewable energy credits through IPA procurements for distributed generation. The balance will be amortized as renewable energy credits are purchased.
(ab)
A regulatory tracking mechanism at Ameren Missouri for the difference between the level of storm costs incurred in a particular year and the level of such costs included in rates. For periods prior to December 2014, the MoPSC's April 2015 electric rate order directed the amortization to occur over a five-year period that began in June 2015. For periods after December 2014, the amortization period will be determined in the July 2016 electric rate case. The April 2015 MoPSC order did not approve the continued use of the storm cost regulatory tracking mechanism.
Property And Plant, Net (Tables)
Schedule Of Property And Plant, Net 
The following table presents property, plant, and equipment, net, for each of the Ameren Companies at December 31, 2016 and 2015:
 
 
Ameren
Missouri(a)
 
Ameren
Illinois
 
Other
 
Ameren(a)
2016
 
 
 
 
 
 
 
 
Property, plant, and equipment at original cost:(b)
 
 
 
 
 
 
 
 
Electric generation
 
$
10,911

 
$
—

 
$
—

 
$
10,911

Electric distribution
 
5,563

 
5,287

 
—

 
10,850

Electric transmission
 
1,151

 
2,016

 
712

 
3,879

Natural gas
 
455

 
2,186

 
—

 
2,641

Other(c)
 
879

 
719

 
239

 
1,837

 
 
18,959

 
10,208

 
951

 
30,118

Less: Accumulated depreciation and amortization
 
7,880

 
2,850

 
231

 
10,961

 
 
11,079

 
7,358

 
720

 
19,157

Construction work in progress:
 
 
 
 
 
 
 
 
Nuclear fuel in process
 
206

 
—

 
—

 
206

Other
 
193

 
111

 
446

 
750

Property and plant, net
 
$
11,478

 
$
7,469

 
$
1,166

 
$
20,113

2015
 
 
 
 
 
 
 
 
Property, plant, and equipment at original cost:(b)
 
 
 
 
 
 
 
 
Electric generation
 
$
10,431

 
$
—

 
$
—

 
$
10,431

Electric distribution
 
5,303

 
4,952

 
—

 
10,255

Electric transmission
 
979

 
1,674

 
121

 
2,774

Natural gas
 
445

 
1,997

 
—

 
2,442

Other(c)
 
808

 
627

 
266

 
1,701

 
 
17,966

 
9,250

 
387

 
27,603

Less: Accumulated depreciation and amortization
 
7,460

 
2,632

 
255

 
10,347

 
 
10,506

 
6,618

 
132

 
17,256

Construction work in progress:
 
 
 
 
 
 
 
 
Nuclear fuel in process
 
275

 
—

 
—

 
275

Other
 
402

 
230

 
636

 
1,268

Property, plant, and equipment, net
 
$
11,183

 
$
6,848

 
$
768

 
$
18,799


(a)
Amounts in Ameren and Ameren Missouri include two CTs under separate capital lease agreements. The gross cumulative asset value of those agreements was $232 million and $233 million at December 31, 2016 and 2015, respectively. The total accumulated depreciation associated with the two CTs was $77 million and $72 million at December 31, 2016 and 2015, respectively. In addition, Ameren Missouri has investments in debt securities, classified as held-to-maturity and recorded in "Other assets" that are related to the two CTs from the city of Bowling Green and Audrain County. As of December 31, 2016 and 2015, the carrying value of these debt securities was $282 million and $288 million, respectively.
(b)
The estimated lives for each asset group are as follows: 5 to 100 years for electric generation, excluding Ameren Missouri's hydro generating assets which have useful lives of up to 150 years, 18 to 75 years for electric distribution, 50 to 75 years for electric transmission, 20 to 80 years for natural gas, and 5 to 55 years for other.
(c)
Other property, plant, and equipment includes assets used to support multiple utility services.
Accrued Capital Expenditures 
The following table provides accrued capital and nuclear fuel expenditures at December 31, 2016, 2015, and 2014, which represent noncash investing activity excluded from the accompanying statements of cash flows:
 
Ameren(a)
 
Ameren
Missouri
 
Ameren
Illinois
Accrued capital expenditures:
 
 
 
 
 
2016
$
251

 
$
116

 
$
87

2015
235

 
85

 
92

2014
181

 
72

 
59

Accrued nuclear fuel expenditures:
 
 
 
 
 
2016
20

 
20

 
(b)

2015
16

 
16

 
(b)

2014
13

 
13

 
(b)


(a)
Includes amounts for Ameren registrant and nonregistrant subsidiaries.
(b)
Not applicable.
Short-Term Debt And Liquidity (Tables)
Schedule Of Maximum Aggregate Amount Available On Credit Agreements 
The following table presents the maximum aggregate amount available to each borrower under each facility (the amount being each borrower's "Borrowing Sublimit"):
 
 
Missouri Credit Agreement
Illinois
Credit Agreement
Ameren
 
$
700

$
500

Ameren Missouri
 
800

(a)

Ameren Illinois
 
  (a)

800

(a)
Not applicable.
Schedule of Commercial Paper 
The following table summarizes the borrowing activity and relevant interest rates under Ameren (parent)'s, Ameren Missouri's and Ameren Illinois' commercial paper programs for the years ended December 31, 2016 and 2015:
 
 
Ameren (parent)
Ameren Missouri
Ameren Illinois
Ameren Consolidated
2016
 
 
 
 
 
 
Average daily commercial paper outstanding
 
$
440

 
$
60

$
52

$
552

Outstanding borrowings at period-end
 
507

 
—

51

558

Weighted-average interest rate
 
0.82
%
 
0.74
%
0.69
%
0.80
%
Peak outstanding commercial paper during period(a)
 
$
574

 
$
208

$
195

$
839

Peak interest rate
 
1.05
%
 
0.85
%
0.90
%
1.05
%
2015
 
 
 
 
 
 
Average daily commercial paper outstanding
 
$
721

 
$
42

$
4

$
767

Outstanding borrowings at period-end
 
301

 
—

—

301

Weighted-average interest rate
 
0.57
%
 
0.50
%
0.44
%
0.55
%
Peak outstanding commercial paper during period(a)
 
$
874

 
$
294

$
48

$
1,108

Peak interest rate
 
0.91
%
 
0.60
%
0.60
%
0.91
%
(a)
The timing of peak outstanding commercial paper issuances varies by company. Therefore, the sum of the peak amounts presented by company might not equal the Ameren Consolidated peak amount for the period.
Long-Term Debt And Equity Financings (Tables)
Schedule of Long-term Debt Instruments 
The following table presents long-term debt outstanding, including maturities due within one year, for the Ameren Companies as of December 31, 2016 and 2015:
 
2016
 
2015
Ameren (Parent):
 
 
 
2.70% Senior unsecured notes due 2020
$
350

 
$
350

3.65% Senior unsecured notes due 2026
350

 
350

Total long-term debt, gross
700

 
700

Less: Unamortized debt issuance costs
(6
)
 
(6
)
Long-term debt, net
$
694

 
$
694

Ameren Missouri:
 
 
 
Senior secured notes:(a)
 
 
 
5.40% Senior secured notes due 2016
—

 
260

6.40% Senior secured notes due 2017
425

 
425

6.00% Senior secured notes due 2018(b)
179

 
179

5.10% Senior secured notes due 2018
199

 
199

6.70% Senior secured notes due 2019(b)
329

 
329

5.10% Senior secured notes due 2019
244

 
244

5.00% Senior secured notes due 2020
85

 
85

3.50% Senior secured notes due 2024
350

 
350

5.50% Senior secured notes due 2034
184

 
184

5.30% Senior secured notes due 2037
300

 
300

8.45% Senior secured notes due 2039(b)
350

 
350

3.90% Senior secured notes due 2042(b)
485

 
485

3.65% Senior secured notes due 2045
400

 
250

Environmental improvement and pollution control revenue bonds:
 
 
 
1992 Series due 2022(c)(d)
47

 
47

1993 5.45% Series due 2028(e)
(e)

 
(e)

1998 Series A due 2033(c)(d)
60

 
60

1998 Series B due 2033(c)(d)
50

 
50

1998 Series C due 2033(c)(d)
50

 
50

Capital lease obligations:
 
 
 
City of Bowling Green capital lease (Peno Creek CT) due 2022
42

 
48

Audrain County capital lease (Audrain County CT) due 2023
240

 
240

Total long-term debt, gross
4,019

 
4,135

Less: Unamortized discount and premium
(6
)
 
(6
)
Less: Unamortized debt issuance costs
(19
)
 
(19
)
Less: Maturities due within one year
(431
)
 
(266
)
Long-term debt, net
$
3,563

 
$
3,844

 
2016
 
2015
Ameren Illinois:
 
 
 
Senior secured notes:
 
 
 
6.20% Senior secured notes due 2016
$
—

 
$
54

6.25% Senior secured notes due 2016
—

 
75

6.125% Senior secured notes due 2017(g)(h)
250

 
250

6.25% Senior secured notes due 2018(g)(h)
144

 
144

9.75% Senior secured notes due 2018(g)(h)
313

 
313

2.70% Senior secured notes due 2022(g)(h)
400

 
400

3.25% Senior secured notes due 2025(g)
300

 
300

6.125% Senior secured notes due 2028(g)
60

 
60

6.70% Senior secured notes due 2036(g)
61

 
61

6.70% Senior secured notes due 2036(f)
42

 
42

4.80% Senior secured notes due 2043(g)
280

 
280

4.30% Senior secured notes due 2044(g)
250

 
250

4.15% Senior secured notes due 2046(g)
490

 
250

Environmental improvement and pollution control revenue bonds:
 
 
 
5.90% Series 1993 due 2023(i)
(i)

 
(i)

5.70% 1994A Series due 2024(j)
(j)

 
(j)

1993 Series B-1 due 2028(d)(k)
17

 
17

Total long-term debt, gross
2,607

 
2,496

Less: Unamortized discount and premium
—

 
(7
)
Less: Unamortized debt issuance costs
(19
)
 
(18
)
Less: Maturities due within one year
(250
)
 
(129
)
Long-term debt, net
$
2,338

 
$
2,342

Ameren consolidated long-term debt, net
$
6,595

 
$
6,880


(a)
These notes are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any first mortgage bonds issued under the Ameren Missouri mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Missouri senior secured notes currently outstanding, we do not expect the first mortgage bond lien protection associated with these notes to fall away before 2042.
(b)
Ameren Missouri has agreed that so long as any of the 3.90% senior secured notes due 2042 are outstanding, Ameren Missouri will not permit a release date to occur, and so long as any of the 6.70% senior secured notes due 2019, 6.00% senior secured notes due 2018, and 8.45% senior secured notes due 2039 are outstanding, Ameren Missouri will not optionally redeem, purchase, or otherwise retire in full the outstanding first mortgage bonds not subject to release provisions.
(c)
These bonds are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture and have a fall-away lien provision similar to that of Ameren Missouri's senior secured notes. The bonds are also backed by an insurance guarantee policy.
(d)
The interest rates and the periods during which such rates apply vary depending on our selection of defined rate modes. Maximum interest rates could reach 18%, depending on the series of bonds. The bonds are callable at 100% of par value. The average interest rates for 2016 and 2015 were as follows:
    
 
2016
 
2015
Ameren Missouri 1992 Series due 2022
0.66%
 
0.06%
Ameren Missouri 1998 Series A due 2033
0.91%
 
0.24%
Ameren Missouri 1998 Series B due 2033
0.92%
 
0.24%
Ameren Missouri 1998 Series C due 2033
0.97%
 
0.24%
Ameren Illinois 1993 Series B-1 due 2028
0.70%
 
0.49%

(e)
These bonds are first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage bond indenture and are secured by substantially all Ameren Missouri property and franchises. The bonds are callable at 100% of par value. Less than $1 million principal amount of the bonds remain outstanding.
(f)
These notes are collaterally secured by first mortgage bonds issued by Ameren Illinois under its 1933 mortgage indenture. The notes have a fall-away lien provision, and Ameren Illinois could cause these notes to become unsecured at any time by redeeming the pollution control bonds 5.90% Series 1993 due 2023 (of which less than $1 million remains outstanding).
(g)
These notes are collaterally secured by mortgage bonds issued by Ameren Illinois under its 1992 mortgage indenture. They are secured by substantially all property of the former IP and CIPS. The notes have a fall-away lien provision and will remain secured only as long as any series of first mortgage bonds issued under its 1992 mortgage indenture remain outstanding. Redemption, purchase, or maturity of all mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Illinois senior secured notes currently outstanding, we do not expect the mortgage bond lien protection associated with these notes to fall away before 2022.
(h)
Ameren Illinois has agreed that so long as any of the 2.70% senior secured notes due 2022 are outstanding, Ameren Illinois will not permit a release date to occur, and so long as any of the 9.75% senior secured notes due 2018, 6.25% senior secured notes due 2018, and 6.125% senior secured notes due 2017 are outstanding, Ameren Illinois will not optionally redeem, purchase or otherwise retire in full the outstanding first mortgage bonds not subject to release provisions; therefore, a release date will not occur so long as any of these notes remain outstanding.
(i)
These bonds are first mortgage bonds issued by Ameren Illinois under its 1933 mortgage indenture. They are secured by substantially all property of the former CILCO. The bonds are callable at 100% of par value. Less than $1 million principal amount of the bonds remain outstanding.
(j)
These bonds are mortgage bonds issued by Ameren Illinois under its 1992 mortgage indenture. They are secured by substantially all property of the former IP and CIPS. The bonds are callable at 100% of par value. The bonds are also backed by an insurance guarantee policy. Less than $1 million principal amount of the bonds remains outstanding.
(k)
The bonds are callable at 100% of par value.
Schedule Of Maturities Of Long-Term Debt 
The following table presents the aggregate maturities of long-term debt, including current maturities, for the Ameren Companies at December 31, 2016:
 
Ameren
(parent)(a)
 
 Ameren
Missouri(a)
 
 Ameren
Illinois(a)
 
Ameren
Consolidated
2017
$
—

 
$
431

 
$
250

 
$
681

2018
—

 
383

 
457

 
840

2019
—

 
581

 
—

 
581

2020
350

 
92

 
—

 
442

2021
—

 
8

 
—

 
8

Thereafter
350

 
2,524

 
1,900

 
4,774

Total
$
700

 
$
4,019

 
$
2,607

 
$
7,326

(a)
Excludes unamortized discount and premium and debt issuance costs of $6 million, $25 million, and $19 million at Ameren (parent), Ameren Missouri, and Ameren Illinois, respectively.
Schedule Of Outstanding Preferred Stock 
The following table presents the outstanding preferred stock of Ameren Missouri and Ameren Illinois, which is redeemable, at the option of the issuer, at the prices shown below as of December 31, 2016 and 2015:
 
 
 
Redemption Price(per share)
 
2016
 
2015
Ameren Missouri:
 
 
 
 
 
 
 
Without par value and stated value of $100 per share, 25 million shares authorized
 
 
 
 
 
 
$3.50 Series
130,000 shares
 
$
110.00

 
$
13

 
$
13

$3.70 Series
40,000 shares
 
104.75

 
4

 
4

$4.00 Series
150,000 shares
 
105.625

 
15

 
15

$4.30 Series
40,000 shares
 
105.00

 
4

 
4

$4.50 Series
213,595 shares
 
110.00

(a) 
21

 
21

$4.56 Series
200,000 shares
 
102.47

 
20

 
20

$4.75 Series
20,000 shares
 
102.176

 
2

 
2

$5.50 Series A
14,000 shares
 
110.00

 
1

 
1

Total
 
 
 
$
80

 
$
80

Ameren Illinois:
 
 
 
 
 
 
 
With par value of $100 per share, 2 million shares authorized
 
 
 
 
 
 
4.00% Series
144,275 shares
 
$
101.00

 
$
14

 
$
14

4.08% Series
45,224 shares
 
103.00

 
5

 
5

4.20% Series
23,655 shares
 
104.00

 
2

 
2

4.25% Series
50,000 shares
 
102.00

 
5

 
5

4.26% Series
16,621 shares
 
103.00

 
2

 
2

4.42% Series
16,190 shares
 
103.00

 
2

 
2

4.70% Series
18,429 shares
 
103.00

 
2

 
2

4.90% Series
73,825 shares
 
102.00

 
7

 
7

4.92% Series
49,289 shares
 
103.50

 
5

 
5

5.16% Series
50,000 shares
 
102.00

 
5

 
5

6.625% Series
124,274 shares
 
100.00

 
12

 
12

7.75% Series
4,542 shares
 
100.00

 
1

 
1

Total
 
 
 
$
62

 
$
62

Total Ameren
 
 
 
$
142

 
$
142

(a)
In the event of voluntary liquidation, $105.50.
Schedule of Required and Actual Debt Ratios 
The following table summarizes the required and actual interest coverage ratios for interest charges, dividend coverage ratios, and bonds and preferred stock issuable as of December 31, 2016, at an assumed interest rate of 5% and dividend rate of 6%.
 
Required Interest
Coverage Ratio(a)
Actual Interest
Coverage Ratio
Bonds Issuable(b)
 
Required Dividend
Coverage Ratio(c)
Actual Dividend
Coverage Ratio
Preferred Stock
Issuable
 
Ameren Missouri
>2.0
4.6

$
4,077

  
>2.5
105.3

$
2,344

 
Ameren Illinois
>2.0
6.9

3,819

(d) 
>1.5
2.8

203

(e) 
(a)
Coverage required on the annual interest charges on first mortgage bonds outstanding and to be issued. Coverage is not required in certain cases when additional first mortgage bonds are issued on the basis of retired bonds.
(b)
Amount of bonds issuable based either on required coverage ratios or unfunded property additions, whichever is more restrictive. The amounts shown also include bonds issuable based on retired bond capacity of $1,206 million and $279 million at Ameren Missouri and Ameren Illinois, respectively.
(c)
Coverage required on the annual dividend on preferred stock outstanding and to be issued, as required in the respective company’s articles of incorporation.
(d)
Amount of bonds issuable by Ameren Illinois based on unfunded property additions and retired bonds solely under its 1992 mortgage indenture.
(e)
Preferred stock issuable is restricted by the amount of preferred stock that is currently authorized by Ameren Illinois' articles of incorporation.
Other Income And Expenses (Tables)
Other Income And Expenses
The following table presents the components of "Other Income and Expenses" in the Ameren Companies’ statements of income (loss) for the years ended December 31, 2016, 2015, and 2014:
 
2016
 
2015
 
2014
 
Ameren:(a)
 
 
 
 
 
 
Miscellaneous income:
 
 
 
 
 
 
Allowance for equity funds used during construction
$
27

 
$
30

 
$
34

 
Interest income on industrial development revenue bonds
27

 
27

 
27

 
Interest income (b)
13

  
14

  
10

 
Other
7

 
3

 
8

(c) 
Total miscellaneous income
$
74

 
$
74

 
$
79

 
Miscellaneous expense:
 
 
 
 
 
 
Donations
$
16

 
$
15

 
$
10

 
Other
16

 
15

 
12

 
Total miscellaneous expense
$
32

 
$
30

 
$
22

 
Ameren Missouri:
 
 
 
 
 
 
Miscellaneous income:
 
 
 
 
 
 
Allowance for equity funds used during construction
$
23

 
$
22

 
$
32

 
Interest income on industrial development revenue bonds
27

 
27

 
27

 
Interest income
1

 
1

 
1

 
Other
1

 
2

 
—

 
Total miscellaneous income
$
52

 
$
52

 
$
60

 
Miscellaneous expense:
 
 
 
 
 
 
Donations
$
4

 
$
5

 
$
6

 
Other
6

 
6

 
6

 
Total miscellaneous expense
$
10

 
$
11

 
$
12

 
Ameren Illinois:
 
 
 
 
 
 
Miscellaneous income:
 
 
 
 
 
 
Allowance for equity funds used during construction
$
4

 
$
8

 
$
2

 
Interest income (b)
12

  
12

  
7

 
Other
5

 
1

 
8

(c) 
Total miscellaneous income
$
21

 
$
21

 
$
17

 
Miscellaneous expense:
 
 
 
 
 
 
Donations
$
6

 
$
5

 
$
4

 
Other
6

 
7

 
4

 
Total miscellaneous expense
$
12

 
$
12

 
$
8

 
(a)
Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
(b)
Includes Ameren Illinois' interest income on the IEIMA revenue requirement reconciliation adjustment regulatory assets.
(c)
Includes Ameren Illinois' income earned in 2014 from customer-requested construction.
Derivative Financial Instruments (Tables)
Open Gross Derivative Volumes By Commodity Type 
The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of December 31, 2016 and 2015. As of December 31, 2016, these contracts extended through October 2019, March 2021, May 2032, and February 2020 for fuel oils, natural gas, power, and uranium, respectively.
  
Quantity (in millions, except as indicated)
 
2016
2015
Commodity
Ameren Missouri
Ameren Illinois
Ameren
Ameren Missouri
Ameren Illinois
Ameren
Fuel oils (in gallons)(a)
30
(b)
30
35
(b)
35
Natural gas (in mmbtu)
25
129
154
30
151
181
Power (in megawatthours)
1
9
10
1
10
11
Uranium (pounds in thousands)
345
(b)
345
494
(b)
494

(a)
Consists of ultra-low-sulfur diesel products.
(b)
Not applicable.
Derivative Instruments Carrying Value 
The following table presents the carrying value and balance sheet location of all derivative commodity contracts, none of which were designated as hedging instruments, as of December 31, 2016 and 2015:
 
Balance Sheet Location
 
Ameren
Missouri
 
Ameren
Illinois
 
Ameren
2016
 
 
 
 
 
 
 
Fuel oils
Other current assets
$
2

$
—

$
2

 
Other assets
 
1

 
—

 
1

Natural gas
Other current assets
 
1

 
11

 
12

 
Other assets
 
1

 
2

 
3

Power
Other current assets
 
9

 
—

 
9

 
Total assets (a)
$
14

$
13

$
27

Fuel oils
Other current liabilities
$
5

$
—

$
5

Natural gas
MTM derivative liabilities
 
(b)

 
3

 
(b)

 
Other current liabilities
 
1

 
—

 
4

 
Other deferred credits and liabilities
 
5

 
5

 
10

Power
MTM derivative liabilities
 
(b)

 
12

 
(b)

 
Other current liabilities
 
3

 
—

 
15

 
Other deferred credits and liabilities
 
—

 
173

 
173

Uranium
Other deferred credits and liabilities
 
4

 
—

 
4

 
Total liabilities (c)
$
18

$
193

$
211

2015
 
 
 
 
 
 
 
Natural gas
Other current assets
$
—

 
1

$
1

 
Other assets
 
1

 
—

 
1

Power
Other current assets
 
16

 
—

 
16

 
Total assets (a)
$
17

$
1

$
18

Fuel oils
Other current liabilities
$
22

$
—

$
22

 
Other deferred credits and liabilities
 
7

 
—

 
7

Natural gas
MTM derivative liabilities
 
(b)

 
32

 
(b)

 
Other current liabilities
 
6

 
—

 
38

 
Other deferred credits and liabilities
 
8

 
18

 
26

Power
MTM derivative liabilities
 
(b)

 
13

 
(b)

 
Other current liabilities
 
—

 
—

 
13

 
Other deferred credits and liabilities
 
—

 
157

 
157

Uranium
Other current liabilities
 
1

 
—

 
1

 
Total liabilities (c)
$
44

$
220

$
264

(a)
The cumulative amount of pretax net gains on all derivative instruments is deferred as a regulatory liability.
(b)
Balance sheet line item not applicable to registrant.
(c)
The cumulative amount of pretax net losses on all derivative instruments is deferred as a regulatory asset.
Derivative Instruments With Credit Risk-Related Contingent Features 
The following table presents, as of December 31, 2016, the aggregate fair value of all derivative instruments with credit risk-related contingent features in a gross liability position, the cash collateral posted, and the aggregate amount of additional collateral that counterparties could require. The additional collateral required is the net liability position allowed under the master netting arrangements or similar agreements, assuming (1) the credit risk-related contingent features underlying these arrangements were triggered on December 31, 2016, and (2) those counterparties with rights to do so requested collateral.
 
Aggregate Fair Value of
Derivative Liabilities(a)
 
Cash
Collateral Posted
 
Potential Aggregate Amount of
Additional Collateral Required(b)
2016
 
 
 
 
 
Ameren Missouri
$
64

 
$
3

 
$
54

Ameren Illinois
33

 
—

 
26

Ameren
$
97

 
$
3

 
$
80

(a)
Before consideration of master netting arrangements or similar agreements and including NPNS and other accrual contract exposures.
(b)
As collateral requirements with certain counterparties are based on master netting arrangements or similar agreements, the aggregate amount of additional collateral required to be posted is determined after consideration of the effects of such arrangements.
Fair Value Measurements (Tables)
Fair Value Inputs, Assets and Liabilities, Quantitative Information 
The following table describes the valuation techniques and unobservable inputs utilized by the Ameren Companies for the fair value of financial assets and liabilities classified as Level 3 in the fair value hierarchy for the periods ended December 31, 2016 and 2015:
 
 
Fair Value
 
 
 
 
Weighted
 
 
Assets
Liabilities
 
Valuation Technique(s)
Unobservable Input
Range
Average
Level 3 Derivative asset and liability – commodity contracts(a):
 
 
 
2016
 
 
 
 
 
 
 
 
 
Fuel oils
$
1

$
—

 
Option model
Volatilities(%)(b)
24 – 66
28
 
 
 
 
 
Discounted cash flow
Counterparty credit risk(%)(c)(d)
0.13 – 0.22
0.15
 
 
 
 
 
 
Ameren Missouri credit risk(%)(c)(d)
0.38
(e)
 
 
 
 
 
 
Escalation rate(%)(b)(f)
(2) – 2
0
 
Natural Gas
1

(1
)
 
Option model
Volatilities(%)(b)
31 – 66
36
 



 

Nodal basis($/mmbtu)(b)
(0.40) – (0.10)
(0.20)
 



 
Discounted cash flow
Nodal basis($/mmbtu)(b)
(0.80) – 0
(0.50)
 



 

Counterparty credit risk(%)(c)(d)
0.13 – 8
1
 



 

Ameren Illinois credit risk(%)(c)(d)
0.38
(e)
 
Power(g)
9

(187
)
 
Discounted cash flow
Average forward peak and off-peak pricing – forwards/swaps($/MWh)(h)
26 – 44
29
 
 
 
 
 
 
Estimated auction price for FTRs($/MW)(b)
(71) – 5,270
125
 
 
 
 
 
 
Nodal basis($/MWh)(h)
(6) – 0
(2)
 
 
 
 
 
 
Ameren Illinois credit risk(%)(c)(d)
0.38
(e)
 
 
 
 
 
Fundamental energy production model
Estimated future natural gas prices($/mmbtu)(b)
3 – 4
3
 
 
 
 
 
 
Escalation rate(%)(b)(i)
5
(e)
 
 
 
 
 
Contract price allocation
Estimated renewable energy credit costs($/credit)(b)
5 – 7
6
 
Uranium
—

(4
)
 
Option model
Volatilities(%)(b)
24
(e)
 
 
 
 
 
Discounted cash flow
Average forward uranium pricing($/pound)(b)
22 – 24
22
 
 
 
 
 
 
Ameren Missouri credit risk(%)(c)(d)
0.38
(e)
2015
 
 
 
 
 
 
 
 
 
Natural Gas
$
1

$
(1
)
 
Option model
Volatilities(%)(b)
35 – 55
45
 
 
 
 
 
 
Nodal basis($/mmbtu)(c)
(0.30) – 0
(0.20)
 
 
 
 
 
Discounted cash flow
Nodal basis($/mmbtu)(b)
(0.10) – 0
(0.10)
 
 
 
 
 
 
Counterparty credit risk(%)(c)(d)
0.40 – 12
7
 
 
 
 
 
 
Ameren Missouri credit risk(%)(c)(d)
0.40
(e)
 
Power(g)
16

(170
)
 
Discounted cash flow
Average forward peak and off-peak pricing – forwards/swaps($/MWh)(h)
22 – 39
29
 
 
 
 
 
 
Estimated auction price for FTRs($/MW)(b)
(270) – 2,057
211
 
 
 
 
 
 
Nodal basis($/MWh)(h)
(10) – (1)
(3)
 
 
Fair Value
 
 
 
 
Weighted
 
 
Assets
Liabilities
 
Valuation Technique(s)
Unobservable Input
Range
Average
 
 
 
 
 
 
Counterparty credit risk(%)(c)(d)
0.86
(e)
 
 
 
 
 
 
Ameren Illinois credit risk(%)(c)(d)
0.40
(e)
 
 
 
 
 
Fundamental energy production model
Estimated future natural gas prices($/mmbtu)(b)
3 – 4
4
 
 
 
 
 
 
Escalation rate(%)(b)(i)
3
(e)
 
 
 
 
 
Contract price allocation
Estimated renewable energy credit costs($/credit)(b)
5 – 7
6
 
Uranium
—

(1
)
 
Option model
Volatilities(%)(b)
20
(e)
 
 
 
 
 
Discounted cash flow
Average forward uranium pricing($/pound)(b)
35 – 42
37
 
 
 
 
 
 
Ameren Missouri credit risk(%)(c)(d)
0.40
(e)
(a)
The derivative asset and liability balances are presented net of counterparty credit considerations.
(b)
Generally, significant increases (decreases) in this input in isolation would result in a significantly higher (lower) fair value measurement.
(c)
Generally, significant increases (decreases) in this input in isolation would result in a significantly lower (higher) fair value measurement.
(d)
Counterparty credit risk is applied only to counterparties with derivative asset balances. Ameren Missouri and Ameren Illinois credit risk is applied only to counterparties with derivative liability balances.
(e)
Not applicable.
(f)
Escalation rate applies to fuel oil prices 2019 and beyond.
(g)
Power valuations use visible third-party pricing evaluated by month for peak and off-peak demand through 2020. Valuations beyond 2020 use fundamentally modeled pricing by month for peak and off-peak demand.
(h)
The balance at Ameren is comprised of Ameren Missouri and Ameren Illinois power contracts, which respond differently to unobservable input changes because of their opposing positions.
(i)
Escalation rate applies to power prices in 2031 and beyond for December 31, 2016, and to power prices in 2026 and beyond for December 31, 2015.
Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis 
The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of December 31, 2016:
 
 
 
Quoted Prices in
Active Markets for
Identical Assets
or Liabilities
(Level 1)
 
Significant Other
Observable
Inputs
(Level 2)
 
Significant Other
Unobservable
Inputs
(Level 3)
 
Total
 
Assets:
 
 
 
 
 
 
 
 
 
 
Ameren
Derivative assets – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Fuel oils
 
$
2

 
$
—

 
$
1

 
$
3

 
 
Natural gas
 
2

 
12

 
1

 
15

 
 
Power
 
—

 
—

 
9

 
9

 
 
Total derivative assets – commodity contracts
 
$
4

 
$
12

 
$
11

 
$
27

 
 
Nuclear decommissioning trust fund:
 
 
 
 
 
 
 
 
 
 
Cash and cash equivalents
 
$
1

 
$
—

 
$
—

 
$
1

 
 
Equity securities:
 
 
 
 
 
 
 
 
 
 
U.S. large capitalization
 
408

 
—

 
—

 
408

 
 
Debt securities:
 
 
 
 
 
 
 
 
 
 
U.S. Treasury and agency securities
 
—

 
112

 
—

 
112

 
 
Corporate bonds
 
—

 
67

 
—

 
67

 
 
Other
 
—

 
17

 
—

 
17

 
 
Total nuclear decommissioning trust fund
 
$
409

 
$
196

 
$
—

 
$
605

(b) 
 
Total Ameren
 
$
413

 
$
208

 
$
11

 
$
632

 
Ameren Missouri
Derivative assets – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
 
 
Quoted Prices in
Active Markets for
Identical Assets
or Liabilities
(Level 1)
 
Significant Other
Observable
Inputs
(Level 2)
 
Significant Other
Unobservable
Inputs
(Level 3)
 
Total
 
 
Fuel oils
 
$
2

 
$
—

 
$
1

 
$
3

 
 
Natural gas
 
—

 
1

 
1

 
2

 
 
Power
 
—

 
—

 
9

 
9

 
 
