Cover Page - shares	3 Months Ended
Cover Page - shares	Mar. 31, 2022	Apr. 29, 2022
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2022
Document Transition Report	false
Entity File Number	1-14756
Entity Registrant Name	Ameren Corporation
Entity Tax Identification Number	43-1723446
Entity Incorporation, State or Country Code	MO
Entity Address, Address Line One	1901 Chouteau Avenue
Entity Address, City or Town	St. Louis
Entity Address, State or Province	MO
Entity Address, Postal Zip Code	63103
City Area Code	(314)
Local Phone Number	621-3222
Title of 12(b) Security	Common Stock, $0.01 par value per share
Trading Symbol(s)	AEE
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Shares outstanding		258,226,506
Entity Central Index Key	0001002910
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q1
Amendment Flag	false
Union Electric Company
Entity Information [Line Items]
Entity File Number	1-2967
Entity Registrant Name	Union Electric Company
Entity Tax Identification Number	43-0559760
Entity Incorporation, State or Country Code	MO
Entity Address, Address Line One	1901 Chouteau Avenue
Entity Address, City or Town	St. Louis
Entity Address, State or Province	MO
Entity Address, Postal Zip Code	63103
City Area Code	(314)
Local Phone Number	621-3222
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Shares outstanding		102,123,834
Entity Central Index Key	0000100826
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q1
Amendment Flag	false
Ameren Illinois Company
Entity Information [Line Items]
Entity File Number	1-3672
Entity Registrant Name	Ameren Illinois Company
Entity Tax Identification Number	37-0211380
Entity Incorporation, State or Country Code	IL
Entity Address, Address Line One	10 Executive Drive
Entity Address, City or Town	Collinsville
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	62234
City Area Code	(618)
Local Phone Number	343-8150
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Shares outstanding		25,452,373
Entity Central Index Key	0000018654
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q1
Amendment Flag	false

Consolidated Statement of Income (Loss) and Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Operating Revenues:
Total operating revenues	$ 1,879	$ 1,566
Operating Expenses:
Fuel	176	65
Purchased power	177	191
Natural gas purchased for resale	293	165
Other operations and maintenance	461	420
Depreciation and amortization	299	281
Taxes other than income taxes	142	128
Total operating expenses	1,548	1,250
Operating Income	331	316
Other Income, Net	60	46
Interest Charges	104	100
Income Before Income Taxes	287	262
Income Taxes	34	27
Net Income	253	235
Less: Net Income Attributable to Noncontrolling Interests	1	2
Net Income Attributable to Ameren Common Shareholders	252	233
Pension and other postretirement benefit plan activity, net of income taxes (benefit)	1	1
Comprehensive Income	254	236
Less: Comprehensive Income Attributable to Noncontrolling Interests	1	2
Comprehensive Income Attributable to Ameren Common Shareholders	$ 253	$ 234
Earnings Per Share, Basic and Diluted [Abstract]
Earnings per Common Share - Basic (in dollars per share)	$ 0.98	$ 0.92
Earnings per Common Share - Diluted (in dollars per share)	$ 0.97	$ 0.91
Weighted Average Common Shares Outstanding - Basic (in shares)	257.9	254.4
Weighted Average Number of Shares Outstanding - Diluted (in shares)	259.0	255.9
Electricity
Operating Revenues:
Total operating revenues	$ 1,318	$ 1,156
Natural gas
Operating Revenues:
Total operating revenues	561	410
Union Electric Company
Operating Revenues:
Total operating revenues	818	704
Operating Expenses:
Fuel	176	65
Purchased power	50	88
Natural gas purchased for resale	46	31
Other operations and maintenance	232	225
Depreciation and amortization	164	156
Taxes other than income taxes	85	77
Total operating expenses	753	642
Operating Income	65	62
Other Income, Net	23	23
Interest Charges	39	39
Income Before Income Taxes	49	46
Income Taxes	(2)	(2)
Net Income	51	48
Preferred Stock Dividends	1	1
Net Income (Loss) Attributable to Parent	50	47
Union Electric Company \| Electricity
Operating Revenues:
Total operating revenues	738	641
Union Electric Company \| Natural gas
Operating Revenues:
Total operating revenues	80	63
Ameren Illinois Company
Operating Revenues:
Total operating revenues	1,024	823
Operating Expenses:
Purchased power	131	106
Natural gas purchased for resale	247	134
Other operations and maintenance	223	194
Depreciation and amortization	124	115
Taxes other than income taxes	53	46
Total operating expenses	778	595
Operating Income	246	228
Other Income, Net	24	14
Interest Charges	42	42
Income Before Income Taxes	228	200
Income Taxes	59	50
Net Income	169	150
Preferred Stock Dividends	0	1
Net Income (Loss) Attributable to Parent	169	149
Ameren Illinois Company \| Electricity
Operating Revenues:
Total operating revenues	543	476
Ameren Illinois Company \| Natural gas
Operating Revenues:
Total operating revenues	$ 481	$ 347

Consolidated Statement of Income (Loss) and Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Income Statement [Abstract]
Pension and other postretirement benefit plan activity, tax	$ 0	$ 0

Consolidated Balance Sheet - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Current Assets:
Cash and cash equivalents	$ 7	$ 8
Accounts receivable - trade (less allowance for doubtful accounts)	560	434
Unbilled revenue	283	301
Miscellaneous accounts receivable	87	85
Inventories	520	592
Mark-to-market derivative assets	137	66
Current regulatory assets	244	319
Current collateral assets	110	66
Other current assets	83	97
Total current assets	2,031	1,968
Property, Plant, and Equipment, Net	29,578	29,261
Investments and Other Assets:
Nuclear decommissioning trust fund	1,094	1,159
Goodwill	411	411
Regulatory assets	1,377	1,289
Pension and other postretirement benefits	772	756
Other assets	934	891
Total investments and other assets	4,588	4,506
TOTAL ASSETS	36,197	35,735
Current Liabilities:
Current maturities of long-term debt	505	505
Short-term debt	1,101	545
Accounts and wages payable	690	1,095
Current regulatory liabilities	219	113
Other current liabilities	630	568
Total current liabilities	3,145	2,826
Long-term Debt, Net	12,563	12,562
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and tax credits, net	3,550	3,499
Regulatory liabilities	5,841	5,848
Asset retirement obligations	769	757
Other deferred credits and liabilities	394	414
Total deferred credits and other liabilities	10,554	10,518
Commitments and Contingencies
Shareholders’ Equity:
Common Stock	3	3
Other paid-in capital, principally premium on common stock	6,507	6,502
Retained earnings	3,282	3,182
Accumulated other comprehensive income	14	13
Total shareholders’ equity	9,806	9,700
Noncontrolling Interests	129	129
Total equity	9,935	9,829
TOTAL LIABILITIES AND EQUITY	36,197	35,735
Union Electric Company
Current Assets:
Cash and cash equivalents	1	0
Accounts receivable - trade (less allowance for doubtful accounts)	190	190
Accounts receivable – affiliates	47	44
Unbilled revenue	134	142
Miscellaneous accounts receivable	57	71
Inventories	414	419
Current regulatory assets	141	127
Current collateral assets	110	66
Other current assets	86	76
Total current assets	1,180	1,135
Property, Plant, and Equipment, Net	15,434	15,296
Investments and Other Assets:
Nuclear decommissioning trust fund	1,094	1,159
Regulatory assets	582	523
Pension and other postretirement benefits	212	208
Other assets	418	401
Total investments and other assets	2,306	2,291
TOTAL ASSETS	18,920	18,722
Current Liabilities:
Current maturities of long-term debt	55	55
Short-term debt	528	165
Accounts and wages payable	342	631
Accounts payable – affiliates	36	46
Taxes accrued	80	34
Mark-to-market derivative liabilities	109	53
Current regulatory liabilities	101	58
Other current liabilities	159	175
Total current liabilities	1,410	1,217
Long-term Debt, Net	5,564	5,564
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and tax credits, net	1,866	1,852
Regulatory liabilities	3,278	3,354
Asset retirement obligations	765	753
Other deferred credits and liabilities	76	71
Total deferred credits and other liabilities	5,985	6,030
Commitments and Contingencies
Shareholders’ Equity:
Common Stock	511	511
Other paid-in capital, principally premium on common stock	2,725	2,725
Preferred stock	80	80
Retained earnings	2,645	2,595
Total shareholders’ equity	5,961	5,911
TOTAL LIABILITIES AND EQUITY	18,920	18,722
Ameren Illinois Company
Current Assets:
Cash and cash equivalents	0	0
Accounts receivable - trade (less allowance for doubtful accounts)	356	228
Accounts receivable – affiliates	12	24
Unbilled revenue	149	159
Miscellaneous accounts receivable	12	1
Inventories	106	173
Mark-to-market derivative assets	79	28
Current regulatory assets	93	180
Other current assets	26	30
Total current assets	833	823
Property, Plant, and Equipment, Net	12,396	12,223
Investments and Other Assets:
Goodwill	411	411
Regulatory assets	780	752
Pension and other postretirement benefits	435	427
Other assets	436	399
Total investments and other assets	2,062	1,989
TOTAL ASSETS	15,291	15,035
Current Liabilities:
Current maturities of long-term debt	400	400
Short-term debt	107	103
Accounts and wages payable	286	361
Accounts payable – affiliates	80	64
Current regulatory liabilities	118	54
Other current liabilities	251	251
Total current liabilities	1,242	1,233
Long-term Debt, Net	3,993	3,992
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and tax credits, net	1,593	1,558
Regulatory liabilities	2,442	2,374
Other deferred credits and liabilities	212	238
Total deferred credits and other liabilities	4,247	4,170
Commitments and Contingencies
Shareholders’ Equity:
Common Stock	0	0
Other paid-in capital, principally premium on common stock	2,914	2,914
Preferred stock	49	49
Retained earnings	2,846	2,677
Total shareholders’ equity	5,809	5,640
TOTAL LIABILITIES AND EQUITY	$ 15,291	$ 15,035

Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Accounts Receivable, Allowance for Credit Loss, Current	$ 28	$ 29
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	400,000,000.0	400,000,000.0
Common Stock, Shares, Outstanding	258,200,000	257,700,000
Union Electric Company
Accounts Receivable, Allowance for Credit Loss, Current	$ 11	$ 13
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized (in shares)	150,000,000.0	150,000,000.0
Common Stock, Shares, Outstanding	102,100,000	102,100,000
Ameren Illinois Company
Accounts Receivable, Allowance for Credit Loss, Current	$ 17	$ 16
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	45,000,000.0	45,000,000.0
Common Stock, Shares, Outstanding	25,500,000	25,500,000

Consolidated Statement of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash Flows From Operating Activities:
Net income	$ 253	$ 235
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	324	295
Amortization of nuclear fuel	22	0
Amortization of debt issuance costs and premium/discounts	4	5
Deferred income taxes and investment tax credits, net	31	26
Allowance for equity funds used during construction	(8)	(7)
Stock-based compensation costs	4	6
Other	11	8
Changes in assets and liabilities:
Receivables	(117)	(5)
Inventories	72	54
Accounts and wages payable	(235)	(252)
Taxes accrued	47	60
Regulatory assets and liabilities	75	(421)
Assets, other	(54)	(9)
Liabilities, other	(26)	(34)
Pension and other postretirement benefits	(15)	4
Net cash provided by (used in) operating activities	388	(35)
Cash Flows From Investing Activities:
Capital expenditures	(774)	(887)
Nuclear fuel expenditures	(16)	(1)
Purchases of securities – nuclear decommissioning trust fund	(97)	(152)
Sales and maturities of securities – nuclear decommissioning trust fund	92	150
Other	15	1
Net cash used in investing activities	(780)	(889)
Cash Flows From Financing Activities:
Dividends on common stock	(152)	(140)
Dividends paid to noncontrolling interest holders	(1)	(2)
Short-term debt, net	555	399
Issuances of long-term debt	0	450
Issuances of common stock	5	125
Redemptions of Ameren Illinois preferred stock	0	(13)
Employee payroll taxes related to stock-based compensation	(16)	(17)
Debt issuance costs	0	(3)
Other	0	(4)
Net cash provided by financing activities	391	795
Net change in cash, cash equivalents, and restricted cash	(1)	(129)
Cash, cash equivalents, and restricted cash at beginning of year	155	301
Cash, cash equivalents, and restricted cash at end of period	154	172
Union Electric Company
Cash Flows From Operating Activities:
Net income	51	48
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	189	171
Amortization of nuclear fuel	22	0
Amortization of debt issuance costs and premium/discounts	1	1
Deferred income taxes and investment tax credits, net	4	4
Allowance for equity funds used during construction	(4)	(4)
Other	0	3
Changes in assets and liabilities:
Receivables	7	20
Inventories	5	24
Accounts and wages payable	(201)	(201)
Taxes accrued	41	39
Regulatory assets and liabilities	(3)	(164)
Assets, other	(34)	13
Liabilities, other	(18)	(9)
Pension and other postretirement benefits	(4)	4
Net cash provided by (used in) operating activities	56	(51)
Cash Flows From Investing Activities:
Capital expenditures	(414)	(534)
Nuclear fuel expenditures	(16)	(1)
Purchases of securities – nuclear decommissioning trust fund	(97)	(152)
Sales and maturities of securities – nuclear decommissioning trust fund	92	150
Money pool advances, net	0	139
Other	18	0
Net cash used in investing activities	(417)	(398)
Cash Flows From Financing Activities:
Dividends on preferred stock	(1)	(1)
Short-term debt, net	363	204
Capital contributions from parent	0	113
Net cash provided by financing activities	362	316
Net change in cash, cash equivalents, and restricted cash	1	(133)
Cash, cash equivalents, and restricted cash at beginning of year	8	145
Cash, cash equivalents, and restricted cash at end of period	9	12
Ameren Illinois Company
Cash Flows From Operating Activities:
Net income	169	150
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	124	115
Amortization of debt issuance costs and premium/discounts	3	3
Deferred income taxes and investment tax credits, net	27	53
Allowance for equity funds used during construction	(4)	(3)
Other	2	6
Changes in assets and liabilities:
Receivables	(126)	(24)
Inventories	67	30
Accounts and wages payable	(18)	(40)
Taxes accrued	32	3
Regulatory assets and liabilities	79	(255)
Assets, other	(18)	(15)
Liabilities, other	13	(9)
Pension and other postretirement benefits	(8)	(1)
Net cash provided by (used in) operating activities	342	13
Cash Flows From Investing Activities:
Capital expenditures	(342)	(337)
Net cash used in investing activities	(342)	(337)
Cash Flows From Financing Activities:
Dividends on preferred stock	0	(1)
Short-term debt, net	4	323
Money pool borrowings, net	0	(19)
Capital contributions from parent	0	40
Redemption of preferred stock	0	(13)
Other	0	(4)
Net cash provided by financing activities	4	326
Net change in cash, cash equivalents, and restricted cash	4	2
Cash, cash equivalents, and restricted cash at beginning of year	133	147
Cash, cash equivalents, and restricted cash at end of period	$ 137	$ 149

Consolidated Statement of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Other Paid-in Capital	Retained Earnings	Deferred Retirement Benefit Costs	Accumulated Other Comprehensive Income	Total Ameren Corporation Shareholders' Equity	Noncontrolling Interests	Union Electric Company	Union Electric Company Common Stock	Union Electric Company Other Paid-in Capital	Union Electric Company Preferred Stock	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	Ameren Illinois Company Retained Earnings
Beginning of year at Dec. 31, 2020			$ 6,179	$ 2,757	$ (1)			$ 142			$ 2,518		$ 2,101			$ 2,652	$ 62	$ 2,252
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Settlement of forward sale agreement through common shares issuance			113
Shares issued under the DRPlus and 401(k) plan			12
Stock-based compensation activity			(9)
Capital contributions from parent									$ 113		113			$ 40		40
Net income	$ 235								48				48	150				150
Net income attributable to Ameren common shareholders	233			233
Dividends on common stock				(140)
Preferred stock dividends													(1)					(1)
Change in deferred retirement benefit costs	1				1
Net income attributable to noncontrolling interest holders	$ (2)							2
Dividends paid to noncontrolling interest holders								(2)
Redemptions of preferred stock								(13)									(13)
Common stock shares outstanding at beginning of year (in shares) at Dec. 31, 2020	253,300,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under forward sale agreement (in shares)	1,600,000
Shares issued under the DRPlus and 401(k) plan	100,000
Shares issued for stock-based compensation (in shares)	500,000
Common stock shares outstanding at end of period (in shares) at Mar. 31, 2021	255,500,000
End of period at Mar. 31, 2021	$ 9,277	$ 3	6,295	2,850	0	$ 0		129		$ 511	2,631	$ 80	2,148		$ 0	2,692	49	2,401
Shareholders' equity, end of year at Mar. 31, 2021							$ 9,148		5,370					5,142
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share (in dollars per share)	$ 0.55
Beginning of year at Dec. 31, 2021	$ 9,829		6,502	3,182	13			129			2,725		2,595			2,914	49	2,677
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Settlement of forward sale agreement through common shares issuance			0
Shares issued under the DRPlus and 401(k) plan			13
Stock-based compensation activity			(8)
Capital contributions from parent									0		0			0		0
Net income	253								$ 51				51	$ 169				169
Net income attributable to Ameren common shareholders	252			252
Dividends on common stock				(152)
Preferred stock dividends													(1)					0
Change in deferred retirement benefit costs	1				1
Net income attributable to noncontrolling interest holders	$ (1)							1
Dividends paid to noncontrolling interest holders								(1)
Redemptions of preferred stock								0									0
Common stock shares outstanding at beginning of year (in shares) at Dec. 31, 2021	257,700,000								102,100,000					25,500,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under forward sale agreement (in shares)	0
Shares issued under the DRPlus and 401(k) plan	100,000
Shares issued for stock-based compensation (in shares)	400,000
Common stock shares outstanding at end of period (in shares) at Mar. 31, 2022	258,200,000								102,100,000					25,500,000
End of period at Mar. 31, 2022	$ 9,935	$ 3	$ 6,507	$ 3,282	$ 14	$ 14		$ 129		$ 511	$ 2,725	$ 80	$ 2,645		$ 0	$ 2,914	$ 49	$ 2,846
Shareholders' equity, end of year at Mar. 31, 2022	$ 9,806						$ 9,806		$ 5,961					$ 5,809
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share (in dollars per share)	$ 0.59

Summary Of Significant Accounting Policies	3 Months Ended
Summary Of Significant Accounting Policies	Mar. 31, 2022
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES General Ameren, headquartered in St. Louis, Missouri, is a public utility holding company whose primary assets are its equity interests in its subsidiaries. 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 has other subsidiaries that conduct other activities, such as providing 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 Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois. •ATXI operates a FERC rate-regulated electric transmission business in the MISO. The COVID-19 pandemic continues to affect our results of operations, financial position, and liquidity. While our electric sales volumes, excluding the estimated effects of weather and customer energy-efficiency programs, were comparable to the same period in 2021, and total sales volume levels were comparable to pre-pandemic levels, there has been a shift in sales volumes by customer class, which began in 2020, with an increase in residential sales, and a decrease in commercial and industrial sales. While the revenues from Ameren Illinois’ electric distribution business, residential and small nonresidential customers of Ameren Illinois’ natural gas distribution business, and Ameren Illinois’ and ATXI’s electric transmission businesses are decoupled from changes in sales volumes, earnings at Ameren Missouri and those associated with Ameren Illinois’ large nonresidential natural gas customers are exposed to such changes. The continued effect of the COVID-19 pandemic on our results of operations, financial position, and liquidity in subsequent periods will depend on its severity and longevity, future regulatory or legislative actions with respect thereto, and the resulting impact on business, economic, and capital market conditions. Ameren’s and Ameren Missouri’s financial statements are prepared on a consolidated basis and therefore include the accounts of their majority-owned subsidiaries. All intercompany transactions have been eliminated. Ameren Missouri’s subsidiaries were created for the ownership of renewable generation projects. Ameren Illinois has no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated. 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 reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates. The results of operations for an interim period may not give a true indication of results that may be expected for a full year. These financial statements should be read in conjunction with the financial statements and accompanying notes included in the Form 10-K. Variable Interest Entities As of March 31, 2022, and December 31, 2021, Ameren had unconsolidated variable interests as a limited partner in various equity method investments, primarily to advance clean and resilient energy technologies, totaling $60 million and $56 million, respectively, included in “Other assets” on Ameren’s consolidated balance sheet. Any earnings or losses related to these investments are included in “Other Income, Net” on Ameren’s consolidated statement of income and comprehensive income. Ameren is not the primary beneficiary of these investments because it does not have the power to direct matters that most significantly affect the activities of these variable interest entities. As of March 31, 2022, the maximum exposure to loss related to these variable interests is limited to the investment in these partnerships of $60 million plus associated outstanding funding commitments of $28 million. Company-owned Life Insurance Ameren and Ameren Illinois have company-owned life insurance, which is recorded at the net cash surrender value. The net cash surrender value is the amount that can be realized under the insurance policies at the balance sheet date. As of March 31, 2022, the cash surrender value of company-owned life insurance at Ameren and Ameren Illinois was $258 million (December 31, 2021 – $278 million) and $112 million (December 31, 2021 – $117 million), respectively, while total borrowings against the policies were $103 million (December 31, 2021 – $109 million) at both Ameren and Ameren Illinois. Ameren and Ameren Illinois have the right to offset the borrowings against the cash surrender value of the policies and, consequently, present the net asset in “Other assets” on their respective balance sheets. The net cash surrender value of Ameren’s company-owned life insurance is affected by the investment performance of a separate account in which Ameren holds a beneficial interest.

