Cover Page - USD ($)	12 Months Ended
Cover Page - USD ($)	Dec. 31, 2023	Jan. 31, 2024	Jun. 30, 2023
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Current Fiscal Year End Date	--12-31
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 Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Emerging growth company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 21,380,504,079
Entity Common Stock, Shares Outstanding		266,288,867
Documents Incorporated by Reference	Portions of the definitive proxy statement of Ameren Corporation and portions of the definitive information statements of Union Electric Company and Ameren Illinois Company for the 2024 annual meetings of shareholders are incorporated by reference into Part III of this Form 10-K.
Entity Central Index Key	0001002910
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Amendment Flag	false
Document Financial Statement Error Correction [Flag]	false
Ameren Missouri
Entity Information [Line Items]
Current Fiscal Year End Date	--12-31
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
Title of 12(g) Security	Preferred Stock, cumulative, no par value, stated value $100 per share
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Emerging growth company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		102,123,834
Entity Central Index Key	0000100826
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Amendment Flag	false
No Trading Symbol Flag	true
Document Financial Statement Error Correction [Flag]	false
Ameren Illinois
Entity Information [Line Items]
Current Fiscal Year End Date	--12-31
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 Richard Mark Way
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
Title of 12(g) Security	Preferred Stock, cumulative, $100 par value
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Emerging growth company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		25,452,373
Entity Central Index Key	0000018654
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Amendment Flag	false
No Trading Symbol Flag	true
Document Financial Statement Error Correction [Flag]	false

Audit Information	12 Months Ended
Audit Information	Dec. 31, 2023
Auditor [Line Items]
Auditor Name	PricewaterhouseCoopers LLP
Auditor Location	St. Louis, Missouri
Auditor Firm ID	238
Ameren Missouri
Auditor [Line Items]
Auditor Name	PricewaterhouseCoopers LLP
Auditor Location	St. Louis, Missouri
Auditor Firm ID	238
Ameren Illinois
Auditor [Line Items]
Auditor Name	PricewaterhouseCoopers LLP
Auditor Location	St. Louis, Missouri
Auditor Firm ID	238

Consolidated Statement Of Income (Loss) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating Revenues:
Operating revenues	$ 7,500	$ 7,957	$ 6,394
Operating Expenses:
Fuel	514	473	581
Purchased power	1,298	1,547	606
Natural gas purchased for resale	355	657	442
Other operations and maintenance	1,866	1,937	1,774
Depreciation and amortization	1,387	1,289	1,146
Taxes other than income taxes	522	539	512
Total operating expenses	5,942	6,442	5,061
Operating Income	1,558	1,515	1,333
Other Income, Net	348	226	202
Interest Charges	566	486	383
Income Before Income Taxes	1,340	1,255	1,152
Income Taxes	183	176	157
Net Income	1,157	1,079	995
Less: Net Income Attributable to Noncontrolling Interests	5	5	5
Net Income Attributable to Ameren Common Shareholders	1,152	1,074	990
Pension and other postretirement benefit plan activity, net of income taxes (benefit)	(5)	(14)	14
Comprehensive Income	1,152	1,065	1,009
Less: Comprehensive Income Attributable to Noncontrolling Interests	5	5	5
Comprehensive Income Attributable to Ameren Common Shareholders	$ 1,147	$ 1,060	$ 1,004
Earnings per Common Share – Basic
Earnings per Common Share – Basic	$ 4.39	$ 4.16	$ 3.86
Earnings per Common Share – Diluted
Earnings per Common Share – Diluted	$ 4.38	$ 4.14	$ 3.84
Weighted-average Common Shares Outstanding – Basic	262.8	258.4	256.3
Weighted-average Common Shares Outstanding – Diluted	263.4	259.5	257.6
Ameren Missouri
Operating Revenues:
Operating revenues	$ 3,859	$ 4,046	$ 3,353
Operating Expenses:
Fuel	514	473	581
Purchased power	483	677	227
Natural gas purchased for resale	79	104	60
Other operations and maintenance	1,003	1,028	948
Depreciation and amortization	783	732	632
Taxes other than income taxes	360	363	343
Total operating expenses	3,222	3,377	2,791
Operating Income	637	669	562
Other Income, Net	130	99	99
Interest Charges	227	213	137