Total derivative assets – commodity contracts
 
$
2

 
$
1

 
$
11

 
$
14

 
 
Nuclear decommissioning trust fund:
 
 
 
 
 
 
 
 
 
 
Cash and cash equivalents
 
$
1

 
$
—

 
$
—

 
$
1

 
 
Equity securities:
 
 
 
 
 
 
 
 
 
 
U.S. large capitalization
 
408

 
—

 
—

 
408

 
 
Debt securities:
 
 
 
 
 
 
 
 
 
 
U.S. Treasury and agency securities
 
—

 
112

 
—

 
112

 
 
Corporate bonds
 
—

 
67

 
—

 
67

 
 
Other
 
—

 
17

 
—

 
17

 
 
Total nuclear decommissioning trust fund
 
$
409

 
$
196

 
$
—

 
$
605

(b) 
 
Total Ameren Missouri
 
$
411

 
$
197

 
$
11

 
$
619

 
Ameren Illinois
Derivative assets – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Natural gas
 
$
2

 
$
11

 
$
—

 
$
13

 
Liabilities:
 
 
 
 
 
 
 
 
 
 
Ameren
Derivative liabilities – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Fuel oils
 
$
5

 
$
—

 
$
—

 
$
5

 
 
Natural gas
 
—

 
13

 
1

 
14

 
 
Power
 
—

 
1

 
187

 
188

 
 
Uranium
 
—

 
—

 
4

 
4

 
 
Total Ameren
 
$
5

 
$
14

 
$
192

 
$
211

 
Ameren Missouri
Derivative liabilities – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Fuel oils
 
$
5

 
$
—

 
$
—

 
$
5

 
 
Natural gas
 
—

 
6

 
—

 
6

 
 
Power
 
—

 
1

 
2

 
3

 
 
Uranium
 
—

 
—

 
4

 
4

 
 
Total Ameren Missouri
 
$
5

 
$
7

 
$
6

 
$
18

 
Ameren Illinois
Derivative liabilities – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Natural gas
 
$
—

 
$
7

 
$
1

 
$
8

 
 
Power
 
—

 
—

 
185

 
185

 
 
Total Ameren Illinois
 
$
—

 
$
7

 
$
186

 
$
193

 
(a)
The derivative asset and liability balances are presented net of counterparty credit considerations.
(b)
Balance excludes $2 million of receivables, payables, and accrued income, net.
The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of December 31, 2015:
 
 
 
Quoted Prices in
Active Markets for
Identical Assets
or Liabilities
(Level 1)
 
Significant Other
Observable
Inputs
(Level 2)
 
Significant Other
Unobservable
Inputs
(Level 3)
 
Total
 
Assets:
 
 
 
 
 
 
 
 
 
 
Ameren
Derivative assets – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Natural gas
 
$
—

 
$
1

 
$
1

 
$
2

 
 
Power
 
—

 
—

 
16

 
16

 
 
Total derivative assets – commodity contracts
 
$
—

 
$
1

 
$
17

 
$
18

 
 
 
 
Quoted Prices in
Active Markets for
Identical Assets
or Liabilities
(Level 1)
 
Significant Other
Observable
Inputs
(Level 2)
 
Significant Other
Unobservable
Inputs
(Level 3)
 
Total
 
 
Nuclear decommissioning trust fund:
 
 
 
 
 
 
 
 
 
 
Cash and cash equivalents
 
$
4

 
$
—

 
$
—

 
$
4

 
 
Equity securities:
 
 
 
 
 
 
 
 
 
 
U.S. large capitalization
 
364

 
—

 
—

 
364

 
 
Debt securities:
 
 
 
 
 
 
 
 
 
 
U.S. Treasury and agency securities
 
—

 
109

 
—

 
109

 
 
Corporate bonds
 
—

 
58

 
—

 
58

 
 
Other
 
—

 
22

 
—

 
22

 
 
Total nuclear decommissioning trust fund
 
$
368

 
$
189

 
$
—

 
$
557

(b) 
 
Total Ameren
 
$
368

 
$
190

 
$
17

 
$
575

 
Ameren Missouri
Derivative assets – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Natural gas
 
$
—

 
$
—

 
$
1

 
$
1

 
 
Power
 
—

 
—

 
16

 
16

 
 
Total derivative assets – commodity contracts
 
$
—

 
$
—

 
$
17

 
$
17

 
 
Nuclear decommissioning trust fund:
 
 
 
 
 
 
 
 
 
 
Cash and cash equivalents
 
$
4

 
$
—

 
$
—

 
$
4

 
 
Equity securities:
 
 
 
 
 
 
 
 
 
 
U.S. large capitalization
 
364

 
—

 
—

 
364

 
 
Debt securities:
 
 
 
 
 
 
 
 
 
 
U.S. Treasury and agency securities
 
—

 
109

 
—

 
109

 
 
Corporate bonds
 
—

 
58

 
—

 
58

 
 
Other
 
—

 
22

 
—

 
22

 
 
Total nuclear decommissioning trust fund
 
$
368

 
$
189

 
$
—

 
$
557

(b) 
 
Total Ameren Missouri
 
$
368

 
$
189

 
$
17

 
$
574

 
Ameren Illinois
Derivative assets – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Natural gas
 
$
—

 
$
1

 
$
—

 
$
1

 
Liabilities:
 
 
 
 
 
 
 
 
 
 
Ameren
Derivative liabilities – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Fuel oils
 
$
29

 
$
—

 
$
—

 
$
29

 
 
Natural gas
 
1

 
62

 
1

 
64

 
 
Power
 
—

 
—

 
170

 
170

 
 
Uranium
 
—

 
—

 
1

 
1

 
 
Total Ameren
 
$
30

 
$
62

 
$
172

 
$
264

 
Ameren Missouri
Derivative liabilities – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Fuel oils
 
$
29

 
$
—

 
$
—

 
$
29

 
 
Natural gas
 
—

 
13

 
1

 
14

 
 
Uranium
 
—

 
—

 
1

 
1

 
 
Total Ameren Missouri
 
$
29

 
$
13

 
$
2

 
$
44

 
Ameren Illinois
Derivative liabilities – commodity contracts(a):
 
 
 
 
 
 
 
 
 
 
Natural gas
 
$
1

 
$
49

 
$
—

 
$
50

 
 
Power
 
—

 
—

 
170

 
170

 
 
Total Ameren Illinois
 
$
1

 
$
49

 
$
170

 
$
220

 
(a)
The derivative asset and liability balances are presented net of counterparty credit considerations.
(b)
Balance excludes $(1) million of receivables, payables, and accrued income, net.
Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level 3 In The Fair Value Hierarchy 
The following table summarizes the changes in the fair value of power financial assets and liabilities classified as Level 3 in the fair value hierarchy:
 
 
Net Derivative Commodity Contracts
 
 
Ameren
Missouri
 
Ameren
Illinois
 
Ameren
For the year ended December 31, 2015
 
 
 
 
 
 
Beginning balance at January 1, 2015
$
9

$
(142
)
$
(133
)
Realized and unrealized gains (losses) included in regulatory assets/liabilities:
 
2

 
(41
)
 
(39
)
Purchases
 
29

 
—

 
29

Settlements
 
(23
)
 
13

 
(10
)
Transfers out of Level 3
 
(1
)
 
—

 
(1
)
Ending balance at December 31, 2015
$
16

$
(170
)
$
(154
)
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2015
$
—

$
(39
)
$
(39
)
For the year ended December 31, 2016
 
 
 
 
 
 
Beginning balance at January 1, 2016
$
16

$
(170
)
$
(154
)
Realized and unrealized gains (losses) included in regulatory assets/liabilities:
 
(1
)
 
(29
)
 
(30
)
Purchases
 
13

 
—

 
13

Settlements
 
(21
)
 
14

 
(7
)
Ending balance at December 31, 2016
$
7

$
(185
)
$
(178
)
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2016
$
—

$
(27
)
$
(27
)

Schedule Of Carrying Amounts And Estimated Fair Values Of Long-Term Debt And Preferred Stock 
The following table presents the carrying amounts and estimated fair values of our long-term debt, capital lease obligations, and preferred stock at December 31, 2016 and 2015:
 
2016
 
2015
 
Carrying Amount
 
Fair Value
 
Carrying Amount
 
Fair Value
Ameren:(a)
 
 
 
 
 
 
 
Long-term debt and capital lease obligations (including current portion)
$
7,276

 
$
7,772

 
$
7,275

 
$
7,814

Preferred stock
142

 
131

 
142

 
125

Ameren Missouri:
 
 
 
 
 
 
 
Long-term debt and capital lease obligations (including current portion)
$
3,994

 
$
4,304

 
$
4,110

 
$
4,449

Preferred stock
80

 
79

 
80

 
75

Ameren Illinois:
 
 
 
 
 
 
 
Long-term debt (including current portion)
$
2,588

 
$
2,765

 
$
2,471

 
$
2,665

Preferred stock
62

 
52

 
62

 
50

(a)
Preferred stock is recorded in "Noncontrolling Interests" on the consolidated balance sheet.
Nuclear Decommissioning Trust Fund Investments (Tables)
Fair Value Of Securities In Nuclear Decommissioning Trust Fund 
The following table presents the costs and fair values of investments in debt and equity securities in Ameren's and Ameren Missouri’s nuclear decommissioning trust fund at December 31, 2016 and 2015:
Security Type
Cost
 
Gross Unrealized Gain
 
Gross Unrealized Loss
 
Fair Value
2016
 
 
 
 
 
 
 
Debt securities
$
197

 
$
3

$
4

 
$
196

Equity securities
161

 
253

 
6

 
408

Cash
1

 
—

 
—

 
1

Other(a)
2

 
—

 
—

 
2

Total
$
361

 
$
256

$
10

 
$
607

2015
 
 
 
 
 
 
 
Debt securities
$
191

 
$
2

$
4

 
$
189

Equity securities
147

 
224

 
7

 
364

Cash
4

 
—

 
—

 
4

Other(a)
(1
)
 
—

 
—

 
(1
)
Total
$
341

 
$
226

$
11

 
$
556


(a)
Represents net receivables and payables relating to pending security sales, interest, and security purchases.
Proceeds From Sale Of Investments In Nuclear Decommissioning Trust Fund And Gross Realized Gains And Losses 
The following table presents proceeds from the sale and maturities of investments in Ameren Missouri’s nuclear decommissioning trust fund and the gross realized gains and losses resulting from those sales for the years ended December 31, 2016, 2015, and 2014:
 
2016
 
2015
 
2014
Proceeds from sales and maturities
$
377

 
$
349

 
$
391

Gross realized gains
7

 
8

 
7

Gross realized losses
4

 
2

 
2

Fair Value Of Securities In Nuclear Decommissioning Trust Fund According To Their Contractual Maturities 
The following table presents the costs and fair values of investments in debt securities in Ameren's and Ameren Missouri’s nuclear decommissioning trust fund according to their contractual maturities at December 31, 2016:
 
Cost
 
Fair Value
Less than 5 years
$
105

 
$
104

5 years to 10 years
47

 
47

Due after 10 years
45

 
45

Total
$
197

 
$
196

Retirement Benefits (Tables)
Summary Of Benefit Liability Recorded 
The following table presents the net benefit liability recorded on the balance sheets of each of the Ameren Companies as of December 31, 2016 and 2015:
 
2016

2015

Ameren(a)
$
774

$
567

Ameren Missouri
293

236

Ameren Illinois
315

219

(a)
Includes amounts for Ameren registrant and nonregistrant subsidiaries.
Funded Status Of Benefit Plans And Amounts Included In Regulatory Assets And OCI 
The following table presents the funded status of Ameren's pension and postretirement benefit plans as of December 31, 2016 and 2015. It also provides the amounts included in regulatory assets and accumulated OCI at December 31, 2016 and 2015, that have not been recognized in net periodic benefit costs.
  
2016
 
2015
  
Pension Benefits(a)
 
Postretirement
Benefits(a)
 
Pension Benefits(a)
 
Postretirement
Benefits(a)
Accumulated benefit obligation at end of year
$
4,288

$
(b)

 
$
3,995

$
(b)

Change in benefit obligation:
 
 
 
 
 
 
 
Net benefit obligation at beginning of year
$
4,197

$
1,094

 
$
4,410

$
1,203

Service cost
81

 
19

 
92

 
24

Interest cost
185

 
50

 
174

 
48

Participant contributions
—

 
8

 
—

 
8

Actuarial (gain) loss
265

 
52

 
(256
)
 
(133
)
Settlement
—

 
—

 
(2
)
 
—

Benefits paid
(210
)
 
(54
)
 
(221
)
 
(56
)
Federal subsidy on benefits paid
(b)

 
1

 
(b)

 
—

Net benefit obligation at end of year
4,518

 
1,170

 
4,197

 
1,094

Change in plan assets:
 
 
 
 
 
 
 
Fair value of plan assets at beginning of year
3,653

 
1,071

 
3,794

 
1,109

Actual return on plan assets
313

 
73

 
(29
)
 
(8
)
Employer contributions
57

 
2

 
111

 
18

Federal subsidy on benefits paid
(b)

 
1

 
(b)

 
—

Participant contributions
—

 
8

 
—

 
8

Settlements
—

 
—

 
(2
)
 
—

Benefits paid
(210
)
 
(54
)
 
(221
)
 
(56
)
Fair value of plan assets at end of year
3,813

 
1,101

 
3,653

 
1,071

Funded status – deficiency
705

 
69

 
544

 
23

Accrued benefit cost at December 31
$
705

$
69

 
$
544

$
23

Amounts recognized in the balance sheet consist of:
 
 
 
 
 
 
 
Noncurrent asset(c)
$
—

$
—

 
$
—

$
(18
)
Current liability(d)
3

 
2

 
3

 
2

Noncurrent liability
702

 
67

 
541

 
39

Net liability recognized
$
705

$
69

 
$
544

$
23

Amounts recognized in regulatory assets consist of:
 
 
 
 
 
 
 
Net actuarial (gain) loss
$
535

$
(29
)
 
$
395

$
(82
)
Prior service cost (credit)
(4
)
 
(8
)
 
(5
)
 
(11
)
Amounts (pretax) recognized in accumulated OCI consist of:
 
 
 
 
 
 
 
Net actuarial (gain) loss
43

 
—

 
17

 
(3
)
Prior service cost (credit)
—

 
(1
)
 
—

 
—

Total
$
574

$
(38
)
 
$
407

$
(96
)
(a)
Includes amounts for Ameren registrant and nonregistrant subsidiaries.
(b)
Not applicable.
(c)
Included in "Other assets" on Ameren's consolidated balance sheet.
(d)
Included in "Other current liabilities" on Ameren's consolidated balance sheet.
Assumptions Used To Determine Benefit Obligations 
The following table presents the assumptions used to determine our benefit obligations at December 31, 2016 and 2015:
  
Pension Benefits
 
Postretirement Benefits
  
2016
 
2015
 
2016
 
2015
Discount rate at measurement date
4.00
%
 
4.50
%
 
4.00
%
 
4.50
%
Increase in future compensation
3.50

 
3.50

 
3.50

 
3.50

Medical cost trend rate (initial)
(a)

 
(a)

 
5.00

 
5.00

Medical cost trend rate (ultimate)
(a)

 
(a)

 
5.00

 
5.00


(a)
Not applicable
Schedule Of Cash Contributions Made To Benefit Plans 
The following table presents the cash contributions made to our defined benefit retirement plan and to our postretirement plans during 2016, 2015, and 2014:
  
Pension Benefits
 
Postretirement Benefits
  
2016
 
2015
 
2014
 
2016
 
2015
 
2014
Ameren Missouri
$
21

 
$
47

 
$
41

 
$
1

 
$
8

 
$
3

Ameren Illinois
30

 
45

 
39

 
1

 
8

 
2

Other
6

 
19

 
19

 
—

 
2

 
1

Ameren
57

 
111

 
99

 
2

 
18

 
6

Target Allocation Of The Plans' Asset Categories 
The following table presents our target allocations for 2017 and our pension and postretirement plans’ asset categories as of December 31, 2016 and 2015:
Asset
Category
Target Allocation
2017
 
Percentage of Plan Assets at December  31,
2016
 
2015
Pension Plan:
 
 
 
 
 
Cash and cash equivalents
0% – 5%
 
1
%
 
1
%
Equity securities:
 
 
 
 
 
U.S. large-capitalization
29% – 39%
 
34
%
 
34
%
U.S. small- and mid-capitalization
3% – 13%
 
9
%
 
7
%
International and emerging markets
9% – 19%
 
14
%
 
13
%
Total equity
51% – 61%
 
57
%
 
54
%
Debt securities
35% – 45%
 
37
%
 
40
%
Real estate
0% –  9%  
 
5
%
 
5
%
Private equity
0% –  5%  
 
(a)

 
(a)

Total
 
 
100
%
 
100
%
Postretirement Plans:
 
 
 
 
 
Cash and cash equivalents
0% – 7%
 
3
%
 
4
%
Equity securities:
 
 
 
 
 
U.S. large-capitalization
34% – 44%
 
40
%
 
39
%
U.S. small- and mid-capitalization
2% – 12%
 
7
%
 
7
%
International
9% – 19%
 
14
%
 
13
%
Total equity
55% – 65%
 
61
%
 
59
%
Debt securities
33% – 43%
 
36
%
 
37
%
Total
 
 
100
%
 
100
%

(a)
Less than 1% of plan assets.
Components Of Net Periodic Benefit Cost 
The following table presents the components of the net periodic benefit cost of Ameren's pension and postretirement benefit plans during 2016, 2015, and 2014:
 
Pension Benefits
 
Postretirement Benefits
2016
 
 
 
Service cost
$
81

 
$
19

Interest cost
185

 
50

Expected return on plan assets
(253
)
 
(72
)
Amortization of:
 
 
 
Prior service credit
(1
)
 
(5
)
Actuarial (gain) loss
32

 
(11
)
Net periodic benefit cost (benefit)
$
44

 
$
(19
)
2015
 
 
 
Service cost
$
92

 
$
24

Interest cost
174

 
48

Expected return on plan assets
(248
)
 
(68
)
Amortization of:
 
 
 
Prior service credit
(1
)
 
(5
)
Actuarial loss
74

 
5

Settlement loss
1

 
—

Net periodic benefit cost (benefit)
$
92

 
$
4

2014
 
 
 
Service cost
$
79

 
$
19

Interest cost
183

 
50

Expected return on plan assets
(229
)
 
(65
)
Amortization of:
 
 
 
Prior service credit
(1
)
 
(5
)
Actuarial (gain) loss
49

 
(7
)
Net periodic benefit cost (benefit)
$
81

 
$
(8
)

Summary Of Estimated Amortizable Amounts From Regulatory Assets and Accumulated OCI Into Net Periodic Benefit Cost 
The estimated amounts that will be amortized from regulatory assets and accumulated OCI into Ameren's net periodic benefit cost in 2017 are as follows:
  
Pension Benefits(a)
 
Postretirement Benefits(a)
Regulatory assets:
 
 
 
Prior service credit
$
(1
)
 
$
(5
)
Net actuarial (gain) loss
50

 
(7
)
Accumulated OCI:
 
 
 
Net actuarial loss
4

 
—

Total
$
53

 
$
(12
)
(a)
Includes amounts for Ameren registrant and nonregistrant subsidiaries.
Summary Of Benefit Plan Costs Incurred 
The Ameren Companies are responsible for their share of the pension and postretirement benefit costs. The following table presents the pension costs and the postretirement benefit costs incurred and included in continuing operations for the years ended December 31, 2016, 2015, and 2014:
  
Pension Costs
 
Postretirement Costs
  
2016
 
2015
 
2014
 
2016
 
2015
 
2014
Ameren Missouri(a)
$
26

 
$
54

 
$
50

 
$
(5
)
 
$
8

 
$
3

Ameren Illinois
22

 
38

 
30

 
(13
)
 
(3
)
 
(9
)
Other
(4
)
 
—

 
1

 
(1
)
 
(1
)
 
(2
)
Ameren
44

 
92

 
81

 
(19
)
 
4

 
(8
)
(a)
Does not include the impact of the regulatory tracking mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates.
Schedule Of Expected Payments From Qualified Trust And Company Funds 
The expected pension and postretirement benefit payments from qualified trust and company funds, which reflect expected future service, as of December 31, 2016, are as follows:
  
Pension Benefits
 
Postretirement Benefits
  
Paid from
Qualified
Trust Funds
 
        Paid from
         Company
      Funds
 
        Paid from
         Qualified
      Trust Funds
 
        Paid from
         Company
      Funds
2017
$
248

 
$
3

 
$
54

 
$
2

2018
254

 
3

 
57

 
2

2019
261

 
3

 
59

 
2

2020
265

 
3

 
61

 
2

2021
273

 
3

 
63

 
2

2022 – 2026
1,405

 
13

 
331

 
12

Assumptions Used To Determine Net Periodic Benefit Cost 
The following table presents the assumptions used to determine net periodic benefit cost for our pension and postretirement benefit plans for the years ended December 31, 2016, 2015, and 2014:
  
Pension Benefits
 
Postretirement Benefits
  
2016
 
2015
 
2014
 
2016
 
2015
 
2014
Discount rate at measurement date
4.50
%
 
4.00
%
 
4.75
%
 
4.50
%
 
4.00
%
 
4.75
%
Expected return on plan assets
7.00

 
7.25

 
7.25

 
7.00

 
7.00

 
7.00

Increase in future compensation
3.50

 
3.50

 
3.50

 
3.50

 
3.50

 
3.50

Medical cost trend rate (initial)
(a)

 
(a)

 
(a)

 
5.00

 
5.00

 
5.00

Medical cost trend rate (ultimate)
(a)

 
(a)

 
(a)

 
5.00

 
5.00

 
5.00


(a)
Not applicable
Schedule Of Potential Changes In Key Assumptions 
The table below reflects the sensitivity of Ameren’s plans to potential changes in key assumptions:
  
Pension Benefits
 
Postretirement Benefits
  
Service Cost
and Interest
Cost
 
    Projected
    Benefit
     Obligation
 
    Service Cost
    and Interest
    Cost
 
    Postretirement
      Benefit
       Obligation
0.25% decrease in discount rate
$
(1
)
 
$
142

 
$
—

 
$
38

0.25% increase in salary scale
2

 
16

 
—

 
—

1.00% increase in annual medical trend
—

 
—

 
3

 
54

1.00% decrease in annual medical trend
—

 
—

 
(3
)
 
(54
)
Schedule Of Matching Contributions 
The following table presents the portion of the matching contribution to the Ameren 401(k) plan attributable to the continuing operations for each of the Ameren Companies for the years ended December 31, 2016, 2015, and 2014:
 
2016
 
2015
 
2014
Ameren Missouri
$
16

 
$
16

 
$
16

Ameren Illinois
12

 
12

 
11

Other
1

 
1

 
1

Ameren
29

 
29

 
28

Target Allocation Of The Plans' Asset Categories 
The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the pension plan assets measured at fair value as of December 31, 2016:
 
Quoted Prices in
Active Markets for
Identified Assets
(Level 1)
 
Significant Other
Observable
Inputs
(Level 2)
 
Significant Other
Unobservable
Inputs
(Level 3)
 
Measured at NAV(a)
 
Total
Cash and cash equivalents
$
—

 
$
—

 
$
—

 
$
33

 
$
33

Equity securities:
 
 
 
 
 
 
 
 
 
U.S. large-capitalization
—

 
—

 
—

 
1,352

 
1,352

U.S. small- and mid-capitalization
361

 
—

 
—

 
—

 
361

International and emerging markets
133

 
—

 
—

 
389

 
522

Debt securities:
 
 
 
 
 
 
 
 
 
Corporate bonds
—

 
617

 
—

 
13

 
630

Municipal bonds
—

 
95

 
—

 
—

 
95

U.S. Treasury and agency securities
—

 
701

 
—

 
—

 
701

Other
—

 
21

 
—

 
—

 
21

Real estate
—

 
—

 
—

 
202

 
202

Private equity
—

 
—

 
—

 
6

 
6

Total
$
494

 
$
1,434

 
$
—

 
$
1,995

 
$
3,923

Less: Medical benefit assets at December 31(b)
 
 
 
 
 
 
 
 
(132
)
Plus: Net receivables at December 31(c)
 
 
 
 
 
 
 
 
22

Fair value of pension plans assets at year end
 
 
 
 
 
 
 
 
$
3,813

(a)
Reflects the adoption of the new authoritative accounting guidance related to investments measured at the NAV practical expedient. See Note 1 - Summary of Significant Accounting Policies for additional information.
(b)
Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation.
(c)
Receivables related to pending security sales, offset by payables related to pending security purchases.
The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the pension plan assets measured at fair value as of December 31, 2015:
 
Quoted Prices in
Active Markets for
Identified Assets or Liabilities
(Level 1)
 
Significant Other
Observable
Inputs
(Level 2)
 
Significant Other
Unobservable
Inputs
(Level 3)
 
Measured at NAV(a)
 
Total
Cash and cash equivalents
$
—

 
$
—

 
$
—

 
$
20

 
$
20

Equity securities:
 
 
 
 
 
 
 
 
 
U.S. large-capitalization
—

 
—

 
—

 
1,296

 
1,296

U.S. small- and mid-capitalization
268

 
—

 
—

 
—

 
268

International and emerging markets
122

 
126

 
—

 
243

 
491

Debt securities:
 
 
 
 
 
 
 
 
 
Corporate bonds
—

 
617

 
—

 
14

 
631

Municipal bonds
—

 
104

 
—

 
—

 
104

U.S. Treasury and agency securities
6

 
751

 
—

 
—

 
757

Other
—

 
5

 
—

 
—

 
5

Real estate
—

 
—

 
—

 
168

 
168

Private equity
—

 
—

 
—

 
8

 
8

Total
$
396

 
$
1,603

 
$
—

 
$
1,749

 
$
3,748

Less: Medical benefit assets at December 31(b)
 
 
 
 
 
 
 
 
(123
)
Plus: Net receivables at December 31(c)
 
 
 
 
 
 
 
 
28

Fair value of pension plans assets at year end
 
 
 
 
 
 
 
 
$
3,653

(a)
Reflects the adoption of the new authoritative accounting guidance related to investments measured at the NAV practical expedient. See Note 1 - Summary of Significant Accounting Policies for additional information.
(b)
Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation.
(c)
Receivables related to pending security sales, offset by payables related to pending security purchases.
Target Allocation Of The Plans' Asset Categories 
The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the postretirement benefit plans assets measured at fair value as of December 31, 2016:
 
Quoted Prices in
Active Markets for
Identified Assets
(Level 1)
 
Significant Other
Observable
Inputs
(Level 2)
 
Significant Other
Unobservable
Inputs
(Level 3)
 
Measured at NAV(a)
 
Total
Cash and cash equivalents
$
53

 
$
—

 
$
—

 
$
—

 
$
53

Equity securities:
 
 
 
 
 
 
 
 
 
U.S. large-capitalization
291

 
—

 
—

 
101

 
392

U.S. small- and mid-capitalization
72

 
—

 
—

 
—

 
72

International
40

 
—

 
—

 
92

 
132

Other
—

 
7

 
—

 
—

 
7

Debt securities:
 
 
 
 
 
 
 
 
 
Corporate bonds
—

 
141

 
—

 
—

 
141

Municipal bonds
—

 
110

 
—

 
—

 
110

U.S. Treasury and agency securities
—

 
68

 
—

 
—

 
68

Other
—

 
—

 
—

 
19

 
19

Total
$
456

 
$
326

 
$
—

 
$
212

 
$
994

Plus: Medical benefit assets at December 31(b)
 
 
 
 
 
 
 
 
132

Less: Net payables at December 31(c)
 
 
 
 
 
 
 
 
(25
)
Fair value of postretirement benefit plans assets at year end
 
 
 
 
 
 
 
 
$
1,101

(a)
Reflects the adoption of the new authoritative accounting guidance related to investments measured at the NAV practical expedient. See Note 1 - Summary of Significant Accounting Policies for additional information.
(b)
Medical benefit (health and welfare) component for 401(h) accounts to fund a portion of the postretirement obligation. These 401(h) assets are included in the pension plan assets shown above.
(c)
Payables related to pending security purchases, offset by interest receivables and receivables related to pending security sales.
The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the postretirement benefit plans assets measured at fair value as of December 31, 2015:
 
Quoted Prices in
Active Markets for
Identified Assets
(Level 1)
 
Significant Other
Observable
Inputs
(Level 2)
 
Significant Other
Unobservable
Inputs
(Level 3)
 
Measured at NAV(a)
 
Total
Cash and cash equivalents
$
61

 
$
—

 
$
—

 
$
—

 
$
61

Equity securities:
 
 
 
 
 
 
 
 
 
U.S. large-capitalization
272

 
—

 
—

 
98

 
370

U.S. small- and mid-capitalization
65

 
—

 
—

 
—

 
65

International
33

 
38

 
—

 
55

 
126

Other
—

 
7

 
—

 
—

 
7

Debt securities:
 
 
 
 
 
 
 
 
 
Corporate bonds
—

 
138

 
—

 
—

 
138

Municipal bonds
—

 
114

 
—

 
—

 
114

U.S. Treasury and agency securities
—

 
55

 
—

 
—

 
55

Other
—

 
4

 
—

 
36

 
40

Total
$
431

 
$
356

 
$
—

 
$
189

 
$
976

Plus: Medical benefit assets at December 31(a)
 
 
 
 
 
 
 
 
123

Less: Net payables at December 31(b)
 
 
 
 
 
 
 
 
(28
)
Fair value of postretirement benefit plans assets at year end
 
 
 
 
 
 
 
 
$
1,071

(a)
Reflects the adoption of the new authoritative accounting guidance related to investments measured at the NAV practical expedient. See Note 1 - Summary of Significant Accounting Policies for additional information.
(b)
Medical benefit (health and welfare) component for 401(h) accounts to fund a portion of the postretirement obligation. These 401(h) assets are included in the pension plan assets shown above.
(c)
Payables related to pending security purchases, offset by Medicare, interest receivables, and receivables related to pending security sales.
Stock-Based Compensation (Tables)
Summary Of Nonvested Shares Related To Long-Term Incentive Plan 
A summary of nonvested performance share units at December 31, 2016, and changes during the year ended December 31, 2016, under the 2006 Incentive Plan and the 2014 Incentive Plan are presented below:
  
Performance Share Units
  
Share
Units
 
Weighted-average
Fair Value per Share Unit
Nonvested at January 1, 2016
1,024,870

 
$
46.08

Granted(a)
588,615

 
44.13

Forfeitures
(15,949
)
 
45.07

Earned and vested(b)
(537,897
)
 
40.12

Nonvested at December 31, 2016
1,059,639

 
$
48.04

(a)
Includes performance share units (share units) granted to certain executive and nonexecutive officers and other eligible employees in 2016 under the 2014 Incentive Plan.
(b)
Includes share units granted in 2014 that vested as of December 31, 2016 and were earned pursuant to the terms of the award grants. Also includes share units that vested due to attainment of retirement eligibility by certain employees. Actual shares issued for retirement-eligible employees will vary depending on actual performance over the three-year measurement period.
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block] 
The following table presents the stock-based compensation expense for the years ended December 31, 2016, 2015 and 2014:
 
2016
 
2015
 
2014
Ameren Missouri
$
4

 
$
5

 
$
5

Ameren Illinois
2

 
3

 
2

Other(a)
11

 
11

 
12

Ameren
17

 
19

 
19

Less income tax benefit
6

 
7

 
7

Stock-based compensation expense, net
$
11

 
$
12

 
$
12

(a)
Represents compensation expense of employees of Ameren Services. These amounts are not included in the Ameren Missouri and Ameren Illinois amounts above.
Income Taxes (Tables)
Schedule Of Effective Income Tax Rate Reconciliation 
The following table presents the principal reasons for the difference between the effective income tax rate and the statutory federal income tax rate for the years ended December 31, 2016, 2015, and 2014:
 
Ameren Missouri
 
Ameren Illinois
 
Ameren
2016
 
 
 
 
 
Statutory federal income tax rate:
35
 %
 
35
 %
 
35
 %
Increases (decreases) from:
 
 
 
 
 
Depreciation differences
1

 
—

 
—

Amortization of deferred investment tax credit
(1
)
 