Rate And Regulatory Matters	3 Months Ended
Rate And Regulatory Matters	Mar. 31, 2022
Public Utilities, General Disclosures [Abstract]
RATE AND REGULATORY MATTERS	RATE AND REGULATORY MATTERS Below is a summary of updates to significant regulatory proceedings and related legal proceedings. See Note 2 – Rate and Regulatory Matters under Part II, Item 8, of the Form 10-K for additional information and a summary of our regulatory frameworks. We are unable to predict the ultimate outcome of these matters, the timing of final decisions of the various agencies and courts, or the impact on our results of operations, financial position, or liquidity. Missouri December 2021 MoPSC Electric and Natural Gas Rate Orders In December 2021, the MoPSC issued orders in Ameren Missouri’s 2021 electric service and natural gas delivery service regulatory rate reviews. The new electric and natural gas rates approved by these orders went into effect on February 28, 2022. MoPSC Staff Review of Planned Rush Island Energy Center Retirement In February 2022, the MoPSC issued an order directing the MoPSC staff to review Ameren Missouri’s planned accelerated retirement of the Rush Island Energy Center as a result of the NSR and Clean Air Act Litigation discussed in Note 9 – Commitments and Contingencies. The MoPSC staff’s review will include potential impacts on the reliability and cost of Ameren Missouri’s service to its customers, Ameren Missouri’s plans to mitigate the customer impacts of the accelerated retirement, and the prudence of Ameren Missouri’s actions and decisions with regard to the Rush Island Energy Center, among other things. In April 2022, the MoPSC staff filed an initial report with the MoPSC in which the staff concluded early retirement of the Rush Island Energy Center may cause reliability concerns. The MoPSC staff is under no deadline to complete this review. Ameren Missouri is unable to predict the results of this matter; however, results of the review could be used in other MoPSC proceedings, which could have a material adverse effect on the results of operations, financial position, and liquidity of Ameren and Ameren Missouri. Illinois MYRP ROE Performance Metrics Under an MYRP, the ROE approved by the ICC would be subject to annual adjustments during the four-year period based on certain performance metrics, with aggregate symmetrical performance-based ROE incentives and penalties ranging from 20 to 60 basis points annually. In January 2022, Ameren Illinois filed a request with the ICC proposing performance metrics that would be used in determining ROE incentives and penalties. The ICC is required to issue an order on this matter by September 30, 2022. Electric Distribution Service Rates Under IEIMA In April 2022, Ameren Illinois filed its annual electric distribution service performance-based formula rate update with the ICC to be used for 2023 rates, requesting an increase of $83 million. This update reflects an increase to the annual performance-based formula rate based on 2021 actual recoverable costs and expected net plant additions for 2022, an increase to include the 2021 revenue requirement reconciliation adjustment including a capital structure composed of 54% common equity, and a decrease for the conclusion of the 2020 revenue requirement reconciliation adjustment, which will be fully collected from customers in 2022, consistent with the ICC’s December 2021 annual update filing order. An ICC decision in this proceeding is required by December 2022, with new rates effective in January 2023. Electric Customer Energy-Efficiency Investments In April 2022, Ameren Illinois filed a revised energy-efficiency plan with the ICC to invest approximately $120 million per year in electric energy-efficiency programs through 2025, which reflects the increased level of annual investments allowed under the IETL. The ICC has the ability to reduce the amount of electric energy-efficiency savings goals in future plan program years if there are insufficient cost-effective programs available, which could reduce the investments in electric energy-efficiency programs. The electric energy-efficiency program investments and the return on those investments are collected from customers through a rider and are not recovered through the electric distribution service performance-based formula ratemaking framework. The ICC is under no deadline to issue an order in this proceeding. QIP Reconciliation Hearing In March 2020, Ameren Illinois filed a request with the ICC for a reconciliation hearing to determine the accuracy and prudence of natural gas capital investments recovered under the QIP rider during 2019. In August 2021, the Illinois Attorney General’s office challenged the recovery of capital investments that were made during 2019, alleging that the ICC should disallow approximately $70 million in natural gas capital investments as improper and imprudent, providing a potential over-recovery of approximately $3 million in 2019. In August and December 2021, the ICC staff filed testimony that supports the prudence and reasonableness of the capital investments made during 2019. Ameren Illinois’ 2019 QIP rate recovery request under review by the ICC is within the rate increase limitations allowed by law. The ICC is under no deadline to issue an order in this proceeding. Federal Transmission Formula Rate Revisions In February 2020, the MISO, on behalf of Ameren Missouri, Ameren Illinois, and ATXI, filed requests with the FERC to revise each company’s transmission formula rate calculations with respect to the calculation used for materials and supplies inventories included in rate base. In May 2020, the FERC issued orders approving the revisions prospectively. In addition, the FERC declined to order refunds for earlier periods, as requested by intervenors in Ameren Illinois’ filing, but directed its audit staff to review historical rate recovery in connection with an ongoing FERC audit. Separately, in March 2021, the FERC issued an order related to an intervenor challenge to Ameren Illinois’ 2020 transmission formula rate update. As a result of this order, in March 2021, Ameren Illinois recorded a regulatory liability of $9 million, largely as a reduction of electric operating revenues, to reflect expected refunds, including interest, primarily related to the historical rate recovery of materials and supplies inventories included in rate base. The refund amount was reflected in rates as of January 2022 and will be refunded to customers by the end of 2022. Ameren Missouri, Ameren Illinois, and ATXI filed appeals of the FERC's May 2020 and March 2021 orders, and related FERC orders denying requests for rehearing, to the United States Court of Appeals for the District of Columbia Circuit. In January 2022, the appeals were consolidated by the court. The court is under no deadline to address the appeal. Regardless of the outcome of the appeal, the impact of the May 2020 and March 2021 orders is not expected to be material to Ameren’s, Ameren Missouri’s, or Ameren Illinois’ results of operations, financial position, or liquidity. FERC Complaint Cases Since November 2013, the allowed base ROE for FERC-regulated transmission rate base under the MISO tariff has been subject to customer complaint cases and has been changed by various FERC orders. In May 2020, the FERC issued an order, which set the allowed base ROE to 10.02%, and required refunds, with interest, for the periods November 2013 to February 2015 and from late September 2016 forward. In June 2020, various parties filed requests for rehearing with the FERC, challenging the new ROE methodology established by the May 2020 order. In July 2020, the FERC denied the rehearing requests without addressing the issues raised, and indicated it will address the requests for rehearing in a future order. Also in July 2020, Ameren Missouri, Ameren Illinois, and ATXI filed an appeal of the May 2020 order to the United States Court of Appeals for the District of Columbia Circuit challenging the refunds required for the period from September 2016 to May 2020. The court is under no deadline to address the appeal. As of March 31, 2022, Ameren and Ameren Illinois had paid the refunds, including interest, associated with the allowed base ROE set by the May 2020 order.

Short-Term Debt And Liquidity

3 Months Ended

Mar. 31, 2022

Debt Disclosure [Abstract]

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, and, in the case of Ameren Missouri and Ameren Illinois, short-term affiliate borrowings. See Note 4 – Short-term Debt and Liquidity under Part II, Item 8, in the Form 10-K for a description of our indebtedness provisions and other covenants as well as a description of money pool arrangements.

Short-term Borrowings

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, subject to borrowing sublimits, and the issuance of letters of credit. As of March 31, 2022, based on commercial paper outstanding and letters of credit issued under the Credit Agreements, along with cash and cash equivalents, the net liquidity available to Ameren (parent), Ameren Missouri, and Ameren Illinois, collectively, was $1.2 billion. The Ameren Companies were in compliance with the covenants in their Credit Agreements as of March 31, 2022. As of March 31, 2022, the ratios of consolidated indebtedness to consolidated total capitalization, calculated in accordance with the provisions of the Credit Agreements, were 59%, 50%, and 44% for Ameren, Ameren Missouri, and Ameren Illinois, respectively.

The following table presents commercial paper outstanding, net of issuance discounts, as of March 31, 2022, and December 31, 2021. There were no borrowings outstanding under the Credit Agreements as of March 31, 2022, or December 31, 2021.


	March 31, 2022		December 31, 2021
Ameren (parent)	$	466	$	277
Ameren Missouri	528		165
Ameren Illinois	107		103
Ameren consolidated	$	1,101	$	545

The following table summarizes the activity and relevant interest rates for Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper issuances and borrowings under the Credit Agreements in the aggregate for the three months ended March 31, 2022 and 2021:


	Ameren (parent)			Ameren Missouri			Ameren Illinois			Ameren Consolidated
2022
Average daily amount outstanding	$	282		$	408		$	99		$	789

Weighted-average interest rate	0.41		%	0.44		%	0.33		%	0.41		%
Peak amount outstanding during period(a)	$	466		$	539		$	142		$	1,101
Peak interest rate	1.05		%	1.06		%	1.15		%	1.15		%
2021
Average daily amount outstanding	$	454		$	99		$	96		$	649

Weighted-average interest rate	0.25		%	0.22		%	0.21		%	0.24		%
Peak amount outstanding during period(a)	$	650		$	206		$	353		$	916
Peak interest rate	0.33		%	0.25		%	0.25		%	0.33		%

(a)The timing of peak outstanding commercial paper issuances and borrowings under the Credit Agreements varies by company. Therefore, the sum of individual company peak amounts may not equal the Ameren consolidated peak for the period.

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. The average interest rate for borrowings under the utility money pool for the three months ended March 31, 2022, was 0.39% (2021 – 0.22% ). See Note 8 – Related-party Transactions for the amount of interest income and expense from the utility money pool arrangements recorded by Ameren Missouri and Ameren Illinois for the three months ended March 31, 2022 and 2021.

Long-Term Debt And Equity Financings	3 Months Ended
Long-Term Debt And Equity Financings	Mar. 31, 2022
Long-Term Debt And Equity Financings [Abstract]
LONG-TERM DEBT AND EQUITY FINANCINGS	LONG-TERM DEBT AND EQUITY FINANCINGS Ameren For the three months ended March 31, 2022, Ameren issued a total of 0.1 million shares of common stock under its DRPlus and 401(k) plan, and received proceeds of $5 million and had a receivable of $8 million. In addition, in the first quarter of 2022, Ameren issued 0.4 million shares of common stock valued at $31 million upon the settlement of stock-based compensation awards. In May 2021, Ameren entered into an equity distribution sales agreement pursuant to which Ameren may offer and sell from time to time up to $750 million of its common stock through an ATM program, which includes the ability to enter into forward sales agreements. There were no shares issued under the ATM program for the three months ended March 31, 2022. As of March 31, 2022, Ameren had approximately $320 million of common stock available to issue under the ATM program, which takes into account the forward sale agreements in effect as of March 31, 2022, discussed below. Ameren has entered into multiple forward sale agreements, including the April 2022 forward sale agreement discussed below, under the ATM program with various counterparties relating to 3.4 million shares of common stock. Ameren expects to settle the forward sale agreements by December 31, 2022. Related to the forward sale agreements outstanding as of March 31, 2022, these agreements can be settled at Ameren’s discretion on or prior to dates ranging from May 3, 2023 to September 30, 2023. On a settlement date or dates, if Ameren elects to physically settle the forward sale agreement, Ameren will issue shares of common stock to the counterparties at the then-applicable forward sale price. The initial forward sale price for the agreements ranged from $86.35 to $88.81 with a weighted average initial sale price of $87.61. Each initial forward sale price is subject to adjustment based on a floating interest rate factor equal to the overnight bank funding rate less a spread of 75 basis points, and will be subject to decrease on certain dates specified in the forward sale agreements by specified amounts related to expected dividends on shares of the common stock during the term of the forward sale agreements. If the overnight bank funding rate is less than the spread on any day, the interest rate factor will result in a reduction of the forward sale price. The forward sale agreements will be physically settled unless Ameren elects to settle in cash or to net share settle. At March 31, 2022, Ameren could have settled the forward sale agreements with physical delivery of 3.2 million shares of common stock to the respective counterparties in exchange for cash of $276 million. The forward sale agreements could have also been settled at March 31, 2022, with delivery of approximately $21 million of cash or approximately 0.2 million shares of common stock to the counterparties. In connection to the forward sale agreements, the various counterparties, or their affiliates, borrowed from third parties and sold 3.2 million shares of common stock. The gross sales price of these shares totaled $280 million. In connection with such sales, the counterparties were deemed to have received commissions of $3 million. Ameren has not received any proceeds from such sales of borrowed shares. The forward sale agreements have been classified as equity transactions. In April 2022, Ameren entered into a forward sale agreement under the ATM program relating to 0.2 million shares of common stock. The April 2022 forward sale can be settled at Ameren’s discretion on or prior to September 30, 2023. The forward sale price was initially $91.41 for the April 2022 forward sale agreement. Ameren Missouri In April 2022, Ameren Missouri issued $525 million of 3.90% first mortgage bonds due April 2052, with interest payable semiannually on April 1 and October 1 of each year, beginning October 1, 2022. Ameren Missouri received net proceeds of $519 million, which were used to repay short-term debt and for near-term capital expenditures. Ameren Missouri intends to allocate an amount equal to the net proceeds to sustainability projects meeting certain eligibility criteria. ATXI In November 2021, pursuant to a note purchase agreement, ATXI agreed to issue $95 million of its 2.96% senior unsecured notes due 2052, with interest payable semiannually on February 25 and August 25 of each year, beginning February 25, 2023, through a private placement offering exempt from registration under the Securities Act of 1933, as amended. ATXI expects to issue the notes and receive net proceeds of $95 million in August 2022, which will be used to refinance the remaining portion of an intercompany long-term note with Ameren (parent), repay a $50 million principal payment of its 3.43% senior unsecured notes, and to repay short-term debt. Indenture Provisions and Other Covenants See Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, in the Form 10-K for a description of our indenture provisions and other covenants, as well as restrictions on the payment of dividends. At March 31, 2022, the Ameren Companies were in compliance with the provisions and covenants contained in their indentures and articles of incorporation, as applicable, and ATXI was in compliance with the provisions and covenants contained in its note purchase agreements. Off-balance-sheet Arrangements At March 31, 2022, none of the Ameren Companies had any significant off-balance-sheet financing arrangements, other than variable interest entities and the multiple forward sale agreements under the ATM program relating to common stock. See Note 1 – Summary of Significant Accounting Policies for further detail concerning variable interest entities.

Other Income, Net

3 Months Ended

Mar. 31, 2022

Other Nonoperating Income (Expense) [Abstract]

OTHER INCOME, NET

The following table presents the components of “Other Income, Net” in the Ameren Companies’ statements of income for the three months ended March 31, 2022 and 2021:


	Three Months
		2022		2021
Ameren:

Allowance for equity funds used during construction		$	8	$	7
Interest income on industrial development revenue bonds		6		6


Non-service cost components of net periodic benefit income(a)		46		34
Miscellaneous income		7		5
Donations		(2)		(3)
Miscellaneous expense		(5)		(3)
Total Other Income, Net		$	60	$	46
Ameren Missouri:

Allowance for equity funds used during construction		$	4	$	4
Interest income on industrial development revenue bonds		6		6

Non-service cost components of net periodic benefit income(a)		14		14
Miscellaneous income		2		1
Donations		(1)		—
Miscellaneous expense		(2)		(2)
Total Other Income, Net		$	23	$	23
Ameren Illinois:

Allowance for equity funds used during construction		$	4	$	3


Non-service cost components of net periodic benefit income		21		14
Miscellaneous income		2		1
Donations		(1)		(3)
Miscellaneous expense		(2)		(1)
Total Other Income, Net		$	24	$	14

(a)For the three months ended March 31, 2022 and 2021, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $6 million and less than $(1) million, respectively, due to a regulatory tracking mechanism for the difference between the level of such costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates.

Derivative Financial Instruments

3 Months Ended

Mar. 31, 2022

Derivative Instruments and Hedging Activities Disclosure [Abstract]

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;

•actual cash outlays for the purchase of these commodities that differ from anticipated cash outlays; and

•actual off-system sales revenues that differ from anticipated revenues.

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.

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. 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. The following disclosures exclude NPNS contracts and other non-derivative commodity contracts that are accounted for under the accrual method of accounting.

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 March 31, 2022, and December 31, 2021, all contracts that met the definition of a derivative and were not eligible for the NPNS exception received regulatory deferral. Cash flows for all derivative financial instruments are classified in cash flows from operating activities.

The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of March 31, 2022, and December 31, 2021. As of March 31, 2022, these contracts extended through October 2024, October 2027, May 2032 and March 2024 for fuel oils, natural gas, power and uranium, respectively.


	Quantity (in millions)
	March 31, 2022			December 31, 2021
Commodity	Ameren Missouri	Ameren Illinois	Ameren	Ameren Missouri	Ameren Illinois	Ameren
Fuel oils (in gallons)	25	—	25	30	—	30
Natural gas (in mmbtu)	36	146	182	35	144	179
Power (in MWhs)	4	6	10	6	6	12
Uranium (pounds in thousands)	496	—	496	586	—	586

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 March 31, 2022, and December 31, 2021:


			March 31, 2022					December 31, 2021
	Balance Sheet Location		Ameren Missouri		Ameren Illinois		Ameren			Ameren Missouri		Ameren Illinois		Ameren





Fuel oils	Mark-to-market derivative assets	$	(a)	$	—	$	18		$	(a)	$	—	$	8

	Other current assets		18		—		—			8		—		—
	Other assets		8		—		8			5		—		5
Natural gas	Mark-to-market derivative assets		(a)		74		90			(a)		28		35

	Other current assets		16		—		—			7		—		—
	Other assets		10		23		33			5		13		18
Power	Mark-to-market derivative assets		(a)		5		24			(a)		—		23

	Other current assets		19		—		—			23		—		—
	Other assets		—		—		—			—		—		—
Uranium	Mark-to-market derivative assets		(a)		—		5			(a)		—		—

	Other current assets		5		—		—			—		—		—
	Other assets		2		—		2			1		—		1
	Total assets	$	78	$	102	$	180		$	49	$	41	$	90




Natural gas	Mark-to-market derivative liabilities		—		(a)		(a)			2		(a)		(a)

	Other current liabilities		—		2		2			—		6		8
	Other deferred credits and liabilities		1		1		2			1		2		3
Power	Mark-to-market derivative liabilities		109		(a)		(a)			50		(a)		(a)

	Other current liabilities		—		1		110			—		9		59
	Other deferred credits and liabilities		26		78		104			23		108		131
Uranium	Mark-to-market derivative liabilities		—		(a)		(a)			1		(a)		(a)

	Other current liabilities		—		—		—			—		—		1

	Total liabilities	$	136	$	82	$	218		$	77	$	125	$	202

(a)Balance sheet line item not applicable to registrant.

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 following table provides the recognized gross derivative balances and the net amounts of those derivatives subject to an enforceable master netting arrangement or similar agreement as of March 31, 2022, and December 31, 2021.


			Gross Amounts Not Offset in the Balance Sheet
Commodity Contracts Eligible to be Offset	Gross Amounts Recognized in the Balance Sheet		Derivative Instruments		Cash Collateral Received/Posted(a)		Net Amount
2022
Assets:
Ameren Missouri	$	78	$	19	$	5	$	54
Ameren Illinois	102		6		9		87
Ameren	$	180	$	25	$	14	$	141
Liabilities:
Ameren Missouri	$	136	$	19	$	92	$	25
Ameren Illinois	82		6		—		76
Ameren	$	218	$	25	$	92	$	101
2021
Assets:
Ameren Missouri	$	49	$	15	$	—	$	34
Ameren Illinois	41		4		—		37
Ameren	$	90	$	19	$	—	$	71
Liabilities:
Ameren Missouri	$	77	$	15	$	47	$	15
Ameren Illinois	125		4		—		121
Ameren	$	202	$	19	$	47	$	136

(a)Cash collateral received reduces gross asset balances and is included in “Other current liabilities” and “Other deferred credits and liabilities” on the balance sheet. Cash collateral posted reduces gross liability balances and is included in “Other current assets” and “Other assets” on the balance sheet.

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. As of March 31, 2022, if counterparty groups were to fail completely to perform on contracts, Ameren, Ameren Missouri, and Ameren Illinois' maximum exposure related to derivative assets, predominantly from financial institutions, was $176 million, $79 million, and $97 million, respectively. The potential loss on counterparty exposures may be reduced or eliminated by the application of master netting arrangements or similar agreements and collateral held. As of March 31, 2022, the potential loss after consideration of the application of master netting arrangements or similar agreements and collateral held for Ameren, Ameren Missouri, and Ameren Illinois was $144 million, $56 million, and $88 million, respectively.

Certain of our derivative instruments contain collateral provisions tied to the Ameren Companies’ credit ratings. If our credit ratings were downgraded below investment grade, 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 additional collateral required is the net liability position allowed under master netting arrangements or similar agreements, assuming (1) the credit risk-related contingent features underlying these arrangements were triggered and (2) those counterparties with rights to do so requested collateral. The following table presents, as of March 31, 2022, 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.



	Aggregate Fair Value of Derivative Liabilities(a)		Cash Collateral Posted		Potential Aggregate Amount of Additional Collateral Required(b)
Ameren Missouri	$	36	$	18	$	7
Ameren Illinois	4		—		4
Ameren	$	40	$	18	$	11

(a)Before consideration of master netting arrangements or similar agreements.

(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

3 Months Ended

Mar. 31, 2022

Fair Value Disclosures [Abstract]

Fair Value Disclosures

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. Fair value measurements are classified in three levels based on the fair value hierarchy as defined by GAAP. See Note 8 – Fair Value Measurements under Part II, Item 8, of the Form 10-K for information related to hierarchy levels and valuation techniques.