Income Before Income Taxes	540	555	524
Income Taxes	(8)	(10)	3
Net Income	548	565	521
Preferred Stock Dividends	3	3	3
Net Income Attributable to Ameren Common Shareholders	545	562	518
Ameren Illinois
Operating Revenues:
Operating revenues	3,482	3,756	2,895
Operating Expenses:
Purchased power	820	880	400
Natural gas purchased for resale	276	553	382
Other operations and maintenance	818	882	820
Depreciation and amortization	556	514	472
Taxes other than income taxes	146	161	153
Total operating expenses	2,616	2,990	2,227
Operating Income	866	766	668
Other Income, Net	156	96	66
Interest Charges	204	168	164
Income Before Income Taxes	818	694	570
Income Taxes	209	179	143
Net Income	609	515	427
Preferred Stock Dividends	2	2	2
Net Income Attributable to Ameren Common Shareholders	607	513	425
Electric
Operating Revenues:
Operating revenues	6,439	6,581	5,297
Electric \| Ameren Missouri
Operating Revenues:
Operating revenues	3,694	3,849	3,212
Electric \| Ameren Illinois
Operating Revenues:
Operating revenues	2,585	2,576	1,938
Natural gas
Operating Revenues:
Operating revenues	1,061	1,376	1,097
Natural gas \| Ameren Missouri
Operating Revenues:
Operating revenues	165	197	141
Natural gas \| Ameren Illinois
Operating Revenues:
Operating revenues	$ 897	$ 1,180	$ 957

Consolidated Statement Of Income (Loss) (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Statement [Abstract]
Pension and other postretirement benefit plan activity, tax (benefit)	$ (2)	$ (4)	$ 4

Consolidated Balance Sheet - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Current Assets:
Cash and cash equivalents	$ 25	$ 10
Accounts receivable - trade (less allowance for doubtful accounts)	494	600
Unbilled revenue	319	446
Advances to money pool	106	54
Inventories	733	667
Current regulatory assets	365	354
Investments in Industrial Development Revenue Bonds	0
Current collateral assets	14	142
Other current assets	125	155
Total current assets	2,181	2,668
Property, Plant, and Equipment, Net	33,776	31,262
Investments and Other Assets:
Nuclear decommissioning trust fund	1,150	958
Goodwill	411	411
Regulatory assets	1,810	1,426
Pension and other postretirement benefits	581	411
Other assets	921	768
Total investments and other assets	4,873	3,974
TOTAL ASSETS	40,830	37,904
Current Liabilities:
Current maturities of long-term debt	849	340
Short-term debt	536	1,070
Accounts and wages payable	1,136	1,159
Customer deposits	176	115
Other current liabilities	648	682
Total current liabilities	3,345	3,366
Long-term Debt, Net	15,121	13,685
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and investment tax credits, net	4,176	3,804
Regulatory liabilities	5,512	5,309
Asset retirement obligations	772	763
Other deferred credits and liabilities	426	340
Total deferred credits and other liabilities	10,886	10,216
Commitments and Contingencies (Notes 2, 9, and 14)
Shareholders' Equity:
Common stock	3	3
Other paid-in capital, principally premium on common stock	7,216	6,860
Retained earnings	4,136	3,646
Accumulated other comprehensive loss	(6)	(1)
Total shareholders' equity	11,349	10,508
Noncontrolling Interests	129	129
Total equity	11,478	10,637
TOTAL LIABILITIES AND EQUITY	$ 40,830	$ 37,904

Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Accounts receivable - trade, allowance for doubtful accounts	$ 30	$ 31
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	400,000,000.0	400,000,000.0
Common Stock, Shares, Outstanding	266,300,000	262,000,000.0	257,700,000	253,300,000

Consolidated Balance Sheet - UE - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Current Assets:
Cash and cash equivalents	$ 25	$ 10
Accounts receivable - trade (less allowance for doubtful accounts)	494	600
Unbilled revenue	319	446
Advances to money pool	106	54
Inventories	733	667
Current regulatory assets	365	354
Investments in Industrial Development Revenue Bonds	0
Current collateral assets	14	142
Other current assets	125	155
Total current assets	2,181	2,668
Property, Plant, and Equipment, Net	33,776	31,262
Investments and Other Assets:
Nuclear decommissioning trust fund	1,150	958
Regulatory assets	1,810	1,426
Pension and other postretirement benefits	581	411
Other assets	921	768
Total investments and other assets	4,873	3,974
TOTAL ASSETS	40,830	37,904
Current Liabilities:
Current maturities of long-term debt	849	340
Short-term debt	536	1,070
Accounts and wages payable	1,136	1,159
Other current liabilities	648	682