—

 
—

State tax
3

 
5

 
4

Stock-based compensation(a)
—

 
—

 
(2
)
Valuation allowance
—

 
—

 
1

Other permanent items
—

 
(2
)
 
(1
)
Effective income tax rate
38
 %
 
38
 %
 
37
 %
2015
 
 
 
 
 
Statutory federal income tax rate:
35
 %
 
35
 %
 
35
 %
Increases (decreases) from:
 
 
 
 
 
Depreciation differences
—

 
(2
)
 
(1
)
Amortization of deferred investment tax credit
(1
)
 
—

 
(1
)
State tax
3

 
5

 
5

Other permanent items
—

 
(1
)
 
—

Effective income tax rate
37
 %
 
37
 %
 
38
 %
2014
 
 
 
 
 
Statutory federal income tax rate:
35
 %
 
35
 %
 
35
 %
Increases (decreases) from:
 
 
 
 
 
Amortization of deferred investment tax credit
(1
)
 
—

 
(1
)
State tax
3

 
6

 
4

Other permanent items
—

 
—

 
1

Effective income tax rate
37
 %
 
41
 %
 
39
 %

(a)
Reflects the adoption of new authoritative accounting guidance related to share-based compensation. See Note 1 – Summary of Significant Accounting Policies for more information.
Schedule Of Components Of Income Tax Expense (Benefit) 
The following table presents the components of income tax expense (benefit) for the years ended December 31, 2016, 2015, and 2014:
 
Ameren Missouri
 
Ameren Illinois
 
Other
 
Ameren
2016
 
 
 
 
 
 
 
Current taxes:
 
 
 
 
 
 
 
Federal
$
31

 
$
(8
)
 
$
(24
)
 
$
(1
)
State
6

 
12

 
(21
)
 
(3
)
Deferred taxes:
 
 
 
 
 
 
 
Federal
161

 
117

 
21

 
299

State
23

 
37

 
32

 
92

Amortization of deferred investment tax credits
(5
)
 
—

 
—

 
(5
)
Total income tax expense
$
216

 
$
158

 
$
8

 
$
382

2015
 
 
 
 
 
 
 
Current taxes:
 
 
 
 
 
 
 
Federal
$
110

 
$
(83
)
 
$
(29
)
 
$
(2
)
State
17

 
(11
)
 
(10
)
 
(4
)
Deferred taxes:
 
 
 
 
 
 
 
Federal
71

 
193

 
35

 
299

State
16

 
29

 
31

 
76

Amortization of deferred investment tax credits
(5
)
 
(1
)
 
—

 
(6
)
Total income tax expense
$
209

 
$
127

 
$
27

 
$
363

2014
 
 
 
 
 
 
 
Current taxes:
 
 
 
 
 
 
 
Federal
$
(13
)
 
$
(51
)
 
$
27

 
$
(37
)
State
(3
)
 
(2
)
 
(32
)
 
(37
)
Deferred taxes:
 
 
 
 
 
 
 
Federal
222

 
159

 
(12
)
 
369

State
28

 
38

 
22

 
88

Amortization of deferred investment tax credits
(5
)
 
(1
)
 
—

 
(6
)
Total income tax expense (benefit)
$
229

 
$
143

 
$
5

 
$
377


Schedule Of Deferred Tax Assets And Liabilities Resulting From Temporary Differences 
The following table presents the deferred tax assets and deferred tax liabilities recorded as a result of temporary differences at December 31, 2016 and 2015:
 
Ameren Missouri
 
Ameren Illinois
 
Other
 
Ameren
2016
 
 
 
 
 
 
 
Accumulated deferred income taxes, net liability (asset):
 
 
 
 
 
 
 
Plant related
$
3,103

 
$
1,769

 
$
147

 
$
5,019

Regulatory assets, net
75

 
(1
)
 
—

 
74

Deferred employee benefit costs
(76
)
 
(38
)
 
(97
)
 
(211
)
Revenue requirement reconciliation adjustments
—

 
34

 
—

 
34

Tax carryforwards
(66
)
 
(138
)
 
(472
)
 
(676
)
Other
(23
)
 
5

 
42

 
24

Total net accumulated deferred income tax liabilities (assets)
$
3,013

 
$
1,631

 
$
(380
)
 
$
4,264

2015
 
 
 
 
 
 
 
Accumulated deferred income taxes, net liability (asset):
 
 
 
 
 
 
 
Plant related
$
2,931

 
$
1,587

 
$
37

 
$
4,555

Regulatory assets, net
81

 
(1
)
 
—

 
80

Deferred employee benefit costs
(76
)
 
(40
)
 
(91
)
 
(207
)
Revenue requirement reconciliation adjustments
—

 
66

 
—

 
66

Tax carryforwards
(65
)
 
(133
)
 
(405
)
 
(603
)
Other
(27
)
 
1

 
20

 
(6
)
Total net accumulated deferred income tax liabilities (assets)
$
2,844

 
$
1,480

 
$
(439
)
 
$
3,885

Schedule Of Net Operating Loss Carryforwards And Tax Credit Carryforwards 
The following table presents the components of deferred tax assets relating to net operating loss carryforwards, tax credit carryforwards, and charitable contribution carryforwards at December 31, 2016 and 2015:
 
Ameren Missouri
 
Ameren Illinois
 
Other
 
Ameren
2016
 
 
 
 
 
 
 
Net operating loss carryforwards:
 
 
 
 
 
 
 
Federal(a)
$
33

 
$
137

 
$
324

 
$
494

State(a)
4

 
—

 
41

 
45

Total net operating loss carryforwards
$
37

 
$
137

 
$
365

 
$
539

Tax credit carryforwards:
 
 
 
 
 
 
 
Federal(a)
$
29

 
$
1

 
$
79

 
$
109

State(b)
—

 
—

 
21

 
21

Total tax credit carryforwards
$
29

 
$
1

 
$
100

 
$
130

Charitable contribution carryforwards(b)
$
—

 
$
—

 
$
18

 
$
18

Valuation allowance(c)
—

 
—

 
(11
)
 
(11
)
Total charitable contribution carryforwards
$
—

 
$
—

 
$
7

 
$
7

2015
 
 
 
 
 
 
 
Net operating loss carryforwards:
 
 
 
 
 
 
 
Federal
$
35

 
$
127

 
$
245

 
$
407

State
4

 
4

 
38

 
46

Total net operating loss carryforwards
$
39

 
$
131

 
$
283

 
$
453

Tax credit carryforwards:
 
 
 
 
 
 
 
Federal
$
26

 
$
1

 
$
78

 
$
105

State
—

 
1

 
40

 
41

State valuation allowance
—

 
—

 
(2
)
 
(2
)
Total tax credit carryforwards
$
26

 
$
2

 
$
116

 
$
144

Charitable contribution carryforwards
$
—

 
$
—

 
$
10

 
$
10

Valuation allowance
—

 
—

 
(4
)
 
(4
)
Total charitable contribution carryforwards
$
—

 
$
—

 
$
6

 
$
6


(a)
Will expire between 2029 and 2036.
(b)
Will expire between 2017 and 2021.
(c)
See Schedule II under Part IV, Item 15, in this report for information on changes in the valuation allowance.
Related Party Transactions (Tables)
Schedule of Related Party Transactions
The following table presents the agreements the companies have entered into, as well as the specified time period, price, and amount of megawatthours included in each agreement:
IPA
 Procurement Event
Time Period
MWh
 
Average Price per MWh
May 2014
January 2015 – February 2017
168,400

$
51
April 2015
June 2015 – June 2017
667,000

 
36
September 2015
November 2015 – May 2018
339,000

 
38
April 2016
June 2017 – September 2018
375,200

 
35
September 2016
May 2017 – September 2018
82,800

 
34
The following table presents the impact on Ameren Missouri and Ameren Illinois of related party transactions for the years ended December 31, 2016, 2015, and 2014. It is based primarily on the agreements discussed above and the money pool arrangements discussed in Note 4 – Short-term Debt and Liquidity.
Agreement
Income Statement Line Item                    
 
  
 
Ameren
Missouri
 
Ameren
Illinois
Ameren Missouri power supply agreements
Operating Revenues
 
2016
$
28

$
(a)

with Ameren Illinois
 
 
2015
 
15

 
(a)

 
 
 
2014
 
5

 
(a)

Ameren Missouri and Ameren Illinois
Operating Revenues
 
2016
 
25

 
5

rent and facility services
 
 
2015
 
25

 
4

 
 
 
2014
 
21

 
2

Ameren Missouri and Ameren Illinois
Operating Revenues
 
2016
 
1

 
(b)

miscellaneous support services
 
 
2015
 
2

 
(b)

 
 
 
2014
 
1

 
(b)

Total Operating Revenues
 
 
2016
$
54

$
5

 
 
 
2015
 
42

 
4

 
 
 
2014
 
27

 
2

Ameren Illinois power supply
Purchased Power
 
2016
$
(a)

$
28

agreements with Ameren Missouri
 
 
2015
 
(a)

 
15

 
 
 
2014
 
(a)

 
5

Ameren Illinois transmission
Purchased Power
 
2016
 
(a)

 
2

services from ATXI
 
 
2015
 
(a)

 
2

 
 
 
2014
 
(a)

 
2

Total Purchased Power
 
 
2016
$
(a)

$
30

 
 
 
2015
 
(a)

 
17

 
 
 
2014
 
(a)

 
7

Ameren Services support services
Other Operations and
 
2016
$
129

$
123

agreement
Maintenance
 
2015
 
131

 
119

 
 
 
2014
 
124

 
109

Money pool borrowings (advances)
Interest (Charges)
 
2016
$
(b)

$
(b)

 
Income
 
2015
 
(b)

 
(b)

 
 
 
2014
 
(b)

 
(b)

(a)
Not applicable.
(b)
Amount less than $1 million.

Commitments And Contingencies (Tables)
Schedule Of Insurance Coverage At Callaway Energy Center 
The following table presents insurance coverage at Ameren Missouri’s Callaway energy center at December 31, 2016. The property coverage and the nuclear liability coverage renewal dates are April 1 and January 1, respectively, of each year.
Type and Source of Coverage
Maximum Coverages
 
Maximum Assessments
 
Public liability and nuclear worker liability:
 
 
 
 
American Nuclear Insurers
$
375

(a) 
$
—

 
Pool participation
12,986

(b)  
127

(c)  
 
$
13,361

(d)  
$
127

 
Property damage:
 
 
 
 
Nuclear Electric Insurance Limited
$
2,710

(e)  
$
30

(f)  
European Mutual Association for Nuclear Insurance
450

(g)  
—

 
 
$
3,160

 
$
30

 
Replacement power:
 
 
 
 
Nuclear Electric Insurance Limited
$
490

(h)  
$
7

(f)  

(a)
Effective January 1, 2017, limit was increased to $450 million.
(b)
Provided through mandatory participation in an industrywide retrospective premium assessment program.
(c)
Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $375 million in the event of an incident at any licensed United States commercial reactor, payable at $19 million per year.
(d)
Limit of liability for each incident under the Price-Anderson liability provisions of the Atomic Energy Act of 1954, as amended. A company could be assessed up to $127 million per incident for each licensed reactor it operates, with a maximum of $19 million per incident to be paid in a calendar year for each reactor. This limit is subject to change to account for the effects of inflation and changes in the number of licensed reactors.
(e)
NEIL provides $2.71 billion in property damage, decontamination, and premature decommissioning insurance for radiation events. NEIL provides $2.3 billion in property damage for nonradiation events.
(f)
All NEIL-insured plants could be subject to assessments should losses exceed the accumulated funds from NEIL.
(g)
European Mutual Association for Nuclear Insurance provides $450 million in excess of the $2.71 billion and $2.3 billion property coverage for radiation and nonradiation events, respectively, provided by NEIL.
(h)
Provides replacement power cost insurance in the event of a prolonged accidental outage. Weekly indemnity is up to $4.5 million for 52 weeks, which commences after the first 12 weeks of an outage, plus up to $3.6 million per week for a minimum of 71 weeks thereafter, for a total not exceeding the policy limit of $490 million. Nonradiation events are sub-limited to $328 million.
Schedule Of Lease Obligations 
We lease various facilities, office equipment, plant equipment, and rail cars under capital and operating leases. The following table presents our lease obligations at December 31, 2016:
 
2017
 
2018
 
2019
 
2020
 
2021
 
After 5 Years
 
Total
Ameren:(a)
 
 
 
 
 
 
 
 
 
 
 
 
 
Minimum capital lease payments(b)
$
33

 
$
32

 
$
32

 
$
32

 
$
32

 
$
297

 
$
458

Less amount representing interest
27

 
26

 
25

 
25

 
25

 
48

 
176

Present value of minimum capital lease payments
$
6

 
$
6

 
$
7

 
$
7

 
$
7

 
$
249

 
$
282

Operating leases(c)
13

 
12

 
12

 
11

 
10

 
23

 
81

Total lease obligations
$
19

 
$
18

 
$
19

 
$
18

 
$
17

 
$
272

 
$
363

Ameren Missouri:
 
 
 
 
 
 
 
 
 
 
 
 
 
Minimum capital lease payments(b)
$
33

 
$
32

 
$
32

 
$
32

 
$
32

 
$
297

 
$
458

Less amount representing interest
27

 
26

 
25

 
25

 
25

 
48

 
176

Present value of minimum capital lease payments
$
6

 
$
6

 
$
7

 
$
7

 
$
7

 
$
249

 
$
282

Operating leases(c)
11

 
11

 
11

 
10

 
9

 
21

 
73

Total lease obligations
$
17

 
$
17

 
$
18

 
$
17

 
$
16

 
$
270

 
$
355

Ameren Illinois:
 
 
 
 
 
 
 
 
 
 
 
 
 
Operating leases(c)
$
1

 
$
1

 
$
1

 
$
1

 
$
1

 
$
1

 
$
6

(a)
Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
(b)
See Properties under Part I, Item 2, and Note 3 – Property, Plant, and Equipment, Net, of this report for additional information.
(c)
Amounts related to certain land-related leases have indefinite payment periods. The annual obligations of $3 million, $2 million, and $1 million for Ameren, Ameren Missouri, and Ameren Illinois for these items are included in the 2017 through 2021 columns, respectively.
Schedule Of Rental Expense 
The following table presents total rental expense included in operating expenses for the years ended December 31, 2016, 2015, and 2014:
 
2016
 
2015
 
2014
Ameren(a)
$
38

 
$
36

 
$
37

Ameren Missouri
34

 
34

 
32

Ameren Illinois
30

 
28

 
25

(a)
Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
Schedule Of Estimated Purchased Commitments 
December 31, 2016. Ameren’s and Ameren Missouri’s purchased power commitments include a 102-megawatt power purchase agreement with a wind farm operator, which expires in 2024. Ameren’s and Ameren Illinois’ purchased power commitments include the Ameren Illinois power purchase agreements entered into as part of the IPA-administered power procurement process. Included in the Other column are minimum purchase commitments under contracts for equipment, design and construction, and meter reading services at December 31, 2016.
 
Coal
 
Natural
Gas(a)
 
Nuclear
Fuel
 
Purchased
Power(b)
 
Methane
Gas
 
Other
 
Total
Ameren:(c)
 
 
 
 
 
 
 
 
 
 
 
 
 
2017
$
599

 
$
238

 
$
45

 
$
255

 
$
3

 
$
118

 
$
1,258

2018
371

 
167

 
70

 
156

 
4

 
60

 
828

2019
311

 
99

 
27

 
79

 
4

 
60

 
580

2020
27

 
45

 
38

 
58

 
5

 
56

 
229

2021
—

 
12

 
44

 
58

 
5

 
29

 
148

Thereafter
—

 
43

 
45

 
478

 
65

 
198

 
829

Total
$
1,308

 
$
604

 
$
269

 
$
1,084

 
$
86

 
$
521

 
$
3,872

Ameren Missouri:
 
 
 
 
 
 
 
 
 
 
 
 
 
2017
$
599

 
$
43

 
$
45

 
$
22

 
$
3

 
$
39

 
$
751

2018
371

 
29

 
70

 
22

 
4

 
29

 
525

2019
311

 
15

 
27

 
22

 
4

 
29

 
408

2020
27

 
10

 
38

 
22

 
5

 
29

 
131

2021
—

 
5

 
44

 
22

 
5

 
28

 
104

Thereafter
—

 
18

 
45

 
59

 
65

 
183

 
370

Total
$
1,308

 
$
120

 
$
269

 
$
169

 
$
86

 
$
337

 
$
2,289

Ameren Illinois:
 
 
 
 
 
 
 
 
 
 
 
 
 
2017
$
—

 
$
195

 
$
—

 
$
233

 
$
—

 
$
36

 
$
464

2018
—

 
138

 
—

 
134

 
—

 
24

 
296

2019
—

 
83

 
—

 
57

 
—

 
27

 
167

2020
—

 
35

 
—

 
36

 
—

 
27

 
98

2021
—

 
8

 
—

 
36

 
—

 
—

 
44

Thereafter
—

 
25

 
—

 
419

 
—

 
—

 
444

Total
$
—

 
$
484

 
$
—

 
$
915

 
$
—

 
$
114

 
$
1,513

(a)
Includes amounts for generation and for distribution.
(b)
The purchased power amounts for Ameren and Ameren Illinois include agreements through 2032 for renewable energy credits with various renewable energy suppliers. The agreements contain a provision that allows Ameren Illinois to reduce the quantity purchased in the event that Ameren Illinois would not be able to recover the costs associated with the renewable energy credits.
(c)
Includes amounts for Ameren registrant and nonregistrant subsidiaries.
Segment Information (Tables)
Schedule Of Segment Reporting Information, By Segment
The following tables present information about the reported revenues and specified items reflected in net income attributable to common shareholders from continuing operations and capital expenditures at Ameren and Ameren Illinois for the years ended December 31, 2016, 2015, and 2014. Ameren, Ameren Missouri, and Ameren Illinois management review segment capital expenditure information rather than any individual or total asset amount.
Ameren
 
Ameren Missouri
 
Ameren Illinois Electric Distribution
 
Ameren Illinois Natural Gas
 
Ameren Transmission
 
Other
 
Intersegment
Eliminations
 
Consolidated
2016
 
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
$
3,469

 
$
1,545

 
$
753

 
$
309

 
$
—

 
$
—

 
$
6,076

Intersegment revenues
54

 
4

 
1

 
46

(a) 
—

 
(105
)
 
—

Depreciation and amortization
514

 
226

 
55

 
43

 
7

 
—

 
845

Interest income
28

 
11

 
—

 
1

 
11

 
(11
)
 
40

Interest charges
211

 
72

 
34

 
58

 
18

 
(11
)
 
382

Income taxes
216

 
78

 
39

 
74

 
(25
)
 
—

 
382

Net income (loss) attributable to Ameren common shareholders from continuing operations
357

 
126

 
59

 
117

 
(6
)
 
—

 
653

Capital expenditures
738

 
470

 
181

 
689

 
4

(b) 
(6
)
 
2,076

2015
 
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
$
3,566

 
$
1,529

 
$
782

 
$
219

 
$
2

 
$
—

 
$
6,098

Intersegment revenues
43

 
3

 
1

 
40

(a) 
—

 
(87
)
 
—

Depreciation and amortization
492

 
212

 
52

 
33

 
7

 
—

 
796

Interest income
28

 
12

 
—

 
—

 
7

 
(6
)
 
41

Interest charges
219

 
71

 
35

 
35

 
1

 
(6
)
 
355

Income taxes
209

 
71

 
24

 
51

 
8

 
—

 
363

Net income (loss) attributable to Ameren common shareholders from continuing operations
352

 
123

 
37

 
83

 
(16
)
 
—

 
579

Capital expenditures
622

 
491

 
133

 
669

 
2

(b) 
—

 
1,917

2014
 
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
$
3,526

 
$
1,401

 
$
976

 
$
150

 
$
—

 
$
—

 
$
6,053

Intersegment revenues
27

 
2

 
—

 
37

(a) 
—

 
(66
)
 
—

Depreciation and amortization
473

 
197

 
41

 
26

 
8

 
—

 
745

Interest income
28

 
7

 
—

 
—

 
5

 
(3
)
 
37

Interest charges
211

 
63

 
28

 
26

 
16

 
(3
)
 
341

Income taxes
229

 
75

 
39

 
38

 
(4
)
 
—

 
377

Net income (loss) attributable to Ameren common shareholders from continuing operations
390

 
113

 
50

 
51

 
(17
)
 
—

 
587

Capital expenditures
747

 
403

 
137

 
491

 
7

(b) 
—

 
1,785


(a)
Ameren Illinois Transmission earns revenue from transmission service provided to Ameren Illinois Electric Distribution. See discussion of transactions above.
(b)
Includes the elimination of intercompany transfers.    


Ameren Illinois
 
Ameren Illinois Electric Distribution
 
Ameren Illinois Natural Gas
 
Ameren Illinois Transmission
 
Intersegment
Eliminations
 
Consolidated
 
2016
 
 
 
 
 
 
 
 
 
 
External revenues
$
1,549

 
$
754

 
$
187

 
$
—

 
$
2,490

 
Intersegment revenues
—

 
—

 
45

(a) 
(45
)
 
—

 
Depreciation and amortization
226

 
55

 
38

 
—

 
319

 
Interest income
11

 
—

 
1

 
—

 
12

 
Interest charges
72

 
34

 
34

 
—

 
140

 
Income taxes
78

 
39

 
41

 
—

 
158

 
Net income available to common shareholder
126

 
59

 
67

 
—

 
252

 
Capital expenditures
470

 
181

 
273

 
—

 
924

 
2015
 
 
 
 
 
 
 
 
 
 
External revenues
$
1,532

 
$
783

 
$
151

 
$
—

 
$
2,466

 
Intersegment revenues
—

 
—

 
38

(a) 
(38
)
 
—

 
Depreciation and amortization
212

 
52

 
31

 
—

 
295

 
Interest income
12

 
—

 
—

 
—

 
12

 
Interest charges
71

 
35

 
25

 
—

 
131

 
Income taxes
71

 
24

 
32

 
—

 
127

 
Net income available to common shareholder
123

 
37

 
54

 
—

 
214

 
Capital expenditures
491

 
133

 
294

 
—

 
918

 
2014
 
 
 
 
 
 
 
 
 
 
External revenues
$
1,403

 
$
976

 
$
119

 
$
—

 
$
2,498

 
Intersegment revenues
—

 
—

 
35

(a) 
(35
)
 
—

 
Depreciation and amortization
197

 
41

 
25

 
—

 
263

 
Interest income
7

 
—

 
—

 
—

 
7

 
Interest charges
63

 
28

 
21

 
—

 
112

 
Income taxes
75

 
39

 
29

 
—

 
143

 
Net income available to common shareholder
113

 
50

 
38

 
—

 
201

 
Capital expenditures
403

 
137

 
295

 
—

 
835

 
(a)
Ameren Illinois Transmission earns revenue from transmission service provided to Ameren Illinois Electric Distribution. See discussion of transactions above.
Selected Quarterly Information (Tables)
Summary Of Selected Quarterly Information
SELECTED QUARTERLY INFORMATION (Unaudited) (In millions, except per share amounts)
Ameren
2016
 
 
2015
Quarter ended
March 31
 
June 30
 
September 30
 
December 31
 
 
March 31
 
June 30
 
September 30
 
December 31
Operating revenues
$
1,434

 
$
1,427

 
$
1,859

 
$
1,356

 
 
$
1,556

 
$
1,401

 
$
1,833

 
$
1,308

Operating income
220

 
325

 
691

 
145

 
 
256

 
237

 
626

 
140

Net income
107

 
148

 
371

 
33

 
 
110

 
151

 
345

 
30

Net income attributable to Ameren common shareholders – continuing operations
$
105

 
$
147

 
$
369

 
$
32

 
 
$
108

 
$
98

 
$
343

 
$
30

Net income (loss) attributable to Ameren common shareholders – discontinued operations
—

 
—

 
—

 
—

 
 
—

 
52

 
—

 
(1
)
Net income attributable to Ameren common shareholders
$
105

 
$
147

 
$
369

 
$
32

 
 
$
108

 
$
150

 
$
343

 
$
29

Earnings per common share – basic – continuing operations
$
0.43

 
$
0.61

 
$
1.52

 
$
0.13

 
 
$
0.45

 
$
0.40

 
$
1.42

 
$
0.12

Earnings per common share – basic – discontinued operations
—

 
—

 
—

 
—

 
 
—

 
0.21

 
—

 
—

Earnings per common share – basic
$
0.43

 
$
0.61

 
$
1.52

 
$
0.13

 
 
$
0.45

 
$
0.61

 
$
1.42

 
$
0.12

Earnings per common share – diluted – continuing operations(a)
$
0.43

 
$
0.61

 
$
1.52

 
$
0.13

 
 
$
0.45

 
$
0.40

 
$
1.41

 
$
0.12

Earnings per common share – diluted – discontinued operations
—

 
—

 
—

 
—

 
 
—

 
0.21

 
—

 
—

Earnings per common share – diluted(a)
$
0.43

 
$
0.61

 
$
1.52

 
$
0.13

 
 
$
0.45

 
$
0.61

 
$
1.41

 
$
0.12

(a)
The sum of quarterly amounts, including per share amounts, may not equal amounts reported for year-to-date periods. This is because of the effects of rounding and the changes in the number of weighted-average diluted shares outstanding each period.
Ameren Missouri Quarter ended
 
Operating
Revenues
 
Operating
Income
 
Net Income
 
Net Income
Available
to Common
Shareholder
March 31, 2016
 
$
741

 
$
63

 
$
15

 
$
14

March 31, 2015
 
800

 
115

 
42

 
41

June 30, 2016
 
867

 
197

 
93

 
92

June 30, 2015
 
884

 
146

 
62

 
61

September 30, 2016
 
1,165

 
431

 
242

 
241

September 30, 2015
 
1,171

 
423

 
240

 
239

December 31, 2016
 
750

 
54

 
10

 
10

December 31, 2015
 
754

 
58

 
11

 
11


Ameren Illinois Quarter ended
 
Operating
Revenues
 
Operating
Income
 
Net Income
 
Net Income
Available
to Common
Shareholder
March 31, 2016
 
$
677

 
$
133

 
$
60

 
$
59

March 31, 2015
 
745

 
120

 
54

 
53

June 30, 2016
 
542

 
107

 
46

 
45

June 30, 2015
 
513

 
83

 
32

 
31

September 30, 2016
 
676

 
230

 
119

 
119

September 30, 2015
 
655

 
189

 
98

 
98

December 31, 2016
 
595

 
74

 
30

 
29

December 31, 2015
 
553

 
74

 
33

 
32

Summary Of Significant Accounting Policies (Narrative) (Details) (USD $)
In Millions, except Per Share data, unless otherwise specified
12 Months Ended 12 Months Ended 1 Months Ended 3 Months Ended 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2016
Ameren Illinois Company
sqmi
people
Dec. 31, 2015
Ameren Illinois Company
Dec. 31, 2014
Ameren Illinois Company
Dec. 31, 2016
Union Electric Company
sqmi
people
Dec. 31, 2015
Union Electric Company
Dec. 31, 2014
Union Electric Company
Dec. 31, 2016
Minimum
Dec. 31, 2015
Minimum
Dec. 31, 2014
Minimum
Dec. 31, 2016
Maximum
Dec. 31, 2015
Maximum
Dec. 31, 2014
Maximum
Dec. 31, 2016
Power
Ameren Illinois Company
customer
Dec. 31, 2016
Power
Union Electric Company
customer
Dec. 31, 2016
Natural Gas
Ameren Illinois Company
customer
Dec. 31, 2016
Natural Gas
Union Electric Company
customer
Dec. 31, 2016
FAC
Union Electric Company
Dec. 31, 2015
State
Dec. 31, 2014
State
Jan. 31, 2014
Elgin, Gibson City and Grand Tower Energy Centers [Member]
Dec. 31, 2013
Elgin, Gibson City and Grand Tower Energy Centers [Member]
Dec. 31, 2015
Elgin, Gibson City and Grand Tower Energy Centers [Member]
Dec. 31, 2016
Asbestos-Related
Dec. 31, 2016
Asbestos-Related
Ameren Illinois Company
Dec. 31, 2016
Ameren Illinois Electric Distribution [Member]
Dec. 31, 2016
Ameren Illinois Gas [Member]
Dec. 31, 2016
Ameren Illinois Transmission [Member]
Dec. 31, 2016
Ameren Transmission [Member]
Accounting Policies [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Public Utilities, Area Serviced
 
 
 
40,000 
 
 
24,000 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Public Utilities, Estimated Population of Service Territory
 
 
 
3,100,000 
 
 
2,800,000 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Public Utilities, Number of Customers
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1,200,000 
1,200,000 
800,000 
100,000 
 
 
 
 
 
 
 
 
 
 
 
 
Asbestos trust fund balance
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
$ 22 
$ 22 
 
 
 
 
Percent of difference to be contributed to the asbestos trust fund if cash expenditures are less than amount included in base electric rates.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
90.00% 
 
 
 
 
 
Sharing Level For Fac
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
95.00% 
 
 
 
 
 
 
 
 
 
 
 
Percent of average depreciable cost
 
 
 
 
 
 
 
 
 
3.00% 
3.00% 
3.00% 
4.00% 
4.00% 
4.00% 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Goodwill
411 
411 
 
411 
411 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
238 
80 
93 
93 
Capital contribution from parent
 
 
 
0 
25 
15 
44 
224 
215 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Noncash Or Part Noncash Capital Contribution From Parent
 
 
 
 
 
 
0 
38 
9 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Return of capital to parent
 
 
 
 
 
 
0 
0 
(215)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Proceeds from Sales of Business, Affiliate and Productive Assets
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
168.0 
137.5 
 
 
 
 
 
 
 
Proceeds from Asset Sale Held in Escrow
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
14 
 
 
 
 
 
 
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities
 
 
18 
 
 
 
 
 
18 
 
 
 
 
 
 
 
 
 
 
 
53 
2 
 
 
 
 
 
 
 
 
 
Adjustments related to Income Tax Benefit from Share-Based Payment
21 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Adjustments related to Income Tax Benefit from Share-Based payment per diluted share
$ 0.09 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Excess Tax Benefit from Share-Based Compensation
 
2 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Payments Related to Tax Withholding for Share-based Compensation
$ 83 
$ 12 
$ 14 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Percentage reporting unit exceeded carrying value
40.00% 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Summary Of Significant Accounting Policies (Schedule Of Inventories) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Dec. 31, 2015
Accounting Policies [Line Items]
 
 
Fuel
$ 172 1
$ 173 1
Gas stored underground
82 
97 
Other materials and supplies
273 
268 
Total Inventories
527 
538 
Union Electric Company
 
 
Accounting Policies [Line Items]
 
 
Fuel
172 1
173 1
Gas stored underground
9 
10 
Other materials and supplies
211 
204 
Total Inventories
392 
387 
Ameren Illinois Company
 
 
Accounting Policies [Line Items]
 
 
Fuel
0 1
0 1
Gas stored underground
73 
87 
Other materials and supplies
62 
64 
Total Inventories
$ 135 
$ 151 
Summary Of Significant Accounting Policies (Schedule Of Rates Used For Allowance For Funds Used During Construction) (Details)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Union Electric Company
 
 
 
Accounting Policies [Line Items]
 
 
 
Allowance for funds used during construction, rate
7.00% 
7.00% 
7.00% 
Ameren Illinois Company
 
 
 
Accounting Policies [Line Items]
 
 
 
Allowance for funds used during construction, rate
5.00% 
6.00% 
2.00% 
Summary Of Significant Accounting Policies (Schedule Of Asset Retirement Obligations) (Details) (USD $)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
 
 
 
Balance
$ 623,000,000 1
$ 396,000,000 
 
Liabilities incurred
3,000,000 
3,000,000 
 
Liabilities settled
(2,000,000)
(2,000,000)
 
Accretion in period
25,000,000 2
23,000,000 2
 
Change in estimates
1,000,000 
203,000,000 3
 
Balance
650,000,000 1
623,000,000 1
 
Other current liabilities
248,000,000 
279,000,000 
 
Callaway energy center decommissioning study [Member]
 
 
 
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
 
 
 
Change in estimates
99,000,000 
 
 
New CCR Rules Estimate [Member]
 
 
 
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
 
 
 