We consider nonperformance risk in our valuation of derivative instruments by analyzing our own credit standing and the credit standing of our counterparties, and by considering any credit enhancements (e.g., collateral). 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 material gains or losses related to valuation adjustments for counterparty default risk were recorded at Ameren, Ameren Missouri, or Ameren Illinois in the three months ended March 31, 2022 or 2021. At March 31, 2022, and December 31, 2021, 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 March 31, 2022, and December 31, 2021:


		March 31, 2022									December 31, 2021
		Level 1		Level 2		Level 3		Total			Level 1		Level 2		Level 3		Total
Assets:
Ameren Missouri
	Derivative assets – commodity contracts:
	Fuel oils	$	24	$	—	$	2	$	26		$	13	$	—	$	—	$	13
	Natural gas	—		26		—		26			—		12		—		12
	Power	18		—		1		19			10		—		13		23
	Uranium	—		—		7		7			—		—		1		1
	Total derivative assets – commodity contracts	$	42	$	26	$	10	$	78		$	23	$	12	$	14	$	49
	Nuclear decommissioning trust fund:

	Equity securities:
	U.S. large capitalization	$	719	$	—	$	—	$	719		$	824	$	—	$	—	$	824
	Debt securities:
	U.S. Treasury and agency securities	—		174		—		174			—		141		—		141
	Corporate bonds	—		133		—		133			—		131		—		131


	Other	—		61		—		61			—		56		—		56
	Total nuclear decommissioning trust fund	$	719	$	368	$	—	$	1,087	(a)	$	824	$	328	$	—	$	1,152	(a)
	Total Ameren Missouri	$	761	$	394	$	10	$	1,165		$	847	$	340	$	14	$	1,201
Ameren Illinois
	Derivative assets – commodity contracts:
	Natural gas	$	7	$	77	$	13	$	97		$	1	$	33	$	7	$	41
	Power	—		—		5		5			—		—		—		—
	Total Ameren Illinois	$	7	$	77	$	18	$	102		$	1	$	33	$	7	$	41
Ameren
	Derivative assets – commodity contracts(b)	$	49	$	103	$	28	$	180		$	24	$	45	$	21	$	90
	Nuclear decommissioning trust fund(c)	719		368		—		1,087		(a)	824		328		—		1,152		(a)
	Total Ameren	$	768	$	471	$	28	$	1,267		$	848	$	373	$	21	$	1,242
Liabilities:
Ameren Missouri
	Derivative liabilities – commodity contracts:

	Natural gas	$	—	$	1	$	—	$	1		$	—	$	2	$	1	$	3
	Power	81		—		54		135			45		—		28		73
	Uranium	—		—		—		—			—		—		1		1
	Total Ameren Missouri	$	81	$	1	$	54	$	136		$	45	$	2	$	30	$	77


		March 31, 2022								December 31, 2021
		Level 1		Level 2		Level 3		Total		Level 1		Level 2		Level 3		Total
Ameren Illinois
	Derivative liabilities – commodity contracts:
	Natural gas	$	—	$	1	$	2	$	3	$	—	$	5	$	3	$	8
	Power	—		—		79		79		—		—		117		117
	Total Ameren Illinois	$	—	$	1	$	81	$	82	$	—	$	5	$	120	$	125
Ameren
	Derivative liabilities – commodity contracts(b)	$	81	$	2	$	135	$	218	$	45	$	7	$	150	$	202

(a)Balance excludes $7 million of cash and cash equivalents, receivables, payables, and accrued income, net, for both March 31, 2022, and December 31, 2021.

(b)See the Ameren Missouri and Ameren Illinois sections of the table for a breakout of the fair value of Ameren’s derivative assets and liabilities by type of commodity.

(c)See the Ameren Missouri section of the table for a breakout of the fair value of Ameren's nuclear decommissioning trust fund by investment type.

Level 3 fuel oils, natural gas, and uranium derivative contract assets and liabilities measured at fair value on a recurring basis were immaterial for all periods presented. The following table presents the fair value reconciliation of Level 3 power derivative contract assets and liabilities measured at fair value on a recurring basis for the three months ended March 31, 2022 and 2021:


	2022						2021
	Ameren Missouri		Ameren Illinois		Ameren			Ameren Missouri		Ameren Illinois		Ameren










For the three months ended March 31:
Beginning balance at January 1	$	(15)	$	(117)	$	(132)		$	2	$	(198)	$	(196)
Realized and unrealized gains/(losses) included in regulatory assets/liabilities	(41)		42		1			(5)		9		4


Settlements	3		1		4			—		4		4


Ending balance at March 31	$	(53)	$	(74)	$	(127)		$	(3)	$	(185)	$	(188)
Change in unrealized gains/(losses) related to assets/liabilities held at March 31	$	(38)	$	42	$	4		$	(3)	$	9	$	6

All gains or losses related to our Level 3 derivative commodity contracts are expected to be recovered or returned through customer rates; therefore, there is no impact to either net income or other comprehensive income resulting from changes in the fair value of these instruments.

The following table describes the valuation techniques and significant unobservable inputs utilized for the fair value of our Level 3 power derivative contract assets and liabilities as of March 31, 2022, and December 31, 2021:


			Fair Value						Weighted Average(b)
	Commodity		Assets		Liabilities	Valuation Technique(s)	Unobservable Input(a)	Range









2022	Power(c)	$	6	$	(133)	Discounted cash flow	Average forward peak and off-peak pricing – forwards/swaps ($/MWh)	35 – 82	51

							Nodal basis ($/MWh)	(16) – 0	(3)


							Trend rate (%)	(e)	(1)








































2021	Power(d)	$	13	$	(145)	Discounted cash flow	Average forward peak and off-peak pricing – forwards/swaps ($/MWh)	32 – 55	40

							Nodal basis ($/MWh)	(14) – 0	(2)


							Trend rate (%)	(e)	0

(a)Generally, significant increases (decreases) in these inputs in isolation would result in a significantly higher (lower) fair value measurement.

(b)Unobservable inputs were weighted by relative fair value.

(c)Valuations through 2031 use visible forward prices adjusted for nodal-to-hub basis differentials. Valuations beyond 2031 use a trend rate factor and are similarly adjusted for nodal-to-hub basis differentials.

(d)Valuations through 2029 use visible forward prices adjusted for nodal-to-hub basis differentials. Valuations beyond 2029 use a trend rate factor and are similarly adjusted for nodal-to-hub basis differentials.

(e)No meaningful range around weighted average.

The following table sets forth the carrying amount and, by level within the fair value hierarchy, the fair value of financial assets and liabilities disclosed, but not recorded, at fair value as of March 31, 2022, and December 31, 2021:


	Carrying Amount			Fair Value
				Level 1		Level 2		Level 3			Total
	March 31, 2022
Ameren:
Cash, cash equivalents, and restricted cash	$	154		$	154	$	—	$	—		$	154
Investments in industrial development revenue bonds(a)	248			—		248		—			248
Short-term debt	1,101			—		1,101		—			1,101
Long-term debt (including current portion)(a)	13,068		(b)	—		12,615		526		(c)	13,141
Ameren Missouri:
Cash, cash equivalents, and restricted cash	$	9		$	9	$	—	$	—		$	9

Investments in industrial development revenue bonds(a)	248			—		248		—			248
Short-term debt	528			—		528		—			528

Long-term debt (including current portion)(a)	5,619		(b)	—		5,701		—			5,701
Ameren Illinois:
Cash, cash equivalents, and restricted cash	$	137		$	137	$	—	$	—		$	137

Short-term debt	107			—		107		—			107

Long-term debt (including current portion)	4,393		(b)	—		4,457		—			4,457
	December 31, 2021
Ameren:
Cash, cash equivalents, and restricted cash	$	155		$	155	$	—	$	—		$	155
Investments in industrial development revenue bonds(a)	248			—		248		—			248
Short-term debt	545			—		545		—			545
Long-term debt (including current portion)(a)	13,067		(b)	—		13,930		591		(c)	14,521
Ameren Missouri:
Cash, cash equivalents, and restricted cash	$	8		$	8	$	—	$	—		$	8

Investments in industrial development revenue bonds(a)	248			—		248		—			248
Short-term debt	165			—		165		—			165
Long-term debt (including current portion)(a)	5,619		(b)	—		6,321		—			6,321
Ameren Illinois:
Cash, cash equivalents, and restricted cash	$	133		$	133	$	—	$	—		$	133
Short-term debt	103			—		103		—			103

Long-term debt (including current portion)	4,392		(b)	—		4,971		—			4,971

(a)Ameren and Ameren Missouri have investments in industrial development revenue bonds, classified as held-to-maturity and recorded in “Other Assets,” that are equal to the finance obligations for the Peno Creek and Audrain CT energy centers. As of March 31, 2022, and December 31, 2021, the carrying amount of both the investments in industrial development revenue bonds and the finance obligations approximated fair value.

(b)Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $94 million, $38 million, and $38 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of March 31, 2022. Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $94 million, $38 million, and $39 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2021.

(c)The Level 3 fair value amount consists of ATXI’s senior unsecured notes.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Related Party Transactions

3 Months Ended

Mar. 31, 2022

RELATED PARTY TRANSACTIONS

RELATED-PARTY TRANSACTIONS

In the ordinary course of business, Ameren Missouri and Ameren Illinois 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 Ameren’s subsidiaries are reported as affiliate transactions on their individual financial statements, but those transactions are eliminated in consolidation for Ameren’s consolidated financial statements. For a discussion of material related-party agreements and money pool arrangements, see Note 13 – Related-party Transactions and Note 4 – Short-term Debt and Liquidity under Part II, Item 8, of the Form 10-K.

Support Services Agreements

At both March 31, 2022 and December 31, 2021, Ameren Missouri and Ameren Illinois had long-term receivables included in “Other assets” from Ameren Services of $77 million and $80 million, respectively, related to Ameren Services’ allocated portion of Ameren’s pension and postretirement benefit plans.

Tax Allocation Agreement

See Note 1 – Summary of Significant Accounting Policies under Part II, Item 8, of the Form 10-K for a discussion of the tax allocation agreement. The following table presents the affiliate balances related to income taxes for Ameren Missouri and Ameren Illinois as of March 31, 2022, and December 31, 2021:


	March 31, 2022				December 31, 2021
	Ameren Missouri		Ameren Illinois		Ameren Missouri		Ameren Illinois
Income taxes payable to parent(a)	$	—	$	42	$	—	$	8
Income taxes receivable from parent(b)	33		—		27		18

(a)Included in “Accounts payable – affiliates” on the balance sheet.

(b)Included in “Accounts receivable – affiliates” on the balance sheet.

Effects of Related-party Transactions on the Statement of Income

The following table presents the impact on Ameren Missouri and Ameren Illinois of related-party transactions for the three months ended March 31, 2022 and 2021:


			Three Months
Agreement	Income Statement Line Item				Ameren Missouri		Ameren Illinois
Ameren Missouri power supply	Operating Revenues	2022		$	4	$	(a)
agreements with Ameren Illinois		2021			2		(a)
Ameren Missouri and Ameren Illinois	Operating Revenues	2022		$	6	$	(b)
rent and facility services		2021			7		(b)
Ameren Missouri and Ameren Illinois miscellaneous	Operating Revenues	2022		$	(b)	$	1
support services and other services provided to ATXI		2021			(b)		(b)
Total Operating Revenues		2022		$	10	$	1
		2021			9		(b)
Ameren Illinois power supply	Purchased Power	2022		$	(a)	$	4
agreements with Ameren Missouri		2021			(a)		2
Ameren Missouri and Ameren Illinois	Purchased Power	2022		$	(b)	$	(b)
transmission services from ATXI		2021			1		(b)
Total Purchased Power		2022		$	(b)	$	4
		2021			1		2
Ameren Missouri and Ameren Illinois	Other Operations and Maintenance	2022		$	(b)	$	1
rent and facility services		2021			(b)		1
Ameren Services support services	Other Operations and Maintenance	2022		$	38	$	35
agreement		2021			35		33
Total Other Operations and		2022		$	38	$	36
Maintenance		2021			35		34
Money pool borrowings (advances)	(Interest Charges)/Other Income, Net	2022		$	(b)	$	(b)
		2021			(b)		(b)

(a)Not applicable.

(b)Amount less than $1 million.

Commitments And Contingencies	3 Months Ended
Commitments And Contingencies	Mar. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
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 the notes to our financial statements in this report and in the Form 10-K, will not have a material adverse effect on our results of operations, financial position, or liquidity. Reference is made to Note 1 – Summary of Significant Accounting Policies, Note 2 – Rate and Regulatory Matters, Note 9 – Callaway Energy Center, Note 13 – Related-party Transactions, and Note 14 – Commitments and Contingencies under Part II, Item 8, of the Form 10-K. See also Note 1 – Summary of Significant Accounting Policies, Note 2 – Rate and Regulatory Matters, Note 8 – Related-party Transactions, and Note 10 – Callaway Energy Center of this report. Environmental Matters Our electric generation, transmission, and distribution and natural gas distribution and storage operations must comply with a variety of statutes and regulations relating to the protection of the environment and human health and safety including permitting programs implemented via federal, state, and local authorities. Such environmental laws address air emissions; discharges to water bodies; the storage, handling and disposal of hazardous substances and waste materials; siting and land use requirements; and potential ecological impacts. 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. We employ dedicated personnel knowledgeable in environmental matters to oversee our business activities’ compliance with regulatory requirements. Environmental regulations have a significant impact on the electric utility industry and compliance with these regulations could be costly for Ameren Missouri, which operates coal-fired power plants. Clean Air Act regulations that apply to the electric utility industry include the NSPS, the CSAPR, the MATS, and the National Ambient Air Quality Standards, which are subject to periodic review for certain pollutants. Collectively, these regulations cover a variety of pollutants, such as SO2, particulate matter, NOx, mercury, toxic metals and acid gases, and CO2 emissions from new power plants. Regulations implementing the Clean Water Act govern both intake and discharges of water, and may require evaluation of the ecological and biological impact of our operations and could require modifications to water intake structures or more stringent limitations on wastewater discharges. Depending upon the scope of modifications ultimately required by state regulators, these capital expenditures could be significant. The management and disposal of coal ash is regulated under the Resource Conservation and Recovery Act and the CCR Rule, which require the closure of our surface impoundments at Ameren Missouri’s coal-fired energy centers. The individual or combined effects of existing and new environmental regulations could result in significant capital expenditures, increased operating costs, or the closure or alteration of operations at some of Ameren Missouri’s energy centers. Ameren and Ameren Missouri expect that such compliance costs would be recoverable through rates, subject to MoPSC prudence review, but the timing of costs and their recovery could be subject to regulatory lag. Ameren and Ameren Missouri estimate that they will need to make capital expenditures of $125 million to $175 million from 2022 through 2026 in order to comply with existing environmental regulations. Additional environmental controls beyond 2026 could be required. This estimate of capital expenditures includes ash pond closure and corrective action measures required by the CCR Rule and the effluent limitation guidelines applicable to steam electric generating units, and potential modifications to cooling water intake structures at existing power plants under Clean Water Act rules, all of which are discussed below. In addition to planned retirements of coal-fired energy centers as set forth in the 2020 IRP and as noted in the NSR and Clean Air Act litigation discussed below, Ameren Missouri’s current plan for compliance with existing air emission regulations includes the closure of the Venice Energy Center by 2030 as discussed below in Illinois Emission Standards, burning low-sulfur coal and installing new or optimizing existing air pollution control equipment. The actual amount of capital expenditures required to comply with existing environmental regulations may vary substantially from the above estimates because of uncertainty as to future permitting requirements made by state regulators and the EPA, potential revisions to regulatory obligations, and the cost of potential compliance strategies, among other things. The following sections describe the more significant environmental laws and rules and environmental enforcement and remediation matters that affect or could affect our operations. The EPA has initiated an administrative review of several regulations and proposed amendments to regulations and guidelines, including the CSAPR, which could ultimately result in the revision of all or part of such rules. Additionally, Ameren Missouri’s wind generation facilities may be subject to operating restrictions to limit the impact on protected species. Seasonal nighttime curtailment began at the High Prairie Renewable Energy Center at the end of March 2022, but the extent and duration of the curtailment is unknown at this time as assessment of mitigation technologies is ongoing. Nighttime operating restrictions may be required during the critical biological season, which typically occurs from April through October. Ameren Missouri does not anticipate these operating curtailments to result in significant impacts on its results of operations, financial position, or liquidity. Clean Air Act Federal and state laws, including CSAPR, regulate emissions of SO2 and NOx through the reduction of emissions at their source and the use and retirement of emission allowances. CSAPR is implemented through a series of phases, and the second phase became effective in 2017. In April 2022, the EPA proposed revisions to the CSAPR and additional emission reduction requirements may apply in subsequent years. Ameren Missouri complies with current CSAPR requirements by minimizing emissions through the use of low-sulfur coal, operation of two scrubbers at its Sioux Energy Center, and optimization of other existing air pollution control equipment. Ameren Missouri could incur additional costs to lower its emissions at one or more of its energy centers to comply with additional CSAPR requirements in future years. These additional costs for compliance are expected to be recovered from customers through the FAC or higher base rates. CO2 Emissions Standards The EPA’s Affordable Clean Energy Rule repealed the Clean Power Plan and replaced it with a new rule that established emission guidelines for states to follow in developing plans to limit CO2 emissions and identified certain efficiency measures as the best system of emission reduction for coal-fired electric generating units. In January 2021, the United States Court of Appeals for the District of Columbia Circuit vacated the Affordable Clean Energy Rule, and ruled that the EPA had the discretion to consider emission reduction measures that include efficiency measures and generation shifting to lower carbon emissions. The United States Supreme Court agreed to review the court of appeals’ ruling and oral arguments occurred in February 2022, with a decision expected by mid-2022. A decision by the United States Supreme Court could impact the EPA’s development of new regulations to address carbon emissions from coal- and natural gas-fired electric generating units. At this time, Ameren Missouri cannot predict the outcome of the legal challenge or future rulemakings. As such, any impact on the results of operations, financial position, and liquidity of Ameren and Ameren Missouri is uncertain. NSR and Clean Air Act Litigation In January 2011, the United States 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 alleging that in performing projects at its coal-fired Rush Island Energy Center in 2007 and 2010, Ameren Missouri violated provisions of the Clean Air Act and Missouri law. In January 2017, the district court issued a liability ruling against Ameren Missouri and, in September 2019, entered a remedy order that required Ameren Missouri to install a flue gas desulfurization system at the Rush Island Energy Center and a dry sorbent injection system at the Labadie Energy Center. Ameren Missouri appealed both the liability and remedy orders and, in August 2021, the United States Court of Appeals for the Eighth Circuit issued a decision that affirmed the liability ruling and the district court’s remedy order as it related to the installation of a flue gas desulfurization system at the Rush Island Energy Center, but reversed the order as it related to the installation of a dry sorbent injection system at the Labadie Energy Center. In November 2021, the court of appeals issued an order denying requests for consideration previously sought by both Ameren Missouri and the United States Department of Justice. Based on its assessment of available legal, operational, and regulatory alternatives, Ameren Missouri has determined not to further appeal the court rulings and, in December 2021, filed a motion with the district court to modify the remedy order to allow the retirement of the Rush Island Energy Center in advance of its previously expected useful life in lieu of installing a flue gas desulfurization system. The district court is under no deadline to issue a ruling revising the remedy order. In January 2022, the MISO completed a preliminary informational assessment regarding potential impacts of the retirement to the regional electric power system, which indicated transmission upgrades and voltage support would be needed in advance of the retirement of the Rush Island Energy Center to address reliability concerns. In February 2022, Ameren Missouri formally notified the MISO of its intent to retire the Rush Island Energy Center and requested the MISO to perform a final reliability assessment, which is expected to be completed in May 2022. The MISO must also separately approve the specific upgrades and transmission support required to address reliability concerns noted in the final assessment. Additionally, the MISO will determine whether reliability concerns require the Rush Island Energy Center to be classified as a system support resource, which should continue operating until the completion of to-be-specified transmission upgrades. If the Rush Island Energy Center were identified as a system support resource, an agreement detailing the manner of and time for continued operation would be filed with the FERC for approval. The district court has the authority to determine the retirement date and operating parameters for the Rush Island Energy Center and is not bound by the MISO determination or FERC’s approval. Related to this matter, in February 2022, the MoPSC issued an order directing the MoPSC staff to review the planned accelerated retirement of the Rush Island Energy Center. See Note 2 – Rate and Regulatory Matters for additional information. In connection with the planned accelerated retirement of the Rush Island Energy Center, Ameren Missouri expects to seek approval from the MoPSC to finance the costs associated with the retirement, including the remaining unrecovered net plant balance associated with the facility, through the issuance of securitized utility tariff bonds pursuant to the Missouri securitization statute that became effective in August 2021. As of March 31, 2022, the Rush Island Energy Center had a net plant balance of approximately $0.6 billion included in plant to be abandoned, net, within “Property, Plant, and Equipment, Net” and a rate base of approximately $0.4 billion. See Note 1 – Summary of Significant Accounting Policies under Part II, Item 8, of the Form 10-K for additional information regarding plant to be abandoned, net. In addition, Ameren Missouri expects to file an update to the 2020 IRP with the MoPSC in June 2022 to reflect the planned acceleration of the retirement of the Rush Island Energy Center from 2039, the retirement year for the facility as reflected in the 2020 IRP and reflected in depreciation rates approved by the December 2021 MoPSC electric rate order. Ameren Missouri is unable to predict the ultimate resolution of this matter; however, such resolution could have a material adverse effect on the results of operations, financial position, and liquidity of Ameren and Ameren Missouri. Clean Water Act The EPA’s regulations implementing Section 316(b) of the Clean Water Act require power plant operators to evaluate cooling water intake structures and identify measures for reducing the number of aquatic organisms impinged on a power plant’s cooling water intake screens or entrained through the plant’s cooling water system. All of Ameren Missouri’s coal-fired and nuclear energy centers are subject to the cooling water intake structures rule. Requirements of the rule are implemented by state regulators through the permit renewal process of each power plant’s water discharge permit, which is expected to be completed by 2023 for Ameren Missouri. In 2015, the EPA issued a rule to revise the effluent limitation guidelines applicable to steam electric generating units. These guidelines established national standards for water discharges, prohibit effluent discharges of certain waste streams, and impose more stringent limitations on certain water discharges from power plants. To meet the requirements of the guidelines, Ameren Missouri installed dry ash handling systems and in 2020 completed construction of wastewater treatment facilities at three of its four coal-fired energy centers. The Meramec Energy Center is scheduled to retire in 2022 and, as a result, does not require new wastewater and dry ash handling systems. CCR Management The EPA’s CCR Rule establishes requirements for the management and disposal of CCR from coal-fired power plants and will result in the closure of certain surface impoundments at Ameren Missouri’s energy centers. Ameren Missouri completed the closure of all surface impoundments at its Labadie and Rush Island energy centers in 2021, and has made significant progress by closing several impoundments at its Sioux and Meramec energy centers. Ameren Missouri plans to complete the closures of the remaining surface impoundments as required by the CCR Rule in 2023. In January 2022, Ameren Missouri received notice of a proposed determination by the EPA that it has rejected Ameren Missouri’s requests to extend the timeline for operating certain impoundments located at the Sioux and Meramec energy centers. Pursuant to the terms of the proposed determination, compliance with the CCR Rule’s requirements for closure of the impoundments would be required 135 days after the EPA issues a final determination, which Ameren Missouri expects to be issued in the spring of 2022. If Ameren Missouri was no longer able to use the surface impoundments at the Sioux or Meramec energy centers, Ameren Missouri would not be able to operate the energy centers unless an alternative for handling the CCR material was available. Ameren Missouri will retire the Meramec Energy Center in 2022, and construction is underway to complete a CCR Rule-compliant impoundment at the Sioux Energy Center to allow for continued operations. Additionally, Ameren Missouri is seeking a reliability determination from the MISO, which, if granted and accepted by the EPA, would extend the deadline to comply with the requirement to close the surface impoundments and allow the energy centers to operate. Ameren expects the MISO determination to be completed in June 2022. Ameren Missouri does not expect that this matter will have a material adverse effect on its results of operations, financial position, or liquidity. Ameren and Ameren Missouri have AROs of $79 million recorded on their respective balance sheets as of March 31, 2022, associated with CCR storage facilities. Ameren Missouri estimates it will need to make capital expenditures of $60 million to $80 million from 2022 through 2026 to implement its CCR management compliance plan, which includes installation of groundwater monitoring equipment and groundwater treatment facilities. Remediation The Ameren Companies are involved in a number of remediation actions to clean up sites impacted by the use or disposal of materials containing hazardous substances. Federal and state laws can require responsible parties to fund remediation regardless of their degree of fault, the legality of original disposal, or the ownership of a disposal site. As of March 31, 2022, Ameren Illinois has remediated the majority of the 44 former MGP sites in Illinois and could substantially conclude remediation efforts at the remaining sites by 2023. The ICC allows Ameren Illinois to recover such remediation and related litigation costs from its electric and natural gas utility customers through environmental cost riders that are subject to annual prudence reviews by the ICC. As of March 31, 2022, Ameren Illinois estimated the remaining obligation related to these former MGP sites at $68 million to $125 million. Ameren and Ameren Illinois recorded a liability of $68 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 actual costs, including unanticipated underground structures, the degree to which groundwater is encountered, regulatory changes, local ordinances, and site accessibility. The actual costs and timing of completion may vary substantially from these estimates. 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 historical practices will result in future environmental commitments or will affect our results of operations, financial position, or liquidity. Illinois Emission Standards The IETL established emission standards that became effective in September 2021. Ameren Missouri's natural gas-fired energy centers in Illinois are subject to limits on emissions, including CO2 and NOx, equal to their unit-specific average emissions from 2018 through 2020, for any rolling twelve-month period beginning October 1, 2021, through 2029. Further reductions to emissions limits will become effective between 2030 and 2040, which could limit the operations of Ameren Missouri's five natural gas-fired energy centers located in the state of Illinois, and will result in the closure of the Venice Energy Center by 2030. These energy centers are utilized to support peak loads. Subject to conditions in the IETL, these energy centers may be allowed to exceed the emissions limits in order to maintain reliability of electric utility service as necessary. Ameren Missouri is reviewing the emission standards and the effect they may have on its generation strategy, including any increases in capital expenditures or operating costs, and changes to the useful life of the Venice Energy Center. Ameren Missouri expects to file an update to the 2020 IRP with the MoPSC in June 2022 to reflect, among other things, the impact of these new emissions standards.