Total current liabilities	3,345	3,366
Long-term Debt, Net	15,121	13,685
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and investment tax credits, net	4,176	3,804
Regulatory liabilities	5,512	5,309
Asset retirement obligations	772	763
Other deferred credits and liabilities	426	340
Total deferred credits and other liabilities	10,886	10,216
Commitments and Contingencies (Notes 2, 9, and 14)
Shareholders' Equity:
Common stock	3	3
Other paid-in capital, principally premium on common stock	7,216	6,860
Retained earnings	4,136	3,646
Total shareholders' equity	11,349	10,508
TOTAL LIABILITIES AND EQUITY	40,830	37,904
Ameren Missouri
Current Assets:
Cash and cash equivalents	0	0
Unbilled revenue	163	184
Advances to money pool	26	18
Inventories	508	434
Current regulatory assets	101	254
Investments in Industrial Development Revenue Bonds	0	240
Current collateral assets	5	101
Other current assets	63	66
Total current assets	1,142	1,592
Property, Plant, and Equipment, Net	17,250	16,124
Investments and Other Assets:
Nuclear decommissioning trust fund	1,150	958
Regulatory assets	755	594
Pension and other postretirement benefits	157	98
Other assets	152	140
Total investments and other assets	2,214	1,790
TOTAL ASSETS	20,606	19,506
Current Liabilities:
Current maturities of long-term debt	350	240
Short-term debt	170	329
Other current liabilities	250	352
Total current liabilities	1,747	1,570
Long-term Debt, Net	5,991	5,846
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and investment tax credits, net	2,122	1,982
Regulatory liabilities	2,959	2,871
Asset retirement obligations	768	759
Other deferred credits and liabilities	56	51
Total deferred credits and other liabilities	5,905	5,663
Commitments and Contingencies (Notes 2, 9, and 14)
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	3,647	3,111
Total shareholders' equity	6,963	6,427
TOTAL LIABILITIES AND EQUITY	20,606	19,506
Ameren Missouri \| Nonrelated Party
Current Assets:
Accounts receivable - trade (less allowance for doubtful accounts)	204	244
Current Liabilities:
Short-term debt	170	329
Accounts and wages payable	618	606
Ameren Missouri \| Related Party
Current Assets:
Accounts receivable - trade (less allowance for doubtful accounts)	72	51
Current Liabilities:
Short-term debt	306	0
Accounts and wages payable	53	43
Ameren Illinois
Current Assets:
Cash and cash equivalents	0	0
Unbilled revenue	156	262
Advances to money pool	44	23
Inventories	225	233
Current regulatory assets	252	87
Other current assets	62	98
Total current assets	1,047	1,056
Property, Plant, and Equipment, Net	14,632	13,353
Investments and Other Assets:
Regulatory assets	1,035	821
Pension and other postretirement benefits	394	318
Other assets	603	482
Total investments and other assets	2,443	2,032
TOTAL ASSETS	18,122	16,441
Current Liabilities:
Current maturities of long-term debt	0	100
Short-term debt	366	264
Other current liabilities	298	232
Total current liabilities	1,433	1,291
Long-term Debt, Net	5,232	4,735
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and investment tax credits, net	1,906	1,699
Regulatory liabilities	2,418	2,313
Other deferred credits and liabilities	308	235
Total deferred credits and other liabilities	4,632	4,247
Commitments and Contingencies (Notes 2, 9, and 14)
Shareholders' Equity:
Common stock	0	0
Other paid-in capital, principally premium on common stock	3,020	2,929
Preferred stock	49	49
Retained earnings	3,756	3,190
Total shareholders' equity	6,825	6,168
TOTAL LIABILITIES AND EQUITY	18,122	16,441
Ameren Illinois \| Nonrelated Party
Current Assets:
Accounts receivable - trade (less allowance for doubtful accounts)	273	341
Current Liabilities:
Short-term debt	366	264
Accounts and wages payable	370	451
Ameren Illinois \| Related Party
Current Assets:
Accounts receivable - trade (less allowance for doubtful accounts)	35	12
Current Liabilities:
Short-term debt	135	0
Accounts and wages payable	$ 52	$ 93

Consolidated Balance Sheet - UE (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Accounts receivable - trade, allowance for doubtful accounts	$ 30	$ 31
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	400,000,000.0	400,000,000.0
Common Stock, Shares, Outstanding	266,300,000	262,000,000.0
Ameren Missouri
Accounts receivable - trade, allowance for doubtful accounts	$ 12	$ 13
Common Stock, No Par Value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized	150,000,000.0	150,000,000.0