Change in estimates
100,000,000 
 
 
Other Estimate Changes [Member]
 
 
 
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
 
 
 
Change in estimates
4,000,000 
 
 
Asset Retirement Obligation Balance [Member]
 
 
 
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
 
 
 
Other current liabilities
15,000,000 
5,000,000 
 
Union Electric Company
 
 
 
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
 
 
 
Balance
617,000,000 1
389,000,000 
 
Liabilities incurred
3,000,000 
3,000,000 
 
Liabilities settled
(2,000,000)
(1,000,000)
 
Accretion in period
25,000,000 2
23,000,000 2
 
Change in estimates
1,000,000 
203,000,000 3
 
Balance
644,000,000 1
617,000,000 1
 
Other current liabilities
123,000,000 
120,000,000 
 
Ameren Illinois Company
 
 
 
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
 
 
 
Balance
6,000,000 4
7,000,000 
 
Liabilities incurred
0 
0 
 
Liabilities settled
(1,000,000)5
(1,000,000)
 
Accretion in period
1,000,000 2 5
1,000,000 2 5
 
Change in estimates
0 
1,000,000 3 5
 
Balance
6,000,000 4
6,000,000 4
 
Other current liabilities
94,000,000 
86,000,000 
 
Asset Retirement Obligation |
Union Electric Company
 
 
 
Asset Retirement Obligation [Line Items]
 
 
 
Noncash Depreciation related to ARO
$ 31,000,000 
$ 13,000,000 
$ 1,000,000 
[3] (c)The ARO increase resulted in a corresponding increase recorded to "Property, Plant, and Equipment, Net." Ameren and Ameren Missouri increased their AROs related to the decommissioning of the Callaway energy center by $99 million to reflect the 2015 cost study and funding analysis filed with the MoPSC, the extension of the estimated operating life until 2044, and a reduction in the discount rate assumption. See Note 10 – Callaway Energy Center for additional information. In addition, as a result of new federal regulations, Ameren and Ameren Missouri recorded an increase of $100 million to their AROs associated with CCR storage facilities. See Note 15 – Commitments and Contingencies for additional information. Ameren and Ameren Missouri also increased their AROs by $4 million due to a change in the estimated retirement dates of the Meramec and Rush Island energy centers as a result of the MoPSC's April 2015 electric rate order.
Summary Of Significant Accounting Policies (Schedule Of Excise Taxes) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Accounting Policies [Line Items]
 
 
 
Excise tax expense
$ 208 
$ 213 
$ 215 
Union Electric Company
 
 
 
Accounting Policies [Line Items]
 
 
 
Excise tax expense
151 
156 
151 
Ameren Illinois Company
 
 
 
Accounting Policies [Line Items]
 
 
 
Excise tax expense
$ 57 
$ 57 
$ 64 
Summary Of Significant Accounting Policies (Basic and Diluted Earnings Per Share Calculations) (Details)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Accounting Policies [Abstract]
 
 
 
Assumed Settlement of Performance Share Units
800,000 
1,000,000 
1,800,000 
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount
0 
0 
0 
Rate And Regulatory Matters Rate and Regulatory Matters (Narrative-Missouri) (Details) (USD $)
12 Months Ended
Dec. 31, 2016
mi
Ameren Transmission Company of Illinois [Member] |
Mark Twain Project [Member]
 
Public Utilities, General Disclosures [Line Items]
 
Transmission Line Miles
95 
Pending Rate Case [Member] |
Union Electric Company |
Electric Distribution
 
Public Utilities, General Disclosures [Line Items]
 
Revenue Requirement
$ 3,400,000,000 
Public Utilities, Requested Rate Increase (Decrease), Amount
92,000,000 
Components of Rate Increase - Net Energy Costs [Member] |
Union Electric Company |
Electric Distribution
 
Public Utilities, General Disclosures [Line Items]
 
Public Utilities, Requested Rate Increase (Decrease), Amount
54,000,000 
Components of Rate Increase - Regulatory Amortizations [Member] |
Union Electric Company |
Electric Distribution
 
Public Utilities, General Disclosures [Line Items]
 
Public Utilities, Requested Rate Increase (Decrease), Amount
26,000,000 
Final Rate Order |
Union Electric Company |
MEEIA |
Electric Distribution
 
Public Utilities, General Disclosures [Line Items]
 
Incentive Award if Energy Efficiency Goals Are Achieved
$ 28,000,000 
Rate And Regulatory Matters (Narrative-Illinois) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2016
Ameren Illinois Company
Dec. 31, 2015
Ameren Illinois Company
Dec. 31, 2016
FEJA [Member]
Electric Distribution
Ameren Illinois Company
Dec. 31, 2016
FEJA 2018 through 2021 [Member]
Electric Distribution
Ameren Illinois Company
Dec. 31, 2016
FEJA 2022 through 2025 [Member]
Electric Distribution
Ameren Illinois Company
Dec. 31, 2016
FEJA 2026 through 2030 [Member]
Electric Distribution
Ameren Illinois Company
Dec. 31, 2016
IEIMA
2016 IEIMA Revenue Requirement Reconciliation [Member]
Electric Distribution
Ameren Illinois Company
Dec. 31, 2016
IEIMA
2015 IEMA Revenue Requirement Reconciliation [Member]
Electric Distribution
Ameren Illinois Company
Dec. 31, 2015
IEIMA
2014 IEMA Revenue Requirement Reconciliation [Member]
Electric Distribution
Ameren Illinois Company
Dec. 31, 2016
IEIMA
Final Rate Order
Electric Distribution
Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
Regulatory assets
$ 1,437 
$ 1,382 
$ 816 
$ 771 
 
 
 
 
$ 23 
 
 
 
Current regulatory assets
149 
260 
108 
167 
 
 
 
 
 
68 
103 
 
Public Utilities, Approved Rate Increase (Decrease), Amount
 
 
 
 
 
 
 
 
 
 
 
14 
Public Utilities, Requested Equity Capital Structure, Percentage
 
 
 
 
50.00% 
 
 
 
 
 
 
 
Public Utilities, Approved Return on Equity, Percentage
 
 
 
 
5.80% 
 
 
 
 
 
 
 
Increase Decrease in Return on Equity for Energy Savings Goals
 
 
 
 
2.00% 
 
 
 
 
 
 
 
FEJA Energy Efficiency Investments
 
 
 
 
 
$ 100 
$ 107 
$ 114 
 
 
 
 
Rate And Regulatory Matters Rate and Regulatory Matters (Narrative-Federal) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended 12 Months Ended 1 Months Ended 12 Months Ended 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2016
New Nuclear Energy Center COL [Member]
Dec. 31, 2016
Ameren Illinois Company
Dec. 31, 2015
Ameren Illinois Company
Dec. 31, 2016
Union Electric Company
Dec. 31, 2015
Union Electric Company
Dec. 31, 2014
Union Electric Company
Dec. 31, 2016
Union Electric Company
New Nuclear Energy Center COL [Member]
Dec. 31, 2016
Administrative Law Judge [Member]
Midwest Independent Transmission System Operator, Inc [Member]
Dec. 31, 2016
Administrative Law Judge [Member]
Midwest Independent Transmission System Operator, Inc [Member]
Maximum
Feb. 28, 2015
Pending Ferc Case [Member]
Midwest Independent Transmission System Operator, Inc [Member]
Dec. 31, 2016
Pending Ferc Case [Member]
Midwest Independent Transmission System Operator, Inc [Member]
Dec. 31, 2016
Pending Ferc Case [Member]
Midwest Independent Transmission System Operator, Inc [Member]
Ameren Illinois Company
Dec. 31, 2016
Final Rate Order
Midwest Independent Transmission System Operator, Inc [Member]
Dec. 31, 2016
Final Rate Order
Midwest Independent Transmission System Operator, Inc [Member]
Maximum
Public Utilities, General Disclosures [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Public Utilities, Approved Return on Equity, Percentage
 
 
 
 
 
 
 
 
 
 
9.70% 
10.20% 
 
12.38% 
 
10.32% 
10.82% 
Customer Requested Rate on Equity
 
 
 
 
 
 
 
 
 
 
 
 
8.67% 
9.15% 
 
 
 
Incentive adder to FERC allowed base return on common equity
 
 
 
 
 
 
 
 
 
 
0.50% 
 
 
 
 
0.50% 
 
Current regulatory liabilities
$ 110 
$ 80 
 
 
$ 78 
$ 39 
$ 12 
$ 28 
 
 
 
 
 
$ 62 
$ 42 
 
 
Investments in Power and Distribution Projects
 
 
 
 
 
 
 
 
 
69 
 
 
 
 
 
 
 
Provision for Callaway construction and operating license
$ 0 
$ 69 
$ 0 
$ 69 
 
 
$ 0 
$ 69 
$ 0 
$ 69 
 
 
 
 
 
 
 
Rate And Regulatory Matters (Schedule Of Regulatory Assets And Liabilities) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Dec. 31, 2015
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
$ 149 
$ 260 
Regulatory assets
1,437 
1,382 
Current regulatory liabilities
110 
80 
Regulatory liabilities
1,985 
1,905 
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
35 
89 
Regulatory assets
619 
605 
Current regulatory liabilities
12 
28 
Regulatory liabilities
1,215 
1,172 
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
108 
167 
Regulatory assets
816 
771 
Current regulatory liabilities
78 
39 
Regulatory liabilities
768 
732 
Under-Recovered FAC
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
21 1 2
37 1 2
Under-Recovered FAC |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
21 1 2
37 1 2
Under-Recovered FAC |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
0 1 2
0 1 2
Under-Recovered Illinois Electric Power Costs
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
3 3
3 3
Under-Recovered Illinois Electric Power Costs |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
0 3
0 3
Under-Recovered Illinois Electric Power Costs |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
3 3
3 3
Under-Recovered PGA
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
4 3
8 3
Under-Recovered PGA |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
0 3
0 3
Under-Recovered PGA |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
4 3
8 3
MTM Derivative Losses
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
24 4
74 4
Regulatory assets
187 4
190 4
MTM Derivative Losses |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
9 4
29 4
Regulatory assets
9 4
15 4
MTM Derivative Losses |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
15 4
45 4
Regulatory assets
178 4
175 4
Energy Efficiency Rider
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
5 5
23 5
Regulatory liabilities
45 5
36 5
Energy Efficiency Rider |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
5 5
23 5
Regulatory liabilities
0 5
0 5
Energy Efficiency Rider |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
0 5
0 5
Regulatory liabilities
45 5
36 5
IEIMA
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
68 1 6
103 1 6
Regulatory assets
23 1 6
62 1 6
IEIMA |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
0 1 6
0 1 6
Regulatory assets
0 1 6
0 1 6
IEIMA |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
68 1 6
103 1 6
Regulatory assets
23 1 6
62 1 6
FERC Revenue Requirement Reconciliation
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
13 1 7
12 1 7
Regulatory assets
10 1 7
11 1 7
FERC Revenue Requirement Reconciliation |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
0 1 7
0 1 7
Regulatory assets
0 1 7
0 1 7
FERC Revenue Requirement Reconciliation |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
7 1 7
8 1 7
Regulatory assets
8 1 7
5 1 7
VBA Rider
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
11 1 8
0 1 8
VBA Rider |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
0 1 8
0 1 8
VBA Rider |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory assets
11 1 8
0 1 8
Pension And Postretirement Benefit Costs
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
494 9
297 9
Pension And Postretirement Benefit Costs |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
175 9
95 9
Pension And Postretirement Benefit Costs |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
319 9
202 9
Income Taxes
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
230 10
251 10
Regulatory liabilities
37 11
42 11
Income Taxes |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
229 10
247 10
Regulatory liabilities
33 11
36 11
Income Taxes |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
1 10
4 10
Regulatory liabilities
4 11
6 11
Uncertain tax positions tracker
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
7 1 12
7 1 12
Regulatory liabilities
3 12
6 12
Uncertain tax positions tracker |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
7 1 12
7 1 12
Regulatory liabilities
3 12
6 12
Uncertain tax positions tracker |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
0 1 12
0 1 12
Asset Retirement Obligation
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
3 13
4 13
Regulatory liabilities
162 13
167 13
Asset Retirement Obligation |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
0 13
0 13
Regulatory liabilities
162 13
167 13
Asset Retirement Obligation |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
3 13
4 13
Regulatory liabilities
0 13
0 13
Callaway Costs
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
29 1 14
32 1 14
Callaway Costs |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
29 1 14
32 1 14
Unamortized Loss On Reacquired Debt
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
124 1 15
138 1 15
Unamortized Loss On Reacquired Debt |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
65 1 15
69 1 15
Unamortized Loss On Reacquired Debt |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
59 1 15
69 1 15
Recoverable Costs Contaminated Facilities
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
196 16
230 16
Recoverable Costs Contaminated Facilities |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
0 16
0 16
Recoverable Costs Contaminated Facilities |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
196 16
230 16
Storm Costs
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
15 1 17
9 1 17
Storm Costs |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
0 1 17
0 1 17
Storm Costs |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
15 1 17
9 1 17
Demand-Side Costs
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
18 1 18
31 1 18
Demand-Side Costs |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
18 1 18
31 1 18
Reserve For Workers' Compensation Liabilities
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
13 19
13 19
Reserve For Workers' Compensation Liabilities |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
6 19
6 19
Reserve For Workers' Compensation Liabilities |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
7 19
7 19
Credit Facilities Fees
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
4 20
4 20
Credit Facilities Fees |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
4 20
4 20
Construction Accounting For Pollution Control Equipment
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
19 1 21
20 1 21
Construction Accounting For Pollution Control Equipment |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
19 1 21
20 1 21
Solar Rebates
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
49 1 22
74 1 22
Solar Rebates |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
49 1 22
74 1 22
Other
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
16 
9 
Regulatory liabilities
9 
3 
Other |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
9 
5 
Regulatory liabilities
5 
2 
Other |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory assets
7 
4 
Regulatory liabilities
4 
1 
Over-Recovered FAC
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory liabilities
0 2
9 2
Over-Recovered FAC |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory liabilities
0 2
9 2
Over-Recovered FAC |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory liabilities
0 2
0 2
Over-Recovered Illinois Electric Power Costs
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory liabilities
25 3
6 3
Over-Recovered Illinois Electric Power Costs |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory liabilities
0 3
0 3
Over-Recovered Illinois Electric Power Costs |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory liabilities
25 3
6 3
Over-Recovered PGA
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory liabilities
0 3
3 3
Over-Recovered PGA |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory liabilities
0 3
3 3
Over-Recovered PGA |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory liabilities
0 3
0 3
MTM Derivative Gains
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory liabilities
23 4
17 4
MTM Derivative Gains |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory liabilities
12 4
16 4
MTM Derivative Gains |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory liabilities
11 4
1 4
Refund Reserves for FERC Orders and Audit Findings
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory liabilities
62 23
45 23
Refund Reserves for FERC Orders and Audit Findings |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory liabilities
0 23
0 23
Refund Reserves for FERC Orders and Audit Findings |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Current regulatory liabilities
42 23
32 23
Removal Costs
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory liabilities
1,669 24
1,605 24
Removal Costs |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory liabilities
970 24
933 24
Removal Costs |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory liabilities
697 24
671 24
Bad Debt Rider
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory liabilities
3 25
6 25
Bad Debt Rider |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory liabilities
0 25
0 25
Bad Debt Rider |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory liabilities
3 25
6 25
Pension And Postretirement Benefit Costs Tracker
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory liabilities
35 26
19 26
Pension And Postretirement Benefit Costs Tracker |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory liabilities
35 26
19 26
Renewable Energy Credits
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory liabilities
15 27
12 27
Renewable Energy Credits |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory liabilities
0 27
0 27
Renewable Energy Credits |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory liabilities
15 27
12 27
Storm Tracker
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory liabilities
7 28
9 28
Storm Tracker |
Union Electric Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory liabilities
7 28
9 28
Storm Tracker |
Ameren Illinois Company
 
 
Public Utilities, General Disclosures [Line Items]
 
 
Regulatory liabilities
$ 0 28
$ 0 28
[5] (e)The Ameren Missouri balance relates to the MEEIA. The MEEIA rider allows Ameren Missouri to collect from or refund to customers any annual difference in the actual amounts incurred and the amounts collected from customers for the MEEIA program costs, net shared benefits, and the throughput disincentive. Under the MEEIA rider, collections from or refunds to customers occur one year after the program costs, net shared benefits, and the throughput disincentive are incurred. The Ameren Illinois balance relates to a regulatory tracking mechanism to recover its electric and natural gas costs associated with developing, implementing, and evaluating customer energy efficiency and demand response programs. Any under-recovery or over-recovery will be collected from or refunded to customers over the year following the plan year.
[18] (q)Demand-side costs incurred prior to implementation of the MEEIA in 2013, including the costs of developing, implementing, and evaluating customer energy efficiency and demand response programs. Costs incurred from May 2008 through September 2008 are being amortized over a 10-year period that began in March 2009. Costs incurred from October 2008 through December 2009 are being amortized until May 2017. Costs incurred from January 2010 through February 2011 are being amortized over a six-year period that began in August 2011. Costs incurred from March 2011 through July 2012 are being amortized over a six-year period that began in January 2013. Costs incurred from August 2012 through December 2012 are being amortized over a six-year period that began in June 2015. The February 2017 stipulation and agreement, if approved, would modify these amortization periods.
Property And Plant, Net (Schedule Of Property And Plant, Net) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
equipment
Dec. 31, 2015
Dec. 31, 2016
Electric Generation Equipment [Member]
Dec. 31, 2015
Electric Generation Equipment [Member]
Dec. 31, 2016
Electric distribution equipment [Member]
Dec. 31, 2015
Electric distribution equipment [Member]
Dec. 31, 2016
Electric transmission equipment [Member]
Dec. 31, 2015
Electric transmission equipment [Member]
Dec. 31, 2016
Gas
Dec. 31, 2015
Gas
Dec. 31, 2016
Property, Plant and Equipment, Other Types [Member]
Dec. 31, 2015
Property, Plant and Equipment, Other Types [Member]
Dec. 31, 2016
Nuclear Fuel
Dec. 31, 2015
Nuclear Fuel
Dec. 31, 2016
Union Electric Company
Dec. 31, 2015
Union Electric Company
Dec. 31, 2016
Union Electric Company
Electric Generation Equipment [Member]
Dec. 31, 2015
Union Electric Company
Electric Generation Equipment [Member]
Dec. 31, 2016
Union Electric Company
Electric distribution equipment [Member]
Dec. 31, 2015
Union Electric Company
Electric distribution equipment [Member]
Dec. 31, 2016
Union Electric Company
Electric transmission equipment [Member]
Dec. 31, 2015
Union Electric Company
Electric transmission equipment [Member]
Dec. 31, 2016
Union Electric Company
Gas
Dec. 31, 2015
Union Electric Company
Gas
Dec. 31, 2016
Union Electric Company
Property, Plant and Equipment, Other Types [Member]
Dec. 31, 2015
Union Electric Company
Property, Plant and Equipment, Other Types [Member]
Dec. 31, 2016
Union Electric Company
Nuclear Fuel
Dec. 31, 2015
Union Electric Company
Nuclear Fuel
Dec. 31, 2016
Ameren Illinois Company
Dec. 31, 2015
Ameren Illinois Company
Dec. 31, 2016
Ameren Illinois Company
Electric Generation Equipment [Member]
Dec. 31, 2015
Ameren Illinois Company
Electric Generation Equipment [Member]
Dec. 31, 2016
Ameren Illinois Company
Electric distribution equipment [Member]
Dec. 31, 2015
Ameren Illinois Company
Electric distribution equipment [Member]
Dec. 31, 2016
Ameren Illinois Company
Electric transmission equipment [Member]
Dec. 31, 2015
Ameren Illinois Company
Electric transmission equipment [Member]
Dec. 31, 2016
Ameren Illinois Company
Gas
Dec. 31, 2015
Ameren Illinois Company
Gas
Dec. 31, 2016
Ameren Illinois Company
Property, Plant and Equipment, Other Types [Member]
Dec. 31, 2015
Ameren Illinois Company
Property, Plant and Equipment, Other Types [Member]
Dec. 31, 2016
Ameren Illinois Company
Nuclear Fuel
Dec. 31, 2015
Ameren Illinois Company
Nuclear Fuel
Dec. 31, 2016
Other
Dec. 31, 2015
Other
Dec. 31, 2016
Other
Electric Generation Equipment [Member]
Dec. 31, 2015
Other
Electric Generation Equipment [Member]
Dec. 31, 2016
Other
Electric distribution equipment [Member]
Dec. 31, 2015
Other
Electric distribution equipment [Member]
Dec. 31, 2016
Other
Electric transmission equipment [Member]
Dec. 31, 2015
Other
Electric transmission equipment [Member]
Dec. 31, 2016
Other
Gas
Dec. 31, 2015
Other
Gas
Dec. 31, 2016
Other
Property, Plant and Equipment, Other Types [Member]
Dec. 31, 2015
Other
Property, Plant and Equipment, Other Types [Member]
Dec. 31, 2016
Other
Nuclear Fuel
Dec. 31, 2015
Other
Nuclear Fuel
Dec. 31, 2016
Minimum
Electric Generation Equipment [Member]
Dec. 31, 2016
Minimum
Electric distribution equipment [Member]
Dec. 31, 2016
Minimum
Electric transmission equipment [Member]
Dec. 31, 2016
Minimum
Gas
Dec. 31, 2016
Minimum
Property, Plant and Equipment, Other Types [Member]
Dec. 31, 2016
Maximum
Electric Generation Equipment [Member]
Dec. 31, 2016
Maximum
Electric distribution equipment [Member]
Dec. 31, 2016
Maximum
Electric transmission equipment [Member]
Dec. 31, 2016
Maximum
Gas
Dec. 31, 2016
Maximum
Property, Plant and Equipment, Other Types [Member]
Dec. 31, 2016
Maximum
Union Electric Company
Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Property and plant, at original cost
$ 30,118 1 2
$ 27,603 1 2
$ 10,911 1 2
$ 10,431 1 2
$ 10,850 1 2
$ 10,255 1 2
$ 3,879 1 2
$ 2,774 1 2
$ 2,641 1 2
$ 2,442 1 2
$ 1,837 1 2 3
$ 1,701 1 2 3
 
 
$ 18,959 1 2
$ 17,966 1 2
$ 10,911 1 2
$ 10,431 1 2
$ 5,563 1 2
$ 5,303 1 2
$ 1,151 1 2
$ 979 1 2
$ 455 1 2
$ 445 1 2
$ 879 1 2 3
$ 808 1 2 3
 
 
$ 10,208 2
$ 9,250 2
$ 0 2
$ 0 2
$ 5,287 2
$ 4,952 2
$ 2,016 2
$ 1,674 2
$ 2,186 2
$ 1,997 2
$ 719 2 3
$ 627 2 3
 
 
$ 951 2
$ 387 2
$ 0 2
$ 0 2
$ 0 2
$ 0 2
$ 712 2
$ 121 2
$ 0 2
$ 0 2
$ 239 2 3
$ 266 2 3
 
 
 
 
 
 
 
 
 
 
 
 
 
Accumulated depreciation and amortization
10,961 1
10,347 1
 
 
 
 
 
 
 
 
 
 
 
 
7,880 1
7,460 1
 
 
 
 
 
 
 
 
 
 
 
 
2,850 
2,632 
 
 
 
 
 
 
 
 
 
 
 
 
231 
255 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Property and plant, before construction work in progress
19,157 1
17,256 1
 
 
 
 
 
 
 
 
 
 
 
 
11,079 1
10,506 1
 
 
 
 
 
 
 
 
 
 
 
 
7,358 
6,618 
 
 
 
 
 
 
 
 
 
 
 
 
720 
132 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Construction work in progress
 
 
 
 
 
 
 
 
 
 
750 1
1,268 1
206 1
275 1
 
 
 
 
 
 
 
 
 
 
193 1
402 1
206 1
275 1
 
 
 
 
 
 
 
 
 
 
111 
230 
0 
0 
 
 
 
 
 
 
 
 
 
 
446 
636 
0 
0 
 
 
 
 
 
 
 
 
 
 
 
Property, Plant and Equipment, Net
20,113 1
18,799 1
 
 
 
 
 
 
 
 
 
 
 
 
11,478 1
11,183 1
 
 
 
 
 
 
 
 
 
 
 
 
7,469 
6,848 
 
 
 
 
 
 
 
 
 
 
 
 
1,166 
768 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Number of combustion turbine electric generation equipment under capital lease agreements
2 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Number of capital lease agreements
2 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Capital lease agreements, gross asset value
232 
233 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Total accumulated depreciation, capital lease agreements
77 
72 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Held-to-maturity Securities
$ 282 
$ 288 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Property, Plant and Equipment, Useful Life
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
5 years 
18 years 
50 years 
20 years 
5 years 
100 years 
75 years 
75 years 
80 years 
55 years 
150 years 
Property And Plant, Net (Accrued Capital Expenditures) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Property, Plant and Equipment [Line Items]
 
 
 
Accrued capital expenditures
$ 251 1
$ 235 1
$ 181 1
Union Electric Company
 
 
 
Property, Plant and Equipment [Line Items]
 
 
 
Accrued capital expenditures
116 
85 
72 
Ameren Illinois Company
 
 
 
Property, Plant and Equipment [Line Items]
 
 
 
Accrued capital expenditures
87 
92 
59 
Nuclear Fuel
 
 
 
Property, Plant and Equipment [Line Items]
 
 
 
Accrued capital expenditures
20 1
16 1
13 1
Nuclear Fuel |
Union Electric Company
 
 
 
Property, Plant and Equipment [Line Items]
 
 
 
Accrued capital expenditures
$ 20 
$ 16 
$ 13 
Short-Term Debt And Liquidity (Narrative) (Details) (USD $)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Illinois Credit Agreement 2012 |
Maximum
 
 
Line of Credit Facility [Line Items]
 
 
Line of credit facility, maximum borrowing capacity
$ 1,300,000,000.0 
 
Illinois Credit Agreement 2012 |
Ameren Illinois Company
 
 
Line of Credit Facility [Line Items]
 
 
Line of credit facility, maximum borrowing capacity
800,000,000 
 
Actual debt-to-capital ratio
0.47 
 
Missouri Credit Agreement 2012 |
Maximum
 
 
Line of Credit Facility [Line Items]
 
 
Line of credit facility, maximum borrowing capacity
1,200,000,000.0 
 
Missouri Credit Agreement 2012 |
Union Electric Company
 
 
Line of Credit Facility [Line Items]
 
 
Line of credit facility, maximum borrowing capacity
800,000,000 
 
Actual debt-to-capital ratio
0.48 
 
Credit Agreements 2012
 
 
Line of Credit Facility [Line Items]
 
 
Line of credit facility, maximum borrowing capacity
1,500,000,000.0 
 
Covenant terms, default provisions, maximum indebtedness
100,000,000 
 
Multiyear Credit Facility
 
 
Line of Credit Facility [Line Items]
 
 
Line of credit facility, maximum borrowing capacity
2,100,000,000 
 
Number of lenders
22 
 
Line of credit facility, maximum borrowing capacity, per lender
118,000,000 
 
Actual debt-to-capital ratio
0.51 
 
Line of Credit Facility, Commitment Fee Amount
$ 100,000,000 
 
Multiyear Credit Facility |
Maximum
 
 
Line of Credit Facility [Line Items]
 
 
Actual debt-to-capital ratio
0.65 
 
Utilities
 
 
Line of Credit Facility [Line Items]
 
 
Short Term Debt, Weighted Average Interest Rate During Period
0.52% 
0.11% 
Short-Term Debt And Liquidity (Schedule Of Maximum Aggregate Amount Available On Credit Agreements) (Details) (USD $)
Dec. 31, 2016
Illinois Credit Agreement 2012 |
Parent Company
 
Line of Credit Facility [Line Items]
 
Line of credit facility, maximum borrowing capacity
$ 500,000,000 
Illinois Credit Agreement 2012 |
Ameren Illinois Company
 
Line of Credit Facility [Line Items]
 
Line of credit facility, maximum borrowing capacity
800,000,000 
Missouri Credit Agreement 2012 |
Parent Company
 
Line of Credit Facility [Line Items]
 
Line of credit facility, maximum borrowing capacity
700,000,000 
Missouri Credit Agreement 2012 |
Union Electric Company
 
Line of Credit Facility [Line Items]
 
Line of credit facility, maximum borrowing capacity
$ 800,000,000 
Short-Term Debt And Liquidity Short-Term Debt And Liquidity (Commercial Paper) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Commercial Paper
 
 
Line of Credit Facility [Line Items]
 
 
Average Daily Commercial Paper Borrowings Outstanding
$ 552 
$ 767 
Commercial paper outstanding
558 
301 
Weighted average interest rate
0.80% 
0.55% 
Peak short-term borrowings
839 1
1,108 1
Peak short-term borrowings interest rate
1.05% 
0.91% 
Parent Company
 
 
Line of Credit Facility [Line Items]
 
 
Average Daily Commercial Paper Borrowings Outstanding
440 
721 
Weighted average interest rate
0.82% 
0.57% 
Peak short-term borrowings
574 1
874 1
Peak short-term borrowings interest rate
1.05% 
0.91% 
Parent Company |
Commercial Paper
 
 
Line of Credit Facility [Line Items]
 
 
Commercial paper outstanding
507 
301 
Union Electric Company
 
 
Line of Credit Facility [Line Items]
 
 
Average Daily Commercial Paper Borrowings Outstanding
60 
42 
Weighted average interest rate
0.74% 
0.50% 
Peak short-term borrowings
208 1
294 1
Peak short-term borrowings interest rate
0.85% 
0.60% 
Ameren Illinois Company
 
 
Line of Credit Facility [Line Items]
 
 
Average Daily Commercial Paper Borrowings Outstanding
52 
4 
Weighted average interest rate
0.69% 
0.44% 
Peak short-term borrowings
195 1
48 1
Peak short-term borrowings interest rate
0.90% 
0.60% 
Ameren Illinois Company |
Commercial Paper
 
 
Line of Credit Facility [Line Items]
 
 
Commercial paper outstanding
51 
0 
Ameren Missouri [Member] |
Commercial Paper
 
 
Line of Credit Facility [Line Items]
 
 
Commercial paper outstanding
$ 0 
$ 0 
Long-Term Debt And Equity Financings (Narrative) (Details) (USD $)
12 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 3 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2016
Union Electric Company
Dec. 31, 2015
Union Electric Company
Dec. 31, 2014
Union Electric Company
Dec. 31, 2016
Ameren Illinois Company
Dec. 31, 2015
Ameren Illinois Company
Dec. 31, 2014
Ameren Illinois Company
Dec. 31, 2016
Parent Company
Dec. 31, 2015
Parent Company
Dec. 31, 2014
Parent Company
May 31, 2014
Parent Company
Oct. 31, 2013
Parent Company
Dec. 31, 2016
Ameren Missouri and Ameren Illinois
Dec. 31, 2016
Senior Unsecured Notes270 due 2020 [Member]
Parent Company
Dec. 31, 2016
Senior Unsecured Notes270 due 2020 [Member]
Parent Company
Unsecured Debt [Member]
Dec. 31, 2015
Senior Unsecured Notes270 due 2020 [Member]
Parent Company
Unsecured Debt [Member]
Dec. 31, 2016
Senior Unsecured Notes365 due 2026 [Member]
Parent Company
Dec. 31, 2016
Senior Unsecured Notes365 due 2026 [Member]
Parent Company
Unsecured Debt [Member]
Dec. 31, 2015
Senior Unsecured Notes365 due 2026 [Member]
Parent Company
Unsecured Debt [Member]
Dec. 31, 2016
5.40% Senior secured notes due 2016
Union Electric Company
Secured Debt
Mar. 31, 2016
5.40% Senior secured notes due 2016
Union Electric Company
Secured Debt
Dec. 31, 2015
5.40% Senior secured notes due 2016
Union Electric Company
Secured Debt
Dec. 31, 2016
Senior Secured Notes, 3.65%, Due 2045 - $150 Issuance [Member]
Union Electric Company
Secured Debt
Dec. 31, 2016
Senior Secured Notes, 3.65%, Due 2045 - $250 Issuance [Member]
Union Electric Company
Secured Debt
Dec. 31, 2016
Senior Secured Notes, 3.65%, Due 2045 [Member]
Union Electric Company
Secured Debt
Dec. 31, 2015
Senior Secured Notes, 3.65%, Due 2045 [Member]
Union Electric Company
Secured Debt
Dec. 31, 2016
Senior Secured Notes 4.75% Due2015 [Member]
Union Electric Company
Dec. 31, 2016
Senior Secured Notes 6.20% Due 2016
Ameren Illinois Company
Secured Debt
Dec. 31, 2015
Senior Secured Notes 6.20% Due 2016
Ameren Illinois Company
Secured Debt
Dec. 31, 2016
Senior Secured Notes 6.25% Due 2016
Ameren Illinois Company
Secured Debt
Dec. 31, 2015
Senior Secured Notes 6.25% Due 2016
Ameren Illinois Company
Secured Debt
Dec. 31, 2016
Senior Secured Notes, 4.15%, Due 2046 - $240 Issuance [Member]
Ameren Illinois Company
Secured Debt
Dec. 31, 2016
Senior Secured Notes, 4.15%, Due 2046 - $250 Issuance [Member]
Ameren Illinois Company
Secured Debt
Dec. 31, 2016
Senior Secured Notes, 4.15%, Due 2046 [Member]
Ameren Illinois Company
Secured Debt
Dec. 31, 2015
Senior Secured Notes, 4.15%, Due 2046 [Member]
Ameren Illinois Company
Secured Debt
Dec. 31, 2016
Minimum
Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Preferred stock, authorized
100,000,000 
 