Callaway Energy Center

3 Months Ended

Mar. 31, 2022

Nuclear Waste Matters [Abstract]

CALLAWAY ENERGY CENTER

See Note 9 – Callaway Energy Center under Part II, Item 8, of the Form 10-K for information regarding spent nuclear fuel recovery, recovery of decommissioning costs, and the nuclear decommissioning trust fund. 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. 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. An updated cost study and funding analysis was filed with the MoPSC in November 2020 and reflected within the ARO. In February 2021, the MoPSC approved no change in electric rates for decommissioning costs based on Ameren Missouri’s updated cost study funding analysis. See Note 13 – Supplemental Information for more information on Ameren Missouri’s AROs.

Maintenance Outage

See Note 9 – Callaway Energy Center under Part II, Item 8, of the Form 10-K for information regarding a maintenance outage from a non-nuclear operating issue related to the Callaway Energy Center’s generator in late December 2020 and subsequent return to service on August 4, 2021, along with the related insurance claims. As of March 31, 2022, a $26 million insurance receivable was included in “Miscellaneous accounts receivable” on Ameren’s and Ameren Missouri’s consolidated balance sheets related to lost sales insurance claims and capital expenditures. In April 2022, Ameren Missouri received $22 million from NEIL related to lost sales insurance claims.

Insurance

The following table presents insurance coverage at Ameren Missouri’s Callaway Energy Center at April 1, 2022:


Type and Source of Coverage	Most Recent Renewal Date	Maximum Coverages			Maximum Assessments for Single Incidents
Public liability and nuclear worker liability:
American Nuclear Insurers	January 1, 2022	$	450		$	—
Pool participation	(a)	13,073		(a)	138		(b)
		$	13,523	(c)	$	138
Property damage:
NEIL and EMANI	April 1, 2022	$	3,200	(d)	$	26	(e)
Accidental outage:
NEIL	April 1, 2022	$	490	(f)	$	7	(e)

(a)Provided through mandatory participation in an industrywide retrospective premium assessment program. The maximum coverage available is dependent on the number of United States commercial reactors participating in the program.

(b)Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $450 million in the event of an incident at any licensed United States commercial reactor, payable at $21 million per year.

(c)Limit of liability for each incident under the Price-Anderson liability provisions of the Atomic Energy Act of 1954, as amended. This limit is subject to change to account for the effects of inflation and changes in the number of licensed power reactors.

(d)NEIL provides $2.7 billion in property damage, stabilization, decontamination, and premature decommissioning insurance for radiation events and $2.3 billion in property damage insurance for nonradiation events. EMANI provides $490 million in property damage insurance for both radiation and nonradiation events.

(e)All NEIL-insured plants could be subject to assessments should losses exceed the accumulated funds from NEIL.

(f)Accidental outage insurance provides for lost sales in the event of a prolonged accidental outage. Weekly indemnity 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 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 November 2018. 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 insured by NEIL are subject to industrywide aggregates, such that terrorist acts against one or more commercial nuclear power plants within a stated time period would be treated as a single event, and the owners of the nuclear power plants would share the limit of liability. NEIL policies have an aggregate limit of $3.2 billion within a 12-month period for radiation events, or $1.8 billion for events not involving radiation contamination, resulting from terrorist attacks. The EMANI policies are not subject to industrywide aggregates in the event of terrorist attacks on nuclear facilities.

If losses from a nuclear incident at the Callaway Energy Center exceed the limits of, or are not covered by insurance, or if 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, or liquidity.

Retirement Benefits

3 Months Ended

Mar. 31, 2022

Retirement Benefits [Abstract]

RETIREMENT BENEFITS

The following table presents the components of the net periodic benefit cost (income) incurred for Ameren’s pension and postretirement benefit plans for the three months ended March 31, 2022 and 2021:


		Pension Benefits					Postretirement Benefits
	Three Months					Three Months
		2022		2021			2022		2021
Service cost(a)		$	33	$	33		$	5	$	6
Non-service cost components:
Interest cost		40		38			8		8
Expected return on plan assets		(80)		(75)			(21)		(20)
Amortization of:

Prior service benefit		—		—			(1)		(1)
Actuarial loss (gain)		6		17			(4)		(1)
Total non-service cost components(b)		$	(34)	$	(20)		$	(18)	$	(14)

Net periodic benefit cost (income)		$	(1)	$	13		$	(13)	$	(8)

(a)Service cost, net of capitalization, is reflected in “Operating Expenses – Other operations and maintenance” on Ameren’s statement of income.

(b)Non-service cost components are reflected in “Other Income, Net” on Ameren’s statement of income. See Note 5 – Other Income, Net, for additional information.

Ameren Missouri and Ameren Illinois are responsible for their respective share of Ameren’s pension and other postretirement costs. The following table presents the respective share of net periodic pension and other postretirement benefit costs (income) incurred for the three months ended March 31, 2022 and 2021:


		Pension Benefits					Postretirement Benefits
	Three Months					Three Months
		2022		2021			2022		2021
Ameren Missouri(a)		$	(1)	$	6		$	(3)	$	(1)
Ameren Illinois		1		8			(10)		(7)
Other		(1)		(1)			—		—
Ameren(a)		$	(1)	$	13		$	(13)	$	(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.

- Definition

The entire disclosure for retirement benefits.

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+ Details

Income Taxes

3 Months Ended

Mar. 31, 2022

Income Tax Disclosure [Abstract]

Income Taxes

INCOME TAXES

The following table presents a reconciliation of the federal statutory corporate income tax rate to the effective income tax rate for the three months ended March 31, 2022 and 2021:


	Ameren				Ameren Missouri				Ameren Illinois
	2022		2021		2022		2021		2022		2021
Three Months
Federal statutory corporate income tax rate	21	%	21	%	21	%	21	%	21	%	21	%
Increases (decreases) from:
Amortization of deferred investment tax credit	—		(1)		(1)		(1)		—		—
Amortization of excess deferred taxes(a)	(8)		(9)		(16)		(17)		(2)		(2)
Depreciation differences	—		—		—		1		—		(1)

Renewable and other tax credits(b)	(5)		(6)		(11)		(11)		—		—
State tax	5		6		3		3		7		7
Stock-based compensation	(1)		(1)		—		—		—		—

Effective income tax rate	12	%	10	%	(4)	%	(4)	%	26	%	25	%

(a)Reflects the amortization of amounts resulting from the revaluation of deferred income taxes subject to regulatory ratemaking, which are being refunded to customers. Deferred income taxes are revalued when federal or state income tax rates change, and the offset to the revaluation of deferred income taxes subject to regulatory ratemaking is recorded to a regulatory asset or liability.

(b)Includes credits associated with the High Prairie and Atchison renewable energy centers. Ameren Missouri placed the High Prairie renewable energy center in service in December 2020. Additionally, Ameren Missouri placed in service the wind turbines at its Atchison renewable energy center throughout the first half of 2021. The benefit of the credits associated with Missouri renewable energy standard compliance is refunded to customers through the RESRAM.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

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+ Details

Supplemental Information

3 Months Ended

Mar. 31, 2022

Supplemental Information [Abstract]

Supplemental Information

SUPPLEMENTAL INFORMATION

Cash, Cash Equivalents, and Restricted Cash

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows at March 31, 2022, and December 31, 2021:


	March 31, 2022						December 31, 2021
	Ameren		Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois
“Cash and cash equivalents”	$	7	$	1	$	—	$	8	$	—	$	—

Restricted cash included in “Other current assets”	10		3		5		16		4		6
Restricted cash included in “Other assets”	132		—		132		127		—		127
Restricted cash included in “Nuclear decommissioning trust fund”	5		5		—		4		4		—
Total cash, cash equivalents, and restricted cash	$	154	$	9	$	137	$	155	$	8	$	133

Restricted cash included in “Other current assets” primarily represents funds held by an irrevocable Voluntary Employee Beneficiary Association (VEBA) trust, which provides health care benefits for active employees. Restricted cash included in “Other assets” on Ameren’s and Ameren Illinois’ balance sheets primarily represents amounts collected under a cost recovery rider restricted for use in the procurement of renewable energy credits and amounts in a trust fund restricted for the use of funding certain asbestos-related claims.

Accounts Receivable

“Accounts receivable – trade” on Ameren’s and Ameren Illinois’ balance sheets include certain receivables purchased at a discount from alternative retail electric suppliers that elect to participate in the utility consolidated billing program. At March 31, 2022, and December 31, 2021, “Other current liabilities” on Ameren’s and Ameren Illinois’ balance sheets included payables for purchased receivables of $29 million and $27 million, respectively.

The following table provides a reconciliation of the beginning and ending amount of the allowance for doubtful accounts for the three months ended March 31, 2022 and 2021:


	Three Months
		2022		2021
Ameren:
Beginning of period		$	29	$	50
Bad debt expense		4		4

Net write-offs		(5)		(7)

End of period		$	28	$	47
Ameren Missouri:
Beginning of period		$	13	$	16
Bad debt expense		1		1

Net write-offs		(3)		(2)
End of period		$	11	$	15
Ameren Illinois:(a)
Beginning of period		$	16	$	34
Bad debt expense		3		3

Net write-offs		(2)		(5)

End of period		$	17	$	32

(a)Ameren Illinois has rate-adjustment mechanisms that allow it to recover the difference between its actual net bad debt write-offs under GAAP, including those associated with receivables purchased from alternative retail electric suppliers, and the amount of net bad debt write-offs included in its base rates.

Supplemental Cash Flow Information

Capital expenditures at Ameren and Ameren Missouri included wind generation expenditures of an immaterial amount for the three months ended March 31, 2022, and $193 million for the three months ended March 31, 2021.

The following table provides noncash financing and investing activity excluded from the statements of cash flows for the three months ended March 31, 2022 and 2021:


	March 31, 2022						March 31, 2021
	Ameren		Ameren Missouri				Ameren Illinois	Ameren		Ameren Missouri		Ameren Illinois
Investing
Accrued capital expenditures	$	345	$	194	$	147		$	271	$	141	$	139

Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund	(71)		(71)		—			22		22		—
Financing
Issuance of common stock for stock-based compensation	$	31	$	—	$	—		$	33	$	—	$	—
Issuance of common stock under the DRPlus	8		—		—			—		—		—

Asset Retirement Obligations

The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the three months ended March 31, 2022:


	Ameren Missouri			Ameren Illinois			Ameren
Balance at December 31, 2021	$	760	(a)	$	4	(b)	$	764	(a)


Accretion	8		(c)	—			8		(c)
Change in estimates	4		(d)	—			4		(d)
Balance at March 31, 2022	$	772	(a)	$	4	(b)	$	776	(a)

(a)Balance included $7 million in “Other current liabilities” on the balance sheet as of both March 31, 2022, and December 31, 2021.

(b)Included in “Other deferred credits and liabilities” on the balance sheet.

(c)Accretion expense attributable to Ameren Missouri was recorded as a decrease to regulatory liabilities.

(d)Ameren Missouri changed its fair value estimate primarily due to the change in useful life of the Sioux Energy Center, as reflected in depreciation rates approved by the December 2021 electric rate order, which became effective in 2022.

Stock-based Compensation

In the first quarter of 2022, Ameren granted 267,849 performance share units with a grant date fair value of $25 million and 122,882 restricted share units with a grant date fair value of $11 million. Awards vest approximately 3 years after the grant date or on a pro-rata basis upon death or eligible retirement. The performance share units vest based on the achievement of certain specified market performance measures (229,566 performance share units) or clean energy transition targets (38,283 performance share units). The exact number of shares issued pursuant to a performance share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the performance goals.

For the three months ended March 31, 2022 and 2021, excess tax benefits associated with the settlement of stock-based compensation awards reduced income tax expense by $5 million in both periods.

Deferred Compensation

At March 31, 2022, and December 31, 2021, the present value of benefits to be paid for deferred compensation obligations was $91 million in both periods, which was primarily reflected in “Other deferred credits and liabilities” on Ameren's consolidated balance sheet.

Operating Revenues

As of March 31, 2022 and 2021, our remaining performance obligations for contracts with a term greater than one year were immaterial. The Ameren Companies elected not to disclose the aggregate amount of the transaction price allocated to the performance obligations that are unsatisfied as of the end of the reporting period for contracts with an initial expected term of one year or less.

See Note 14 – Segment Information for disaggregated revenue information.

Excise Taxes

Ameren Missouri and Ameren Illinois collect from their customers excise taxes, including municipal and state excise taxes and gross receipts taxes that are levied on the sale or distribution of natural gas and electricity. The following table presents the excise taxes recorded on a gross basis in “Operating Revenues – Electric,” “Operating Revenues – Natural gas” and “Operating Expenses – Taxes other than income taxes” on the statements of income for the three months ended March 31, 2022 and 2021:


	Three Months
		2022		2021
Ameren Missouri		$	34	$	31
Ameren Illinois		45		39
Ameren		$	79	$	70

Earnings per Share

The following table reconciles the basic weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the three months ended March 31, 2022 and 2021:


	Three Months
		2022	2021


Weighted-average Common Shares Outstanding – Basic		257.9	254.4
Assumed settlement of performance share units and restricted stock units		1.1	1.5

Weighted-average Common Shares Outstanding – Diluted(a)		259.0	255.9

(a)There was an immaterial number of anti-dilutive securities excluded from the earnings per diluted share calculations for the three months ended March 31, 2022. There were no anti-dilutive securities excluded from the earnings per diluted share calculations for the three months ended March 31, 2021.

Segment Information

3 Months Ended

Mar. 31, 2022

Segment Reporting [Abstract]

SEGMENT INFORMATION

The following tables present revenues, net income attributable to common shareholders, and capital expenditures by segment at Ameren and Ameren Illinois for the three months ended March 31, 2022 and 2021. Ameren, Ameren Missouri, and Ameren Illinois management review segment capital expenditure information rather than any individual or total asset amount. For additional information about our segments, see Note 16 – Segment Information under Part II, Item 8, of the Form 10-K.

Ameren


	Ameren Missouri			Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission			Other		Intersegment Eliminations		Ameren










Three Months 2022:
External revenues	$	808		$	464	$	481	$	126		$	—	$	—	$	1,879
Intersegment revenues	10			1		—		20			—		(31)		—
Net income attributable to Ameren common shareholders	50			49		80		58		(a)	15		—		252
Capital expenditures	414			138		49		172			2		(1)		774
Three Months 2021:
External revenues	$	695		$	411	$	347	$	113		$	—	$	—	$	1,566
Intersegment revenues	9			—		—		17			—		(26)		—
Net income attributable to Ameren common shareholders	47			46		75		47		(a)	18		—		233
Capital expenditures	534		(b)	157		48		141			1		6		887		(b)

(a)Ameren Transmission earnings reflect an allocation of financing costs from Ameren (parent).

(b)Includes $193 million at Ameren and Ameren Missouri for wind generation expenditures for the three months ended March 31, 2021.

Ameren Illinois


	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Intersegment Eliminations		Ameren Illinois










Three Months 2022:
External revenues	$	465	$	481	$	78	$	—	$	1,024
Intersegment revenues	—		—		20		(20)		—
Net income available to common shareholder	49		80		40		—		169
Capital expenditures	138		49		155		—		342
Three Months 2021:
External revenues	$	411	$	347	$	65	$	—	$	823
Intersegment revenues	—		—		16		(16)		—
Net income available to common shareholder	46		75		28		—		149
Capital expenditures	157		48		132		—		337

The following tables present disaggregated revenues by segment at Ameren and Ameren Illinois for the three months ended March 31, 2022 and 2021. Economic factors affect the nature, timing, amount, and uncertainty of revenues and cash flows in a similar manner across customer classes. Revenues from alternative revenue programs have a similar distribution among customer classes as revenues from contracts with customers. Other revenues not associated with contracts with customers are presented in the Other customer classification, along with electric transmission and off-system revenues.

Ameren


	Ameren Missouri		Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission		Intersegment Eliminations		Ameren
























Three Months 2022:
Residential	$	332	$	263	$	—	$	—	$	—	$	595
Commercial	240		158		—		—		—		398
Industrial	57		45		—		—		—		102
Other	109		(1)		—		146		(31)		223
Total electric revenues	$	738	$	465	$	—	$	146	$	(31)	$	1,318
Residential	$	51	$	—	$	369	$	—	$	—	$	420
Commercial	22		—		97		—		—		119
Industrial	2		—		17		—		—		19
Other	5		—		(2)		—		—		3
Total natural gas revenues	$	80	$	—	$	481	$	—	$	—	$	561
Total revenues(a)	$	818	$	465	$	481	$	146	$	(31)	$	1,879
Three Months 2021:
Residential	$	312	$	229	$	—	$	—	$	—	$	541
Commercial	216		132		—		—		—		348
Industrial	52		34		—		—		—		86
Other	61		16		—		130		(26)		181
Total electric revenues	$	641	$	411	$	—	$	130	$	(26)	$	1,156
Residential	$	34	$	—	$	251	$	—	$	—	$	285
Commercial	15		—		64		—		—		79
Industrial	1		—		14		—		—		15
Other	13		—		18		—		—		31
Total natural gas revenues	$	63	$	—	$	347	$	—	$	—	$	410
Total revenues(a)	$	704	$	411	$	347	$	130	$	(26)	$	1,566

(a)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the three months ended March 31, 2022 and 2021:


	Ameren Missouri			Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission		Ameren








Three Months 2022:
Revenues from alternative revenue programs	$	(6)		$	55	$	(5)	$	1	$	45
Other revenues not from contracts with customers	—		(a)	2		1		—		3		(a)

Three Months 2021:
Revenues from alternative revenue programs	$	(10)		$	61	$	3	$	(1)	$	53
Other revenues not from contracts with customers	(2)			3		1		—		2

(a)Includes insurance recoveries related to lost sales associated with the Callaway Energy Center maintenance outage. See Note 10 – Callaway Energy Center for additional information.