Common Stock, Shares, Outstanding	102,100,000	102,100,000

Consolidated Balance Sheet - AIC - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Current Assets:
Cash and cash equivalents	$ 25	$ 10
Accounts receivable - trade (less allowance for doubtful accounts)	494	600
Unbilled revenue	319	446
Advances to money pool	106	54
Inventories	733	667
Current regulatory assets	365	354
Other current assets	125	155
Total current assets	2,181	2,668
Property, Plant, and Equipment, Net	33,776	31,262
Investments and Other Assets:
Goodwill	411	411
Regulatory assets	1,810	1,426
Pension and other postretirement benefits	581	411
Other assets	921	768
Total investments and other assets	4,873	3,974
TOTAL ASSETS	40,830	37,904
Current Liabilities:
Current maturities of long-term debt	849	340
Short-term debt	536	1,070
Accounts and wages payable	1,136	1,159
Customer deposits	176	115
Current regulatory liabilities	87	136
Other current liabilities	648	682
Total current liabilities	3,345	3,366
Long-term Debt, Net	15,121	13,685
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and investment tax credits, net	4,176	3,804
Regulatory liabilities	5,512	5,309
Other deferred credits and liabilities	426	340
Total deferred credits and other liabilities	10,886	10,216
Commitments and Contingencies (Notes 2, 9, and 14)
Shareholders' Equity:
Common stock	3	3
Other paid-in capital, principally premium on common stock	7,216	6,860
Retained earnings	4,136	3,646
Total shareholders' equity	11,349	10,508
TOTAL LIABILITIES AND EQUITY	40,830	37,904
Ameren Illinois
Current Assets:
Cash and cash equivalents	0	0
Unbilled revenue	156	262
Advances to money pool	44	23
Inventories	225	233
Current regulatory assets	252	87
Other current assets	62	98
Total current assets	1,047	1,056
Property, Plant, and Equipment, Net	14,632	13,353
Investments and Other Assets:
Goodwill	411	411
Regulatory assets	1,035	821
Pension and other postretirement benefits	394	318
Other assets	603	482
Total investments and other assets	2,443	2,032
TOTAL ASSETS	18,122	16,441
Current Liabilities:
Current maturities of long-term debt	0	100
Short-term debt	366	264
Customer deposits	141	87
Current regulatory liabilities	71	64
Other current liabilities	298	232
Total current liabilities	1,433	1,291
Long-term Debt, Net	5,232	4,735
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and investment tax credits, net	1,906	1,699
Regulatory liabilities	2,418	2,313
Other deferred credits and liabilities	308	235
Total deferred credits and other liabilities	4,632	4,247
Commitments and Contingencies (Notes 2, 9, and 14)
Shareholders' Equity:
Common stock	0	0
Other paid-in capital, principally premium on common stock	3,020	2,929
Preferred stock	49	49
Retained earnings	3,756	3,190
Total shareholders' equity	6,825	6,168
TOTAL LIABILITIES AND EQUITY	18,122	16,441
Ameren Illinois \| Nonrelated Party
Current Assets:
Accounts receivable - trade (less allowance for doubtful accounts)	273	341
Current Liabilities:
Short-term debt	366	264
Accounts and wages payable	370	451
Ameren Illinois \| Related Party
Current Assets:
Accounts receivable - trade (less allowance for doubtful accounts)	35	12
Current Liabilities:
Short-term debt	135	0
Accounts and wages payable	52	93
Ameren Missouri
Current Assets:
Cash and cash equivalents	0	0
Unbilled revenue	163	184
Advances to money pool	26	18
Inventories	508	434
Current regulatory assets	101	254
Other current assets	63	66
Total current assets	1,142	1,592
Property, Plant, and Equipment, Net	17,250	16,124
Investments and Other Assets:
Regulatory assets	755	594
Pension and other postretirement benefits	157	98
Other assets	152	140
Total investments and other assets	2,214	1,790
TOTAL ASSETS	20,606	19,506
Current Liabilities:
Current maturities of long-term debt	350	240
Short-term debt	170	329
Current regulatory liabilities	15	70
Other current liabilities	250	352
Total current liabilities	1,747	1,570
Long-term Debt, Net	5,991	5,846
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and investment tax credits, net	2,122	1,982
Regulatory liabilities	2,959	2,871
Other deferred credits and liabilities	56	51
Total deferred credits and other liabilities	5,905	5,663
Commitments and Contingencies (Notes 2, 9, and 14)
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	3,647	3,111
Total shareholders' equity	6,963	6,427
TOTAL LIABILITIES AND EQUITY	20,606	19,506
Ameren Missouri \| Nonrelated Party
Current Assets:
Accounts receivable - trade (less allowance for doubtful accounts)	204	244
Current Liabilities:
Short-term debt	170	329
Accounts and wages payable	618	606
Ameren Missouri \| Related Party
Current Assets:
Accounts receivable - trade (less allowance for doubtful accounts)	72	51
Current Liabilities:
Short-term debt	306	0
Accounts and wages payable	$ 53	$ 43

Consolidated Balance Sheet - AIC (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Accounts receivable - trade, allowance for doubtful accounts	$ 30	$ 31
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	400,000,000.0	400,000,000.0
Common Stock, Shares, Outstanding	266,300,000	262,000,000.0
Ameren Illinois
Accounts receivable - trade, allowance for doubtful accounts	$ 18	$ 18
Common Stock, No Par Value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized	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	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash Flows From Operating Activities:
Net income	$ 1,157	$ 1,079	$ 995
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	1,432	1,373	1,219
Amortization of nuclear fuel	68	65	58
Amortization of debt issuance costs and premium/discounts	16	21	23
Deferred income taxes and investment tax credits, net	229	170	156
Allowance for equity funds used during construction	(54)	(43)	(43)
Stock-based compensation costs	26	24	22
Other	16	68	19
Changes in assets and liabilities:
Receivables	144	(317)	(74)
Inventories	(67)	(77)	(71)
Accounts and wages payable	(104)	136	28
Taxes accrued	(4)	(13)	1
Regulatory assets and liabilities	(165)	(72)	(439)
Assets, other	(109)	(74)	(71)
Liabilities, other	115	52	(75)
Pension and other postretirement benefits	(283)	(65)	(33)
Counterparty collateral, net	147	(64)	(54)
Net cash provided by operating activities	2,564	2,263	1,661
Cash Flows From Investing Activities:
Capital expenditures	(3,597)	(3,351)	(3,479)
Nuclear fuel expenditures	(174)	(29)	(44)
Purchases of securities – nuclear decommissioning trust fund	(266)	(229)	(452)
Proceeds from sales and maturities	240	216	439
Other	(1)	23	8
Net cash used in investing activities	(3,798)	(3,370)	(3,528)
Cash Flows From Financing Activities:
Dividends on common stock	(662)	(610)	(565)
Dividends paid to noncontrolling interest holders	(5)	(5)	(5)
Short-term debt, net	(533)	522	55
Maturities of long-term debt	(100)	(505)	(8)
Issuances of long-term debt	2,295	1,467	1,997
Issuances of common stock	346	333	308
Redemptions of Ameren Illinois preferred stock	0	0	(13)
Employee payroll taxes related to stock-based compensation	(20)	(16)	(17)
Debt issuance costs	(21)	(18)	(18)
Other	(10)	0	(13)
Net cash provided by financing activities	1,290	1,168	1,721
Net change in cash, cash equivalents, and restricted cash	56	61	(146)
Cash, cash equivalents, and restricted cash at beginning of year	216	155	301
Cash Paid (Refunded) During the Year:
Interest (net of amounts capitalized, respectively)	546	476	426
Income Taxes Paid, Net	(24)	(8)	(1)
Ameren Missouri
Cash Flows From Operating Activities:
Net income	548	565	521
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	827	816	704
Amortization of nuclear fuel	68	65	58
Amortization of debt issuance costs and premium/discounts	7	7	6
Deferred income taxes and investment tax credits, net	28	21	3
Allowance for equity funds used during construction	(30)	(24)	(26)
Other	(8)	14	19
Changes in assets and liabilities:
Receivables	39	(68)	(60)
Inventories	(74)	(15)	(32)
Accounts and wages payable	(8)	19	28
Taxes accrued	(17)	(21)	(27)
Regulatory assets and liabilities	(7)	(206)	(207)
Assets, other	(25)	1	28
Liabilities, other	3	7	(29)
Pension and other postretirement benefits	(106)	(16)	(2)
Counterparty collateral, net	96	(35)	(55)
Net cash provided by operating activities	1,341	1,130	929
Cash Flows From Investing Activities:
Capital expenditures	(1,760)	(1,690)	(2,015)
Nuclear fuel expenditures	(174)	(29)	(44)
Purchases of securities – nuclear decommissioning trust fund	(266)	(229)	(452)
Proceeds from sales and maturities	240	216	439
Money pool advances, net	0	0	139
Other	0	29	11
Net cash used in investing activities	(1,960)	(1,703)	(1,922)
Cash Flows From Financing Activities:
Dividends on common stock	(9)	(46)	(24)
Dividends on preferred stock	(3)	(3)	(3)
Short-term debt, net	(159)	164	165
Money pool borrowings, net	306	0	0
Maturities of long-term debt	0	(55)	(8)
Issuances of long-term debt	499	524	524
Debt issuance costs	(8)	(6)	(5)