 
7,500,000.0 
 
 
2,600,000.0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Preferred stock, par value
$ 0.01 
 
 
$ 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Preferred stock, shares outstanding
0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Debt instrument face amount
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
$ 350,000,000 
$ 350,000,000 
 
$ 350,000,000 
$ 350,000,000 
$ 0 1
$ 260,000,000 
$ 260,000,000 1
$ 150,000,000 
$ 250,000,000 
$ 400,000,000 1
$ 250,000,000 1
 
$ 0 
$ 54,000,000 
$ 0 
$ 75,000,000 
$ 240,000,000 
$ 250,000,000 
$ 490,000,000 2
$ 250,000,000 2
 
Long-term debt interest rate
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2.70% 
2.70% 
 
3.65% 
3.65% 
 
5.40% 
 
 
 
 
3.65% 
 
4.75% 
6.20% 
 
6.25% 
 
 
 
4.15% 
 
 
Proceeds from issuance of secured debt
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
348,000,000 
 
 
347,000,000 
 
 
 
 
148,000,000 
247,000,000 
 
 
 
 
 
 
 
245,000,000 
245,000,000 
 
 
 
Common stock, shares authorized
400,000,000 
400,000,000 
 
150,000,000 
150,000,000 
 
45,000,000 
45,000,000 
 
 
 
 
8,600,000.0 
4,000,000 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Restricted Cash and Cash Equivalents
8,000,000 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Repayments of Other Long-term Debt
395,000,000 
120,000,000 
697,000,000 
266,000,000 
120,000,000 
109,000,000 
129,000,000 
0 
163,000,000 
0 
0 
425,000,000 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
114,000,000 
54,000,000 
 
75,000,000 
 
 
 
 
 
 
Bonds interest rate assumption
 
 
 
 
 
 
 
 
 
 
 
 
 
 
5.00% 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Dividend rate on preferred shares, percentage
 
 
 
 
 
 
 
 
 
 
 
 
 
 
6.00% 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Debt Default Provision Excess
$ 25,000,000 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Common stock equity to capitalization ratio
 
 
 
 
 
 
51.00% 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
30.00% 
[1] (a)These notes are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any first mortgage bonds issued under the Ameren Missouri mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Missouri senior secured notes currently outstanding, we do not expect the first mortgage bond lien protection associated with these notes to fall away before 2042.
[2] These notes are collaterally secured by mortgage bonds issued by Ameren Illinois under its 1992 mortgage indenture. They are secured by substantially all property of the former IP and CIPS. The notes have a fall-away lien provision and will remain secured only as long as any series of first mortgage bonds issued under its 1992 mortgage indenture remain outstanding. Redemption, purchase, or maturity of all mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Illinois senior secured notes currently outstanding, we do not expect the mortgage bond lien protection associated with these notes to fall away before 2022.
Long-Term Debt And Equity Financings (Schedule Of Long-Term Debt Outstanding) (Details) (USD $)
12 Months Ended
Dec. 31, 2016
Mar. 31, 2016
Dec. 31, 2015
Debt Instrument [Line Items]
 
 
 
Less: Maturities due within one year
$ (681,000,000)
 
$ (395,000,000)
Long-term Debt, Net
6,595,000,000 
 
6,880,000,000 
Parent Company
 
 
 
Debt Instrument [Line Items]
 
 
 
Long-term debt, gross
700,000,000 
 
700,000,000 
Debt Issuance Costs, Net
(6,000,000)
 
(6,000,000)
Long-term Debt, Net
694,000,000 
 
694,000,000 
Parent Company |
Senior Unsecured Notes270 due 2020 [Member]
 
 
 
Debt Instrument [Line Items]
 
 
 
Long-term debt interest rate
2.70% 
 
 
Long-term debt maturity date
2020 
 
 
Parent Company |
Senior Unsecured Notes365 due 2026 [Member]
 
 
 
Debt Instrument [Line Items]
 
 
 
Long-term debt interest rate
3.65% 
 
 
Long-term debt maturity date
2026 
 
 
Ameren Illinois Company
 
 
 
Debt Instrument [Line Items]
 
 
 
Long-term debt, gross
2,607,000,000 
 
2,496,000,000 
Less: Unamortized discount and premium
0 
 
(7,000,000)
Debt Issuance Costs, Net
(19,000,000)
 
(18,000,000)
Less: Maturities due within one year
(250,000,000)
 
(129,000,000)
Long-term Debt, Net
2,338,000,000 
 
2,342,000,000 
Union Electric Company
 
 
 
Debt Instrument [Line Items]
 
 
 
Long-term debt, gross
4,019,000,000 
 
4,135,000,000 
Less: Unamortized discount and premium
(6,000,000)
 
(6,000,000)
Debt Issuance Costs, Net
(19,000,000)
 
(19,000,000)
Less: Maturities due within one year
(431,000,000)
 
(266,000,000)
Long-term Debt, Net
3,563,000,000 
 
3,844,000,000 
Union Electric Company |
City Of Bowling Green Capital Lease Peno Creek Ct
 
 
 
Debt Instrument [Line Items]
 
 
 
Capital lease obligations
42,000,000 
 
48,000,000 
Long-term debt maturity date
2022 
 
 
Union Electric Company |
Audrain County Capital Lease Audrain County Ct
 
 
 
Debt Instrument [Line Items]
 
 
 
Capital lease obligations
240,000,000 
 
240,000,000 
Long-term debt maturity date
2023 
 
 
Unsecured Debt [Member] |
Parent Company |
Senior Unsecured Notes270 due 2020 [Member]
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
350,000,000 
 
350,000,000 
Long-term debt interest rate
2.70% 
 
 
Unsecured Debt [Member] |
Parent Company |
Senior Unsecured Notes365 due 2026 [Member]
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
350,000,000 
 
350,000,000 
Long-term debt interest rate
3.65% 
 
 
Secured Debt |
Ameren Illinois Company |
Senior Secured Notes 6.20% Due 2016
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
0 
 
54,000,000 
Long-term debt interest rate
6.20% 
 
 
Long-term debt maturity date
2016 
 
 
Secured Debt |
Ameren Illinois Company |
Senior Secured Notes 6.25% Due 2016
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
0 
 
75,000,000 
Long-term debt interest rate
6.25% 
 
 
Long-term debt maturity date
2016 
 
 
Secured Debt |
Ameren Illinois Company |
Senior Secured Notes 6.125% Due 2017
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
250,000,000 1 2
 
250,000,000 2 3
Long-term debt interest rate
6.125% 
 
 
Long-term debt maturity date
2017 
 
 
Secured Debt |
Ameren Illinois Company |
Senior Secured Notes 6.25% Due 2018
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
144,000,000 1 2
 
144,000,000 1 2
Long-term debt interest rate
6.25% 
 
 
Long-term debt maturity date
2018 
 
 
Secured Debt |
Ameren Illinois Company |
Senior Secured Notes 9.75% Due 2018
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
313,000,000 1 2
 
313,000,000 1 2
Long-term debt interest rate
9.75% 
 
 
Long-term debt maturity date
2018 
 
 
Secured Debt |
Ameren Illinois Company |
Senior Secured Notes, 2.70%, Due 2022
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
400,000,000 1 2
 
400,000,000 1 2
Long-term debt interest rate
2.70% 
 
 
Long-term debt maturity date
2022 
 
 
Secured Debt |
Ameren Illinois Company |
Senior Secured Notes, 3.25%, Due 2025
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
300,000,000 1
 
300,000,000 1
Long-term debt interest rate
3.25% 
 
 
Long-term debt maturity date
2025 
 
 
Secured Debt |
Ameren Illinois Company |
Senior Secured Notes 6.125% Due 2028
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
60,000,000 1
 
60,000,000 1
Long-term debt interest rate
6.125% 
 
 
Long-term debt maturity date
2028 
 
 
Secured Debt |
Ameren Illinois Company |
Senior Secured Notes 6.70% Due 2036
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
61,000,000 1
 
61,000,000 1
Long-term debt interest rate
6.70% 
 
 
Long-term debt maturity date
2036 
 
 
Secured Debt |
Ameren Illinois Company |
Senior Secured Notes 6.70% Due 2036
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
42,000,000 4
 
42,000,000 4
Long-term debt interest rate
6.70% 
 
 
Long-term debt maturity date
2036 
 
 
Secured Debt |
Ameren Illinois Company |
Senior Secured Notes 4.80% Due 2043
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
280,000,000 1
 
280,000,000 1
Long-term debt interest rate
4.80% 
 
 
Long-term debt maturity date
2043 
 
 
Secured Debt |
Ameren Illinois Company |
Senior Secured Notes 4.30% Due 2044
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
250,000,000 1
 
250,000,000 1
Long-term debt interest rate
4.30% 
 
 
Long-term debt maturity date
2044 
 
 
Secured Debt |
Ameren Illinois Company |
Senior Secured Notes, 4.15%, Due 2046 [Member]
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
490,000,000 1
 
250,000,000 1
Long-term debt interest rate
4.15% 
 
 
Long-term debt maturity date
2046 
 
 
Secured Debt |
Ameren Illinois Company |
Series 1993 5.90% Due 2023
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
1,000,000 4
 
 
Long-term debt interest rate
5.90% 
 
 
Secured Debt |
Union Electric Company |
5.40% Senior secured notes due 2016
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
0 5
260,000,000 
260,000,000 5
Long-term debt interest rate
5.40% 
 
 
Long-term debt maturity date
2016 
 
 
Secured Debt |
Union Electric Company |
6.40% Senior secured notes due 2017
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
425,000,000 5
 
425,000,000 5
Long-term debt interest rate
6.40% 
 
 
Long-term debt maturity date
2017 
 
 
Secured Debt |
Union Electric Company |
6.00% Senior secured notes due 2018
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
179,000,000 5 6
 
179,000,000 5 6
Long-term debt interest rate
6.00% 
 
 
Long-term debt maturity date
2018 
 
 
Secured Debt |
Union Electric Company |
5.10% Senior secured notes due 2018
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
199,000,000 5
 
199,000,000 5
Long-term debt interest rate
5.10% 
 
 
Long-term debt maturity date
2018 
 
 
Secured Debt |
Union Electric Company |
6.70% Senior secured notes due 2019
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
329,000,000 5 6
 
329,000,000 5 6
Long-term debt interest rate
6.70% 
 
 
Long-term debt maturity date
2019 
 
 
Secured Debt |
Union Electric Company |
5.10% Senior secured notes due 2019
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
244,000,000 5
 
244,000,000 5
Long-term debt interest rate
5.10% 
 
 
Long-term debt maturity date
2019 
 
 
Secured Debt |
Union Electric Company |
5.00% Senior secured notes due 2020
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
85,000,000 5
 
85,000,000 5
Long-term debt interest rate
5.00% 
 
 
Long-term debt maturity date
2020 
 
 
Secured Debt |
Union Electric Company |
Senior Secured Notes350 Due2024 [Member]
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
350,000,000 5
 
350,000,000 5
Long-term debt interest rate
3.50% 
 
 
Long-term debt maturity date
2024 
 
 
Secured Debt |
Union Electric Company |
5.50% Senior secured notes due 2034
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
184,000,000 5
 
184,000,000 5
Long-term debt interest rate
5.50% 
 
 
Long-term debt maturity date
2034 
 
 
Secured Debt |
Union Electric Company |
5.30% Senior secured notes due 2037
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
300,000,000 5
 
300,000,000 5
Long-term debt interest rate
5.30% 
 
 
Long-term debt maturity date
2037 
 
 
Secured Debt |
Union Electric Company |
8.45% Senior secured notes due 2039
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
350,000,000 5 6
 
350,000,000 5 6
Long-term debt interest rate
8.45% 
 
 
Long-term debt maturity date
2039 
 
 
Secured Debt |
Union Electric Company |
3.90% Senior secured notes due 2042
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
485,000,000 5 6
 
485,000,000 5 6
Long-term debt interest rate
3.90% 
 
 
Long-term debt maturity date
2042 
 
 
Secured Debt |
Union Electric Company |
Senior Secured Notes, 3.65%, Due 2045 [Member]
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
400,000,000 5
 
250,000,000 5
Long-term debt interest rate
3.65% 
 
 
Long-term debt maturity date
2045 
 
 
Environmental Improvement And Pollution Control Revenue Bonds |
Ameren Illinois Company |
Series 1993 5.90% Due 2023
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
1,000,000 3 4
 
1,000,000 3
Long-term debt interest rate
5.90% 
 
 
Long-term debt maturity date
2023 
 
 
Redemption price, percentage
100.00% 
 
 
Environmental Improvement And Pollution Control Revenue Bonds |
Ameren Illinois Company |
Series 1994 A 5.70% Due 2024
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
1,000,000 4 7
 
1,000,000 7
Long-term debt interest rate
5.70% 
 
 
Long-term debt maturity date
2024 
 
 
Redemption price, percentage
100.00% 
 
 
Environmental Improvement And Pollution Control Revenue Bonds |
Ameren Illinois Company |
Series B-1 1993 Due 2028
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
17,000,000 8 9
 
17,000,000 8 9
Long-term debt maturity date
2028 
 
 
Redemption price, percentage
100.00% 
 
 
Environmental Improvement And Pollution Control Revenue Bonds |
Union Electric Company |
1992 Series due 2022
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
47,000,000 10 9
 
47,000,000 10 9
Long-term debt maturity date
2022 
 
 
Environmental Improvement And Pollution Control Revenue Bonds |
Union Electric Company |
1993 5.45% Series due 2028
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
1,000,000 11
 
 
Long-term debt interest rate
5.45% 
 
 
Long-term debt maturity date
2028 
 
 
Redemption price, percentage
100.00% 
 
 
Environmental Improvement And Pollution Control Revenue Bonds |
Union Electric Company |
1998 Series A due 2033
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
60,000,000 10 9
 
60,000,000 10 9
Long-term debt maturity date
2033 
 
 
Environmental Improvement And Pollution Control Revenue Bonds |
Union Electric Company |
1998 Series B due 2033
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
50,000,000 10 9
 
50,000,000 10 9
Long-term debt maturity date
2033 
 
 
Environmental Improvement And Pollution Control Revenue Bonds |
Union Electric Company |
1998 Series C due 2033
 
 
 
Debt Instrument [Line Items]
 
 
 
Debt instrument face amount
$ 50,000,000 10 9
 
$ 50,000,000 10 9
Long-term debt maturity date
2033 
 
 
Maximum |
Environmental Improvement And Pollution Control Revenue Bonds |
Union Electric Company |
1992 Series due 2022
 
 
 
Debt Instrument [Line Items]
 
 
 
Long-term debt interest rate
18.00% 
 
 
Maximum |
Environmental Improvement And Pollution Control Revenue Bonds |
Union Electric Company |
1998 Series A due 2033
 
 
 
Debt Instrument [Line Items]
 
 
 
Long-term debt interest rate
0.00% 
 
 
Maximum |
Environmental Improvement And Pollution Control Revenue Bonds |
Union Electric Company |
1998 Series B due 2033
 
 
 
Debt Instrument [Line Items]
 
 
 
Long-term debt interest rate
0.00% 
 
 
Maximum |
Environmental Improvement And Pollution Control Revenue Bonds |
Union Electric Company |
1998 Series C due 2033
 
 
 
Debt Instrument [Line Items]
 
 
 
Long-term debt interest rate
0.00% 
 
 
[1] These notes are collaterally secured by mortgage bonds issued by Ameren Illinois under its 1992 mortgage indenture. They are secured by substantially all property of the former IP and CIPS. The notes have a fall-away lien provision and will remain secured only as long as any series of first mortgage bonds issued under its 1992 mortgage indenture remain outstanding. Redemption, purchase, or maturity of all mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Illinois senior secured notes currently outstanding, we do not expect the mortgage bond lien protection associated with these notes to fall away before 2022.
[5] (a)These notes are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any first mortgage bonds issued under the Ameren Missouri mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Missouri senior secured notes currently outstanding, we do not expect the first mortgage bond lien protection associated with these notes to fall away before 2042.
Long-Term Debt And Equity Financings (Schedule Of Average Interest Rates) (Details)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
1992 Series due 2022 |
Union Electric Company
 
 
Debt Instrument [Line Items]
 
 
Debt instrument, interest rate during period
0.66% 
0.06% 
1998 Series A due 2033 |
Union Electric Company
 
 
Debt Instrument [Line Items]
 
 
Debt instrument, interest rate during period
0.91% 
0.24% 
1998 Series B due 2033 |
Union Electric Company
 
 
Debt Instrument [Line Items]
 
 
Debt instrument, interest rate during period
0.92% 
0.24% 
1998 Series C due 2033 |
Union Electric Company
 
 
Debt Instrument [Line Items]
 
 
Debt instrument, interest rate during period
0.97% 
0.24% 
Series B-1 1993 Due 2028 |
Ameren Illinois Company
 
 
Debt Instrument [Line Items]
 
 
Debt instrument, interest rate during period
0.70% 
0.49% 
Long-Term Debt And Equity Financings (Schedule Of Maturities Of Long-Term Debt) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Debt Instrument [Line Items]
 
2017
$ 681 
2018
840 
2019
581 
2020
442 
2021
8 
Thereafter
4,774 
Total
7,326 
Parent Company
 
Debt Instrument [Line Items]
 
2020
350 1
Thereafter
350 1
Total
700 1
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs
(6)
Union Electric Company
 
Debt Instrument [Line Items]
 
2017
431 1
2018
383 1
2019
581 1
2020
92 1
2021
8 1
Thereafter
2,524 1
Total
4,019 1
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs
(25)
Ameren Illinois Company
 
Debt Instrument [Line Items]
 
2017
250 1
2018
457 1
Thereafter
1,900 1
Total
2,607 1
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs
$ (19)
Long-Term Debt And Equity Financings (Schedule Of Outstanding Preferred Stock) (Details) (USD $)
In Millions, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Long-Term Debt And Equity Financings [Line Items]
 
 
Preferred stock, par value
$ 0.01 
 
Preferred stock, authorized
100,000,000 
 
Preferred stock, shares outstanding
0 
 
Preferred stock, voluntary liquidation
$ 106 
 
Union Electric Company and Ameren Illinois [Member]
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Preferred stock, issued
$ 142 
$ 142 
Union Electric Company
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Preferred stock, par value
$ 1 
 
Preferred stock, authorized
7,500,000 
 
Preferred stock, issued
80 
80 
Union Electric Company |
Par Value $100 [Member]
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Preferred stock, par value
$ 100 
 
Preferred stock, authorized
25,000,000 
 
Union Electric Company |
$3.50 Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, per-dollar amount
$ 3.50 
 
Preferred stock, shares outstanding
130,000 
 
Preferred stock, redemption price per share
$ 110 
 
Preferred stock, issued
13 
13 
Union Electric Company |
$3.70 Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, per-dollar amount
$ 3.70 
 
Preferred stock, shares outstanding
40,000 
 
Preferred stock, redemption price per share
$ 105 
 
Preferred stock, issued
4 
4 
Union Electric Company |
$4.00 Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, per-dollar amount
$ 4.00 
 
Preferred stock, shares outstanding
150,000 
 
Preferred stock, redemption price per share
$ 106 
 
Preferred stock, issued
15 
15 
Union Electric Company |
$4.30 Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, per-dollar amount
$ 4.30 
 
Preferred stock, shares outstanding
40,000 
 
Preferred stock, redemption price per share
$ 105 
 
Preferred stock, issued
4 
4 
Union Electric Company |
$4.50 Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, per-dollar amount
$ 4.50 
 
Preferred stock, shares outstanding
213,595 
 
Preferred stock, redemption price per share
$ 110 1
 
Preferred stock, issued
21 
21 
Union Electric Company |
$4.56 Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, per-dollar amount
$ 4.56 
 
Preferred stock, shares outstanding
200,000 
 
Preferred stock, redemption price per share
$ 102 
 
Preferred stock, issued
20 
20 
Union Electric Company |
$4.75 Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, per-dollar amount
$ 4.75 
 
Preferred stock, shares outstanding
20,000 
 
Preferred stock, redemption price per share
$ 102 
 
Preferred stock, issued
2 
2 
Union Electric Company |
$5.50 Series A
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, per-dollar amount
$ 5.50 
 
Preferred stock, shares outstanding
14,000 
 
Preferred stock, redemption price per share
$ 110 
 
Preferred stock, issued
1 
1 
Ameren Illinois Company
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Preferred stock, authorized
2,600,000 
 
Preferred stock, issued
62 
62 
Ameren Illinois Company |
Par Value $100 [Member]
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Preferred stock, par value
$ 100 
 
Preferred stock, authorized
2,000,000 
 
Ameren Illinois Company |
4.00% Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, percentage
4.00% 
 
Preferred stock, shares outstanding
144,275 
 
Preferred stock, redemption price per share
$ 101 
 
Preferred stock, issued
14 
14 
Ameren Illinois Company |
4.08% Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, percentage
4.08% 
 
Preferred stock, shares outstanding
45,224 
 
Preferred stock, redemption price per share
$ 103 
 
Preferred stock, issued
5 
5 
Ameren Illinois Company |
4.20% Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, percentage
4.20% 
 
Preferred stock, shares outstanding
23,655 
 
Preferred stock, redemption price per share
$ 104 
 
Preferred stock, issued
2 
2 
Ameren Illinois Company |
4.25% Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, percentage
4.25% 
 
Preferred stock, shares outstanding
50,000 
 
Preferred stock, redemption price per share
$ 102 
 
Preferred stock, issued
5 
5 
Ameren Illinois Company |
4.26% Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, percentage
4.26% 
 
Preferred stock, shares outstanding
16,621 
 
Preferred stock, redemption price per share
$ 103 
 
Preferred stock, issued
2 
2 
Ameren Illinois Company |
4.42% Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, percentage
4.42% 
 
Preferred stock, shares outstanding
16,190 
 
Preferred stock, redemption price per share
$ 103 
 
Preferred stock, issued
2 
2 
Ameren Illinois Company |
4.70% Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, percentage
4.70% 
 
Preferred stock, shares outstanding
18,429 
 
Preferred stock, redemption price per share
$ 103 
 
Preferred stock, issued
2 
2 
Ameren Illinois Company |
4.90% Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, percentage
4.90% 
 
Preferred stock, shares outstanding
73,825 
 
Preferred stock, redemption price per share
$ 102 
 
Preferred stock, issued
7 
7 
Ameren Illinois Company |
4.92% Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, percentage
4.92% 
 
Preferred stock, shares outstanding
49,289 
 
Preferred stock, redemption price per share
$ 104 
 
Preferred stock, issued
5 
5 
Ameren Illinois Company |
5.16% Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, percentage
5.16% 
 
Preferred stock, shares outstanding
50,000 
 
Preferred stock, redemption price per share
$ 102 
 
Preferred stock, issued
5 
5 
Ameren Illinois Company |
6.625% Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, percentage
6.625% 
 
Preferred stock, shares outstanding
124,274 
 
Preferred stock, redemption price per share
$ 100 
 
Preferred stock, issued
12 
12 
Ameren Illinois Company |
7.75% Series
 
 
Long-Term Debt And Equity Financings [Line Items]
 
 
Dividend rate on preferred shares, percentage
7.75% 
 
Preferred stock, shares outstanding
4,542 
 
Preferred stock, redemption price per share
$ 100 
 
Preferred stock, issued
$ 1 
$ 1 
Long-Term Debt and Equity Financings (Schedule of Required and Actual Debt Ratios) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Union Electric Company
 
Debt Instrument [Line Items]
 
Bonds Issuable Based On Coverage Ratio
$ 4,077 1
Preferred Stock Issuable Based On Coverage Ratio
2,344 
Retired Bond Capacity
1,206 
Union Electric Company |
Actual Interest Coverage Ratio
 
Debt Instrument [Line Items]
 
Interest Coverage Ratio
4.6 
Dividend Coverage Ratio
105.3 
Ameren Illinois Company
 
Debt Instrument [Line Items]
 
Bonds Issuable Based On Coverage Ratio
3,819 1 2
Preferred Stock Issuable Based On Coverage Ratio
203 3
Retired Bond Capacity
$ 279 
Ameren Illinois Company |
Actual Interest Coverage Ratio
 
Debt Instrument [Line Items]
 
Interest Coverage Ratio
6.9 
Dividend Coverage Ratio
2.8 
Minimum |
Union Electric Company |
Required Dividend Coverage Ratio
 
Debt Instrument [Line Items]
 
Interest Coverage Ratio
2.0 4
Dividend Coverage Ratio
2.5 5
Minimum |
Ameren Illinois Company |
Required Dividend Coverage Ratio
 
Debt Instrument [Line Items]
 
Interest Coverage Ratio
2.0 4
Dividend Coverage Ratio
1.5 5
Other Income And Expenses (Other Income And Expenses) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Other Nonoperating Income (Expense) [Line Items]
 
 
 
Allowance for equity funds used during construction
$ 27 1
$ 30 1
$ 34 1
Interest income on industrial development revenue bonds
27 1
27 1
27 1
Interest and dividend income
13 1 2
14 1 2
10 1 2
Other
7 1
3 1
8 1 3
Total miscellaneous income
74 1
74 1
79 1
Donations
16 1
15 1
10 1
Other
16 1
15 1
12 1
Total miscellaneous expense
32 1
30 1
22 1
Union Electric Company
 
 
 
Other Nonoperating Income (Expense) [Line Items]
 
 
 
Allowance for equity funds used during construction
23 
22 
32 
Interest income on industrial development revenue bonds
27 
27 
27 
Interest and dividend income
1 
1 
1 
Other
1 
2 
0 
Total miscellaneous income
52 
52 
60 
Donations
4 
5 
6 
Other
6 
6 
6 
Total miscellaneous expense
10 
11 
12 
Ameren Illinois Company
 
 
 
Other Nonoperating Income (Expense) [Line Items]
 
 
 
Allowance for equity funds used during construction
4 
8 
2 
Interest and dividend income
12 2
12 2
7 2
Other
5 
1 
8 3
Total miscellaneous income
21 
21 
17 
Donations
6 
5 
4 
Other
6 
7 
4 
Total miscellaneous expense
$ 12 
$ 12 
$ 8 
Derivative Financial Instruments (Open Gross Derivative Volumes By Commodity Type) (Details)
Dec. 31, 2016
gal
Dec. 31, 2015
gal
Fuel Oils
 
 
Derivative [Line Items]
 
 
Quantity
30,000,000 1
35,000,000 1
Natural Gas
 
 
Derivative [Line Items]
 
 
Quantity
154,000,000 
181,000,000 
Power
 
 
Derivative [Line Items]
 
 
Quantity
10,000,000 
11,000,000 
Uranium
 
 
Derivative [Line Items]
 
 
Quantity
345,000 
494,000 
Union Electric Company |
Fuel Oils
 
 
Derivative [Line Items]
 
 
Quantity
30,000,000 1
35,000,000 1
Union Electric Company |
Natural Gas
 
 
Derivative [Line Items]
 
 
Quantity
25,000,000 
30,000,000 
Union Electric Company |
Power
 
 
Derivative [Line Items]
 
 
Quantity
1,000,000 
1,000,000 
Union Electric Company |
Uranium
 
 
Derivative [Line Items]
 
 
Quantity
345,000 
494,000 
Ameren Illinois Company |
Natural Gas
 
 
Derivative [Line Items]
 
 
Quantity
129,000,000 
151,000,000 
Ameren Illinois Company |
Power
 
 
Derivative [Line Items]
 
 
Quantity
9,000,000 
10,000,000 
Derivative Financial Instruments (Derivative Instruments Carrying Value) (Details) (Not Designated As Hedging Instrument, USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Dec. 31, 2015
Derivative [Line Items]
 
 
Derivative assets
$ 27 1
$ 18 1
Derivative liabilities
211 2
264 2
Fuel Oils |
Other current assets
 
 
Derivative [Line Items]
 
 
Derivative assets
2 
 
Fuel Oils |
Other current liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
5 
22 
Fuel Oils |
Other deferred credits and liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
 
7 
Natural Gas |
Other current assets
 
 
Derivative [Line Items]
 
 
Derivative assets
12 
1 
Natural Gas |
Other assets
 
 
Derivative [Line Items]
 
 
Derivative assets
3 
 
Natural Gas |
Other current liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
4 
38 
Natural Gas |
Other deferred credits and liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
10 
26 
Power |
Other current assets
 
 
Derivative [Line Items]
 
 
Derivative assets
9 
16 
Power |
Other current liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
15 
13 
Power |
Other deferred credits and liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
173 
157 
Uranium |
Other current liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
 
1 
Union Electric Company
 
 
Derivative [Line Items]
 
 
Derivative assets
14 1
17 1
Derivative liabilities
18 2
44 2
Union Electric Company |
Fuel Oils |
Other current assets
 
 
Derivative [Line Items]
 
 
Derivative assets
2 
 
Union Electric Company |
Fuel Oils |
Other assets
 
 
Derivative [Line Items]
 
 
Derivative assets
1 1
 
Union Electric Company |
Fuel Oils |
Other current liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
5 
22 
Union Electric Company |
Fuel Oils |
Other deferred credits and liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
 
7 
Union Electric Company |
Natural Gas |
Other current assets
 
 
Derivative [Line Items]
 
 
Derivative assets
1 
 
Union Electric Company |
Natural Gas |
Other assets
 
 
Derivative [Line Items]
 
 
Derivative assets
1 
1 1
Union Electric Company |
Natural Gas |
Other current liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
1 
6 
Union Electric Company |
Natural Gas |
Other deferred credits and liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
5 
8 
Union Electric Company |
Power |
Other current assets
 
 
Derivative [Line Items]
 
 
Derivative assets
9 
16 
Union Electric Company |
Power |
Other current liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
3 
 
Union Electric Company |
Uranium |
Other current liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
 
1 
Union Electric Company |
Uranium |
Other deferred credits and liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
4 1
 
Ameren Illinois Company
 
 
Derivative [Line Items]
 
 
Derivative assets
13 1
1 1
Derivative liabilities
193 2
220 2
Ameren Illinois Company |
Natural Gas |
Other current assets
 
 
Derivative [Line Items]
 
 
Derivative assets
11 
1 
Ameren Illinois Company |
Natural Gas |
Other assets
 
 
Derivative [Line Items]
 
 
Derivative assets
2 
 
Ameren Illinois Company |
Natural Gas |
MTM derivative liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
3 
32 
Ameren Illinois Company |
Natural Gas |
Other deferred credits and liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
5 
18 
Ameren Illinois Company |
Power |
MTM derivative liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
12 
13 
Ameren Illinois Company |
Power |
Other deferred credits and liabilities
 
 
Derivative [Line Items]
 
 
Derivative liabilities
$ 173 
$ 157 
Fair Value Measurements (Schedule of Valuation Process and Unobservable Inputs) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Fuel Oils
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative assets
$ 3 1
 