Ameren Illinois


	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Intersegment Eliminations		Ameren Illinois












Three Months 2022:
Residential	$	263	$	369	$	—	$	—	$	632
Commercial	158		97		—		—		255
Industrial	45		17		—		—		62
Other	(1)		(2)		98		(20)		75
Total revenues(a)	$	465	$	481	$	98	$	(20)	$	1,024
Three Months 2021:
Residential	$	229	$	251	$	—	$	—	$	480
Commercial	132		64		—		—		196
Industrial	34		14		—		—		48
Other	16		18		81		(16)		99
Total revenues(a)	$	411	$	347	$	81	$	(16)	$	823

(a)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the Ameren Illinois segments for the three months ended March 31, 2022 and 2021:


	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Ameren Illinois








Three Months 2022:
Revenues from alternative revenue programs	$	55	$	(5)	$	1	$	51
Other revenues not from contracts with customers	2		1		—		3

Three Months 2021:
Revenues from alternative revenue programs	$	61	$	3	$	(1)	$	63
Other revenues not from contracts with customers	3		1		—		4

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

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+ Details

Summary Of Significant Accounting Policies (Policies)	3 Months Ended
Summary Of Significant Accounting Policies (Policies)	Mar. 31, 2022
Accounting Policies [Abstract]
Nature of Operations	Ameren, headquartered in St. Louis, Missouri, is a public utility holding company whose primary assets are its equity interests in its subsidiaries. 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 has other subsidiaries that conduct other activities, such as providing 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 Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois. •ATXI operates a FERC rate-regulated electric transmission business in the MISO.
Consolidation	Ameren’s and Ameren Missouri’s financial statements are prepared on a consolidated basis and therefore include the accounts of their majority-owned subsidiaries. All intercompany transactions have been eliminated. Ameren Missouri’s subsidiaries were created for the ownership of renewable generation projects. Ameren Illinois has no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated. 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 reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates. The results of operations for an interim period may not give a true indication of results that may be expected for a full year. These financial statements should be read in conjunction with the financial statements and accompanying notes included in the Form 10-K.
Consolidation, Variable Interest Entity, Policy	Variable Interest Entities As of March 31, 2022, and December 31, 2021, Ameren had unconsolidated variable interests as a limited partner in various equity method investments, primarily to advance clean and resilient energy technologies, totaling $60 million and $56 million, respectively, included in “Other assets” on Ameren’s consolidated balance sheet. Any earnings or losses related to these investments are included in “Other Income, Net” on Ameren’s consolidated statement of income and comprehensive income. Ameren is not the primary beneficiary of these investments because it does not have the power to direct matters that most significantly affect the activities of these variable interest entities. As of March 31, 2022, the maximum exposure to loss related to these variable interests is limited to the investment in these partnerships of $60 million plus associated outstanding funding commitments of $28 million.
Derivatives, Policy	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; •actual cash outlays for the purchase of these commodities that differ from anticipated cash outlays; and •actual off-system sales revenues that differ from anticipated revenues. 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. 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. 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. The following disclosures exclude NPNS contracts and other non-derivative commodity contracts that are accounted for under the accrual method of accounting. 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.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.
Life Insurance, Corporate Or Bank Owned	Company-owned Life Insurance Ameren and Ameren Illinois have company-owned life insurance, which is recorded at the net cash surrender value. The net cash surrender value is the amount that can be realized under the insurance policies at the balance sheet date.
Deferred Compensation	Deferred Compensation At March 31, 2022, and December 31, 2021, the present value of benefits to be paid for deferred compensation obligations was $91 million in both periods, which was primarily reflected in “Other deferred credits and liabilities” on Ameren's consolidated balance sheet.
Revenue from Contract with Customer	Operating Revenues As of March 31, 2022 and 2021, our remaining performance obligations for contracts with a term greater than one year were immaterial. The Ameren Companies elected not to disclose the aggregate amount of the transaction price allocated to the performance obligations that are unsatisfied as of the end of the reporting period for contracts with an initial expected term of one year or less. See Note 14 – Segment Information for disaggregated revenue information.
Excise Taxes	Excise TaxesAmeren Missouri and Ameren Illinois collect from their customers excise taxes, including municipal and state excise taxes and gross receipts taxes that are levied on the sale or distribution of natural gas and electricity.

- Definition

Disclosure of accounting policy for revenue from contract with customer.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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+ Details

Short-Term Debt and Liquidity (Tables)

3 Months Ended

Mar. 31, 2022

Debt Disclosure [Abstract]

Schedule of Short-term Debt

The following table presents commercial paper outstanding, net of issuance discounts, as of March 31, 2022, and December 31, 2021. There were no borrowings outstanding under the Credit Agreements as of March 31, 2022, or December 31, 2021.


	March 31, 2022		December 31, 2021
Ameren (parent)	$	466	$	277
Ameren Missouri	528		165
Ameren Illinois	107		103
Ameren consolidated	$	1,101	$	545

The following table summarizes the activity and relevant interest rates for Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper issuances and borrowings under the Credit Agreements in the aggregate for the three months ended March 31, 2022 and 2021:


	Ameren (parent)			Ameren Missouri			Ameren Illinois			Ameren Consolidated
2022
Average daily amount outstanding	$	282		$	408		$	99		$	789

Weighted-average interest rate	0.41		%	0.44		%	0.33		%	0.41		%
Peak amount outstanding during period(a)	$	466		$	539		$	142		$	1,101
Peak interest rate	1.05		%	1.06		%	1.15		%	1.15		%
2021
Average daily amount outstanding	$	454		$	99		$	96		$	649

Weighted-average interest rate	0.25		%	0.22		%	0.21		%	0.24		%
Peak amount outstanding during period(a)	$	650		$	206		$	353		$	916
Peak interest rate	0.33		%	0.25		%	0.25		%	0.33		%

(a)The timing of peak outstanding commercial paper issuances and borrowings under the Credit Agreements varies by company. Therefore, the sum of individual company peak amounts may not equal the Ameren consolidated peak for the period.

Other Income, Net (Tables)

3 Months Ended

Mar. 31, 2022

Other Nonoperating Income (Expense) [Abstract]

Other Income And Expenses

The following table presents the components of “Other Income, Net” in the Ameren Companies’ statements of income for the three months ended March 31, 2022 and 2021:


	Three Months
		2022		2021
Ameren:

Allowance for equity funds used during construction		$	8	$	7
Interest income on industrial development revenue bonds		6		6


Non-service cost components of net periodic benefit income(a)		46		34
Miscellaneous income		7		5
Donations		(2)		(3)
Miscellaneous expense		(5)		(3)
Total Other Income, Net		$	60	$	46
Ameren Missouri:

Allowance for equity funds used during construction		$	4	$	4
Interest income on industrial development revenue bonds		6		6

Non-service cost components of net periodic benefit income(a)		14		14
Miscellaneous income		2		1
Donations		(1)		—
Miscellaneous expense		(2)		(2)
Total Other Income, Net		$	23	$	23
Ameren Illinois:

Allowance for equity funds used during construction		$	4	$	3


Non-service cost components of net periodic benefit income		21		14
Miscellaneous income		2		1
Donations		(1)		(3)
Miscellaneous expense		(2)		(1)
Total Other Income, Net		$	24	$	14

(a)For the three months ended March 31, 2022 and 2021, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $6 million and less than $(1) million, respectively, due to a regulatory tracking mechanism for the difference between the level of such costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates.

Derivative Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2022

Derivative Instruments and Hedging Activities Disclosure [Abstract]

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 March 31, 2022, and December 31, 2021. As of March 31, 2022, these contracts extended through October 2024, October 2027, May 2032 and March 2024 for fuel oils, natural gas, power and uranium, respectively.


	Quantity (in millions)
	March 31, 2022			December 31, 2021
Commodity	Ameren Missouri	Ameren Illinois	Ameren	Ameren Missouri	Ameren Illinois	Ameren
Fuel oils (in gallons)	25	—	25	30	—	30
Natural gas (in mmbtu)	36	146	182	35	144	179
Power (in MWhs)	4	6	10	6	6	12
Uranium (pounds in thousands)	496	—	496	586	—	586

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 March 31, 2022, and December 31, 2021:


			March 31, 2022					December 31, 2021
	Balance Sheet Location		Ameren Missouri		Ameren Illinois		Ameren			Ameren Missouri		Ameren Illinois		Ameren





Fuel oils	Mark-to-market derivative assets	$	(a)	$	—	$	18		$	(a)	$	—	$	8

	Other current assets		18		—		—			8		—		—
	Other assets		8		—		8			5		—		5
Natural gas	Mark-to-market derivative assets		(a)		74		90			(a)		28		35

	Other current assets		16		—		—			7		—		—
	Other assets		10		23		33			5		13		18
Power	Mark-to-market derivative assets		(a)		5		24			(a)		—		23

	Other current assets		19		—		—			23		—		—
	Other assets		—		—		—			—		—		—
Uranium	Mark-to-market derivative assets		(a)		—		5			(a)		—		—

	Other current assets		5		—		—			—		—		—
	Other assets		2		—		2			1		—		1
	Total assets	$	78	$	102	$	180		$	49	$	41	$	90




Natural gas	Mark-to-market derivative liabilities		—		(a)		(a)			2		(a)		(a)

	Other current liabilities		—		2		2			—		6		8
	Other deferred credits and liabilities		1		1		2			1		2		3
Power	Mark-to-market derivative liabilities		109		(a)		(a)			50		(a)		(a)

	Other current liabilities		—		1		110			—		9		59
	Other deferred credits and liabilities		26		78		104			23		108		131
Uranium	Mark-to-market derivative liabilities		—		(a)		(a)			1		(a)		(a)

	Other current liabilities		—		—		—			—		—		1

	Total liabilities	$	136	$	82	$	218		$	77	$	125	$	202

(a)Balance sheet line item not applicable to registrant.

Offsetting Assets and Liabilities

The following table provides the recognized gross derivative balances and the net amounts of those derivatives subject to an enforceable master netting arrangement or similar agreement as of March 31, 2022, and December 31, 2021.


			Gross Amounts Not Offset in the Balance Sheet
Commodity Contracts Eligible to be Offset	Gross Amounts Recognized in the Balance Sheet		Derivative Instruments		Cash Collateral Received/Posted(a)		Net Amount
2022
Assets:
Ameren Missouri	$	78	$	19	$	5	$	54
Ameren Illinois	102		6		9		87
Ameren	$	180	$	25	$	14	$	141
Liabilities:
Ameren Missouri	$	136	$	19	$	92	$	25
Ameren Illinois	82		6		—		76
Ameren	$	218	$	25	$	92	$	101
2021
Assets:
Ameren Missouri	$	49	$	15	$	—	$	34
Ameren Illinois	41		4		—		37
Ameren	$	90	$	19	$	—	$	71
Liabilities:
Ameren Missouri	$	77	$	15	$	47	$	15
Ameren Illinois	125		4		—		121
Ameren	$	202	$	19	$	47	$	136

(a)Cash collateral received reduces gross asset balances and is included in “Other current liabilities” and “Other deferred credits and liabilities” on the balance sheet. Cash collateral posted reduces gross liability balances and is included in “Other current assets” and “Other assets” on the balance sheet.

Derivative Instruments With Credit Risk-Related Contingent Features

The following table presents, as of March 31, 2022, 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.



	Aggregate Fair Value of Derivative Liabilities(a)		Cash Collateral Posted		Potential Aggregate Amount of Additional Collateral Required(b)
Ameren Missouri	$	36	$	18	$	7
Ameren Illinois	4		—		4
Ameren	$	40	$	18	$	11

(a)Before consideration of master netting arrangements or similar agreements.

(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)

3 Months Ended

Mar. 31, 2022

Fair Value Disclosures [Abstract]

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 March 31, 2022, and December 31, 2021:


		March 31, 2022									December 31, 2021
		Level 1		Level 2		Level 3		Total			Level 1		Level 2		Level 3		Total
Assets:
Ameren Missouri
	Derivative assets – commodity contracts:
	Fuel oils	$	24	$	—	$	2	$	26		$	13	$	—	$	—	$	13
	Natural gas	—		26		—		26			—		12		—		12
	Power	18		—		1		19			10		—		13		23
	Uranium	—		—		7		7			—		—		1		1
	Total derivative assets – commodity contracts	$	42	$	26	$	10	$	78		$	23	$	12	$	14	$	49
	Nuclear decommissioning trust fund:

	Equity securities:
	U.S. large capitalization	$	719	$	—	$	—	$	719		$	824	$	—	$	—	$	824
	Debt securities:
	U.S. Treasury and agency securities	—		174		—		174			—		141		—		141
	Corporate bonds	—		133		—		133			—		131		—		131


	Other	—		61		—		61			—		56		—		56
	Total nuclear decommissioning trust fund	$	719	$	368	$	—	$	1,087	(a)	$	824	$	328	$	—	$	1,152	(a)
	Total Ameren Missouri	$	761	$	394	$	10	$	1,165		$	847	$	340	$	14	$	1,201
Ameren Illinois
	Derivative assets – commodity contracts:
	Natural gas	$	7	$	77	$	13	$	97		$	1	$	33	$	7	$	41
	Power	—		—		5		5			—		—		—		—
	Total Ameren Illinois	$	7	$	77	$	18	$	102		$	1	$	33	$	7	$	41
Ameren
	Derivative assets – commodity contracts(b)	$	49	$	103	$	28	$	180		$	24	$	45	$	21	$	90
	Nuclear decommissioning trust fund(c)	719		368		—		1,087		(a)	824		328		—		1,152		(a)
	Total Ameren	$	768	$	471	$	28	$	1,267		$	848	$	373	$	21	$	1,242
Liabilities:
Ameren Missouri
	Derivative liabilities – commodity contracts:

	Natural gas	$	—	$	1	$	—	$	1		$	—	$	2	$	1	$	3
	Power	81		—		54		135			45		—		28		73
	Uranium	—		—		—		—			—		—		1		1
	Total Ameren Missouri	$	81	$	1	$	54	$	136		$	45	$	2	$	30	$	77


		March 31, 2022								December 31, 2021
		Level 1		Level 2		Level 3		Total		Level 1		Level 2		Level 3		Total
Ameren Illinois
	Derivative liabilities – commodity contracts:
	Natural gas	$	—	$	1	$	2	$	3	$	—	$	5	$	3	$	8
	Power	—		—		79		79		—		—		117		117
	Total Ameren Illinois	$	—	$	1	$	81	$	82	$	—	$	5	$	120	$	125
Ameren
	Derivative liabilities – commodity contracts(b)	$	81	$	2	$	135	$	218	$	45	$	7	$	150	$	202

(a)Balance excludes $7 million of cash and cash equivalents, receivables, payables, and accrued income, net, for both March 31, 2022, and December 31, 2021.

(b)See the Ameren Missouri and Ameren Illinois sections of the table for a breakout of the fair value of Ameren’s derivative assets and liabilities by type of commodity.

(c)See the Ameren Missouri section of the table for a breakout of the fair value of Ameren's nuclear decommissioning trust fund by investment type.

Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level Three In The Fair Value Hierarchy

The following table presents the fair value reconciliation of Level 3 power derivative contract assets and liabilities measured at fair value on a recurring basis for the three months ended March 31, 2022 and 2021:


	2022						2021
	Ameren Missouri		Ameren Illinois		Ameren			Ameren Missouri		Ameren Illinois		Ameren










For the three months ended March 31:
Beginning balance at January 1	$	(15)	$	(117)	$	(132)		$	2	$	(198)	$	(196)
Realized and unrealized gains/(losses) included in regulatory assets/liabilities	(41)		42		1			(5)		9		4


Settlements	3		1		4			—		4		4


Ending balance at March 31	$	(53)	$	(74)	$	(127)		$	(3)	$	(185)	$	(188)
Change in unrealized gains/(losses) related to assets/liabilities held at March 31	$	(38)	$	42	$	4		$	(3)	$	9	$	6

Fair Value, Assets and Liabilities Measured on Nonrecurring Basis, Valuation Techniques

The following table describes the valuation techniques and significant unobservable inputs utilized for the fair value of our Level 3 power derivative contract assets and liabilities as of March 31, 2022, and December 31, 2021:


			Fair Value						Weighted Average(b)
	Commodity		Assets		Liabilities	Valuation Technique(s)	Unobservable Input(a)	Range









2022	Power(c)	$	6	$	(133)	Discounted cash flow	Average forward peak and off-peak pricing – forwards/swaps ($/MWh)	35 – 82	51

							Nodal basis ($/MWh)	(16) – 0	(3)


							Trend rate (%)	(e)	(1)








































2021	Power(d)	$	13	$	(145)	Discounted cash flow	Average forward peak and off-peak pricing – forwards/swaps ($/MWh)	32 – 55	40

							Nodal basis ($/MWh)	(14) – 0	(2)


							Trend rate (%)	(e)	0

(a)Generally, significant increases (decreases) in these inputs in isolation would result in a significantly higher (lower) fair value measurement.

(b)Unobservable inputs were weighted by relative fair value.

(c)Valuations through 2031 use visible forward prices adjusted for nodal-to-hub basis differentials. Valuations beyond 2031 use a trend rate factor and are similarly adjusted for nodal-to-hub basis differentials.

(d)Valuations through 2029 use visible forward prices adjusted for nodal-to-hub basis differentials. Valuations beyond 2029 use a trend rate factor and are similarly adjusted for nodal-to-hub basis differentials.

(e)No meaningful range around weighted average.

Schedule of Financial Assets and Liabilities

The following table sets forth the carrying amount and, by level within the fair value hierarchy, the fair value of financial assets and liabilities disclosed, but not recorded, at fair value as of March 31, 2022, and December 31, 2021:


	Carrying Amount			Fair Value
				Level 1		Level 2		Level 3			Total
	March 31, 2022
Ameren:
Cash, cash equivalents, and restricted cash	$	154		$	154	$	—	$	—		$	154
Investments in industrial development revenue bonds(a)	248			—		248		—			248
Short-term debt	1,101			—		1,101		—			1,101
Long-term debt (including current portion)(a)	13,068		(b)	—		12,615		526		(c)	13,141
Ameren Missouri:
Cash, cash equivalents, and restricted cash	$	9		$	9	$	—	$	—		$	9

Investments in industrial development revenue bonds(a)	248			—		248		—			248
Short-term debt	528			—		528		—			528

Long-term debt (including current portion)(a)	5,619		(b)	—		5,701		—			5,701
Ameren Illinois:
Cash, cash equivalents, and restricted cash	$	137		$	137	$	—	$	—		$	137

Short-term debt	107			—		107		—			107

Long-term debt (including current portion)	4,393		(b)	—		4,457		—			4,457
	December 31, 2021
Ameren:
Cash, cash equivalents, and restricted cash	$	155		$	155	$	—	$	—		$	155
Investments in industrial development revenue bonds(a)	248			—		248		—			248
Short-term debt	545			—		545		—			545
Long-term debt (including current portion)(a)	13,067		(b)	—		13,930		591		(c)	14,521
Ameren Missouri:
Cash, cash equivalents, and restricted cash	$	8		$	8	$	—	$	—		$	8

Investments in industrial development revenue bonds(a)	248			—		248		—			248
Short-term debt	165			—		165		—			165
Long-term debt (including current portion)(a)	5,619		(b)	—		6,321		—			6,321
Ameren Illinois:
Cash, cash equivalents, and restricted cash	$	133		$	133	$	—	$	—		$	133
Short-term debt	103			—		103		—			103

Long-term debt (including current portion)	4,392		(b)	—		4,971		—			4,971

(a)Ameren and Ameren Missouri have investments in industrial development revenue bonds, classified as held-to-maturity and recorded in “Other Assets,” that are equal to the finance obligations for the Peno Creek and Audrain CT energy centers. As of March 31, 2022, and December 31, 2021, the carrying amount of both the investments in industrial development revenue bonds and the finance obligations approximated fair value.

(b)Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $94 million, $38 million, and $38 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of March 31, 2022. Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $94 million, $38 million, and $39 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2021.

(c)The Level 3 fair value amount consists of ATXI’s senior unsecured notes.

Related Party Transactions (Tables)

3 Months Ended

Mar. 31, 2022

Schedule of Affiliate Receivables and Payables

The following table presents the affiliate balances related to income taxes for Ameren Missouri and Ameren Illinois as of March 31, 2022, and December 31, 2021:


	March 31, 2022				December 31, 2021
	Ameren Missouri		Ameren Illinois		Ameren Missouri		Ameren Illinois
Income taxes payable to parent(a)	$	—	$	42	$	—	$	8
Income taxes receivable from parent(b)	33		—		27		18

(a)Included in “Accounts payable – affiliates” on the balance sheet.

(b)Included in “Accounts receivable – affiliates” on the balance sheet.

Schedule of Related Party Transactions

The following table presents the impact on Ameren Missouri and Ameren Illinois of related-party transactions for the three months ended March 31, 2022 and 2021:


			Three Months
Agreement	Income Statement Line Item				Ameren Missouri		Ameren Illinois
Ameren Missouri power supply	Operating Revenues	2022		$	4	$	(a)
agreements with Ameren Illinois		2021			2		(a)
Ameren Missouri and Ameren Illinois	Operating Revenues	2022		$	6	$	(b)
rent and facility services		2021			7		(b)
Ameren Missouri and Ameren Illinois miscellaneous	Operating Revenues	2022		$	(b)	$	1
support services and other services provided to ATXI		2021			(b)		(b)
Total Operating Revenues		2022		$	10	$	1
		2021			9		(b)
Ameren Illinois power supply	Purchased Power	2022		$	(a)	$	4
agreements with Ameren Missouri		2021			(a)		2
Ameren Missouri and Ameren Illinois	Purchased Power	2022		$	(b)	$	(b)
transmission services from ATXI		2021			1		(b)
Total Purchased Power		2022		$	(b)	$	4
		2021			1		2
Ameren Missouri and Ameren Illinois	Other Operations and Maintenance	2022		$	(b)	$	1
rent and facility services		2021			(b)		1
Ameren Services support services	Other Operations and Maintenance	2022		$	38	$	35
agreement		2021			35		33
Total Other Operations and		2022		$	38	$	36
Maintenance		2021			35		34
Money pool borrowings (advances)	(Interest Charges)/Other Income, Net	2022		$	(b)	$	(b)
		2021			(b)		(b)

(a)Not applicable.

(b)Amount less than $1 million.

Callaway Energy Center (Tables)

3 Months Ended

Mar. 31, 2022

Nuclear Waste Matters [Abstract]

Schedule of Insurance Coverage at Callaway Energy Center

The following table presents insurance coverage at Ameren Missouri’s Callaway Energy Center at April 1, 2022:


Type and Source of Coverage	Most Recent Renewal Date	Maximum Coverages			Maximum Assessments for Single Incidents
Public liability and nuclear worker liability:
American Nuclear Insurers	January 1, 2022	$	450		$	—
Pool participation	(a)	13,073		(a)	138		(b)
		$	13,523	(c)	$	138
Property damage:
NEIL and EMANI	April 1, 2022	$	3,200	(d)	$	26	(e)
Accidental outage:
NEIL	April 1, 2022	$	490	(f)	$	7	(e)

(a)Provided through mandatory participation in an industrywide retrospective premium assessment program. The maximum coverage available is dependent on the number of United States commercial reactors participating in the program.