Capital contribution from parent	0	0	207
Other	(10)	0	0
Net cash provided by financing activities	616	578	856
Net change in cash, cash equivalents, and restricted cash	(3)	5	(137)
Cash, cash equivalents, and restricted cash at beginning of year	13	8	145
Cash Paid (Refunded) During the Year:
Interest (net of amounts capitalized, respectively)	225	230	205
Income Taxes Paid, Net	(19)	(20)	19
Ameren Illinois
Cash Flows From Operating Activities:
Net income	609	515	427
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	557	514	471
Amortization of debt issuance costs and premium/discounts	5	11	13
Deferred income taxes and investment tax credits, net	177	117	165
Allowance for equity funds used during construction	(19)	(18)	(17)
Other	40	29	10
Changes in assets and liabilities:
Receivables	129	(250)	(17)
Inventories	7	(62)	(40)
Accounts and wages payable	(107)	117	2
Taxes accrued	(73)	34	22
Regulatory assets and liabilities	(152)	134	(222)
Assets, other	(123)	(67)	(75)
Liabilities, other	106	42	(46)
Pension and other postretirement benefits	(112)	(39)	(32)
Counterparty collateral, net	54	(29)	1
Net cash provided by operating activities	1,098	1,048	662
Cash Flows From Investing Activities:
Capital expenditures	(1,731)	(1,601)	(1,432)
Other	(2)	(1)	(5)
Net cash used in investing activities	(1,733)	(1,602)	(1,437)
Cash Flows From Financing Activities:
Dividends on common stock	(41)	0	0
Dividends on preferred stock	(2)	(2)	(2)
Short-term debt, net	102	161	103
Money pool borrowings, net	135	0	(19)
Maturities of long-term debt	(100)	(400)	0
Issuances of long-term debt	498	848	449
Redemption of preferred stock	0	0	(13)
Debt issuance costs	(5)	(10)	(6)
Capital contribution from parent	91	15	262
Other	0	0	(13)
Net cash provided by financing activities	678	612	761
Net change in cash, cash equivalents, and restricted cash	43	58	(14)
Cash, cash equivalents, and restricted cash at beginning of year	191	133	147
Cash Paid (Refunded) During the Year:
Interest (net of amounts capitalized, respectively)	195	152	148
Income Taxes Paid, Net	$ 102	$ 23	$ (41)

Consolidated Statement Of Cash Flows (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Interest Paid, Capitalized, Investing Activities	$ 48	$ 26	$ 17
Proceeds from Income Tax Refunds	49	0	0
Ameren Missouri
Interest Paid, Capitalized, Investing Activities	27	13	10
Proceeds from Income Tax Refunds	49	0	0
Ameren Illinois
Interest Paid, Capitalized, Investing Activities	$ 17	$ 12	$ 7

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 (Loss)	Total Ameren Corporation Stockholders' Equity	Noncontrolling Interest	Ameren Missouri	Ameren Missouri Common Stock	Ameren Missouri Other Paid-In Capital	Ameren Missouri Preferred Stock Not Subject To Mandatory Redemption	Ameren Missouri Retained Earnings	Ameren Illinois	Ameren Illinois Common Stock	Ameren Illinois Other Paid-In Capital	Ameren Illinois Preferred Stock Not Subject To Mandatory Redemption	Ameren Illinois Retained Earnings
Common Stock 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 non-ATM program forward sale agreement through common shares issuance			113
Stock Issued During Period, Value, New Issues			148
Shares issued under the DRPlus and 401(k) plan			47
Stock-based compensation activity			15
Capital contribution from parent									$ 207		207			$ 262		262
Net income	$ 995								521				521	427				427
Net Income (Loss) Available to Common Stockholders, Basic	990			990
Common stock dividends				(565)									(24)					0
Preferred stock dividends													(3)					(2)
Change in deferred retirement benefit costs	14				14
Net income attributable to noncontrolling interest holders	$ (5)							5
Dividends paid to noncontrolling interest holders								(5)
Redemptions of preferred stock								(13)									(13)
Beginning of year (shares) at Dec. 31, 2020	253,300,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under non-ATM program forward sale agreement	1,600,000
Stock Issued During Period, Shares, New Issues	1,800,000
Shares issued under the DRPlus and 401(k) plan	500,000
Shares issued (in shares)	500,000
End of year (shares) at Dec. 31, 2021	257,700,000
End of year at Dec. 31, 2021	$ 9,829	$ 3	6,502	3,182	13	$ 13		129		$ 511	2,725	$ 80	2,595		$ 0	2,914	49	2,677
Stockholders' equity, end of year at Dec. 31, 2021							$ 9,700		5,911					5,640
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 2.20