Derivative liabilities
(5)1
(29)1
Natural Gas
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative assets
15 1
2 1
Derivative liabilities
(14)1
(64)1
Power
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative assets
9 1
16 1
Derivative liabilities
(188)1
(170)1
Uranium
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative liabilities
(4)1
(1)1
Union Electric Company |
Fuel Oils
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative assets
3 1
 
Derivative liabilities
(5)1
(29)1
Union Electric Company |
Natural Gas
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative assets
2 1
1 1
Derivative liabilities
(6)1
(14)1
Union Electric Company |
Power
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative assets
9 1
16 1
Derivative liabilities
(3)1
 
Union Electric Company |
Uranium
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative liabilities
(4)1
(1)1
Ameren Illinois Company |
Natural Gas
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative assets
13 1
1 1
Derivative liabilities
(8)1
(50)1
Ameren Illinois Company |
Power
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative liabilities
(185)1
(170)1
Discounted Cash Flow |
Minimum |
Fuel Oils
 
 
Fair Value Inputs [Abstract]
 
 
Escalation rate
(2.00%)2 3
 
Counterparty credit risk
0.13% 4 5
 
Credit risk
0.38% 4 5
 
Discounted Cash Flow |
Minimum |
Natural Gas
 
 
Fair Value Inputs [Abstract]
 
 
Counterparty credit risk
0.13% 4 5
0.40% 4 5
Credit risk
0.38% 4 5
0.40% 4 5
Nodal basis
(0.80)2
(0.10)2
Discounted Cash Flow |
Minimum |
Power
 
 
Fair Value Inputs [Abstract]
 
 
Counterparty credit risk
 
0.86% 4 5
Credit risk
0.38% 4 5
0.40% 4 5
Average bid/ask consensus peak and off-peak pricing
26 6
22 6
Estimated auction price for FTRs
(71)2
(270)2
Nodal basis
(6)6
(10)6
Discounted Cash Flow |
Minimum |
Uranium
 
 
Fair Value Inputs [Abstract]
 
 
Credit risk
0.38% 4 5
0.40% 4 5
Average bid/ask consensus pricing
22 2
35 2
Discounted Cash Flow |
Maximum |
Fuel Oils
 
 
Fair Value Inputs [Abstract]
 
 
Escalation rate
2.00% 2 3
 
Counterparty credit risk
0.22% 4 5
 
Credit risk
0.38% 4 5
 
Discounted Cash Flow |
Maximum |
Natural Gas
 
 
Fair Value Inputs [Abstract]
 
 
Counterparty credit risk
8.00% 4 5
12.00% 4 5
Credit risk
0.38% 4 5
0.40% 4 5
Nodal basis
0 2
0 2
Discounted Cash Flow |
Maximum |
Power
 
 
Fair Value Inputs [Abstract]
 
 
Counterparty credit risk
 
0.86% 4 5
Credit risk
0.38% 4 5
0.40% 4 5
Average bid/ask consensus peak and off-peak pricing
44 6
39 6
Estimated auction price for FTRs
5,270 2
2,057 2
Nodal basis
0 6
(1)6
Discounted Cash Flow |
Maximum |
Uranium
 
 
Fair Value Inputs [Abstract]
 
 
Credit risk
0.38% 4 5
0.40% 4 5
Average bid/ask consensus pricing
24 2
42 2
Discounted Cash Flow |
Weighted Average |
Fuel Oils
 
 
Fair Value Inputs [Abstract]
 
 
Escalation rate
0.00% 2 3
 
Counterparty credit risk
0.15% 4 5
 
Credit risk
0.38% 4 5
 
Discounted Cash Flow |
Weighted Average |
Natural Gas
 
 
Fair Value Inputs [Abstract]
 
 
Counterparty credit risk
1.00% 4 5
7.00% 4 5
Credit risk
0.38% 4 5
0.40% 4 5
Nodal basis
(0.50)2
(0.10)2
Discounted Cash Flow |
Weighted Average |
Power
 
 
Fair Value Inputs [Abstract]
 
 
Counterparty credit risk
 
0.86% 4 5
Credit risk
0.38% 4 5
0.40% 4 5
Average bid/ask consensus peak and off-peak pricing
29 6
29 6
Estimated auction price for FTRs
125 2
211 2
Nodal basis
(2)6
(3)6
Discounted Cash Flow |
Weighted Average |
Uranium
 
 
Fair Value Inputs [Abstract]
 
 
Credit risk
0.38% 4 5
0.40% 4 5
Average bid/ask consensus pricing
22 2
37 2
Option Model |
Minimum |
Fuel Oils
 
 
Fair Value Inputs [Abstract]
 
 
Volatilities
24.00% 2
 
Option Model |
Minimum |
Natural Gas
 
 
Fair Value Inputs [Abstract]
 
 
Volatilities
31.00% 2
35.00% 2
Nodal basis
(0.40)2
(0.30)5
Option Model |
Minimum |
Uranium
 
 
Fair Value Inputs [Abstract]
 
 
Volatilities
24.00% 2
20.00% 2
Option Model |
Maximum |
Fuel Oils
 
 
Fair Value Inputs [Abstract]
 
 
Volatilities
66.00% 2
 
Option Model |
Maximum |
Natural Gas
 
 
Fair Value Inputs [Abstract]
 
 
Volatilities
66.00% 2
55.00% 2
Nodal basis
(0.10)2
0 5
Option Model |
Maximum |
Uranium
 
 
Fair Value Inputs [Abstract]
 
 
Volatilities
24.00% 2
20.00% 2
Option Model |
Weighted Average |
Fuel Oils
 
 
Fair Value Inputs [Abstract]
 
 
Volatilities
28.00% 2
 
Option Model |
Weighted Average |
Natural Gas
 
 
Fair Value Inputs [Abstract]
 
 
Volatilities
36.00% 2
45.00% 2
Nodal basis
(0.20)2
(0.20)5
Option Model |
Weighted Average |
Uranium
 
 
Fair Value Inputs [Abstract]
 
 
Volatilities
24.00% 2
20.00% 2
Fundamental Energy Production Model |
Minimum |
Power
 
 
Fair Value Inputs [Abstract]
 
 
Escalation rate
5.00% 2 7
3.00% 2 7
Estimated future gas prices
3 2
3 2
Fundamental Energy Production Model |
Maximum |
Power
 
 
Fair Value Inputs [Abstract]
 
 
Escalation rate
5.00% 2 7
3.00% 2 7
Estimated future gas prices
4 2
4 2
Fundamental Energy Production Model |
Weighted Average |
Power
 
 
Fair Value Inputs [Abstract]
 
 
Escalation rate
5.00% 2 7
3.00% 2 7
Estimated future gas prices
3 2
4 2
Contract Price Allocation |
Minimum |
Power
 
 
Fair Value Inputs [Abstract]
 
 
Estimated renewable energy credit costs
5 2
5 2
Contract Price Allocation |
Maximum |
Power
 
 
Fair Value Inputs [Abstract]
 
 
Estimated renewable energy credit costs
7 2
7 2
Contract Price Allocation |
Weighted Average |
Power
 
 
Fair Value Inputs [Abstract]
 
 
Estimated renewable energy credit costs
6 2
6 2
Derivative liabilities |
Fuel Oils
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative liabilities
0 1
 
Derivative liabilities |
Natural Gas
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative liabilities
(1)1
(1)1
Derivative liabilities |
Power
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative liabilities
(187)1 8
(170)1 8
Derivative liabilities |
Uranium
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative liabilities
(4)1
(1)1
Derivative assets |
Fuel Oils
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative assets
1 1
 
Derivative assets |
Natural Gas
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative assets
1 1
1 1
Derivative assets |
Power
 
 
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
 
 
Derivative assets
$ 9 1 8
$ 16 1 8
Fair Value Measurements (Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
$ 605 1
$ 557 2
Assets
632 3
575 3
Excluded receivables, payables, and accrued income, net
2 
(1)
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
409 
368 
Assets
413 3
368 3
Significant Other Observable Inputs (Level 2)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
196 
189 
Assets
208 3
190 3
Significant Other Unobservable Inputs (Level 3)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Assets
11 3
17 3
Cash And Cash Equivalents
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
1 
4 
Cash And Cash Equivalents |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
1 
4 
Commodity Contract
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
27 3
18 3
Derivative liabilities
211 3
264 3
Commodity Contract |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
4 3
 
Derivative liabilities
5 3
30 3
Commodity Contract |
Significant Other Observable Inputs (Level 2)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
12 3
1 3
Derivative liabilities
14 3
62 3
Commodity Contract |
Significant Other Unobservable Inputs (Level 3)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
11 3
17 3
Derivative liabilities
192 3
172 3
Fuel Oils
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
3 3
 
Derivative liabilities
5 3
29 3
Fuel Oils |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
2 3
 
Derivative liabilities
5 3
29 3
Fuel Oils |
Significant Other Unobservable Inputs (Level 3)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
1 3
 
Derivative liabilities
   3
 
Natural Gas
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
15 3
2 3
Derivative liabilities
14 3
64 3
Natural Gas |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
2 3
 
Derivative liabilities
0 3
1 3
Natural Gas |
Significant Other Observable Inputs (Level 2)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
12 3
1 3
Derivative liabilities
13 3
62 3
Natural Gas |
Significant Other Unobservable Inputs (Level 3)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
1 3
 
Derivative liabilities
1 3
1 3
Power
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
9 3
16 3
Derivative liabilities
188 3
170 3
Power |
Significant Other Observable Inputs (Level 2)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
 
0 3
Derivative liabilities
1 3
0 3
Power |
Significant Other Unobservable Inputs (Level 3)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
9 3
 
Derivative liabilities
187 3
170 3
Uranium
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative liabilities
4 3
1 3
Uranium |
Significant Other Unobservable Inputs (Level 3)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative liabilities
4 3
1 3
Equity Securities |
U.S. Large Capitalization
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
408 
364 
Equity Securities |
U.S. Large Capitalization |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
408 
364 
Debt Securities |
Corporate Bonds
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
67 
58 
Debt Securities |
Corporate Bonds |
Significant Other Observable Inputs (Level 2)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
67 
58 
Debt Securities |
U.S. treasury and agency securities
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
112 
109 
Debt Securities |
U.S. treasury and agency securities |
Significant Other Observable Inputs (Level 2)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
112 
109 
Debt Securities |
Other debt securities
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
17 
22 
Debt Securities |
Other debt securities |
Significant Other Observable Inputs (Level 2)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
17 
22 
Union Electric Company
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
605 1
557 2
Assets
619 3
574 3
Union Electric Company |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
409 
368 
Assets
411 3
368 3
Union Electric Company |
Significant Other Observable Inputs (Level 2)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
196 
189 
Assets
197 3
189 3
Union Electric Company |
Significant Other Unobservable Inputs (Level 3)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Assets
11 3
17 3
Union Electric Company |
Cash And Cash Equivalents
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
1 
4 
Union Electric Company |
Cash And Cash Equivalents |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
1 
4 
Union Electric Company |
Commodity Contract
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
14 3
17 3
Derivative liabilities
18 3
44 3
Union Electric Company |
Commodity Contract |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
2 3
 
Derivative liabilities
5 3
29 3
Union Electric Company |
Commodity Contract |
Significant Other Observable Inputs (Level 2)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
1 3
0 3
Derivative liabilities
7 3
13 3
Union Electric Company |
Commodity Contract |
Significant Other Unobservable Inputs (Level 3)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
11 3
17 3
Derivative liabilities
6 3
2 3
Union Electric Company |
Fuel Oils
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
3 3
 
Derivative liabilities
5 3
29 3
Union Electric Company |
Fuel Oils |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
2 3
 
Derivative liabilities
5 3
29 3
Union Electric Company |
Fuel Oils |
Significant Other Unobservable Inputs (Level 3)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
1 3
 
Union Electric Company |
Natural Gas
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
2 3
1 3
Derivative liabilities
6 3
14 3
Union Electric Company |
Natural Gas |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative liabilities
 
0 3
Union Electric Company |
Natural Gas |
Significant Other Observable Inputs (Level 2)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
1 3
 
Derivative liabilities
6 3
13 3
Union Electric Company |
Natural Gas |
Significant Other Unobservable Inputs (Level 3)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
1 3
1 3
Derivative liabilities
 
1 3
Union Electric Company |
Power
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
9 3
16 3
Derivative liabilities
3 3
 
Union Electric Company |
Power |
Significant Other Observable Inputs (Level 2)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
 
0 3
Derivative liabilities
1 3
 
Union Electric Company |
Power |
Significant Other Unobservable Inputs (Level 3)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
9 3
16 3
Derivative liabilities
2 3
 
Union Electric Company |
Uranium
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative liabilities
4 3
1 3
Union Electric Company |
Uranium |
Significant Other Unobservable Inputs (Level 3)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative liabilities
4 3
1 3
Union Electric Company |
Equity Securities |
U.S. Large Capitalization
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
408 
364 
Union Electric Company |
Equity Securities |
U.S. Large Capitalization |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
408 
364 
Union Electric Company |
Debt Securities |
Corporate Bonds
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
67 
58 
Union Electric Company |
Debt Securities |
Corporate Bonds |
Significant Other Observable Inputs (Level 2)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
67 
58 
Union Electric Company |
Debt Securities |
U.S. treasury and agency securities
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
112 
109 
Union Electric Company |
Debt Securities |
U.S. treasury and agency securities |
Significant Other Observable Inputs (Level 2)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
112 
109 
Union Electric Company |
Debt Securities |
Other debt securities
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
17 
22 
Union Electric Company |
Debt Securities |
Other debt securities |
Significant Other Observable Inputs (Level 2)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Nuclear Decommissioning Trust Fund
17 
22 
Ameren Illinois Company |
Commodity Contract
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative liabilities
193 3
220 3
Ameren Illinois Company |
Commodity Contract |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative liabilities
 
1 3
Ameren Illinois Company |
Commodity Contract |
Significant Other Observable Inputs (Level 2)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative liabilities
7 3
49 3
Ameren Illinois Company |
Commodity Contract |
Significant Other Unobservable Inputs (Level 3)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative liabilities
186 3
170 3
Ameren Illinois Company |
Natural Gas
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
13 3
1 3
Derivative liabilities
8 3
50 3
Ameren Illinois Company |
Natural Gas |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
2 3
 
Derivative liabilities
 
1 3
Ameren Illinois Company |
Natural Gas |
Significant Other Observable Inputs (Level 2)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative assets
11 3
1 3
Derivative liabilities
7 3
49 3
Ameren Illinois Company |
Natural Gas |
Significant Other Unobservable Inputs (Level 3)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative liabilities
1 3
 
Ameren Illinois Company |
Power
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative liabilities
185 3
170 3
Ameren Illinois Company |
Power |
Significant Other Unobservable Inputs (Level 3)
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Derivative liabilities
$ 185 3
$ 170 3
Fair Value Measurements (Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level 3 In The Fair Value Hierarchy) (Details) (Power, USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
 
 
 
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value
$ 178 
$ (154)
$ (133)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
 
 
 
Included in regulatory assets/liabilities
(30)
(39)
 
Purchases
13 
29 
 
Settlements
(7)
(10)
 
Transfers out of Level 3
 
(1)
 
Change in unrealized gains (losses) related to assets/liabilities still held
(27)
(39)
 
Union Electric Company
 
 
 
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
 
 
 
Beginning balance
16 
9 
 
Included in regulatory assets/liabilities
(1)
2 
 
Purchases
13 
29 
 
Settlements
(21)
(23)
 
Transfers out of Level 3
 
(1)
 
Ending balance
7 
16 
 
Change in unrealized gains (losses) related to assets/liabilities still held
0 
0 
 
Ameren Illinois Company
 
 
 
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
 
 
 
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value
185 
(170)
(142)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
 
 
 
Included in regulatory assets/liabilities
(29)
(41)
 
Settlements
14 
13 
 
Change in unrealized gains (losses) related to assets/liabilities still held
$ (27)
$ (39)
 
Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Long-Term Debt And Preferred Stock) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Dec. 31, 2015
Carrying Amount
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Long-term Debt and Capital Lease Obligations
$ 7,276 1
$ 7,275 1
Preferred stock
142 1
142 1
Fair Value
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Long-term debt and capital lease obligations (including current portion)
7,772 1
7,814 1
Preferred stock
131 1
125 1
Union Electric Company |
Carrying Amount
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Long-term Debt and Capital Lease Obligations
3,994 
4,110 
Preferred stock
80 
80 
Union Electric Company |
Fair Value
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Long-term debt and capital lease obligations (including current portion)
4,304 
4,449 
Preferred stock
79 
75 
Ameren Illinois Company |
Carrying Amount
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Long-term Debt and Capital Lease Obligations
2,588 
2,471 
Preferred stock
62 
62 
Ameren Illinois Company |
Fair Value
 
 
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
 
 
Long-term debt and capital lease obligations (including current portion)
2,765 
2,665 
Preferred stock
$ 52 
$ 50 
Nuclear Decommissioning Trust Fund Investments (Fair Values Of Investments In Debt And Equity Securities In Nuclear Decommissioning Trust Fund) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Dec. 31, 2015
Nuclear Decommissioning Trust Fund Investments [Line Items]
 
 
Cost
$ 361 
$ 341 
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax
256 
226 
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax
10 
11 
Fair Value
607 
556 
Debt Securities
 
 
Nuclear Decommissioning Trust Fund Investments [Line Items]
 
 
Cost
197 
191 
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax
3 
2 
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax
4 
4 
Fair Value
196 
189 
Equity Securities
 
 
Nuclear Decommissioning Trust Fund Investments [Line Items]
 
 
Cost
161 
147 
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax
253 
224 
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax
6 
7 
Fair Value
408 
364 
Cash
 
 
Nuclear Decommissioning Trust Fund Investments [Line Items]
 
 
Cost
1 
4 
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax
0 
0 
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax
0 
0 
Fair Value
1 
4 
Other Debt And Equity Securities
 
 
Nuclear Decommissioning Trust Fund Investments [Line Items]
 
 
Cost
2 1
1 1
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax
0 
0 
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax
0 
0 
Fair Value
$ 2 1
$ 1 1
Nuclear Decommissioning Trust Fund Investments (Costs And Fair Values Of Investments In Debt Securities In Nuclear Decommissioning Trust Fund According To Contractual Maturities) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
 
Cost, Less than 5 years
$ 105 
Cost, 5 years to 10 years
47 
Cost, Due after 10 years
45 
Cost, Total
197 
Fair Value, Less than 5 years
104 
Fair Value, 5 years to 10 years
47 
Fair Value, Due after 10 years
45 
Fair Value, Total
$ 196 
Callaway Energy Center (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
mill
Dec. 31, 2015
Dec. 31, 2014
Loss Contingencies [Line Items]
 
 
 
Nwf Fee Number Of Mills
1 
 
 
Former Gain Contingency, Recognized in Current Period
$ 24 
$ 14 
$ 15 
Nuclear Plant
 
 
 
Loss Contingencies [Line Items]
 
 
 
Annual decommissioning costs included in costs of service
$ 7 
 
 
Retirement Benefits (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Defined Benefit Plan, Funded Status of Plan
$ 774 1
$ 567 1
 
Defined Benefit Plan Assumptions Used Calculating Benefit Obligation, Change in Discount Rate
0.50% 
 
 
Number of high-quality corporate bonds
700 
 
 
Defined benefit plan, estimated future employer contributions during the next five years
290 
 
 
Amortization basis, straight line, in years
10 years 
 
 
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Defined Benefit Plan, Funded Status of Plan
(705)1
(544)1
 
Expected return on plan assets
7.00% 
7.25% 
7.25% 
Postretirement Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Defined Benefit Plan, Funded Status of Plan
(69)1
(23)1
 
Expected return on plan assets
7.00% 
7.00% 
7.00% 
Minimum
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Defined benefit plan, estimated future employer contributions during the next five years
50 
 
 
Maximum
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Defined benefit plan, estimated future employer contributions during the next five years
$ 70 
 
 
Union Electric Company |
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Future funding requirement, percentage
35.00% 
 
 
Ameren Illinois Company |
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Future funding requirement, percentage
55.00% 
 
 
Retirement Benefits (Summary Of Benefit Liability Recorded) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
 
 
Benefit liability recorded on the balance sheet
$ 774 1
$ 567 1
Union Electric Company
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Benefit liability recorded on the balance sheet
293 
236 
Ameren Illinois Company
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Benefit liability recorded on the balance sheet
$ 315 
$ 219 
Retirement Benefits (Funded Status Of Benefit Plans And Amounts Included In Regulatory Assets And OCI) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Change in plan assets:
 
 
 
Funded status – deficiency
$ (774)1
$ (567)1
 
Amounts recognized in the balance sheet consist of:
 
 
 
Noncurrent liability
769 
580 
 
Net liability recognized
774 1
567 1
 
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Accumulated benefit obligation at end of year
4,288 1
3,995 1
 
Change in benefit obligation:
 
 
 
Net benefit obligation at beginning of year
4,197 1
4,410 1
 
Service cost
81 1
92 1
79 
Interest cost
185 1
174 1
183 
Actuarial (gain) loss
265 1
(256)1
 
Settlement
 
(2)1
 
Benefits paid
(210)1
(221)1
 
Net benefit obligation at end of year
4,518 1
4,197 1
4,410 1
Change in plan assets:
 
 
 
Fair value of plan assets at beginning of year
3,653 1
3,794 1
 
Actual return on plan assets
313 1
(29)1
 
Employer contributions
57 1
111 1
99 
Settlement
 
(2)1
 
Benefits paid
(210)1
(221)1
 
Fair value of plan assets at end of year
3,813 1
3,653 1
3,794 1
Funded status – deficiency
705 1
544 1
 
Accrued benefit cost at December 31
705 1
544 1
 
Amounts recognized in the balance sheet consist of:
 
 
 
Current liability(d)
3 1 2
3 1 2
 
Noncurrent liability
702 1
541 1
 
Net liability recognized
705 1
544 1
 
Amounts recognized in regulatory assets consist of:
 
 
 
Net actuarial (gain) loss
535 1
395 1
 
Prior service cost (credit)
(4)1
(5)1
 
Amounts (pretax) recognized in accumulated OCI consist of:
 
 
 
Net actuarial (gain) loss
43 1
17 1
 
Prior service cost (credit)
 
0 1
 
Total
574 1
407 1
 
Postretirement Benefits
 
 
 
Change in benefit obligation:
 
 
 
Net benefit obligation at beginning of year
1,094 1
1,203 1
 
Service cost
19 1
24 1
19 
Interest cost
50 1
48 1
50 
Participant contributions
8 1
8 1
 
Actuarial (gain) loss
52 1
(133)1
 
Benefits paid
(54)1
(56)1
 
Federal subsidy on benefits paid
1 1
0 1
 
Net benefit obligation at end of year
1,170 1
1,094 1
1,203 1
Change in plan assets:
 
 
 
Fair value of plan assets at beginning of year
1,071 1
1,109 1
 
Actual return on plan assets
73 1
(8)1
 
Employer contributions
2 1
18 1
6 
Federal subsidy on benefits paid
1 1
0 1
 
Participant contributions
8 1
8 1
 
Benefits paid
(54)1
(56)1
 
Fair value of plan assets at end of year
1,101 1
1,071 1
1,109 1
Funded status – deficiency
69 1
23 1
 
Accrued benefit cost at December 31
69 1
23 1
 
Amounts recognized in the balance sheet consist of:
 
 
 
Noncurrent asset
0 1 3
(18)1 3
 
Current liability(d)
2 1 2
2 1 2
 
Noncurrent liability
67 1
39 1
 
Net liability recognized
69 1
23 1
 
Amounts recognized in regulatory assets consist of:
 
 
 
Net actuarial (gain) loss
(29)1
(82)1
 
Prior service cost (credit)
(8)1
(11)1
 
Amounts (pretax) recognized in accumulated OCI consist of:
 
 
 
Net actuarial (gain) loss
0 1
(3)1
 
Prior service cost (credit)
(1)1
0 1
 
Total
$ (38)1
$ (96)1
 
Retirement Benefits (Assumptions Used To Determine Benefit Obligations) (Details)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Discount rate at measurement date
4.00% 
4.50% 
 
Increase in future compensation
3.50% 
3.50% 
 
Postretirement Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Discount rate at measurement date
4.00% 
4.50% 
 
Increase in future compensation
3.50% 
3.50% 
 
Medical cost trend rate (initial)
5.00% 
5.00% 
5.00% 
Medical cost trend rate (ultimate)
5.00% 
5.00% 
5.00% 
Retirement Benefits (Cash Contributions Made To Benefit Plans) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Cash contributions to benefit plans
$ 57 1
$ 111 1
$ 99 
Postretirement Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Cash contributions to benefit plans
2 1
18 1
6 
Union Electric Company |
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Cash contributions to benefit plans
21 
47 
41 
Union Electric Company |
Postretirement Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Cash contributions to benefit plans
1 
8 
3 
Ameren Illinois Company |
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Cash contributions to benefit plans
30 
45 
39 
Ameren Illinois Company |
Postretirement Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Cash contributions to benefit plans
1 
8 
2 
Other |
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Cash contributions to benefit plans
6 
19 
19 
Other |
Postretirement Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Cash contributions to benefit plans
$ 0 
$ 2 
$ 1 
Retirement Benefits (Target Allocation Of The Plans' Asset Categories) (Details)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Pension Benefits
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Defined Benefit Plan, Actual Plan Asset Allocations
100.00% 
100.00% 
Pension Benefits |
Cash And Cash Equivalents
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Minimum Target Allocation
0.00% 
 
Maximum Target Allocation
5.00% 
 
Defined Benefit Plan, Actual Plan Asset Allocations
1.00% 
1.00% 
Pension Benefits |
Equity Securities
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Minimum Target Allocation
51.00% 
 
Maximum Target Allocation
61.00% 
 
Defined Benefit Plan, Actual Plan Asset Allocations
57.00% 
54.00% 
Pension Benefits |
U.S. large capitalization
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Minimum Target Allocation
29.00% 
 
Maximum Target Allocation
39.00% 
 
Defined Benefit Plan, Actual Plan Asset Allocations
34.00% 
34.00% 
Pension Benefits |
U.S. small and mid-capitalization
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Minimum Target Allocation
3.00% 
 
Maximum Target Allocation
13.00% 
 
Defined Benefit Plan, Actual Plan Asset Allocations
9.00% 
7.00% 
Pension Benefits |
International and emerging markets
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Minimum Target Allocation
9.00% 
 
Maximum Target Allocation
19.00% 
 
Defined Benefit Plan, Actual Plan Asset Allocations
14.00% 
13.00% 
Pension Benefits |
Debt Securities
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Minimum Target Allocation
35.00% 
 
Maximum Target Allocation
45.00% 
 
Defined Benefit Plan, Actual Plan Asset Allocations
37.00% 
40.00% 
Pension Benefits |
Real estate
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Minimum Target Allocation
0.00% 
 
Maximum Target Allocation
9.00% 
 
Defined Benefit Plan, Actual Plan Asset Allocations
5.00% 
5.00% 
Pension Benefits |
Private equity
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Minimum Target Allocation
0.00% 
 
Maximum Target Allocation
5.00% 
 
Defined Benefit Plan, Actual Plan Asset Allocations
1.00% 1
1.00% 1
Postretirement Benefits
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Defined Benefit Plan, Actual Plan Asset Allocations
100.00% 
100.00% 
Postretirement Benefits |
Cash And Cash Equivalents
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Minimum Target Allocation
0.00% 
 
Maximum Target Allocation
7.00% 
 
Defined Benefit Plan, Actual Plan Asset Allocations
3.00% 
4.00% 
Postretirement Benefits |
Equity Securities
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Minimum Target Allocation
55.00% 
 
Maximum Target Allocation
65.00% 
 
Defined Benefit Plan, Actual Plan Asset Allocations
61.00% 
59.00% 
Postretirement Benefits |
U.S. large capitalization
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Minimum Target Allocation
34.00% 
 
Maximum Target Allocation
44.00% 
 
Defined Benefit Plan, Actual Plan Asset Allocations
40.00% 
39.00% 
Postretirement Benefits |
U.S. small and mid-capitalization
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Minimum Target Allocation
2.00% 
 
Maximum Target Allocation
12.00% 
 
Defined Benefit Plan, Actual Plan Asset Allocations
7.00% 
7.00% 
Postretirement Benefits |
International
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Minimum Target Allocation
9.00% 
 
Maximum Target Allocation
19.00% 
 
Defined Benefit Plan, Actual Plan Asset Allocations
14.00% 
13.00% 
Postretirement Benefits |
Debt Securities
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
Minimum Target Allocation
33.00% 
 
Maximum Target Allocation
43.00% 
 
Defined Benefit Plan, Actual Plan Asset Allocations
36.00% 
37.00% 
Retirement Benefits (Fair Value Of Plan Assets Utilizing Fair Value Hierarchy) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
$ 3,813 1
$ 3,653 1
$ 3,794 1
Alternative Investments, Fair Value Disclosure
1,995 2
1,749 2
 
Pension Benefits |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
494 
396 
 
Pension Benefits |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
1,434 
1,603 
 
Pension Benefits |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
Cash And Cash Equivalents
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
33 
20 
 
Alternative Investments, Fair Value Disclosure
33 2
20 2
 
Pension Benefits |
Cash And Cash Equivalents |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
Cash And Cash Equivalents |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
Cash And Cash Equivalents |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
U.S. large capitalization
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
1,352 
1,296 
 
Alternative Investments, Fair Value Disclosure
1,352 2
1,296 2
 
Pension Benefits |
U.S. large capitalization |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
U.S. large capitalization |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
U.S. large capitalization |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
U.S. small and mid-capitalization
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
361 
268 
 
Alternative Investments, Fair Value Disclosure
0 2
0 2
 
Pension Benefits |
U.S. small and mid-capitalization |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
361 
268 
 
Pension Benefits |
U.S. small and mid-capitalization |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
U.S. small and mid-capitalization |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
International and emerging markets
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
522 
491 
 
Alternative Investments, Fair Value Disclosure
389 2
243 2
 
Pension Benefits |
International and emerging markets |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
133 
122 
 
Pension Benefits |
International and emerging markets |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
126 
 
Pension Benefits |
International and emerging markets |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
Corporate Bonds
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
630 
631 
 
Alternative Investments, Fair Value Disclosure
13 2
14 2
 
Pension Benefits |
Corporate Bonds |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
Corporate Bonds |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
617 
617 
 
Pension Benefits |
Corporate Bonds |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
Municipal Bonds
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
95 
104 
 
Alternative Investments, Fair Value Disclosure
0 2
0 2
 
Pension Benefits |
Municipal Bonds |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
Municipal Bonds |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
95 
104 
 
Pension Benefits |
Municipal Bonds |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
U.S. treasury and agency securities
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
701 
757 
 
Alternative Investments, Fair Value Disclosure
0 2
0 2
 
Pension Benefits |
U.S. treasury and agency securities |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
6 
 
Pension Benefits |
U.S. treasury and agency securities |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
701 
751 
 
Pension Benefits |
U.S. treasury and agency securities |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
Other
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
21 
5 
 
Alternative Investments, Fair Value Disclosure
0 2
0 2
 
Pension Benefits |
Other |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
Other |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
21 
5 
 
Pension Benefits |
Other |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
Real estate
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
202 
168 
 
Alternative Investments, Fair Value Disclosure
202 2
168 2
 
Pension Benefits |
Real estate |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
Real estate |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
Real estate |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
Private equity
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
6 
8 
 
Alternative Investments, Fair Value Disclosure
6 2
8 2
 
Pension Benefits |
Private equity |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
Private equity |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
Private equity |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Pension Benefits |
Medical benefit assets
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
(132)3
(123)3
 
Pension Benefits |
Net receivables
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
22 4
28 4
 
Pension Benefits |
Includes Medical Benefit Component Under Section401 H And Excludes Receivables Related To Pending Security Sales [Member]
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
3,923 
3,748 
 
Pension Benefits |
Excludes Medical Benefit Component Under Section401 H And Includes Receivables Related To Pending Security Sales [Member]
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
3,813 
3,653 
 
Postretirement Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
1,101 1
1,071 1
1,109 1
Alternative Investments, Fair Value Disclosure
212 2
189 2
 
Postretirement Benefits |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
456 
431 
 