(b)Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $450 million in the event of an incident at any licensed United States commercial reactor, payable at $21 million per year.

(c)Limit of liability for each incident under the Price-Anderson liability provisions of the Atomic Energy Act of 1954, as amended. This limit is subject to change to account for the effects of inflation and changes in the number of licensed power reactors.

(d)NEIL provides $2.7 billion in property damage, stabilization, decontamination, and premature decommissioning insurance for radiation events and $2.3 billion in property damage insurance for nonradiation events. EMANI provides $490 million in property damage insurance for both radiation and nonradiation events.

(e)All NEIL-insured plants could be subject to assessments should losses exceed the accumulated funds from NEIL.

(f)Accidental outage insurance provides for lost sales in the event of a prolonged accidental outage. Weekly indemnity 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 limited to $328 million.

Retirement Benefits (Tables)

3 Months Ended

Mar. 31, 2022

Retirement Benefits [Abstract]

Components Of Net Periodic Benefit Cost

The following table presents the components of the net periodic benefit cost (income) incurred for Ameren’s pension and postretirement benefit plans for the three months ended March 31, 2022 and 2021:


		Pension Benefits					Postretirement Benefits
	Three Months					Three Months
		2022		2021			2022		2021
Service cost(a)		$	33	$	33		$	5	$	6
Non-service cost components:
Interest cost		40		38			8		8
Expected return on plan assets		(80)		(75)			(21)		(20)
Amortization of:

Prior service benefit		—		—			(1)		(1)
Actuarial loss (gain)		6		17			(4)		(1)
Total non-service cost components(b)		$	(34)	$	(20)		$	(18)	$	(14)

Net periodic benefit cost (income)		$	(1)	$	13		$	(13)	$	(8)

(a)Service cost, net of capitalization, is reflected in “Operating Expenses – Other operations and maintenance” on Ameren’s statement of income.

(b)Non-service cost components are reflected in “Other Income, Net” on Ameren’s statement of income. See Note 5 – Other Income, Net, for additional information.

Summary Of Benefit Plan Costs Incurred

Ameren Missouri and Ameren Illinois are responsible for their respective share of Ameren’s pension and other postretirement costs. The following table presents the respective share of net periodic pension and other postretirement benefit costs (income) incurred for the three months ended March 31, 2022 and 2021:


		Pension Benefits					Postretirement Benefits
	Three Months					Three Months
		2022		2021			2022		2021
Ameren Missouri(a)		$	(1)	$	6		$	(3)	$	(1)
Ameren Illinois		1		8			(10)		(7)
Other		(1)		(1)			—		—
Ameren(a)		$	(1)	$	13		$	(13)	$	(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.

Income Taxes Income Taxes (Tables)

3 Months Ended

Mar. 31, 2022

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation

The following table presents a reconciliation of the federal statutory corporate income tax rate to the effective income tax rate for the three months ended March 31, 2022 and 2021:


	Ameren				Ameren Missouri				Ameren Illinois
	2022		2021		2022		2021		2022		2021
Three Months
Federal statutory corporate income tax rate	21	%	21	%	21	%	21	%	21	%	21	%
Increases (decreases) from:
Amortization of deferred investment tax credit	—		(1)		(1)		(1)		—		—
Amortization of excess deferred taxes(a)	(8)		(9)		(16)		(17)		(2)		(2)
Depreciation differences	—		—		—		1		—		(1)

Renewable and other tax credits(b)	(5)		(6)		(11)		(11)		—		—
State tax	5		6		3		3		7		7
Stock-based compensation	(1)		(1)		—		—		—		—

Effective income tax rate	12	%	10	%	(4)	%	(4)	%	26	%	25	%

(a)Reflects the amortization of amounts resulting from the revaluation of deferred income taxes subject to regulatory ratemaking, which are being refunded to customers. Deferred income taxes are revalued when federal or state income tax rates change, and the offset to the revaluation of deferred income taxes subject to regulatory ratemaking is recorded to a regulatory asset or liability.

(b)Includes credits associated with the High Prairie and Atchison renewable energy centers. Ameren Missouri placed the High Prairie renewable energy center in service in December 2020. Additionally, Ameren Missouri placed in service the wind turbines at its Atchison renewable energy center throughout the first half of 2021. The benefit of the credits associated with Missouri renewable energy standard compliance is refunded to customers through the RESRAM.

Supplemental Information (Tables)

3 Months Ended

Mar. 31, 2022

Supplemental Information [Abstract]

Schedule of Cash and Cash Equivalents Including Restricted Cash

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows at March 31, 2022, and December 31, 2021:


	March 31, 2022						December 31, 2021
	Ameren		Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois
“Cash and cash equivalents”	$	7	$	1	$	—	$	8	$	—	$	—

Restricted cash included in “Other current assets”	10		3		5		16		4		6
Restricted cash included in “Other assets”	132		—		132		127		—		127
Restricted cash included in “Nuclear decommissioning trust fund”	5		5		—		4		4		—
Total cash, cash equivalents, and restricted cash	$	154	$	9	$	137	$	155	$	8	$	133

Schedule of Accounts, Notes, Loans and Financing Receivable

The following table provides a reconciliation of the beginning and ending amount of the allowance for doubtful accounts for the three months ended March 31, 2022 and 2021:


	Three Months
		2022		2021
Ameren:
Beginning of period		$	29	$	50
Bad debt expense		4		4

Net write-offs		(5)		(7)

End of period		$	28	$	47
Ameren Missouri:
Beginning of period		$	13	$	16
Bad debt expense		1		1

Net write-offs		(3)		(2)
End of period		$	11	$	15
Ameren Illinois:(a)
Beginning of period		$	16	$	34
Bad debt expense		3		3

Net write-offs		(2)		(5)

End of period		$	17	$	32

(a)Ameren Illinois has rate-adjustment mechanisms that allow it to recover the difference between its actual net bad debt write-offs under GAAP, including those associated with receivables purchased from alternative retail electric suppliers, and the amount of net bad debt write-offs included in its base rates.

Schedule of Cash Flow, Supplemental Disclosures

The following table provides noncash financing and investing activity excluded from the statements of cash flows for the three months ended March 31, 2022 and 2021:


	March 31, 2022						March 31, 2021
	Ameren		Ameren Missouri				Ameren Illinois	Ameren		Ameren Missouri		Ameren Illinois
Investing
Accrued capital expenditures	$	345	$	194	$	147		$	271	$	141	$	139

Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund	(71)		(71)		—			22		22		—
Financing
Issuance of common stock for stock-based compensation	$	31	$	—	$	—		$	33	$	—	$	—
Issuance of common stock under the DRPlus	8		—		—			—		—		—

Asset Retirement Obligation Disclosure

The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the three months ended March 31, 2022:


	Ameren Missouri			Ameren Illinois			Ameren
Balance at December 31, 2021	$	760	(a)	$	4	(b)	$	764	(a)


Accretion	8		(c)	—			8		(c)
Change in estimates	4		(d)	—			4		(d)
Balance at March 31, 2022	$	772	(a)	$	4	(b)	$	776	(a)

(a)Balance included $7 million in “Other current liabilities” on the balance sheet as of both March 31, 2022, and December 31, 2021.

(b)Included in “Other deferred credits and liabilities” on the balance sheet.

(c)Accretion expense attributable to Ameren Missouri was recorded as a decrease to regulatory liabilities.

(d)Ameren Missouri changed its fair value estimate primarily due to the change in useful life of the Sioux Energy Center, as reflected in depreciation rates approved by the December 2021 electric rate order, which became effective in 2022.

Schedule of excise taxes

The following table presents the excise taxes recorded on a gross basis in “Operating Revenues – Electric,” “Operating Revenues – Natural gas” and “Operating Expenses – Taxes other than income taxes” on the statements of income for the three months ended March 31, 2022 and 2021:


	Three Months
		2022		2021
Ameren Missouri		$	34	$	31
Ameren Illinois		45		39
Ameren		$	79	$	70

Schedule of Earnings Per Share, Basic and Diluted

The following table reconciles the basic weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the three months ended March 31, 2022 and 2021:


	Three Months
		2022	2021


Weighted-average Common Shares Outstanding – Basic		257.9	254.4
Assumed settlement of performance share units and restricted stock units		1.1	1.5

Weighted-average Common Shares Outstanding – Diluted(a)		259.0	255.9

(a)There was an immaterial number of anti-dilutive securities excluded from the earnings per diluted share calculations for the three months ended March 31, 2022. There were no anti-dilutive securities excluded from the earnings per diluted share calculations for the three months ended March 31, 2021.

Segment Information (Tables)

3 Months Ended

Mar. 31, 2022

Segment Reporting [Abstract]

Schedule Of Segment Reporting Information By Segment

The following tables present revenues, net income attributable to common shareholders, and capital expenditures by segment at Ameren and Ameren Illinois for the three months ended March 31, 2022 and 2021. Ameren, Ameren Missouri, and Ameren Illinois management review segment capital expenditure information rather than any individual or total asset amount. For additional information about our segments, see Note 16 – Segment Information under Part II, Item 8, of the Form 10-K.

Ameren


	Ameren Missouri			Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission			Other		Intersegment Eliminations		Ameren










Three Months 2022:
External revenues	$	808		$	464	$	481	$	126		$	—	$	—	$	1,879
Intersegment revenues	10			1		—		20			—		(31)		—
Net income attributable to Ameren common shareholders	50			49		80		58		(a)	15		—		252
Capital expenditures	414			138		49		172			2		(1)		774
Three Months 2021:
External revenues	$	695		$	411	$	347	$	113		$	—	$	—	$	1,566
Intersegment revenues	9			—		—		17			—		(26)		—
Net income attributable to Ameren common shareholders	47			46		75		47		(a)	18		—		233
Capital expenditures	534		(b)	157		48		141			1		6		887		(b)

(a)Ameren Transmission earnings reflect an allocation of financing costs from Ameren (parent).

(b)Includes $193 million at Ameren and Ameren Missouri for wind generation expenditures for the three months ended March 31, 2021.

Ameren Illinois


	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Intersegment Eliminations		Ameren Illinois










Three Months 2022:
External revenues	$	465	$	481	$	78	$	—	$	1,024
Intersegment revenues	—		—		20		(20)		—
Net income available to common shareholder	49		80		40		—		169
Capital expenditures	138		49		155		—		342
Three Months 2021:
External revenues	$	411	$	347	$	65	$	—	$	823
Intersegment revenues	—		—		16		(16)		—
Net income available to common shareholder	46		75		28		—		149
Capital expenditures	157		48		132		—		337

Disaggregation of Revenue

The following tables present disaggregated revenues by segment at Ameren and Ameren Illinois for the three months ended March 31, 2022 and 2021. Economic factors affect the nature, timing, amount, and uncertainty of revenues and cash flows in a similar manner across customer classes. Revenues from alternative revenue programs have a similar distribution among customer classes as revenues from contracts with customers. Other revenues not associated with contracts with customers are presented in the Other customer classification, along with electric transmission and off-system revenues.

Ameren


	Ameren Missouri		Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission		Intersegment Eliminations		Ameren
























Three Months 2022:
Residential	$	332	$	263	$	—	$	—	$	—	$	595
Commercial	240		158		—		—		—		398
Industrial	57		45		—		—		—		102
Other	109		(1)		—		146		(31)		223
Total electric revenues	$	738	$	465	$	—	$	146	$	(31)	$	1,318
Residential	$	51	$	—	$	369	$	—	$	—	$	420
Commercial	22		—		97		—		—		119
Industrial	2		—		17		—		—		19
Other	5		—		(2)		—		—		3
Total natural gas revenues	$	80	$	—	$	481	$	—	$	—	$	561
Total revenues(a)	$	818	$	465	$	481	$	146	$	(31)	$	1,879
Three Months 2021:
Residential	$	312	$	229	$	—	$	—	$	—	$	541
Commercial	216		132		—		—		—		348
Industrial	52		34		—		—		—		86
Other	61		16		—		130		(26)		181
Total electric revenues	$	641	$	411	$	—	$	130	$	(26)	$	1,156
Residential	$	34	$	—	$	251	$	—	$	—	$	285
Commercial	15		—		64		—		—		79
Industrial	1		—		14		—		—		15
Other	13		—		18		—		—		31
Total natural gas revenues	$	63	$	—	$	347	$	—	$	—	$	410
Total revenues(a)	$	704	$	411	$	347	$	130	$	(26)	$	1,566

(a)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the three months ended March 31, 2022 and 2021:


	Ameren Missouri			Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission		Ameren








Three Months 2022:
Revenues from alternative revenue programs	$	(6)		$	55	$	(5)	$	1	$	45
Other revenues not from contracts with customers	—		(a)	2		1		—		3		(a)

Three Months 2021:
Revenues from alternative revenue programs	$	(10)		$	61	$	3	$	(1)	$	53
Other revenues not from contracts with customers	(2)			3		1		—		2

(a)Includes insurance recoveries related to lost sales associated with the Callaway Energy Center maintenance outage. See Note 10 – Callaway Energy Center for additional information.

Ameren Illinois


	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Intersegment Eliminations		Ameren Illinois












Three Months 2022:
Residential	$	263	$	369	$	—	$	—	$	632
Commercial	158		97		—		—		255
Industrial	45		17		—		—		62
Other	(1)		(2)		98		(20)		75
Total revenues(a)	$	465	$	481	$	98	$	(20)	$	1,024
Three Months 2021:
Residential	$	229	$	251	$	—	$	—	$	480
Commercial	132		64		—		—		196
Industrial	34		14		—		—		48
Other	16		18		81		(16)		99
Total revenues(a)	$	411	$	347	$	81	$	(16)	$	823

(a)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the Ameren Illinois segments for the three months ended March 31, 2022 and 2021:


	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Ameren Illinois








Three Months 2022:
Revenues from alternative revenue programs	$	55	$	(5)	$	1	$	51
Other revenues not from contracts with customers	2		1		—		3

Three Months 2021:
Revenues from alternative revenue programs	$	61	$	3	$	(1)	$	63
Other revenues not from contracts with customers	3		1		—		4

Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Basis Of Presentation And Significant Accounting Policies [Line Items]
Unconsolidated variable interest	$ 60	$ 56
Cash Surrender Value of Life Insurance	258	278
Corporate owned life insurance, borrowings	103	109
Ameren Illinois Company
Basis Of Presentation And Significant Accounting Policies [Line Items]
Cash Surrender Value of Life Insurance	112	117
Corporate owned life insurance, borrowings	103	$ 109
Partnership Funding Commitment
Basis Of Presentation And Significant Accounting Policies [Line Items]
Outstanding funding commitments	$ 28

Rate And Regulatory Matters (Narrative-Illinois) (Details) - Ameren Illinois Company $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($)
Rate And Regulatory Matters [Line Items]
Annual investment in energy-efficiency programs	$ 120
Electric Distribution \| Minimum
Rate And Regulatory Matters [Line Items]
Return on equity adjustment	0.20%
Electric Distribution \| Maximum
Rate And Regulatory Matters [Line Items]
Return on equity adjustment	0.60%
Pending Rate Case \| Electric Distribution \| IEIMA
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 83
Public Utilities, Requested Equity Capital Structure, Percentage	54.00%
Pending Rate Case \| Natural gas
Rate And Regulatory Matters [Line Items]
Natural Gas Capital Investment Prudency Challenge	$ 70
Challenged Recoveries Under the QIP	$ 3

Rate And Regulatory Matters (Narrative-Federal) (Details) - USD ($) $ in Millions	1 Months Ended
	May 31, 2020	Mar. 31, 2022	Dec. 31, 2021
Rate And Regulatory Matters [Line Items]
Regulatory liabilities		$ 5,841	$ 5,848
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Regulatory liabilities		2,442	$ 2,374
Final Rate Order \| Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Regulatory liabilities		$ 9
Midwest Independent Transmission System Operator, Inc \| Final Rate Order
Rate And Regulatory Matters [Line Items]
Approved return on equity percentage	10.02%

Short-Term Debt And Liquidity (Narrative) (Details) $ in Billions	3 Months Ended
	Mar. 31, 2022 USD ($)	Mar. 31, 2021
Credit Agreements
Short-term Debt [Line Items]
Net Liquidity Available	$ 1.2
Actual debt-to-capital ratio	0.59
Utilities
Short-term Debt [Line Items]
Short-term Debt, Weighted Average Interest Rate, over Time	0.39%	0.22%
Union Electric Company \| Missouri Credit Agreement
Short-term Debt [Line Items]
Actual debt-to-capital ratio	0.50
Ameren Illinois Company \| Illinois Credit Agreement
Short-term Debt [Line Items]
Actual debt-to-capital ratio	0.44

Short-Term Debt and Liquidity (Short-Term Debt outstanding) (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Short-term Debt [Line Items]
Short-term debt	$ 1,101	$ 545
Union Electric Company
Short-term Debt [Line Items]
Short-term debt	528	165
Ameren Illinois Company
Short-term Debt [Line Items]
Short-term debt	107	103
Commercial Paper
Short-term Debt [Line Items]
Short-term debt	1,101	545
Commercial Paper \| Parent Company
Short-term Debt [Line Items]
Short-term debt	466	277
Commercial Paper \| Union Electric Company
Short-term Debt [Line Items]
Short-term debt	528	165
Commercial Paper \| Ameren Illinois Company
Short-term Debt [Line Items]
Short-term debt	$ 107	$ 103

Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Short-term Debt [Line Items]
Average daily amount outstanding	$ 789	$ 649
Weighted-average interest rate	0.41%	0.24%
Short-term Debt, Maximum Amount Outstanding During Period	$ 1,101	$ 916
Peak interest rate	1.15%	0.33%
Parent Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 282	$ 454
Weighted-average interest rate	0.41%	0.25%
Short-term Debt, Maximum Amount Outstanding During Period	$ 466	$ 650
Peak interest rate	1.05%	0.33%
Union Electric Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 408	$ 99
Weighted-average interest rate	0.44%	0.22%
Short-term Debt, Maximum Amount Outstanding During Period	$ 539	$ 206
Peak interest rate	1.06%	0.25%
Ameren Illinois Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 99	$ 96
Weighted-average interest rate	0.33%	0.21%
Short-term Debt, Maximum Amount Outstanding During Period	$ 142	$ 353
Peak interest rate	1.15%	0.25%

Long-Term debt and Equity Financings (Details) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended		3 Months Ended
	Aug. 31, 2022 USD ($)	Apr. 30, 2022 USD ($) $ / shares shares	Mar. 31, 2022 USD ($) $ / shares shares	Sep. 30, 2021 USD ($) shares	Mar. 31, 2021 USD ($) shares	May 31, 2021 USD ($)
Long-Term Debt And Equity Financings [Line Items]
Shares issued under the DRPlus and 401(k) plan \| shares			0.1		0.1
Stock Issued During Period, Shares, Other \| shares			0.4	0.4	0.5
Stock Issued During Period, Value, Other				$ 31.0
Maximum Value Of Shares To Be Issued Under ATM Program						$ 750.0
Value of Shares Available to be Issued Under ATM Program			$ 320.0
Forward Contract Indexed to Issuer's Equity, Basis Spread			75
Issuances of common stock			$ 5.0		$ 125.0
Minimum
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share \| $ / shares			$ 86.35
Maximum
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share \| $ / shares			88.81
Weighted Average
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share \| $ / shares			$ 87.61
Dividend reinvestment and 401 (k) plans
Long-Term Debt And Equity Financings [Line Items]
Accrued Proceeds from Issuance of Common Stock			$ 8.0
Issuances of common stock			$ 5.0
Forward Sale Agreements Outstanding
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Shares, at Fair Value \| shares			3.2
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value			$ 276.0
Period End Net Cash Settlement Price			21.0
Period End Net Share Settlement Price			0.2
Forward Sale Agreement Equity Offering Shares			3.2
Forward Sale Agreement Gross Sales Price			280.0
Forward Sale Agreement, Compensation Received by Counterparty			3.0
Subsequent Event \| Forward Sale Agreements Outstanding
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Indexed Shares (in shares) \| shares		3.4
Subsequent Event \| April 1, 2022 Forward Sale
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Indexed Shares (in shares) \| shares		0.2
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share \| $ / shares		$ 91.41
Other Paid-in Capital
Long-Term Debt And Equity Financings [Line Items]
Shares issued under the DRPlus and 401(k) plan			13.0		$ 12.0
Union Electric Company \| Secured Debt \| Senior Secured Notes 3.90% Due 2052 \| Subsequent Event
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount		$ 525.0
Debt Instrument, Interest Rate, Stated Percentage		3.90%
Proceeds from Issuance of Secured Debt		$ 519.0
Ameren Transmission Company of Illinois \| Unsecured Debt \| Senior Unsecured Notes, 2.96%, Due 2052
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount			$ 95.0
Debt Instrument, Interest Rate, Stated Percentage			2.96%
Ameren Transmission Company of Illinois \| Unsecured Debt \| Senior Unsecured Notes, 2.96%, Due 2052 \| Subsequent Event
Long-Term Debt And Equity Financings [Line Items]
Proceeds from Issuance of Debt	$ 95.0
Ameren Transmission Company of Illinois \| Unsecured Debt \| Senior Unsecured Notes, 3.43%, Due 2050
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.43%
Long-Term Debt, Maturity, Year One			$ 50.0

Other Income, Net (Details) - USD ($) $ in Millions	3 Months Ended
Other Income, Net (Details) - USD ($) $ in Millions	Mar. 31, 2022	Mar. 31, 2021
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	$ 8	$ 7
Interest income on industrial development revenue bonds	6	6
Non-service cost components of net periodic benefit income	46	34
Miscellaneous income	7	5
Donations	(2)	(3)
Miscellaneous expense	(5)	(3)
Total Other Income, Net	60	46
Union Electric Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	4	4
Interest income on industrial development revenue bonds	6	6
Non-service cost components of net periodic benefit income	14	14
Miscellaneous income	2	1
Donations	(1)	0
Miscellaneous expense	(2)	(2)
Total Other Income, Net	23	23
Defined Benefit Plan, Non-service Cost or Income Components - Tracker	6	(1)
Ameren Illinois Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	4	3
Non-service cost components of net periodic benefit income	21	14
Miscellaneous income	2	1
Donations	(1)	(3)
Miscellaneous expense	(2)	(1)
Total Other Income, Net	$ 24	$ 14