Settlement of non-ATM program forward sale agreement through common shares issuance			0
Stock Issued During Period, Value, New Issues			292
Shares issued under the DRPlus and 401(k) plan			49
Stock-based compensation activity			17
Capital contribution from parent									0		0			15		15
Net income	$ 1,079								$ 565				565	$ 515				515
Net Income (Loss) Available to Common Stockholders, Basic	1,074			1,074
Common stock dividends				(610)									(46)					0
Preferred stock dividends													(3)					(2)
Change in deferred retirement benefit costs	(14)				(14)
Net income attributable to noncontrolling interest holders	$ (5)							5
Dividends paid to noncontrolling interest holders								(5)
Redemptions of preferred stock								0									0
Shares issued under non-ATM program forward sale agreement	0
Stock Issued During Period, Shares, New Issues	3,400,000
Shares issued under the DRPlus and 401(k) plan	500,000
Shares issued (in shares)	400,000
End of year (shares) at Dec. 31, 2022	262,000,000.0								102,100,000					25,500,000
End of year at Dec. 31, 2022	$ 10,637	3	6,860	3,646	(1)	(1)		129		511	2,725	80	3,111		0	2,929	49	3,190
Stockholders' equity, end of year at Dec. 31, 2022	$ 10,508						10,508		$ 6,427					$ 6,168
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 2.36
Settlement of non-ATM program forward sale agreement through common shares issuance			0
Stock Issued During Period, Value, New Issues			299
Shares issued under the DRPlus and 401(k) plan			46
Stock-based compensation activity			11
Capital contribution from parent									0		0			91		91
Net income	$ 1,157								$ 548				548	$ 609				609
Net Income (Loss) Available to Common Stockholders, Basic	1,152			1,152
Common stock dividends				(662)									(9)					(41)
Preferred stock dividends													(3)					(2)
Change in deferred retirement benefit costs	(5)				(5)
Net income attributable to noncontrolling interest holders	$ (5)							5
Dividends paid to noncontrolling interest holders								(5)
Redemptions of preferred stock								0									0
Shares issued under non-ATM program forward sale agreement	0
Stock Issued During Period, Shares, New Issues	3,200,000
Shares issued under the DRPlus and 401(k) plan	600,000
Shares issued (in shares)	500,000
End of year (shares) at Dec. 31, 2023	266,300,000								102,100,000					25,500,000
End of year at Dec. 31, 2023	$ 11,478	$ 3	$ 7,216	$ 4,136	$ (6)	$ (6)		$ 129		$ 511	$ 2,725	$ 80	$ 3,647		$ 0	$ 3,020	$ 49	$ 3,756
Stockholders' equity, end of year at Dec. 31, 2023	$ 11,349						$ 11,349		$ 6,963					$ 6,825
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 2.52

Summary Of Significant Accounting Policies	12 Months Ended
Summary Of Significant Accounting Policies	Dec. 31, 2023
Accounting Policies [Abstract]
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 also 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 Missouri was incorporated in Missouri in 1922 and is successor to a number of companies, the oldest of which was organized in 1881. It is the largest electric utility in the state of Missouri. It supplies electric and natural gas service to a 24,000-square-mile area in central and eastern Missouri, which includes the Greater St. Louis area. Ameren Missouri supplies electric service to 1.2 million customers and natural gas service to 0.1 million customers. •Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois. Ameren Illinois was incorporated in Illinois in 1923 and is the successor to a number of companies, the oldest of which was organized in 1902. Ameren Illinois supplies electric and natural gas utility service to a 43,700 square mile area in central and southern Illinois. Ameren Illinois supplies electric service to 1.2 million customers and natural gas service to 0.8 million customers. •ATXI operates a FERC rate-regulated electric transmission business in the MISO. ATXI was incorporated in Illinois in 2006. ATXI operates, among other assets, the Spoon River, Mark Twain, and Illinois Rivers transmission lines. 