Postretirement Benefits |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
326 
356 
 
Postretirement Benefits |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
Cash And Cash Equivalents
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
53 
61 
 
Alternative Investments, Fair Value Disclosure
0 2
0 2
 
Postretirement Benefits |
Cash And Cash Equivalents |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
53 
61 
 
Postretirement Benefits |
Cash And Cash Equivalents |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
Cash And Cash Equivalents |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
U.S. large capitalization
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
392 
370 
 
Alternative Investments, Fair Value Disclosure
101 2
98 2
 
Postretirement Benefits |
U.S. large capitalization |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
291 
272 
 
Postretirement Benefits |
U.S. large capitalization |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
U.S. large capitalization |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
U.S. small and mid-capitalization
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
72 
65 
 
Alternative Investments, Fair Value Disclosure
0 2
0 2
 
Postretirement Benefits |
U.S. small and mid-capitalization |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
72 
65 
 
Postretirement Benefits |
U.S. small and mid-capitalization |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
U.S. small and mid-capitalization |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
International
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
132 
126 
 
Alternative Investments, Fair Value Disclosure
92 2
55 2
 
Postretirement Benefits |
International |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
40 
33 
 
Postretirement Benefits |
International |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
38 
 
Postretirement Benefits |
International |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
Other Equity
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
7 
7 
 
Alternative Investments, Fair Value Disclosure
0 2
0 2
 
Postretirement Benefits |
Other Equity |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
Other Equity |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
7 
7 
 
Postretirement Benefits |
Other Equity |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
Corporate Bonds
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
141 
138 
 
Alternative Investments, Fair Value Disclosure
0 2
0 2
 
Postretirement Benefits |
Corporate Bonds |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
Corporate Bonds |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
141 
138 
 
Postretirement Benefits |
Corporate Bonds |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
Municipal Bonds
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
110 
114 
 
Alternative Investments, Fair Value Disclosure
0 2
0 2
 
Postretirement Benefits |
Municipal Bonds |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
Municipal Bonds |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
110 
114 
 
Postretirement Benefits |
Municipal Bonds |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
U.S. treasury and agency securities
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
68 
55 
 
Alternative Investments, Fair Value Disclosure
0 2
0 2
 
Postretirement Benefits |
U.S. treasury and agency securities |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
U.S. treasury and agency securities |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
68 
55 
 
Postretirement Benefits |
U.S. treasury and agency securities |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
Other
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
19 
40 
 
Alternative Investments, Fair Value Disclosure
19 2
36 2
 
Postretirement Benefits |
Other |
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
Other |
Significant Other Observable Inputs (Level 2)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
4 
 
Postretirement Benefits |
Other |
Significant Other Unobservable Inputs (Level 3)
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
0 
0 
 
Postretirement Benefits |
Medical benefit assets
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
132 3
123 3
 
Postretirement Benefits |
Net payables
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
(25)5
(28)5
 
Postretirement Benefits |
Excludes Medical Benefit Component Under Section401 H And Excludes Payables Related To Pending Security Sales [Member]
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
994 
976 
 
Postretirement Benefits |
Includes Medical Benefit Component Under Section401 H And Excludes Payables Related To Pending Security Sales [Member]
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Fair value of plan assets
$ 1,101 
$ 1,071 
 
Retirement Benefits (Components Of Net Periodic Benefit Cost) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Service cost
$ 81 1
$ 92 1
$ 79 
Interest cost
185 1
174 1
183 
Expected return on plan assets
(253)
(248)
(229)
Prior service credit
(1)
(1)
(1)
Actuarial (gain) loss
32 
74 
49 
Settlement Loss
 
1 
 
Net periodic benefit cost (benefit)
44 
92 
81 
Postretirement Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Service cost
19 1
24 1
19 
Interest cost
50 1
48 1
50 
Expected return on plan assets
(72)
(68)
(65)
Prior service credit
(5)
(5)
(5)
Actuarial (gain) loss
(11)
5 
(7)
Settlement Loss
 
0 
 
Net periodic benefit cost (benefit)
$ (19)
$ 4 
$ (8)
Retirement Benefits (Summary Of Estimated Amortizable Amounts From Regulatory Assets and Accumulated OCI Into Net Periodic Benefit Cost) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Pension Benefits
 
Defined Benefit Plan Disclosure [Line Items]
 
Prior service credit
$ (1)1
Net actuarial (gain) loss
50 1
Net actuarial loss
4 1
Net periodic benefit cost
53 1
Postretirement Benefits
 
Defined Benefit Plan Disclosure [Line Items]
 
Prior service credit
(5)1
Net actuarial (gain) loss
(7)1
Net actuarial loss
0 1
Net periodic benefit cost
$ (12)1
Retirement Benefits (Summary Of Benefit Plan Costs Incurred) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Net periodic benefit cost
$ 44 
$ 92 
$ 81 
Postretirement Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Net periodic benefit cost
(19)
4 
(8)
Union Electric Company |
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Net periodic benefit cost
26 1
54 1
50 1
Union Electric Company |
Postretirement Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Net periodic benefit cost
(5)1
8 1
3 1
Ameren Illinois Company |
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Net periodic benefit cost
22 
38 
30 
Ameren Illinois Company |
Postretirement Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Net periodic benefit cost
(13)
(3)
(9)
Other |
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Net periodic benefit cost
(4)
0 
1 
Other |
Postretirement Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Net periodic benefit cost
(1)
(1)
(2)
Parent Company |
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Net periodic benefit cost
44 
92 
81 
Parent Company |
Postretirement Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Net periodic benefit cost
$ (19)
$ 4 
$ (8)
Retirement Benefits (Schedule Of Expected Payments From Qualified Trust And Company Funds) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Pension Benefits |
Paid From Qualified Trust
 
Defined Benefit Plan Disclosure [Line Items]
 
2017
$ 248 
2018
254 
2019
261 
2020
265 
2021
273 
2022 - 2026
1,405 
Pension Benefits |
Paid From Company Funds
 
Defined Benefit Plan Disclosure [Line Items]
 
2017
3 
2018
3 
2019
3 
2020
3 
2021
3 
2022 - 2026
13 
Postretirement Benefits |
Paid From Qualified Trust
 
Defined Benefit Plan Disclosure [Line Items]
 
2017
54 
2018
57 
2019
59 
2020
61 
2021
63 
2022 - 2026
331 
Postretirement Benefits |
Paid From Company Funds
 
Defined Benefit Plan Disclosure [Line Items]
 
2017
2 
2018
2 
2019
2 
2020
2 
2021
2 
2022 - 2026
$ 12 
Retirement Benefits (Assumptions Used To Determine Net Periodic Benefit Cost) (Details)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Pension Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Discount rate at measurement date
4.50% 
4.00% 
4.75% 
Expected return on plan assets
7.00% 
7.25% 
7.25% 
Increase in future compensation
3.50% 
3.50% 
3.50% 
Postretirement Benefits
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Discount rate at measurement date
4.50% 
4.00% 
4.75% 
Expected return on plan assets
7.00% 
7.00% 
7.00% 
Increase in future compensation
3.50% 
3.50% 
3.50% 
Medical cost trend rate (initial)
5.00% 
5.00% 
5.00% 
Medical cost trend rate (ultimate)
5.00% 
5.00% 
5.00% 
Retirement Benefits (Schedule Of Potential Changes In Key Assumptions) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Pension Benefits
 
Defined Benefit Plan Disclosure [Line Items]
 
Service Cost and Interest Cost, .25% decrease in discount rate
$ (1)
Benefit Obligation, .25% decrease in discount rate
142 
Service Cost and Interest Cost, .25% increase in salary rate
2 
Benefit Obligation, .25% increase in salary rate
16 
Postretirement Benefits
 
Defined Benefit Plan Disclosure [Line Items]
 
Service Cost and Interest Cost, .25% decrease in discount rate
0 
Benefit Obligation, .25% decrease in discount rate
38 
Service Cost and Interest Cost, 1.00% increase in annual medical trend
3 
Benefit Obligation, 1.00% increase in annual medical trend
54 
Service Cost and Interest Cost, 1.00% decrease in annual medical trend
(3)
Benefit Obligation, 1.00% decrease in annual medical trend
$ (54)
Retirement Benefits (Schedule Of Matching Contributions) (Details) (401 (K), USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Employer contributions
$ 29 
$ 29 
$ 28 
Union Electric Company
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Employer contributions
16 
16 
16 
Ameren Illinois Company
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Employer contributions
12 
12 
11 
Other
 
 
 
Defined Benefit Plan Disclosure [Line Items]
 
 
 
Employer contributions
$ 1 
$ 1 
$ 1 
Stock-Based Compensation (Narrative) (Details) (USD $)
In Millions, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
 
 
 
 
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized
8,000,000 
 
 
 
Maximum shares available for grants
5,800,000 
 
 
 
Performance Share Units
 
 
 
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
 
 
 
 
Performance period
3 years 
 
 
 
Percentage of shares issued per share unit, minimum
0.00% 
 
 
 
Percentage of shares issued per share unit, maximum
200.00% 
 
 
 
Amounts paid to settle share units
$ 83 
$ 27 
$ 33 
 
Compensation cost not yet recognized
$ 25 
 
 
 
Expected weighted average recognition period for share-based compensation expense, in months
22 months 
 
 
 
Fair value of each share unit, per share
$ 44.13 1
$ 52.88 
$ 38.90 
 
Closing common share price
 
$ 43.23 
$ 46.13 
$ 36.16 
Three-year risk-free rate
1.31% 
1.10% 
0.78% 
 
Volatility rate, minimum
15.00% 
12.00% 
12.00% 
 
Volatility rate, maximum
20.00% 
18.00% 
18.00% 
 
Stock-Based Compensation (Summary Of Nonvested Shares) (Details) (Performance Share Units, USD $)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Performance Share Units
 
 
 
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
 
 
 
Share Units, Nonvested at beginning of year
1,024,870 
 
 
Share Units, Granted
588,615 1
 
 
Share Units, Unearned or forfeited
(15,949)
 
 
Share Units, Earned and vested
(537,897)2
 
 
Share Units, Nonvested at end of year
1,059,639 
1,024,870 
 
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
 
 
 
Weighted-average Fair Value per Unit, Nonvested at beginning of year
$ 46.08 
 
 
Weighted-averageFair Value per Unit, granted
$ 44.13 1
$ 52.88 
$ 38.90 
Weighted-average Fair Value per Unit, Unearned or forfeited
$ 45.07 
 
 
Weighted-average Fair Value per Unit, Earned and vested
$ 40.12 2
 
 
Weighted-average Fair Value per Unit, Nonvested at end of year
$ 48.04 
$ 46.08 
 
Stock-Based Compensation Stock-Based Compensation (Summary of Expense) (Details) (Performance Share Units, USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
 
 
 
Share-based compensation expense
$ 17 
$ 19 
$ 19 
Employee service share-based compensation, tax benefit from compensation expense
6 
7 
7 
Share-based Compensation Expense, Net of Tax
11 
12 
12 
Ameren Missouri [Member]
 
 
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
 
 
 
Share-based compensation expense
4 
5 
5 
Ameren Illinois Company
 
 
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
 
 
 
Share-based compensation expense
2 
3 
2 
Other
 
 
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
 
 
 
Share-based compensation expense
$ 11 1
$ 11 1
$ 12 1
Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Income Taxes [Line Items]
 
 
 
Statutory federal income tax rate:
35.00% 
35.00% 
35.00% 
Depreciation differences
0.00% 
(1.00%)
 
Amortization of deferred investment tax credit
0.00% 
(1.00%)
(1.00%)
State tax
4.00% 
5.00% 
4.00% 
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Compensation Cost, Percent
(2.00%)1
 
 
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent
1.00% 
 
 
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent
(1.00%)
 
1.00% 
Effective income tax rate
37.00% 
38.00% 
39.00% 
Union Electric Company
 
 
 
Income Taxes [Line Items]
 
 
 
Statutory federal income tax rate:
35.00% 
35.00% 
35.00% 
Depreciation differences
1.00% 
0.00% 
 
Amortization of deferred investment tax credit
(1.00%)
(1.00%)
(1.00%)
State tax
3.00% 
3.00% 
3.00% 
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Compensation Cost, Percent
0.00% 1
 
 
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent
0.00% 
 
 
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent
0.00% 
0.00% 
0.00% 
Effective income tax rate
38.00% 
37.00% 
37.00% 
Ameren Illinois Company
 
 
 
Income Taxes [Line Items]
 
 
 
Statutory federal income tax rate:
35.00% 
35.00% 
35.00% 
Depreciation differences
0.00% 
(2.00%)
 
Amortization of deferred investment tax credit
0.00% 
0.00% 
0.00% 
State tax
5.00% 
5.00% 
6.00% 
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Compensation Cost, Percent
0.00% 1
 
 
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent
0.00% 
 
 
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent
(2.00%)
(1.00%)
 
Effective income tax rate
38.00% 
37.00% 
41.00% 
Income Taxes (Schedule Of Components Of Income Tax Expense (Benefit)) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Income Taxes [Line Items]
 
 
 
Current Federal taxes
$ (1)
$ (2)
$ (37)
Current State taxes
(3)
(4)
(37)
Deferred Federal taxes
299 
299 
369 
Deferred State taxes
92 
76 
88 
Deferred investment tax credits, amortization
(5)
(6)
(6)
Total income tax expense
382 
363 
377 
Union Electric Company
 
 
 
Income Taxes [Line Items]
 
 
 
Current Federal taxes
31 
110 
(13)
Current State taxes
6 
17 
(3)
Deferred Federal taxes
161 
71 
222 
Deferred State taxes
23 
16 
28 
Deferred investment tax credits, amortization
(5)
(5)
(5)
Total income tax expense
216 
209 
229 
Ameren Illinois Company
 
 
 
Income Taxes [Line Items]
 
 
 
Current Federal taxes
(8)
(83)
(51)
Current State taxes
12 
(11)
(2)
Deferred Federal taxes
117 
193 
159 
Deferred State taxes
37 
29 
38 
Deferred investment tax credits, amortization
0 
(1)
(1)
Total income tax expense
158 
127 
143 
Other
 
 
 
Income Taxes [Line Items]
 
 
 
Current Federal taxes
(24)
(29)
27 
Current State taxes
(21)
(10)
(32)
Deferred Federal taxes
21 
35 
(12)
Deferred State taxes
32 
31 
22 
Deferred investment tax credits, amortization
0 
0 
0 
Total income tax expense
$ 8 
$ 27 
$ 5 
Income Taxes (Schedule Of Deferred Tax Assets And Liabilities Resulting From Temporary Differences) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Dec. 31, 2015
Income Taxes [Line Items]
 
 
Plant related
$ 5,019 
$ 4,555 
Regulatory assets, net
74 
80 
Deferred benefit costs
(211)
(207)
Revenue Requirement Reconciliation Adjustment
34 
66 
Tax carryforwards
(676)
(603)
Other
24 
 
Other
 
(6)
Total net accumulated deferred income tax liabilities
4,264 
3,885 
Union Electric Company
 
 
Income Taxes [Line Items]
 
 
Plant related
3,103 
2,931 
Regulatory assets, net
75 
81 
Deferred benefit costs
(76)
(76)
Revenue Requirement Reconciliation Adjustment
0 
0 
Tax carryforwards
(66)
(65)
Other
(23)
(27)
Total net accumulated deferred income tax liabilities
3,013 
2,844 
Ameren Illinois Company
 
 
Income Taxes [Line Items]
 
 
Plant related
1,769 
1,587 
Regulatory assets, net
(1)
(1)
Deferred benefit costs
(38)
(40)
Revenue Requirement Reconciliation Adjustment
34 
66 
Tax carryforwards
(138)
(133)
Other
5 
1 
Total net accumulated deferred income tax liabilities
1,631 
1,480 
Other
 
 
Income Taxes [Line Items]
 
 
Plant related
147 
37 
Regulatory assets, net
0 
0 
Deferred benefit costs
(97)
(91)
Revenue Requirement Reconciliation Adjustment
0 
0 
Tax carryforwards
(472)
(405)
Other
42 
20 
Total net accumulated deferred income tax liabilities
$ (380)
$ (439)
Income Taxes (Schedule Of Net Operating Loss Carryforwards And Tax Credit Carryforwards) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2016
Federal
Dec. 31, 2015
Federal
Dec. 31, 2016
State
Dec. 31, 2015
State
Dec. 31, 2016
Union Electric Company
Dec. 31, 2015
Union Electric Company
Dec. 31, 2016
Union Electric Company
Federal
Dec. 31, 2015
Union Electric Company
Federal
Dec. 31, 2016
Union Electric Company
State
Dec. 31, 2015
Union Electric Company
State
Dec. 31, 2016
Ameren Illinois Company
Dec. 31, 2015
Ameren Illinois Company
Dec. 31, 2016
Ameren Illinois Company
Federal
Dec. 31, 2015
Ameren Illinois Company
Federal
Dec. 31, 2016
Ameren Illinois Company
State
Dec. 31, 2015
Ameren Illinois Company
State
Dec. 31, 2016
Other
Dec. 31, 2015
Other
Dec. 31, 2016
Other
Federal
Dec. 31, 2015
Other
Federal
Dec. 31, 2016
Other
State
Dec. 31, 2015
Other
State
Dec. 31, 2016
Minimum
Federal
Dec. 31, 2016
Minimum
State
Dec. 31, 2016
Maximum
Federal
Dec. 31, 2016
Maximum
State
Operating Loss Carryforwards [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Net operating loss carryforwards
$ 539 
$ 453 
$ 494 1
$ 407 
$ 45 1
$ 46 
$ 37 
$ 39 
$ 33 1
$ 35 
$ 4 1
$ 4 
$ 137 
$ 131 
$ 137 1
$ 127 
$ 0 1
$ 4 
$ 365 
$ 283 
$ 324 1
$ 245 
$ 41 1
$ 38 
 
 
 
 
Tax credit carryforwards
130 
144 
109 1
105 
21 2
41 
29 
26 
29 1
26 
0 2
0 
1 
2 
1 1
1 
0 2
1 
100 
116 
79 1
78 
21 2
40 
 
 
 
 
Tax Credit Carryforward, Valuation Allowance
 
 
 
 
 
(2)
 
 
 
 
 
0 
 
 
 
 
 
0 
 
 
 
 
 
(2)
 
 
 
 
Deferred Tax Assets, Charitable Contribution Carryforwards
18 2
10 
 
 
 
 
0 2
0 
 
 
 
 
0 2
0 
 
 
 
 
18 2
10 
 
 
 
 
 
 
 
 
Deferred Tax Assets, Valuation Allowance, Noncurrent
(11)3
(4)
 
 
 
 
0 3
0 
 
 
 
 
0 3
0 
 
 
 
 
(11)3
(4)
 
 
 
 
 
 
 
 
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent
$ 7 
$ 6 
 
 
 
 
$ 0 
$ 0 
 
 
 
 
$ 0 
$ 0 
 
 
 
 
$ 7 
$ 6 
 
 
 
 
 
 
 
 
Net operating loss carryforward, expiration period start
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Jan. 01, 2029 
Jan. 01, 2029 
Jan. 01, 2036 
Jan. 01, 2036 
Tax credit carryforward, expiration period start
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Jan. 01, 2029 
Jan. 01, 2017 
Jan. 01, 2036 
Jan. 01, 2021 
Income Taxes (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Income Taxes [Line Items]
 
 
 
State corporate income tax rate
4.00% 
5.00% 
4.00% 
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities
 
 
$ 18 
Union Electric Company
 
 
 
Income Taxes [Line Items]
 
 
 
State corporate income tax rate
3.00% 
3.00% 
3.00% 
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities
 
 
18 
State
 
 
 
Income Taxes [Line Items]
 
 
 
State corporate income tax rate
 
7.75% 
 
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities
 
53 
2 
State |
Minimum
 
 
 
Income Taxes [Line Items]
 
 
 
State corporate income tax rate
7.30% 
 
 
State |
Maximum
 
 
 
Income Taxes [Line Items]
 
 
 
State corporate income tax rate
 
 
9.50% 
2007 through 2011 tax year [Member]
 
 
 
Income Taxes [Line Items]
 
 
 
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities
 
 
20 
2007 through 2011 tax year [Member] |
Union Electric Company
 
 
 
Income Taxes [Line Items]
 
 
 
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities
 
 
$ 13 
Related Party Transactions (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Union Electric Company |
Ameren Missouri Power Supply Agreements with Ameren Illinois
 
 
 
Related Party Transaction [Line Items]
 
 
 
Operating Revenues
$ 28 
$ 15 
$ 5 
Union Electric Company |
Ameren Missouri and Ameren Illinois Rent and Facility Services
 
 
 
Related Party Transaction [Line Items]
 
 
 
Operating Revenues
25 
25 
21 
Union Electric Company |
Ameren Missouri and Ameren Illinois miscellaneous support services
 
 
 
Related Party Transaction [Line Items]
 
 
 
Operating Revenues
1 
2 
1 
Union Electric Company |
Total Related Party Operating Revenues [Member]
 
 
 
Related Party Transaction [Line Items]
 
 
 
Operating Revenues
54 
42 
27 
Union Electric Company |
Ameren Services Support Services Agreement
 
 
 
Related Party Transaction [Line Items]
 
 
 
Operating Expenses
129 
131 
124 
Union Electric Company |
Money Pool
 
 
 
Related Party Transaction [Line Items]
 
 
 
Interest (Charges) Income
1 1
1 1
1 1
Ameren Illinois Company
 
 
 
Related Party Transaction [Line Items]
 
 
 
Operating Revenues
0 
0 
0 
Ameren Illinois Company |
Ameren Missouri and Ameren Illinois Rent and Facility Services
 
 
 
Related Party Transaction [Line Items]
 
 
 
Operating Revenues
5 
4 
2 
Ameren Illinois Company |
Ameren Missouri and Ameren Illinois miscellaneous support services
 
 
 
Related Party Transaction [Line Items]
 
 
 
Operating Revenues
1 
1 1
1 1
Ameren Illinois Company |
Total Related Party Operating Revenues [Member]
 
 
 
Related Party Transaction [Line Items]
 
 
 
Operating Revenues
5 
4 
2 
Ameren Illinois Company |
Ameren Illinois Power Supply Agreements with Ameren Missouri
 
 
 
Related Party Transaction [Line Items]
 
 
 
Operating Expenses
28 
15 
5 
Ameren Illinois Company |
Ameren Illinois transmission agreements with ATXI
 
 
 
Related Party Transaction [Line Items]
 
 
 
Operating Expenses
2 
2 
2 
Ameren Illinois Company |
Purchased Power
 
 
 
Related Party Transaction [Line Items]
 
 
 
Operating Expenses
30 
17 
7 
Ameren Illinois Company |
Ameren Services Support Services Agreement
 
 
 
Related Party Transaction [Line Items]
 
 
 
Operating Expenses
123 
119 
109 
Ameren Illinois Company |
Money Pool
 
 
 
Related Party Transaction [Line Items]
 
 
 
Interest (Charges) Income
$ 1 1
$ 1 1
$ 1 1
Related Party Transactions (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
May 31, 2014 |
Union Electric Company
 
Related Party Transaction [Line Items]
 
Energy Supply Agreements Amount
$ 1 
May 31, 2015 |
Union Electric Company
 
Related Party Transaction [Line Items]
 
Energy Supply Agreements Amount
3 
May 31, 2017 |
Union Electric Company
 
Related Party Transaction [Line Items]
 
Energy Supply Agreements Amount
$ 15 
May 2014 Procurement [Member] |
Ameren Illinois Power Supply Agreements with Ameren Missouri |
Ameren Illinois Company
 
Related Party Transaction [Line Items]
 
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power
168,400,000,000 
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power, Rate
51,000,000 
April 2015 Procurement [Member] |
Ameren Illinois Power Supply Agreements with Ameren Missouri |
Ameren Illinois Company
 
Related Party Transaction [Line Items]
 
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power
667,000,000,000 
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power, Rate
36,000,000 
September 2015 Procurement [Member] |
Ameren Illinois Power Supply Agreements with Ameren Missouri |
Ameren Illinois Company
 
Related Party Transaction [Line Items]
 
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power
339,000,000,000 
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power, Rate
38,000,000 
April 2016 Procurement [Member] |
Ameren Illinois Power Supply Agreements with Ameren Missouri |
Ameren Illinois Company
 
Related Party Transaction [Line Items]
 
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power
375,200,000,000 
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power, Rate
35,000,000 
September 2016 Procurement [Member] |
Ameren Illinois Power Supply Agreements with Ameren Missouri |
Ameren Illinois Company
 
Related Party Transaction [Line Items]
 
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power
82,800,000,000 
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power, Rate
34,000,000 
Commitments And Contingencies (Callaway Nuclear Energy Center) (Details) (USD $)
12 Months Ended
Dec. 31, 2016
Commitments and Contingencies [Line Items]
 
Insurance aggregate maximum coverage
$ 13,361,000,000 1
Insurance maximum coverage per incident
127,000,000 
Threshold Amount For Retrospective Insurance Assessment For Covered Loss Under Public Liability And Nuclear Worker Liability Insurance Policy
375,000,000 
Annual payment in the event of an incident at any licensed commercial reactor
19,000,000 
Aggregate maximum assessment per incident under Price-Anderson liability provisions of Atomic Energy Act
127,000,000 
Maximum annual payment to be paid in a calendar year per reactor incident under liability provisions of Atomic Energy Act
19,000,000 
Amount of coverage in excess of primary property liability coverage
2,300,000,000.0 
Amount of weekly indemnity coverage commencing eight weeks after power outage
4,500,000 
Number of weeks of coverage after the first eight weeks of an outage
1 year 
Amount of additional weekly indemnity coverage commencing after initial indemnity coverage
3,600,000 
Number of additional weeks after initial indemnity coverage for power outage, minimum
1 year 4 months 10 days 
Amount of weekly indemnity coverage thereafter not exceeding policy limit
490,000,000 
Number Of Years The Limit Of Liability And The Maximum Potential Annual Payments Are Adjusted
5 years 
Aggregate nuclear power industry insurance policy limit for losses from terrorist attacks within twelve month period
3,240,000,000 
Public Liability And Nuclear Worker Liability - American Nuclear Insurers
 
Commitments and Contingencies [Line Items]
 
Insurance aggregate maximum coverage
375,000,000 2
Insurance maximum coverage per incident
0 
Public Liability And Nuclear Worker Liability - Pool Participation
 
Commitments and Contingencies [Line Items]
 
Insurance aggregate maximum coverage
12,986,000,000 3
Insurance maximum coverage per incident
127,000,000 4
Property Damage - Nuclear Electric Insurance Ltd
 
Commitments and Contingencies [Line Items]
 
Insurance aggregate maximum coverage
2,710,000,000 5
Insurance maximum coverage per incident
30,000,000 6
Replacement Power - Nuclear Electric Insurance Ltd
 
Commitments and Contingencies [Line Items]
 
Insurance aggregate maximum coverage
490,000,000 7
Insurance maximum coverage per incident
7,000,000 6
Sub-limit of Amount of Weekly indemnity Coverage Thereafter Not Exceeding Policy Limit for Non-Nuclear Events
328,000,000 
Property Damage European Mutual Association for Nuclear Insurance
 
Commitments and Contingencies [Line Items]
 
Insurance aggregate maximum coverage
450,000,000 7
Amount of primary property liability coverage
450,000,000 
Property Damage
 
Commitments and Contingencies [Line Items]
 
Insurance aggregate maximum coverage
3,160,000,000 
Insurance maximum coverage per incident
30,000,000 
Radiation Event
 
Commitments and Contingencies [Line Items]
 
Insurance aggregate maximum coverage
2,710,000,000 
Non-radiation event
 
Commitments and Contingencies [Line Items]
 
Insurance aggregate maximum coverage
2,300,000,000 
Aggregate nuclear power industry insurance policy limit for losses from terrorist attacks within twelve month period
$ 1,830,000,000 
Commitments And Contingencies (Schedule Of Lease Obligations) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Commitments and Contingencies [Line Items]
 
 
 
Capital lease payments, due in one year
$ 33 1 2
 
 
Capital lease payments, due in two years
32 1 2
 
 
Capital lease payments, due in three years
32 1 2
 
 
Capital lease payments, due in four years
32 1 2
 
 
Capital lease payments, due in five years
32 1 2
 
 
Capital lease payments, After 5 Years
297 1 2
 
 
Capital lease payments, Total
458 1 2
 
 
Less Amount representing interest, due in one year
27 1
 
 
Less Amount representing interest, due in two years
26 1
 
 
Less Amount representing interest, due in three years
25 1
 
 
Less Amount representing interest, due in four years
25 1
 
 
Less Amount representing interest, due in 5 years
25 1
 
 
Less Amount representing interest, After 5 Years
48 1
 
 
Less Amount representing interest, Total
176 1
 
 
Present value of minimum capital lease payments, due in one year
6 1
 
 
Present value of minimum capital lease payments, due in two years
6 1
 
 
Present value of minimum capital lease payments, due in three years
7 1
 
 
Present value of minimum capital lease payments, due in four years
7 1
 
 
Present value of minimum capital lease payments, due in five years
7 1
 
 
Present value of minimum capital lease payments, After 5 Years
249 1
 
 
Present value of minimum capital lease payments, Total
282 1
 
 
Operating leases, due in one year
13 1 3
 
 
Operating leases, due in two years
12 1 3
 
 
Operating leases, due in three years
12 1 3
 
 
Operating leases, due in four years
11 1 3
 
 
Operating leases, due in five years
10 1 3
 
 
Operating leases, After 5 Years
23 1 3
 
 
Operating leases, Total
81 1 3
 
 
Total lease obligations, due in one year
19 1
 
 
Total lease obligations, due in two years
18 1
 
 
Total lease obligations, due in three years
19 1
 
 
Total lease obligations, due in four years
18 1
 
 
Total lease obligations, due in five years
17 1
 
 
Total lease obligations, After 5 Years
272 1
 
 
Total lease obligations, Total
363 1
 
 
Annual obligation for real estate leases and railroad licenses
3 
 
 
Total rental expense
38 4
36 4
37 4
Union Electric Company
 
 
 
Commitments and Contingencies [Line Items]
 
 
 
Capital lease payments, due in one year
33 2
 
 
Capital lease payments, due in two years
32 2
 
 
Capital lease payments, due in three years
32 2
 
 
Capital lease payments, due in four years
32 2
 
 
Capital lease payments, due in five years
32 2
 
 
Capital lease payments, After 5 Years
297 2
 
 
Capital lease payments, Total
458 2
 
 
Less Amount representing interest, due in one year
27 
 
 
Less Amount representing interest, due in two years
26 
 
 
Less Amount representing interest, due in three years
25 
 
 
Less Amount representing interest, due in four years
25 
 
 
Less Amount representing interest, due in 5 years
25 
 
 
Less Amount representing interest, After 5 Years
48 
 
 
Less Amount representing interest, Total
176 
 
 
Present value of minimum capital lease payments, due in one year
6 
 
 
Present value of minimum capital lease payments, due in two years
6 
 
 
Present value of minimum capital lease payments, due in three years
7 
 
 
Present value of minimum capital lease payments, due in four years
7 
 
 
Present value of minimum capital lease payments, due in five years
7 
 
 
Present value of minimum capital lease payments, After 5 Years
249 
 
 
Present value of minimum capital lease payments, Total
282 
 
 
Operating leases, due in one year
11 3
 
 
Operating leases, due in two years
11 3
 
 
Operating leases, due in three years
11 3
 
 
Operating leases, due in four years
10 3
 
 
Operating leases, due in five years
9 3
 
 
Operating leases, After 5 Years
21 3
 
 
Operating leases, Total
73 3
 
 
Total lease obligations, due in one year
17 
 
 
Total lease obligations, due in two years
17 
 
 
Total lease obligations, due in three years
18 
 
 
Total lease obligations, due in four years
17 
 
 
Total lease obligations, due in five years
16 
 
 
Total lease obligations, After 5 Years
270 
 
 
Total lease obligations, Total
355 
 
 
Annual obligation for real estate leases and railroad licenses
2 
 
 
Total rental expense
34 
34 
32 
Ameren Illinois Company
 
 
 
Commitments and Contingencies [Line Items]
 
 
 