Derivative Financial Instruments (Open Gross Derivative Volumes By Commodity Type) (Detail) lb in Thousands, gal in Millions, MWh in Millions, MMBTU in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022 MMBTU MWh lb gal	Dec. 31, 2021 MMBTU MWh lb gal
Fuel oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume \| gal	25	30
Natural gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure \| MMBTU	182	179
Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure \| MWh	10	12
Uranium
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Mass \| lb	496	586
Union Electric Company \| Fuel oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume \| gal	25	30
Union Electric Company \| Natural gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure \| MMBTU	36	35
Union Electric Company \| Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure \| MWh	4	6
Union Electric Company \| Uranium
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Mass \| lb	496	586
Ameren Illinois Company \| Fuel oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume \| gal	0	0
Ameren Illinois Company \| Natural gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure \| MMBTU	146	144
Ameren Illinois Company \| Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure \| MWh	6	6
Ameren Illinois Company \| Uranium
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Mass \| lb	0	0

Derivative Financial Instruments (Derivative Instruments Carrying Value) (Detail) - Not Designated As Hedging Instrument - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Derivative [Line Items]
Derivative assets	$ 180	$ 90
Derivative Liability	218	202
Fuel oils \| Mark-to-market derivative assets
Derivative [Line Items]
Derivative assets	18	8
Fuel oils \| Other current assets
Derivative [Line Items]
Derivative assets	0	0
Fuel oils \| Other assets
Derivative [Line Items]
Derivative assets	8	5
Natural gas \| Mark-to-market derivative assets
Derivative [Line Items]
Derivative assets	90	35
Natural gas \| Other current assets
Derivative [Line Items]
Derivative assets	0	0
Natural gas \| Other assets
Derivative [Line Items]
Derivative assets	33	18
Natural gas \| Other current liabilities
Derivative [Line Items]
Derivative Liability	2	8
Natural gas \| Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	2	3
Power \| Mark-to-market derivative assets
Derivative [Line Items]
Derivative assets	24	23
Power \| Other current assets
Derivative [Line Items]
Derivative assets	0	0
Power \| Other assets
Derivative [Line Items]
Derivative assets	0	0
Power \| Other current liabilities
Derivative [Line Items]
Derivative Liability	110	59
Power \| Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	104	131
Uranium \| Mark-to-market derivative assets
Derivative [Line Items]
Derivative assets	5	0
Uranium \| Other current assets
Derivative [Line Items]
Derivative assets	0	0
Uranium \| Other assets
Derivative [Line Items]
Derivative assets	2	1
Uranium \| Other current liabilities
Derivative [Line Items]
Derivative Liability	0	1
Union Electric Company
Derivative [Line Items]
Derivative assets	78	49
Derivative Liability	136	77
Union Electric Company \| Fuel oils \| Other current assets
Derivative [Line Items]
Derivative assets	18	8
Union Electric Company \| Fuel oils \| Other assets
Derivative [Line Items]
Derivative assets	8	5
Union Electric Company \| Natural gas \| Other current assets
Derivative [Line Items]
Derivative assets	16	7
Union Electric Company \| Natural gas \| Other assets
Derivative [Line Items]
Derivative assets	10	5
Union Electric Company \| Natural gas \| Mark-to-market derivative liabilities
Derivative [Line Items]
Derivative Liability	0	2
Union Electric Company \| Natural gas \| Other current liabilities
Derivative [Line Items]
Derivative Liability	0	0
Union Electric Company \| Natural gas \| Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	1	1
Union Electric Company \| Power \| Other current assets
Derivative [Line Items]
Derivative assets	19	23
Union Electric Company \| Power \| Other assets
Derivative [Line Items]
Derivative assets	0	0
Union Electric Company \| Power \| Mark-to-market derivative liabilities
Derivative [Line Items]
Derivative Liability	109	50
Union Electric Company \| Power \| Other current liabilities
Derivative [Line Items]
Derivative Liability	0	0
Union Electric Company \| Power \| Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	26	23
Union Electric Company \| Uranium \| Other current assets
Derivative [Line Items]
Derivative assets	5	0
Union Electric Company \| Uranium \| Other assets
Derivative [Line Items]
Derivative assets	2	1
Union Electric Company \| Uranium \| Mark-to-market derivative liabilities
Derivative [Line Items]
Derivative Liability	0	1
Union Electric Company \| Uranium \| Other current liabilities
Derivative [Line Items]
Derivative Liability	0	0
Ameren Illinois Company
Derivative [Line Items]
Derivative assets	102	41
Derivative Liability	82	125
Ameren Illinois Company \| Fuel oils \| Mark-to-market derivative assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company \| Fuel oils \| Other current assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company \| Fuel oils \| Other assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company \| Natural gas \| Mark-to-market derivative assets
Derivative [Line Items]
Derivative assets	74	28
Ameren Illinois Company \| Natural gas \| Other current assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company \| Natural gas \| Other assets
Derivative [Line Items]
Derivative assets	23	13
Ameren Illinois Company \| Natural gas \| Other current liabilities
Derivative [Line Items]
Derivative Liability	2	6
Ameren Illinois Company \| Natural gas \| Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	1	2
Ameren Illinois Company \| Power \| Mark-to-market derivative assets
Derivative [Line Items]
Derivative assets	5	0
Ameren Illinois Company \| Power \| Other current assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company \| Power \| Other assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company \| Power \| Other current liabilities
Derivative [Line Items]
Derivative Liability	1	9
Ameren Illinois Company \| Power \| Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	78	108
Ameren Illinois Company \| Uranium \| Mark-to-market derivative assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company \| Uranium \| Other current assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company \| Uranium \| Other assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company \| Uranium \| Other current liabilities
Derivative [Line Items]
Derivative Liability	$ 0	$ 0

Derivative Financial Instruments (Offsetting Assets and Liabilities) (Details) - Not Designated As Hedging Instrument - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	$ 180	$ 90
Gross derivative instruments not offset in the balance sheet	25	19
Gross cash collateral received not offset in the balance sheet	14	0
Net derivative asset	141	71
Gross derivative liability amount recognized on the balance sheet	218	202
Gross derivative instruments not offset in the balance sheet	25	19
Gross cash collateral posted not offset in the balance sheet	92	47
Net derivative liability	101	136
Union Electric Company
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	78	49
Gross derivative instruments not offset in the balance sheet	19	15
Gross cash collateral received not offset in the balance sheet	5	0
Net derivative asset	54	34
Gross derivative liability amount recognized on the balance sheet	136	77
Gross derivative instruments not offset in the balance sheet	19	15
Gross cash collateral posted not offset in the balance sheet	92	47
Net derivative liability	25	15
Ameren Illinois Company
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	102	41
Gross derivative instruments not offset in the balance sheet	6	4
Gross cash collateral received not offset in the balance sheet	9	0
Net derivative asset	87	37
Gross derivative liability amount recognized on the balance sheet	82	125
Gross derivative instruments not offset in the balance sheet	6	4
Gross cash collateral posted not offset in the balance sheet	0	0
Net derivative liability	$ 76	$ 121

Derivative Financial Instruments (Credit Risk) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($)
Credit Derivatives [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	$ 176
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	144
Union Electric Company
Credit Derivatives [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	79
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	56
Ameren Illinois Company
Credit Derivatives [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	97
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	$ 88

Derivative Financial Instruments (Derivative Instruments With Credit Risk-Related Contingent Features (Details) $ in Millions	Mar. 31, 2022 USD ($)
Derivative [Line Items]
Aggregate Fair Value of Derivative Liabilities	$ 40
Cash Collateral Posted	18
Potential Aggregate Amount of Additional Collateral Required	11
Union Electric Company
Derivative [Line Items]
Aggregate Fair Value of Derivative Liabilities	36
Cash Collateral Posted	18
Potential Aggregate Amount of Additional Collateral Required	7
Ameren Illinois Company
Derivative [Line Items]
Aggregate Fair Value of Derivative Liabilities	4
Cash Collateral Posted	0
Potential Aggregate Amount of Additional Collateral Required	$ 4

Fair Value Measurements (Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	$ 1,087	$ 1,152
Assets fair value	1,267	1,242
Excluded receivables, payables, and accrued income, net	7	7
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	719	824
Assets fair value	768	848
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	368	328
Assets fair value	471	373
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Assets fair value	28	21
Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	180	90
Derivative Liability	218	202
Commodity Contract \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	49	24
Derivative Liability	81	45
Commodity Contract \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	103	45
Derivative Liability	2	7
Commodity Contract \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	28	21
Derivative Liability	135	150
Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	1,087	1,152
Assets fair value	1,165	1,201
Union Electric Company \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	719	824
Assets fair value	761	847
Union Electric Company \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	368	328
Assets fair value	394	340
Union Electric Company \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Assets fair value	10	14
Union Electric Company \| Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	78	49
Derivative Liability	136	77
Union Electric Company \| Commodity Contract \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	42	23
Derivative Liability	81	45
Union Electric Company \| Commodity Contract \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	26	12
Derivative Liability	1	2
Union Electric Company \| Commodity Contract \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	10	14
Derivative Liability	54	30
Union Electric Company \| Fuel oils \| Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	26	13
Union Electric Company \| Fuel oils \| Commodity Contract \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	24	13
Union Electric Company \| Fuel oils \| Commodity Contract \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Union Electric Company \| Fuel oils \| Commodity Contract \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	2	0
Union Electric Company \| Natural gas \| Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	26	12
Derivative Liability	1	3
Union Electric Company \| Natural gas \| Commodity Contract \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative Liability	0	0
Union Electric Company \| Natural gas \| Commodity Contract \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	26	12
Derivative Liability	1	2
Union Electric Company \| Natural gas \| Commodity Contract \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative Liability	0	1
Union Electric Company \| Power \| Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	19	23
Derivative Liability	135	73
Union Electric Company \| Power \| Commodity Contract \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	18	10
Derivative Liability	81	45
Union Electric Company \| Power \| Commodity Contract \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative Liability	0	0
Union Electric Company \| Power \| Commodity Contract \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	1	13
Derivative Liability	54	28
Union Electric Company \| Uranium \| Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	7	1
Derivative Liability	0	1
Union Electric Company \| Uranium \| Commodity Contract \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative Liability	0	0
Union Electric Company \| Uranium \| Commodity Contract \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative Liability	0	0
Union Electric Company \| Uranium \| Commodity Contract \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	7	1
Derivative Liability	0	1
Union Electric Company \| Equity securities: \| U.S. large capitalization
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	719	824
Union Electric Company \| Equity securities: \| U.S. large capitalization \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	719	824
Union Electric Company \| Equity securities: \| U.S. large capitalization \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company \| Equity securities: \| U.S. large capitalization \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
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:	174	141
Union Electric Company \| Debt securities: \| U.S. Treasury and agency securities \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company \| Debt securities: \| U.S. Treasury and agency securities \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	174	141
Union Electric Company \| Debt securities: \| U.S. Treasury and agency securities \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company \| Debt securities: \| Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	133	131
Union Electric Company \| Debt securities: \| Corporate bonds \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company \| Debt securities: \| Corporate bonds \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	133	131
Union Electric Company \| Debt securities: \| Corporate bonds \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company \| Debt securities: \| Other Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	61	56
Union Electric Company \| Debt securities: \| Other Debt Securities \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company \| Debt securities: \| Other Debt Securities \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	61	56
Union Electric Company \| Debt securities: \| Other Debt Securities \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	102	41
Ameren Illinois Company \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	7	1
Ameren Illinois Company \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	77	33
Ameren Illinois Company \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	18	7
Ameren Illinois Company \| Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	82	125
Ameren Illinois Company \| Commodity Contract \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	0	0
Ameren Illinois Company \| Commodity Contract \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	1	5
Ameren Illinois Company \| Commodity Contract \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	81	120
Ameren Illinois Company \| Natural gas \| Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	97	41
Derivative Liability	3	8
Ameren Illinois Company \| Natural gas \| Commodity Contract \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	7	1
Derivative Liability	0	0
Ameren Illinois Company \| Natural gas \| Commodity Contract \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	77	33
Derivative Liability	1	5
Ameren Illinois Company \| Natural gas \| Commodity Contract \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	13	7
Derivative Liability	2	3
Ameren Illinois Company \| Power \| Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	5	0
Derivative Liability	79	117
Ameren Illinois Company \| Power \| Commodity Contract \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative Liability	0	0
Ameren Illinois Company \| Power \| Commodity Contract \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative Liability	0	0
Ameren Illinois Company \| Power \| Commodity Contract \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	5	0
Derivative Liability	$ 79	$ 117

Fair Value Measurements (Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level Three In The Fair Value Hierarchy) (Details) - Power - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (132)	$ (196)
Included in regulatory assets/liabilities	1	4
Settlements, assets	4	4
Change in unrealized gains (losses) related to assets/liabilities held at period end	4	6
Ending balance	(127)	(188)
Union Electric Company
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(15)	2
Included in regulatory assets/liabilities	(41)	(5)
Settlements, assets	3	0
Change in unrealized gains (losses) related to assets/liabilities held at period end	(38)	(3)
Ending balance	(53)	(3)
Ameren Illinois Company
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(117)	(198)
Included in regulatory assets/liabilities	42	9
Settlements, assets	1	4
Change in unrealized gains (losses) related to assets/liabilities held at period end	42	9
Ending balance	$ (74)	$ (185)

Fair Value Measurements (Schedule Of Valuation Process And Unobservable Inputs) (Details) - Power $ in Millions	Mar. 31, 2022 USD ($) $ / MWh $ / MMBTU	Dec. 31, 2021 USD ($) $ / MWh $ / MMBTU
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Derivative assets \| $	$ 6	$ 13
Derivative liabilities \| $	$ (133)	$ (145)
Commodity Forward Price \| Discounted cash flow \| Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	35	32
Commodity Forward Price \| Discounted cash flow \| Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	82	55
Commodity Forward Price \| Discounted cash flow \| Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	51	40
Nodal Basis \| Discounted cash flow \| Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	(16)	(14)
Nodal Basis \| Discounted cash flow \| Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	0	0
Nodal Basis \| Discounted cash flow \| Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	(3)	(2)
Commodity Future Price \| Discounted cash flow \| Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input \| $ / MMBTU	(1)	0

Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Financial Assets and Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	$ 154	$ 155	$ 172	$ 301
Short-term debt	1,101	545
Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	9	8	12	145
Short-term debt	528	165
Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	137	133	$ 149	$ 147
Short-term debt	107	103
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	154	155
Investments in industrial development revenue bonds	248	248
Short-term debt	1,101	545
Long-term debt (including current portion)	13,068	13,067
Debt Issuance Costs, Net	94	94
Carrying Amount \| Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	9	8
Investments in industrial development revenue bonds	248	248
Short-term debt	528	165
Long-term debt (including current portion)	5,619	5,619
Debt Issuance Costs, Net	38	38
Carrying Amount \| Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	137	133
Short-term debt	107	103
Long-term debt (including current portion)	4,393	4,392
Debt Issuance Costs, Net	38	39
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	154	155
Investments, Fair Value Disclosure	248	248
Short-term Debt, Fair Value	1,101	545
Long-term Debt, Fair Value	13,141	14,521
Fair Value \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	154	155
Investments, Fair Value Disclosure	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Fair Value \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	0	0
Investments, Fair Value Disclosure	248	248
Short-term Debt, Fair Value	1,101	545
Long-term Debt, Fair Value	12,615	13,930
Fair Value \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	0	0
Investments, Fair Value Disclosure	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	526	591
Fair Value \| Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	9	8
Investments, Fair Value Disclosure	248	248
Short-term Debt, Fair Value	528	165
Long-term Debt, Fair Value	5,701	6,321
Fair Value \| Union Electric Company \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	9	8
Investments, Fair Value Disclosure	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Fair Value \| Union Electric Company \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	0	0
Investments, Fair Value Disclosure	248	248
Short-term Debt, Fair Value	528	165
Long-term Debt, Fair Value	5,701	6,321
Fair Value \| Union Electric Company \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	0	0
Investments, Fair Value Disclosure	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Fair Value \| Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	137	133
Short-term Debt, Fair Value	107	103
Long-term Debt, Fair Value	4,457	4,971
Fair Value \| Ameren Illinois Company \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	137	133
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Fair Value \| Ameren Illinois Company \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	0	0
Short-term Debt, Fair Value	107	103
Long-term Debt, Fair Value	4,457	4,971
Fair Value \| Ameren Illinois Company \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	$ 0	$ 0

Related Party Transactions (Narrative) (Details) - Ameren Services Support Services Agreement - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Union Electric Company
Related Party Transaction [Line Items]
Due from Related Parties	$ 77	$ 77
Ameren Illinois Company
Related Party Transaction [Line Items]
Due from Related Parties	$ 80	$ 80

- Definition

For an unclassified balance sheet, amounts due from related parties including affiliates, employees, joint ventures, officers and stockholders, immediate families thereof, and pension funds.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(k)(1))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iv))
-URI http://asc.fasb.org/extlink&oid=124359900&loc=SL124442526-122756

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(5))
-URI http://asc.fasb.org/extlink&oid=124359900&loc=SL124442526-122756

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(5))
-URI http://asc.fasb.org/extlink&oid=124359900&loc=SL124442552-122756

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10(3))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iii)(C))
-URI http://asc.fasb.org/extlink&oid=124359900&loc=SL124442552-122756

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iv))
-URI http://asc.fasb.org/extlink&oid=124359900&loc=SL124442552-122756

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iii)(B))
-URI http://asc.fasb.org/extlink&oid=124359900&loc=SL124442526-122756

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.3)
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

Related Party Transactions (Schedule of Affiliate Receivables and Payables) (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Union Electric Company
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	$ 36	$ 46
Accounts Receivable, Related Parties, Current	47	44
Union Electric Company \| Income taxes payable to parent
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	0	0
Union Electric Company \| Income taxes receivable from parent
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	33	27
Ameren Illinois Company
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	80	64
Accounts Receivable, Related Parties, Current	12	24
Ameren Illinois Company \| Income taxes payable to parent
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	42	8
Ameren Illinois Company \| Income taxes receivable from parent
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	$ 0	$ 18

Related Party Transactions (Effects of Related-party Transactions on the Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Union Electric Company \| Ameren Missouri Power Supply Agreements with Ameren Illinois
Related Party Transaction [Line Items]
Operating Revenues	$ 4	$ 2
Union Electric Company \| Ameren Missouri and Ameren Illinois Rent and Facility Services
Related Party Transaction [Line Items]
Operating Revenues	6	7
Operating Expenses	1	1
Union Electric Company \| Ameren Missouri and Ameren Illinois Miscellaneous Support Services
Related Party Transaction [Line Items]
Operating Revenues	1	1
Union Electric Company \| Total Related Party Operating Revenues
Related Party Transaction [Line Items]
Operating Revenues	10	9
Union Electric Company \| Ameren Missouri and Ameren Illinois Transmission Services from ATXI
Related Party Transaction [Line Items]
Operating Expenses	1	1
Union Electric Company \| Purchased Power
Related Party Transaction [Line Items]
Operating Expenses	1	1
Union Electric Company \| Ameren Services Support Services Agreement
Related Party Transaction [Line Items]
Operating Expenses	38	35
Union Electric Company \| Total Related Party Other Operations and Maintenance
Related Party Transaction [Line Items]
Operating Expenses	38	35
Union Electric Company \| Money pool borrowings (advances)
Related Party Transaction [Line Items]
Interest Charges (Income)	1	1
Ameren Illinois Company \| Ameren Missouri and Ameren Illinois Rent and Facility Services
Related Party Transaction [Line Items]
Operating Revenues	1	1
Operating Expenses	1	1
Ameren Illinois Company \| Ameren Missouri and Ameren Illinois Miscellaneous Support Services
Related Party Transaction [Line Items]
Operating Revenues	1	1
Ameren Illinois Company \| Total Related Party Operating Revenues
Related Party Transaction [Line Items]
Operating Revenues	1	1
Ameren Illinois Company \| Ameren Illinois Power Supply Agreements with Ameren Missouri
Related Party Transaction [Line Items]
Operating Expenses	4	2
Ameren Illinois Company \| Ameren Missouri and Ameren Illinois Transmission Services from ATXI
Related Party Transaction [Line Items]
Operating Expenses	1	1
Ameren Illinois Company \| Purchased Power
Related Party Transaction [Line Items]
Operating Expenses	4	2
Ameren Illinois Company \| Ameren Services Support Services Agreement
Related Party Transaction [Line Items]
Operating Expenses	35	33
Ameren Illinois Company \| Total Related Party Other Operations and Maintenance
Related Party Transaction [Line Items]
Operating Expenses	36	34
Ameren Illinois Company \| Money pool borrowings (advances)
Related Party Transaction [Line Items]
Interest Charges (Income)	$ 1	$ 1

Commitments And Contingencies (Environmental Matters) (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($) energyCenter scrubber site	Dec. 31, 2021 USD ($)
Loss Contingencies [Line Items]
Asset Retirement Obligation	$ 776	$ 764
Minimum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	125
Maximum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	$ 175
Union Electric Company
Loss Contingencies [Line Items]
Number of Energy Center Scrubbers \| scrubber	2
Number of Energy Centers Constructing Wastewater Treatment Facilities \| energyCenter	3
Number of energy centers \| energyCenter	4
Number of Days to Comply after Final EPA Determination	135 days
Asset Retirement Obligation	$ 772	760
Number of Ameren Missouri Natural Gas Energy Centers Subject To IETL \| energyCenter	5
Union Electric Company \| Coal Fired Electric Generation Equipment
Loss Contingencies [Line Items]
Plant To Be Abandoned, Net	$ 600
Union Electric Company \| Minimum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	125
Union Electric Company \| Maximum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	175
Ameren Illinois Company
Loss Contingencies [Line Items]
Asset Retirement Obligation	4	$ 4
Coal Combustion Residuals Estimate \| Union Electric Company \| Minimum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	60
Coal Combustion Residuals Estimate \| Union Electric Company \| Maximum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	80
Manufactured Gas Plant
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 68
Manufactured Gas Plant \| Ameren Illinois Company
Loss Contingencies [Line Items]
Number of remediation sites \| site	44
Accrual for environmental loss contingencies	$ 68
Manufactured Gas Plant \| Ameren Illinois Company \| Minimum
Loss Contingencies [Line Items]
Estimate of possible loss	68
Manufactured Gas Plant \| Ameren Illinois Company \| Maximum
Loss Contingencies [Line Items]
Estimate of possible loss	125
Rush Island Energy Center \| Union Electric Company
Loss Contingencies [Line Items]
Rate Base	400
New CCR Rules Estimate
Loss Contingencies [Line Items]
Asset Retirement Obligation	79
New CCR Rules Estimate \| Union Electric Company
Loss Contingencies [Line Items]
Asset Retirement Obligation	$ 79

Callaway Energy Center (Insurance Disclosure) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Apr. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Nuclear Waste Matters [Line Items]
Decommissioning Cost		$ 7.0
Frequency of Decommissioning Cost Study		3 years
Miscellaneous accounts receivable		$ 87.0	$ 85.0
Number Of Years The Limit Of Liability And The Maximum Potential Annual Payments Are Adjusted		5 years
Number Of Weeks Of Coverage After The First Twelve Weeks Of An Outage		1
Number Of Additional Weeks After Initial Indemnity Coverage For Power Outage		1.365
Subsequent Event
Nuclear Waste Matters [Line Items]
Proceeds from Insurance Settlement, Investing Activities	$ 22.0
Union Electric Company
Nuclear Waste Matters [Line Items]
Miscellaneous accounts receivable		$ 57.0	$ 71.0
Public Liability And Nuclear Worker Liability - American Nuclear Insurers
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage		450.0
Insurance Maximum Coverage per Incident		0.0
Public Liability And Nuclear Worker Liability - Pool Participation
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage		13,073.0
Insurance Maximum Coverage per Incident		138.0
Threshold Amount For Retrospective Insurance Assessment For Covered Loss Under Public Liability And Nuclear Worker Liability Insurance Policy		450.0
Maximum Annual Payment Per Incident At Licensed Commercial Nuclear Reactor		21.0
Public Liability
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage		13,523.0
Insurance Maximum Coverage per Incident		138.0
Property Damage - Nuclear Electric Insurance Ltd
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage		3,200.0
Insurance Maximum Coverage per Incident		26.0
Accidental Outage - Nuclear Electric Insurance Ltd
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage		490.0
Insurance Maximum Coverage per Incident		7.0
Amount Of Weekly Indemnity Coverage Commencing Twelve Weeks After Power Outage		4.5
Amount Of Additional Weekly Indemnity Coverage Commencing After Initial Indemnity Coverage		3.6
Amount Of Weekly Indemnity Coverage Thereafter Not Exceeding Policy Limit		490.0
Sub-Limit Of Amount Of Weekly Indemnity Coverage Thereafter Not Exceeding Policy Limit For Non-Nuclear Events		328.0
Radiation Event
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage		2,700.0
Aggregate Nuclear Power Industry Insurance Policy Limit For Losses From Terrorist Attacks Within Twelve Month Period		3,200.0
Non-Radiation Event
Nuclear Waste Matters [Line Items]
Miscellaneous accounts receivable		26.0
Insurance Aggregate Maximum Coverage		2,300.0
Aggregate Nuclear Power Industry Insurance Policy Limit For Losses From Terrorist Attacks Within Twelve Month Period		1,800.0
Property Damage European Mutual Association for Nuclear Insurance
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage		$ 490.0

Retirement Benefits (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total non-service cost components	$ (46)	$ (34)
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	33	33
Interest cost	40	38
Expected return on plan assets	(80)	(75)
Prior service benefit	0	0
Actuarial loss (gain)	6	17
Total non-service cost components	(34)	(20)
Net periodic benefit cost (income)	(1)	13
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	5	6
Interest cost	8	8
Expected return on plan assets	(21)	(20)
Prior service benefit	(1)	(1)
Actuarial loss (gain)	(4)	(1)
Total non-service cost components	(18)	(14)
Net periodic benefit cost (income)	$ (13)	$ (8)

Retirement Benefits (Summary of Benefit Plan Costs Incurred) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	$ (1)	$ 13
Pension Plan \| Union Electric Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(1)	6
Pension Plan \| Ameren Illinois Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	1	8
Pension Plan \| Other Affiliated Entities And Intercompany Eliminations
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(1)	(1)
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(13)	(8)
Other Postretirement Benefit Plan, Defined Benefit \| Union Electric Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(3)	(1)
Other Postretirement Benefit Plan, Defined Benefit \| Ameren Illinois Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(10)	(7)
Other Postretirement Benefit Plan, Defined Benefit \| Other Affiliated Entities And Intercompany Eliminations
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	$ 0	$ 0

Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21.00%	21.00%
Increases (decreases) from:
Amortization of deferred investment tax credit	0.00%	(1.00%)
Amortization of excess deferred taxes	(8.00%)	(9.00%)
Depreciation differences	0.00%	0.00%
Renewable and other tax credits	(5.00%)	(6.00%)
State tax	5.00%	6.00%
Stock-based compensation	(1.00%)	(1.00%)
Effective income tax rate	12.00%	10.00%
Union Electric Company
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21.00%	21.00%
Increases (decreases) from:
Amortization of deferred investment tax credit	(1.00%)	(1.00%)
Amortization of excess deferred taxes	(16.00%)	(17.00%)
Depreciation differences	0.00%	1.00%
Renewable and other tax credits	(11.00%)	(11.00%)
State tax	3.00%	3.00%
Stock-based compensation	0.00%	0.00%
Effective income tax rate	(4.00%)	(4.00%)
Ameren Illinois Company
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21.00%	21.00%
Increases (decreases) from:
Amortization of deferred investment tax credit	0.00%	0.00%
Amortization of excess deferred taxes	(2.00%)	(2.00%)
Depreciation differences	0.00%	(1.00%)
Renewable and other tax credits	0.00%	0.00%
State tax	7.00%	7.00%
Stock-based compensation	0.00%	0.00%
Effective income tax rate	26.00%	25.00%

Supplemental Information (Cash and Cash Equivalents) (Details) - USD ($)	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	$ 7,000,000	$ 8,000,000
Restricted cash included in “Other current assets”	10,000,000	16,000,000
Restricted cash included in “Other assets”	132,000,000	127,000,000
Restricted cash included in “Nuclear decommissioning trust fund”	5,000,000	4,000,000
Total cash, cash equivalents, and restricted cash	154,000,000	155,000,000	$ 172,000,000	$ 301,000,000
Union Electric Company
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	1,000,000	0
Restricted cash included in “Other current assets”	3,000,000	4,000,000
Restricted cash included in “Other assets”	0	0
Restricted cash included in “Nuclear decommissioning trust fund”	5,000,000	4,000,000
Total cash, cash equivalents, and restricted cash	9,000,000	8,000,000	12,000,000	145,000,000
Ameren Illinois Company
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	0	0
Restricted cash included in “Other current assets”	5,000,000	6,000,000
Restricted cash included in “Other assets”	132,000,000	127,000,000
Restricted cash included in “Nuclear decommissioning trust fund”	0	0
Total cash, cash equivalents, and restricted cash	$ 137,000,000	$ 133,000,000	$ 149,000,000	$ 147,000,000

Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	$ 29	$ 50
Bad debt expense	4	4
Net write-offs	(5)	(7)
End of period	28	47
Payables for purchased receivables	29		$ 27
Union Electric Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	13	16
Bad debt expense	1	1
Net write-offs	(3)	(2)
End of period	11	15
Ameren Illinois Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	16	34
Bad debt expense	3	3
Net write-offs	(2)	(5)
End of period	17	$ 32
Payables for purchased receivables	$ 29		$ 27

Supplemental Information (Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Supplemental Cash Flow Information [Line Items]
Wind generation expenditures	$ 0	$ 193
Accrued capital expenditures	345	271
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund	(71)	22
Issuance of common stock for stock-based compensation
Supplemental Cash Flow Information [Line Items]
Stock Issued	31	33
Issuance of common stock under the DRPlus
Supplemental Cash Flow Information [Line Items]
Stock Issued	8	0
Union Electric Company
Supplemental Cash Flow Information [Line Items]
Wind generation expenditures	0	193
Accrued capital expenditures	194	141
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund	(71)	22
Union Electric Company \| Issuance of common stock for stock-based compensation
Supplemental Cash Flow Information [Line Items]
Stock Issued	0	0
Union Electric Company \| Issuance of common stock under the DRPlus
Supplemental Cash Flow Information [Line Items]
Stock Issued	0	0
Ameren Illinois Company
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures	147	139
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund	0	0
Ameren Illinois Company \| Issuance of common stock for stock-based compensation
Supplemental Cash Flow Information [Line Items]
Stock Issued	0	0
Ameren Illinois Company \| Issuance of common stock under the DRPlus
Supplemental Cash Flow Information [Line Items]
Stock Issued	$ 0	$ 0

Supplemental Information (Schedule of Asset Retirement Obligations) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	$ 764
Accretion	8
Change in estimates	4
Asset Retirement Obligation, Ending Balance	776
Other current liabilities	630	$ 568
Union Electric Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	760
Accretion	8
Change in estimates	4
Asset Retirement Obligation, Ending Balance	772
Other current liabilities	159	175
Ameren Illinois Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	4
Accretion	0
Change in estimates	0
Asset Retirement Obligation, Ending Balance	4
Other current liabilities	251	251
Asset Retirement Obligation Balance
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Other current liabilities	7	7
Asset Retirement Obligation Balance \| Union Electric Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Other current liabilities	$ 7	$ 7

Supplemental Information (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount	$ 5	$ 5
Deferred Compensation Liability, Classified, Noncurrent	$ 91		$ 91
Q1 2022 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Performance Shares \| Q1 2022 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	267,849
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Fair Value	$ 25
Stock Issued During Period Percentage Conversion Of Units, Low End	0.00%
Stock Issued During Period Percentage Conversion Of Units, High End	200.00%
Performance Shares \| Market performance measures achievement \| Q1 2022 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	229,566
Performance Shares \| Renewable generation and energy storage installation targets \| Q1 2022 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	38,283
Restricted Stock Units (RSUs) \| Q1 2022 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	122,882
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Fair Value	$ 11

Supplemental Information (Schedule Of Excise Taxes) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Accounting Policies [Line Items]
Excise tax expense	$ 79	$ 70
Union Electric Company
Accounting Policies [Line Items]
Excise tax expense	34	31
Ameren Illinois Company
Accounting Policies [Line Items]
Excise tax expense	$ 45	$ 39

Supplemental Information (Earnings Per Share) (Details) - shares	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Earnings Per Share Reconciliation [Abstract]
Weighted-average Common Shares Outstanding – Basic	257,900,000	254,400,000
Assumed settlement of performance share units and restricted stock units	1,100,000	1,500,000
Weighted-average Common Shares Outstanding – Diluted	259,000,000.0	255,900,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)	0	0

Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Revenues	$ 1,879	$ 1,566
Net income (loss) attributable to common shareholders	252	233
Capital expenditures	774	887
Wind generation expenditures	0	193
Union Electric Company
Segment Reporting Information [Line Items]
Revenues	818	704
Net income (loss) attributable to common shareholders	50	47
Wind generation expenditures	0	193
Ameren Illinois Company
Segment Reporting Information [Line Items]
Revenues	1,024	823
Net income (loss) attributable to common shareholders	169	149
Capital expenditures	342	337
Operating Segments \| Union Electric Company
Segment Reporting Information [Line Items]
Revenues	808	695
Net income (loss) attributable to common shareholders	50	47
Capital expenditures	414	534
Operating Segments \| Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Revenues	464	411
Net income (loss) attributable to common shareholders	49	46
Capital expenditures	138	157
Operating Segments \| Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Revenues	481	347
Net income (loss) attributable to common shareholders	80	75
Capital expenditures	49	48
Operating Segments \| Ameren Transmission
Segment Reporting Information [Line Items]
Revenues	126	113
Net income (loss) attributable to common shareholders	58	47
Capital expenditures	172	141
Operating Segments \| Ameren Illinois Company \| Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Revenues	465	411
Net income (loss) attributable to common shareholders	49	46
Capital expenditures	138	157
Operating Segments \| Ameren Illinois Company \| Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Revenues	481	347
Net income (loss) attributable to common shareholders	80	75
Capital expenditures	49	48
Operating Segments \| Ameren Illinois Company \| Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Revenues	78	65
Net income (loss) attributable to common shareholders	40	28
Capital expenditures	155	132
Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment revenues	(31)	(26)
Capital expenditures	(1)	6
Intersegment Eliminations \| Union Electric Company
Segment Reporting Information [Line Items]
Intersegment revenues	(10)	(9)
Intersegment Eliminations \| Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	(1)	0
Intersegment Eliminations \| Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Intersegment revenues	0	0
Intersegment Eliminations \| Ameren Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	(20)	(17)
Intersegment Eliminations \| Ameren Illinois Company
Segment Reporting Information [Line Items]
Intersegment revenues	(20)	(16)
Intersegment Eliminations \| Ameren Illinois Company \| Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	0	0
Intersegment Eliminations \| Ameren Illinois Company \| Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Intersegment revenues	0	0
Intersegment Eliminations \| Ameren Illinois Company \| Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	(20)	(16)
Other
Segment Reporting Information [Line Items]
Net income (loss) attributable to common shareholders	15	18
Capital expenditures	$ 2	$ 1

Segment Information (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenues	$ 1,879	$ 1,566
Revenues	1,879	1,566
Revenues from alternative revenue programs	45	53
Other revenues not from contracts with customers	3	2
Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(6)	(10)
Other revenues not from contracts with customers	0	(2)
Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	55	61
Other revenues not from contracts with customers	2	3
Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(5)	3
Other revenues not from contracts with customers	1	1
Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	1	(1)
Other revenues not from contracts with customers	0	0
Electricity
Disaggregation of Revenue [Line Items]
Revenues	1,318	1,156
Revenues	1,318	1,156
Electricity \| Residential
Disaggregation of Revenue [Line Items]
Revenues	595	541
Electricity \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	398	348
Electricity \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	102	86
Electricity \| Other
Disaggregation of Revenue [Line Items]
Revenues	223	181
Natural gas
Disaggregation of Revenue [Line Items]
Revenues	561	410
Revenues	561	410
Natural gas \| Residential
Disaggregation of Revenue [Line Items]
Revenues	420	285
Natural gas \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	119	79
Natural gas \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	19	15
Natural gas \| Other
Disaggregation of Revenue [Line Items]
Revenues	3	31
Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Revenues	1,024	823
Revenues	1,024	823
Revenues from alternative revenue programs	51	63
Other revenues not from contracts with customers	3	4
Ameren Illinois Company \| Residential
Disaggregation of Revenue [Line Items]
Revenues	632	480
Ameren Illinois Company \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	255	196
Ameren Illinois Company \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	62	48
Ameren Illinois Company \| Other
Disaggregation of Revenue [Line Items]
Revenues	75	99
Ameren Illinois Company \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	55	61
Other revenues not from contracts with customers	2	3
Ameren Illinois Company \| Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(5)	3
Other revenues not from contracts with customers	1	1
Ameren Illinois Company \| Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	1	(1)
Other revenues not from contracts with customers	0	0
Ameren Illinois Company \| Electricity
Disaggregation of Revenue [Line Items]
Revenues	543	476
Ameren Illinois Company \| Natural gas
Disaggregation of Revenue [Line Items]
Revenues	481	347
Operating Segments \| Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	808	695
Revenues	818	704
Operating Segments \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	464	411
Revenues	465	411
Operating Segments \| Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	481	347
Revenues	481	347
Operating Segments \| Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	126	113
Revenues	146	130
Operating Segments \| Electricity \| Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	738	641
Operating Segments \| Electricity \| Union Electric Company \| Residential
Disaggregation of Revenue [Line Items]
Revenues	332	312
Operating Segments \| Electricity \| Union Electric Company \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	240	216
Operating Segments \| Electricity \| Union Electric Company \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	57	52
Operating Segments \| Electricity \| Union Electric Company \| Other
Disaggregation of Revenue [Line Items]
Revenues	109	61
Operating Segments \| Electricity \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	465	411
Operating Segments \| Electricity \| Ameren Illinois Electric Distribution \| Residential
Disaggregation of Revenue [Line Items]
Revenues	263	229
Operating Segments \| Electricity \| Ameren Illinois Electric Distribution \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	158	132
Operating Segments \| Electricity \| Ameren Illinois Electric Distribution \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	45	34
Operating Segments \| Electricity \| Ameren Illinois Electric Distribution \| Other
Disaggregation of Revenue [Line Items]
Revenues	(1)	16
Operating Segments \| Electricity \| Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Electricity \| Ameren Illinois Natural Gas \| Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Electricity \| Ameren Illinois Natural Gas \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Electricity \| Ameren Illinois Natural Gas \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Electricity \| Ameren Illinois Natural Gas \| Other
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Electricity \| Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	146	130
Operating Segments \| Electricity \| Ameren Transmission \| Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Electricity \| Ameren Transmission \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Electricity \| Ameren Transmission \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Electricity \| Ameren Transmission \| Other
Disaggregation of Revenue [Line Items]
Revenues	146	130
Operating Segments \| Natural gas \| Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	80	63
Operating Segments \| Natural gas \| Union Electric Company \| Residential
Disaggregation of Revenue [Line Items]
Revenues	51	34
Operating Segments \| Natural gas \| Union Electric Company \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	22	15
Operating Segments \| Natural gas \| Union Electric Company \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	2	1
Operating Segments \| Natural gas \| Union Electric Company \| Other
Disaggregation of Revenue [Line Items]
Revenues	5	13
Operating Segments \| Natural gas \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Natural gas \| Ameren Illinois Electric Distribution \| Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Natural gas \| Ameren Illinois Electric Distribution \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Natural gas \| Ameren Illinois Electric Distribution \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Natural gas \| Ameren Illinois Electric Distribution \| Other
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Natural gas \| Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	481	347
Operating Segments \| Natural gas \| Ameren Illinois Natural Gas \| Residential
Disaggregation of Revenue [Line Items]
Revenues	369	251
Operating Segments \| Natural gas \| Ameren Illinois Natural Gas \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	97	64
Operating Segments \| Natural gas \| Ameren Illinois Natural Gas \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	17	14
Operating Segments \| Natural gas \| Ameren Illinois Natural Gas \| Other
Disaggregation of Revenue [Line Items]
Revenues	(2)	18
Operating Segments \| Natural gas \| Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Natural gas \| Ameren Transmission \| Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Natural gas \| Ameren Transmission \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Natural gas \| Ameren Transmission \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Natural gas \| Ameren Transmission \| Other
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Ameren Illinois Company \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	465	411
Operating Segments \| Ameren Illinois Company \| Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	481	347
Operating Segments \| Ameren Illinois Company \| Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	78	65
Operating Segments \| Ameren Illinois Company \| Electricity \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	465	411
Operating Segments \| Ameren Illinois Company \| Electricity \| Ameren Illinois Electric Distribution \| Residential
Disaggregation of Revenue [Line Items]
Revenues	263	229
Operating Segments \| Ameren Illinois Company \| Electricity \| Ameren Illinois Electric Distribution \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	158	132
Operating Segments \| Ameren Illinois Company \| Electricity \| Ameren Illinois Electric Distribution \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	45	34
Operating Segments \| Ameren Illinois Company \| Electricity \| Ameren Illinois Electric Distribution \| Other
Disaggregation of Revenue [Line Items]
Revenues	(1)	16
Operating Segments \| Ameren Illinois Company \| Electricity \| Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	98	81
Operating Segments \| Ameren Illinois Company \| Electricity \| Ameren Illinois Transmission \| Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Ameren Illinois Company \| Electricity \| Ameren Illinois Transmission \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Ameren Illinois Company \| Electricity \| Ameren Illinois Transmission \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments \| Ameren Illinois Company \| Electricity \| Ameren Illinois Transmission \| Other
Disaggregation of Revenue [Line Items]
Revenues	98	81
Operating Segments \| Ameren Illinois Company \| Natural gas \| Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	481	347
Operating Segments \| Ameren Illinois Company \| Natural gas \| Ameren Illinois Natural Gas \| Residential
Disaggregation of Revenue [Line Items]
Revenues	369	251
Operating Segments \| Ameren Illinois Company \| Natural gas \| Ameren Illinois Natural Gas \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	97	64
Operating Segments \| Ameren Illinois Company \| Natural gas \| Ameren Illinois Natural Gas \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	17	14
Operating Segments \| Ameren Illinois Company \| Natural gas \| Ameren Illinois Natural Gas \| Other
Disaggregation of Revenue [Line Items]
Revenues	(2)	18
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(31)	(26)
Revenues	(31)	(26)
Intersegment Eliminations \| Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	(10)	(9)
Intersegment Eliminations \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	(1)	0
Intersegment Eliminations \| Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations \| Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	(20)	(17)
Intersegment Eliminations \| Electricity
Disaggregation of Revenue [Line Items]
Revenues	(31)	(26)
Intersegment Eliminations \| Electricity \| Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations \| Electricity \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations \| Electricity \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations \| Electricity \| Other
Disaggregation of Revenue [Line Items]
Revenues	(31)	(26)
Intersegment Eliminations \| Natural gas
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations \| Natural gas \| Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations \| Natural gas \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations \| Natural gas \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations \| Natural gas \| Other
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations \| Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Revenues	(20)	(16)
Revenues	(20)	(16)
Intersegment Eliminations \| Ameren Illinois Company \| Residential
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations \| Ameren Illinois Company \| Commercial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations \| Ameren Illinois Company \| Industrial
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations \| Ameren Illinois Company \| Other
Disaggregation of Revenue [Line Items]
Revenues	(20)	(16)
Intersegment Eliminations \| Ameren Illinois Company \| Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations \| Ameren Illinois Company \| Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations \| Ameren Illinois Company \| Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	$ (20)	$ (16)