Operating leases, due in one year
1 3
 
 
Operating leases, due in two years
1 3
 
 
Operating leases, due in three years
1 3
 
 
Operating leases, due in four years
1 3
 
 
Operating leases, due in five years
1 3
 
 
Operating leases, After 5 Years
1 3
 
 
Operating leases, Total
6 3
 
 
Annual obligation for real estate leases and railroad licenses
1 
 
 
Total rental expense
$ 30 
$ 28 
$ 25 
Commitments And Contingencies (Schedule Of Estimated Purchased Power Commitments) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
$ 1,258 1
2018
828 1
2019
580 1
2020
229 1
2021
148 1
Thereafter
829 1
Total
3,872 1
Coal
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
599 1
2018
371 1
2019
311 1
2020
27 1
2021
0 1
Thereafter
0 1
Total
1,308 1
Natural Gas
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
238 1 2
2018
167 1 2
2019
99 1 2
2020
45 1 2
2021
12 1 2
Thereafter
43 1 2
Total
604 1 2
Nuclear Fuel
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
45 1
2018
70 1
2019
27 1
2020
38 1
2021
44 1
Thereafter
45 1
Total
269 1
Purchased Power
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
255 1 3
2018
156 1 3
2019
79 1 3
2020
58 1 3
2021
58 1 3
Thereafter
478 1 3
Total
1,084 1 3
Methane Gas
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
3 1
2018
4 1
2019
4 1
2020
5 1
2021
5 1
Thereafter
65 1
Total
86 1
Other
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
118 1
2018
60 1
2019
60 1
2020
56 1
2021
29 1
Thereafter
198 1
Total
521 1
Union Electric Company
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
751 
2018
525 
2019
408 
2020
131 
2021
104 
Thereafter
370 
Total
2,289 
Union Electric Company |
Coal
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
599 
2018
371 
2019
311 
2020
27 
2021
0 
Thereafter
0 
Total
1,308 
Union Electric Company |
Natural Gas
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
43 2
2018
29 2
2019
15 2
2020
10 2
2021
5 2
Thereafter
18 2
Total
120 2
Union Electric Company |
Nuclear Fuel
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
45 
2018
70 
2019
27 
2020
38 
2021
44 
Thereafter
45 
Total
269 
Union Electric Company |
Purchased Power
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
22 
2018
22 
2019
22 
2020
22 
2021
22 
Thereafter
59 
Total
169 
Union Electric Company |
Methane Gas
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
3 
2018
4 
2019
4 
2020
5 
2021
5 
Thereafter
65 
Total
86 
Union Electric Company |
Other
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
39 
2018
29 
2019
29 
2020
29 
2021
28 
Thereafter
183 
Total
337 
Ameren Illinois Company
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
464 
2018
296 
2019
167 
2020
98 
2021
44 
Thereafter
444 
Total
1,513 
Ameren Illinois Company |
Natural Gas
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
195 2
2018
138 2
2019
83 2
2020
35 2
2021
8 2
Thereafter
25 2
Total
484 2
Ameren Illinois Company |
Purchased Power
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
233 3
2018
134 3
2019
57 3
2020
36 3
2021
36 3
Thereafter
419 3
Total
915 3
Ameren Illinois Company |
Other
 
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
 
2017
36 
2018
24 
2019
27 
2020
27 
2021
0 
Thereafter
0 
Total
$ 114 
Commitments And Contingencies (Environmental Matters) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Sep. 30, 2016
scrubber
Percentage of Rate Base Related to Carbon Dioxide Energy Centers
18.00% 
 
Union Electric Company
 
 
Percentage of Rate Base Related to Carbon Dioxide Energy Centers
34.00% 
 
Number of Energy Center Scrubbers
 
2 
Manufactured Gas Plant
 
 
Accrual for environmental loss contingencies
$ 200 
 
Manufactured Gas Plant |
Ameren Illinois Company
 
 
Number of remediation sites
44 
 
Accrual for environmental loss contingencies
200 
 
Sauget Area 2 |
Union Electric Company
 
 
Accrual for environmental loss contingencies
1 
 
Minimum
 
 
Estimated capital costs to comply with existing and known federal and state air emissions regulations
425 
 
Minimum |
Manufactured Gas Plant |
Ameren Illinois Company
 
 
Loss contingency, estimate of possible loss
200.0 
 
Minimum |
Sauget Area 2 |
Union Electric Company
 
 
Loss contingency, estimate of possible loss
1.0 
 
Maximum
 
 
Estimated capital costs to comply with existing and known federal and state air emissions regulations
525 
 
Maximum |
Manufactured Gas Plant |
Ameren Illinois Company
 
 
Loss contingency, estimate of possible loss
268.0 
 
Maximum |
Sauget Area 2 |
Union Electric Company
 
 
Loss contingency, estimate of possible loss
$ 2.5 
 
Segment Information (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Sep. 30, 2016
segment
Dec. 31, 2016
segment
Dec. 31, 2015
Dec. 31, 2014
Segment Reporting Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
Number of reportable segments
 
 
 
 
 
 
 
 
2 
4 
 
 
External revenues
$ 1,356 
$ 1,859 
$ 1,427 
$ 1,434 
$ 1,308 
$ 1,833 
$ 1,401 
$ 1,556 
 
$ 6,076 
$ 6,098 
$ 6,053 
Depreciation and amortization
 
 
 
 
 
 
 
 
 
845 
796 
745 
Interest charges
 
 
 
 
 
 
 
 
 
382 
355 
341 
Income taxes (benefit)
 
 
 
 
 
 
 
 
 
382 
363 
377 
Net income (loss) attributable to Ameren common shareholders from continuing operations
32 
369 
147 
105 
30 
343 
98 
108 
 
653 
579 
587 
Capital expenditures
 
 
 
 
 
 
 
 
 
2,076 
1,917 
1,785 
Union Electric Company
 
 
 
 
 
 
 
 
 
 
 
 
Segment Reporting Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
Number of reportable segments
 
 
 
 
 
 
 
 
 
1 
 
 
Segment, Continuing Operations
 
 
 
 
 
 
 
 
 
 
 
 
Segment Reporting Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
 
 
 
 
 
 
 
 
 
6,076 
6,098 
6,053 
Intersegment revenues
 
 
 
 
 
 
 
 
 
0 
0 
0 
Depreciation and amortization
 
 
 
 
 
 
 
 
 
845 
796 
745 
Interest income
 
 
 
 
 
 
 
 
 
40 
41 
37 
Interest charges
 
 
 
 
 
 
 
 
 
382 
355 
341 
Income taxes (benefit)
 
 
 
 
 
 
 
 
 
382 
363 
377 
Net income (loss) attributable to Ameren common shareholders from continuing operations
 
 
 
 
 
 
 
 
 
653 
579 
587 
Capital expenditures
 
 
 
 
 
 
 
 
 
2,076 
1,917 
1,785 
Ameren Illinois Company
 
 
 
 
 
 
 
 
 
 
 
 
Segment Reporting Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
Number of reportable segments
 
 
 
 
 
 
 
 
 
3 
 
 
Ameren Illinois Company
 
 
 
 
 
 
 
 
 
 
 
 
Segment Reporting Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
595 
676 
542 
677 
553 
655 
513 
745 
 
2,490 
2,466 
2,498 
Intersegment revenues
 
 
 
 
 
 
 
 
 
0 
0 
0 
Depreciation and amortization
 
 
 
 
 
 
 
 
 
319 
295 
263 
Interest income
 
 
 
 
 
 
 
 
 
12 
12 
7 
Interest charges
 
 
 
 
 
 
 
 
 
140 
131 
112 
Income taxes (benefit)
 
 
 
 
 
 
 
 
 
158 
127 
143 
Net Income (Loss) Available to Common Shareholder
29 
119 
45 
59 
32 
98 
31 
53 
 
252 
214 
201 
Capital expenditures
 
 
 
 
 
 
 
 
 
924 
918 
835 
Intersegment Elimination
 
 
 
 
 
 
 
 
 
 
 
 
Segment Reporting Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
 
 
 
 
 
 
 
 
 
0 
0 
0 
Intersegment revenues
 
 
 
 
 
 
 
 
 
(105)
(87)
(66)
Depreciation and amortization
 
 
 
 
 
 
 
 
 
0 
0 
0 
Interest income
 
 
 
 
 
 
 
 
 
(11)
(6)
(3)
Interest charges
 
 
 
 
 
 
 
 
 
(11)
(6)
(3)
Income taxes (benefit)
 
 
 
 
 
 
 
 
 
0 
0 
0 
Net Income (Loss) Available to Common Shareholder
 
 
 
 
 
 
 
 
 
0 
0 
0 
Capital expenditures
 
 
 
 
 
 
 
 
 
(6)
0 
0 
Intersegment Elimination |
Ameren Illinois Company
 
 
 
 
 
 
 
 
 
 
 
 
Segment Reporting Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
 
 
 
 
 
 
 
 
 
0 
0 
0 
Intersegment revenues
 
 
 
 
 
 
 
 
 
(45)
(38)
(35)
Depreciation and amortization
 
 
 
 
 
 
 
 
 
0 
0 
0 
Interest income
 
 
 
 
 
 
 
 
 
0 
0 
0 
Interest charges
 
 
 
 
 
 
 
 
 
0 
0 
0 
Income taxes (benefit)
 
 
 
 
 
 
 
 
 
0 
0 
0 
Net Income (Loss) Available to Common Shareholder
 
 
 
 
 
 
 
 
 
0 
0 
0 
Capital expenditures
 
 
 
 
 
 
 
 
 
0 
0 
0 
Operating Segments [Member] |
Union Electric Company
 
 
 
 
 
 
 
 
 
 
 
 
Segment Reporting Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
 
 
 
 
 
 
 
 
 
3,469 
3,566 
3,526 
Intersegment revenues
 
 
 
 
 
 
 
 
 
54 
43 
27 
Depreciation and amortization
 
 
 
 
 
 
 
 
 
514 
492 
473 
Interest income
 
 
 
 
 
 
 
 
 
28 
28 
28 
Interest charges
 
 
 
 
 
 
 
 
 
211 
219 
211 
Income taxes (benefit)
 
 
 
 
 
 
 
 
 
216 
209 
229 
Net Income (Loss) Available to Common Shareholder
 
 
 
 
 
 
 
 
 
357 
352 
390 
Capital expenditures
 
 
 
 
 
 
 
 
 
738 
622 
747 
Operating Segments [Member] |
Ameren Illinois Electric Distribution [Member]
 
 
 
 
 
 
 
 
 
 
 
 
Segment Reporting Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
 
 
 
 
 
 
 
 
 
1,545 
1,529 
1,401 
Intersegment revenues
 
 
 
 
 
 
 
 
 
4 
3 
2 
Depreciation and amortization
 
 
 
 
 
 
 
 
 
226 
212 
197 
Interest income
 
 
 
 
 
 
 
 
 
11 
12 
7 
Interest charges
 
 
 
 
 
 
 
 
 
72 
71 
63 
Income taxes (benefit)
 
 
 
 
 
 
 
 
 
78 
71 
75 
Net Income (Loss) Available to Common Shareholder
 
 
 
 
 
 
 
 
 
126 
123 
113 
Capital expenditures
 
 
 
 
 
 
 
 
 
470 
491 
403 
Operating Segments [Member] |
Ameren Illinois Gas [Member]
 
 
 
 
 
 
 
 
 
 
 
 
Segment Reporting Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
 
 
 
 
 
 
 
 
 
753 
782 
976 
Intersegment revenues
 
 
 
 
 
 
 
 
 
1 
1 
0 
Depreciation and amortization
 
 
 
 
 
 
 
 
 
55 
52 
41 
Interest income
 
 
 
 
 
 
 
 
 
0 
0 
0 
Interest charges
 
 
 
 
 
 
 
 
 
34 
35 
28 
Income taxes (benefit)
 
 
 
 
 
 
 
 
 
39 
24 
39 
Net Income (Loss) Available to Common Shareholder
 
 
 
 
 
 
 
 
 
59 
37 
50 
Capital expenditures
 
 
 
 
 
 
 
 
 
181 
133 
137 
Operating Segments [Member] |
Ameren Transmission [Member]
 
 
 
 
 
 
 
 
 
 
 
 
Segment Reporting Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
 
 
 
 
 
 
 
 
 
309 
219 
150 
Intersegment revenues
 
 
 
 
 
 
 
 
 
46 1
40 1
37 1
Depreciation and amortization
 
 
 
 
 
 
 
 
 
43 
33 
26 
Interest income
 
 
 
 
 
 
 
 
 
1 
0 
0 
Interest charges
 
 
 
 
 
 
 
 
 
58 
35 
26 
Income taxes (benefit)
 
 
 
 
 
 
 
 
 
74 
51 
38 
Net Income (Loss) Available to Common Shareholder
 
 
 
 
 
 
 
 
 
117 
83 
51 
Capital expenditures
 
 
 
 
 
 
 
 
 
689 
669 
491 
Operating Segments [Member] |
Other Segment
 
 
 
 
 
 
 
 
 
 
 
 
Segment Reporting Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
 
 
 
 
 
 
 
 
 
0 
2 
0 
Intersegment revenues
 
 
 
 
 
 
 
 
 
0 
0 
0 
Depreciation and amortization
 
 
 
 
 
 
 
 
 
7 
7 
8 
Interest income
 
 
 
 
 
 
 
 
 
11 
7 
5 
Interest charges
 
 
 
 
 
 
 
 
 
18 
1 
16 
Income taxes (benefit)
 
 
 
 
 
 
 
 
 
(25)
8 
(4)
Net Income (Loss) Available to Common Shareholder
 
 
 
 
 
 
 
 
 
(6)
(16)
(17)
Capital expenditures
 
 
 
 
 
 
 
 
 
4 2
2 2
7 2
Operating Segments [Member] |
Ameren Illinois Company |
Ameren Illinois Electric Distribution [Member]
 
 
 
 
 
 
 
 
 
 
 
 
Segment Reporting Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
 
 
 
 
 
 
 
 
 
1,549 
1,532 
1,403 
Intersegment revenues
 
 
 
 
 
 
 
 
 
0 
0 
0 
Depreciation and amortization
 
 
 
 
 
 
 
 
 
226 
212 
197 
Interest income
 
 
 
 
 
 
 
 
 
11 
12 
7 
Interest charges
 
 
 
 
 
 
 
 
 
72 
71 
63 
Income taxes (benefit)
 
 
 
 
 
 
 
 
 
78 
71 
75 
Net Income (Loss) Available to Common Shareholder
 
 
 
 
 
 
 
 
 
126 
123 
113 
Capital expenditures
 
 
 
 
 
 
 
 
 
470 
491 
403 
Operating Segments [Member] |
Ameren Illinois Company |
Ameren Illinois Gas [Member]
 
 
 
 
 
 
 
 
 
 
 
 
Segment Reporting Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
 
 
 
 
 
 
 
 
 
754 
783 
976 
Intersegment revenues
 
 
 
 
 
 
 
 
 
0 
0 
0 
Depreciation and amortization
 
 
 
 
 
 
 
 
 
55 
52 
41 
Interest income
 
 
 
 
 
 
 
 
 
0 
0 
0 
Interest charges
 
 
 
 
 
 
 
 
 
34 
35 
28 
Income taxes (benefit)
 
 
 
 
 
 
 
 
 
39 
24 
39 
Net Income (Loss) Available to Common Shareholder
 
 
 
 
 
 
 
 
 
59 
37 
50 
Capital expenditures
 
 
 
 
 
 
 
 
 
181 
133 
137 
Operating Segments [Member] |
Ameren Illinois Company |
Ameren Illinois Transmission [Member]
 
 
 
 
 
 
 
 
 
 
 
 
Segment Reporting Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
 
External revenues
 
 
 
 
 
 
 
 
 
187 
151 
119 
Intersegment revenues
 
 
 
 
 
 
 
 
 
45 1
38 1
35 1
Depreciation and amortization
 
 
 
 
 
 
 
 
 
38 
31 
25 
Interest income
 
 
 
 
 
 
 
 
 
1 
0 
0 
Interest charges
 
 
 
 
 
 
 
 
 
34 
25 
21 
Income taxes (benefit)
 
 
 
 
 
 
 
 
 
41 
32 
29 
Net Income (Loss) Available to Common Shareholder
 
 
 
 
 
 
 
 
 
67 
54 
38 
Capital expenditures
 
 
 
 
 
 
 
 
 
$ 273 
$ 294 
$ 295 
Selected Quarterly Information (Summary Of Selected Quarterly Information) (Details) (USD $)
In Millions, except Per Share data, unless otherwise specified
3 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Selected Quarterly Financial Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
Operating revenues
$ 1,356 
$ 1,859 
$ 1,427 
$ 1,434 
$ 1,308 
$ 1,833 
$ 1,401 
$ 1,556 
$ 6,076 
$ 6,098 
$ 6,053 
Operating Income
145 
691 
325 
220 
140 
626 
237 
256 
1,381 
1,259 
1,254 
Net income
33 
371 
148 
107 
30 
345 
151 
110 
659 
636 
592 
Net income attributable to Ameren common shareholders - continuing operations
32 
369 
147 
105 
30 
343 
98 
108 
653 
579 
587 
Net Income (Loss) Attributable to Ameren common shareholders- Discontinued Operations
0 
0 
0 
0 
(1)
0 
52 
0 
0 
51 
(1)
Net income attributable to Ameren common shareholders
32 
369 
147 
105 
29 
343 
150 
108 
653 
630 
586 
Earnings per common share - basic - continuing operations
$ 0.13 
$ 1.52 
$ 0.61 
$ 0.43 
$ 0.12 
$ 1.42 
$ 0.40 
$ 0.45 
$ 2.69 
$ 2.39 
$ 2.42 
Earnings per common share - basic - discontinued operations
$ 0.00 
$ 0.00 
$ 0.00 
$ 0.00 
$ 0.00 
$ 0.00 
$ 0.21 
$ 0.00 
$ 0.00 
$ 0.21 
$ 0.00 
Earnings per common share - basic
$ 0.13 
$ 1.52 
$ 0.61 
$ 0.43 
$ 0.12 
$ 1.42 
$ 0.61 
$ 0.45 
$ 2.69 
$ 2.60 
$ 2.42 
Earnings per common share - diluted - continuing operations
$ 0.13 
$ 1.52 
$ 0.61 
$ 0.43 
$ 0.12 
$ 1.41 
$ 0.40 
$ 0.45 
$ 2.68 
$ 2.38 
$ 2.40 
Earnings per common share - diluted - discontinued operations
$ 0.00 
$ 0.00 
$ 0.00 
$ 0.00 
$ 0.00 
$ 0.00 
$ 0.21 
$ 0.00 
$ 0.00 
$ 0.21 
$ 0.00 
Earnings per common share - diluted
$ 0.13 
$ 1.52 
$ 0.61 
$ 0.43 
$ 0.12 
$ 1.41 
$ 0.61 
$ 0.45 
$ 2.68 
$ 2.59 
$ 2.40 
Union Electric Company
 
 
 
 
 
 
 
 
 
 
 
Selected Quarterly Financial Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
Operating revenues
750 
1,165 
867 
741 
754 
1,171 
884 
800 
3,523 
3,609 
3,553 
Operating Income
54 
431 
197 
63 
58 
423 
146 
115 
745 
742 
785 
Net income
10 
242 
93 
15 
11 
240 
62 
42 
360 
355 
393 
Net Income Available to Common Shareholder
10 
241 
92 
14 
11 
239 
61 
41 
357 
352 
390 
Ameren Illinois Company
 
 
 
 
 
 
 
 
 
 
 
Selected Quarterly Financial Information [Line Items]
 
 
 
 
 
 
 
 
 
 
 
Operating revenues
595 
676 
542 
677 
553 
655 
513 
745 
2,490 
2,466 
2,498 
Operating Income
74 
230 
107 
133 
74 
189 
83 
120 
544 
466 
450 
Net income
30 
119 
46 
60 
33 
98 
32 
54 
255 
217 
204 
Net Income Available to Common Shareholder
$ 29 
$ 119 
$ 45 
$ 59 
$ 32 
$ 98 
$ 31 
$ 53 
$ 252 
$ 214 
$ 201 
Schedule I - Condensed Financial Information Of Parent (Statement of Income) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
 
 
 
 
 
 
 
 
 
 
 
Operating revenues
$ 1,356 
$ 1,859 
$ 1,427 
$ 1,434 
$ 1,308 
$ 1,833 
$ 1,401 
$ 1,556 
$ 6,076 
$ 6,098 
$ 6,053 
Operating expenses
 
 
 
 
 
 
 
 
4,695 
4,839 
4,799 
Operating loss
145 
691 
325 
220 
140 
626 
237 
256 
1,381 
1,259 
1,254 
Interest income from affiliates
 
 
 
 
 
 
 
 
13 1 2
14 1 2
10 1 2
Other Nonoperating Income (Expense)
 
 
 
 
 
 
 
 
42 
44 
57 
Interest charges
 
 
 
 
 
 
 
 
382 
355 
341 
Income taxes (benefit)
 
 
 
 
 
 
 
 
382 
363 
377 
Net income attributable to Ameren common shareholders - continuing operations
32 
369 
147 
105 
30 
343 
98 
108 
653 
579 
587 
Net Income (Loss) Attributable to Ameren common shareholders- Discontinued Operations
0 
0 
0 
0 
(1)
0 
52 
0 
0 
51 
(1)
Net income attributable to Ameren common shareholders
32 
369 
147 
105 
29 
343 
150 
108 
653 
630 
586 
Comprehensive Income from Continuing Operations
 
 
 
 
 
 
 
 
 
 
 
Pension and other postretirement activity, net of income taxes (benefit)
 
 
 
 
 
 
 
 
(20)
6 
(12)
Comprehensive Income from Continuing Operations Attributable to Ameren Common Shareholders
 
 
 
 
 
 
 
 
633 
585 
575 
Comprehensive Income (Loss) from Discontinued Operations Attributable to Ameren Common shareholders
 
 
 
 
 
 
 
 
0 
51 
(1)
Comprehensive Income (Loss) Attributable to Ameren Common Shareholders
 
 
 
 
 
 
 
 
633 
636 
574 
Other Comprehensive Income (Loss), Taxes:
 
 
 
 
 
 
 
 
 
 
 
Pension and other postretirement activity, tax (benefit)
 
 
 
 
 
 
 
 
(7)
3 
(7)
Parent Company
 
 
 
 
 
 
 
 
 
 
 
Condensed Financial Statements, Captions [Line Items]
 
 
 
 
 
 
 
 
 
 
 
Operating expenses
 
 
 
 
 
 
 
 
14 
14 
11 
Operating loss
 
 
 
 
 
 
 
 
(14)
(14)
(11)
Equity in earnings of subsidiaries
 
 
 
 
 
 
 
 
663 
600 
607 
Interest income from affiliates
 
 
 
 
 
 
 
 
10 
6 
3 
Other Nonoperating Income (Expense)
 
 
 
 
 
 
 
 
(5)
(5)
2 
Interest charges
 
 
 
 
 
 
 
 
28 
3 
16 
Income taxes (benefit)
 
 
 
 
 
 
 
 
(27)
5 
(2)
Net income attributable to Ameren common shareholders - continuing operations
 
 
 
 
 
 
 
 
653 
579 
587 
Net Income (Loss) Attributable to Ameren common shareholders- Discontinued Operations
 
 
 
 
 
 
 
 
0 
51 
(1)
Net income attributable to Ameren common shareholders
 
 
 
 
 
 
 
 
653 
630 
586 
Comprehensive Income from Continuing Operations
 
 
 
 
 
 
 
 
 
 
 
Pension and other postretirement activity, net of income taxes (benefit)
 
 
 
 
 
 
 
 
(20)
6 
(12)
Comprehensive Income from Continuing Operations Attributable to Ameren Common Shareholders
 
 
 
 
 
 
 
 
633 
585 
575 
Comprehensive Income (Loss) from Discontinued Operations Attributable to Ameren Common shareholders
 
 
 
 
 
 
 
 
0 
51 
(1)
Comprehensive Income (Loss) Attributable to Ameren Common Shareholders
 
 
 
 
 
 
 
 
633 
636 
574 
Other Comprehensive Income (Loss), Taxes:
 
 
 
 
 
 
 
 
 
 
 
Pension and other postretirement activity, tax (benefit)
 
 
 
 
 
 
 
 
$ (7)
$ 3 
$ (7)
Schedule I - Condensed Financial Information Of Parent (Balance Sheet) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
ASSETS
 
 
 
 
Cash and cash equivalents
$ 9 
$ 292 
$ 5 
$ 30 
Miscellaneous accounts and notes receivable
63 
98 
 
 
Other current assets
98 
88 
 
 
Total current assets
1,593 
1,917 
 
 
Accumulated deferred income taxes, net
7 
6 
 
 
Other assets
538 
575 
 
 
TOTAL ASSETS
24,699 
23,640 
 
 
LIABILITIES AND EQUITY
 
 
 
 
Short-term debt
558 
301 
 
 
Other current liabilities
248 
279 
 
 
Total current liabilities
2,674 
2,093 
 
 
Long-term Debt, Net
6,595 
6,880 
 
 
Pension and other postretirement benefits
769 
580 
 
 
Other deferred credits and liabilities
477 
531 
 
 
Commitments and Contingencies
   
   
 
 
Retained earnings
1,568 
1,331 
 
 
Accumulated other comprehensive loss
(23)
(3)
 
 
Total equity
7,245 
7,088 
6,855 
 
TOTAL LIABILITIES AND EQUITY
24,699 
23,640 
 
 
Parent Company
 
 
 
 
ASSETS
 
 
 
 
Cash and cash equivalents
1 
0 
1 
11 
Advances to money pool
27 
0 
 
 
Accounts receivable - affiliates
31 
53 
 
 
Miscellaneous accounts and notes receivable
26 
3 
 
 
Other current assets
8 
9 
 
 
Total current assets
93 
65 
 
 
Investments in subsidiaries
7,498 
7,227 
 
 
Note receivable - affiliates
350 
290 
 
 
Accumulated deferred income taxes, net
419 
426 
 
 
Other assets
135 
158 
 
 
TOTAL ASSETS
8,495 
8,166 
 
 
LIABILITIES AND EQUITY
 
 
 
 
Short-term debt
507 
301 
 
 
Borrowings from money pool
33 
14 
 
 
Accounts payable – affiliates
13 
75 
 
 
Other current liabilities
17 
22 
 
 
Total current liabilities
570 
412 
 
 
Long-term Debt, Net
694 
694 
 
 
Pension and other postretirement benefits
45 
33 
 
 
Other deferred credits and liabilities
83 
81 
 
 
Total liabilities
1,392 
1,220 
 
 
Common stock, $.01 par value, 400.0 shares authorized – shares outstanding of 242.6
2 
2 
 
 
Other paid-in capital, principally premium on common stock
5,556 
5,616 
 
 
Retained earnings
1,568 
1,331 
 
 
Accumulated other comprehensive loss
(23)
(3)
 
 
Total equity
7,103 
6,946 
 
 
TOTAL LIABILITIES AND EQUITY
$ 8,495 
$ 8,166 
 
 
Schedule I - Condensed Financial Information Of Parent (Statement of Cash Flows) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
 
 
 
Net cash provided by operating activities
$ 2,123 
$ 2,031 
$ 1,565 
Cash Flows From Investing Activities:
 
 
 
Proceeds from Collection of Notes Receivable
0 
20 
95 
Contributions to Note Receivable
0 
(8)
(89)
Other
5 
20 
11 
Net Cash Provided by (Used in) Investing Activities
(2,141)
(1,976)
(1,717)
Cash flows from financing activities:
 
 
 
Dividends on common stock
(416)
(402)
(390)
Short-term debt, net
257 
(413)
346 
Repayments of Other Long-term Debt
(395)
(120)
(697)
Issuances of Long-term debt
389 
1,197 
898 
Capital issuance costs
(9)
(12)
(11)
Share-based payments
(83)
(12)
(14)
Net cash provided by (used in) financing activities
(265)
232 
127 
Net change in cash and cash equivalents
(283)
287 
(25)
Cash and cash equivalents at beginning of year
292 
5 
30 
Cash and cash equivalents at end of year
9 
292 
5 
Parent Company
 
 
 
Condensed Financial Statements, Captions [Line Items]
 
 
 
Net cash provided by operating activities
483 
551 
528 
Cash Flows From Investing Activities:
 
 
 
Money pool advances, net
(27)
55 
279 
Intercompany notes receivable, net
(60)
(96)
(134)
Investments in subsidiaries
(123)
(509)
(280)
Return of investments
0 
0 
215 
Proceeds from Collection of Notes Receivable
0 
20 
95 
Contributions to Note Receivable
0 
(8)
(89)
Other
2 
(24)
(12)
Net Cash Provided by (Used in) Investing Activities
(208)
(562)
74 
Cash flows from financing activities:
 
 
 
Dividends on common stock
(416)
(402)
(390)
Short-term debt, net
206 
(284)
217 
Money pool borrowings, net
19 
14 
0 
Repayments of Other Long-term Debt
0 
0 
(425)
Issuances of Long-term debt
0 
700 
0 
Capital issuance costs
0 
(6)
0 
Share-based payments
(83)
(12)
(14)
Net cash provided by (used in) financing activities
(274)
10 
(612)
Net change in cash and cash equivalents
1 
(1)
(10)
Cash and cash equivalents at beginning of year
0 
1 
11 
Cash and cash equivalents at end of year
1 
0 
1 
Cash dividends received from consolidated subsidiaries
465 
575 
340 
Noncash Investing activity- investment in subsidiaries
$ 0 
$ (38)
$ (19)
Schedule I - Condensed Financial Information Of Parent Outstanding gurarantee (Details) (Parent Company, USD $)
In Millions, unless otherwise specified
Dec. 31, 2016
Parent Company
 
Other Commitments [Line Items]
 
Guarantees Outstanding
$ 51 
Schedule II - Valuation And Qualifying Accounts (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Allowance For Doubtful Accounts
 
 
 
Valuation and Qualifying Accounts Disclosure [Line Items]
 
 
 
Balance at Beginning of Period
$ 19 
$ 21 
$ 18 
Charged to Costs and Expenses
32 
33 
36 
Charged to Other Accounts
3 1
5 1
4 1
Deductions
35 2
40 2
37 2
Balance at End of Period
19 
19 
21 
Valuation Allowance of Deferred Tax Assets
 
 
 
Valuation and Qualifying Accounts Disclosure [Line Items]
 
 
 
Balance at Beginning of Period
6 
10 
7 
Charged to Costs and Expenses
7 
4 
3 
Charged to Other Accounts
(2)1
(8)1
0 1
Deductions
0 
0 
0 
Balance at End of Period
11 
6 
10 
Union Electric Company |
Allowance For Doubtful Accounts
 
 
 
Valuation and Qualifying Accounts Disclosure [Line Items]
 
 
 
Balance at Beginning of Period
7 
8 
5 
Charged to Costs and Expenses
10 
13 
16 
Charged to Other Accounts
0 1
0 1
0 1
Deductions
10 2
14 2
13 2
Balance at End of Period
7 
7 
8 
Union Electric Company |
Valuation Allowance of Deferred Tax Assets
 
 
 
Valuation and Qualifying Accounts Disclosure [Line Items]
 
 
 
Balance at Beginning of Period
0 
1 
1 
Charged to Costs and Expenses
0 
0 
0 
Charged to Other Accounts
0 1
(1)1
0 1
Deductions
0 
0 
0 
Balance at End of Period
0 
0 
1 
Ameren Illinois Company |
Allowance For Doubtful Accounts
 
 
 
Valuation and Qualifying Accounts Disclosure [Line Items]
 
 
 
Balance at Beginning of Period
12 
13 
13 
Charged to Costs and Expenses
22 
20 
20 
Charged to Other Accounts
3 1
5 1
4 1
Deductions
25 2
26 2
24 2
Balance at End of Period
12 
12 
13 
Ameren Illinois Company |
Valuation Allowance of Deferred Tax Assets
 
 
 
Valuation and Qualifying Accounts Disclosure [Line Items]
 
 
 
Balance at Beginning of Period
0 
1 
1 
Charged to Costs and Expenses
0 
0 
0 
Charged to Other Accounts
0 1
(1)1
0 1
Deductions
0 
0 
0 
Balance at End of Period
$ 0 
$ 0 
$ 1