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 the reported amounts of revenues and expenses during the reported periods. Actual results could differ from those estimates. Regulation Our customer rates are regulated by the MoPSC, the ICC, and the FERC. We defer certain costs as assets pursuant to actions of rate regulators or because of expectations that we will be able to recover such costs in future rates charged to customers. We also defer certain amounts as liabilities pursuant to actions of rate regulators or based on the expectation that such amounts will be refunded to customers in future rates. Regulatory assets and liabilities are amortized consistent with the period of expected regulatory treatment. See Note 2 – Rate and Regulatory Matters for additional information on our regulatory frameworks, regulatory recovery mechanisms, and regulatory assets and liabilities recorded at December 31, 2023 and 2022. We continually assess the recoverability of our regulatory assets and probability of refund of our regulatory liabilities. Regulatory assets are charged to earnings when it is no longer probable that such amounts will be recovered through future revenues. To the extent that refunds to customers related to regulatory liabilities are no longer probable, the amounts are credited to earnings. Cash, Cash Equivalents, and Restricted Cash Cash and cash equivalents include short-term, highly liquid investments purchased with an original maturity of three months or less. Cash and cash equivalents subject to legal or contractual restrictions and not readily available for use for general corporate purposes are classified as restricted cash. See Note 15 – Supplemental Information for a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows. Allowance for Doubtful Accounts Receivable The allowance for doubtful accounts represents our estimate of existing accounts receivable that will ultimately be uncollectible. The allowance is calculated by applying estimated loss factors to various classes of outstanding receivables, including unbilled revenue. The loss factors used to estimate uncollectible accounts are based upon both historical collections experience and management’s estimate of future collections success given the existing and anticipated future collections environment. Ameren Illinois has bad debt riders that adjust rates for net write-offs of customer accounts receivable above or below those being collected in rates. Inventories Inventories are recorded at the lower of weighted-average cost or net realizable value. Inventories are capitalized when purchased and then expensed as consumed or capitalized as property, plant, and equipment when installed, as appropriate using the weighted-average cost method. See Note 15 – Supplemental Information for the components of inventories. Property, Plant, and Equipment, Net We capitalize the cost of additions to, and betterments of, units of property, plant, and equipment. The cost includes labor, material, applicable taxes, and overhead. An allowance for funds used during construction, as discussed below, is also capitalized as a cost of our rate-regulated assets. Maintenance expenses related to scheduled Callaway nuclear refueling and maintenance outages are deferred and amortized over the number of expected months until the completion of the next refueling outage, which historically has been approximately 18 months. Other maintenance expenditures are expensed as incurred. When units of depreciable property are retired, the original costs, and the associated removal cost, net of salvage, are charged to accumulated depreciation. If environmental expenditures are related to assets currently in use, as in the case of the installation of pollution control equipment, the cost is capitalized and depreciated over the expected life of the asset. See Asset Retirement Obligations and Removal Costs section below and Note 3 – Property, Plant, and Equipment, Net for additional information. Ameren Missouri’s cost of nuclear fuel is capitalized as a part of “Property, Plant, and Equipment, Net” on Ameren and Ameren Missouri’s balance sheets and then amortized to “Operating Expenses – Fuel” in their respective statements of income on a unit-of-production basis. Nuclear fuel amortization is reflected as a part of “Depreciation and amortization” on their respective statements of cash flow. Plant to be Abandoned, Net When it becomes probable an asset will be retired significantly in advance of its previously expected useful life and in the near term, the Ameren Companies must assess the probability of recovery of the remaining net book value of the asset to be abandoned. We recognize a loss on abandonment when it becomes probable that all or part of the cost of an asset, including a return at the applicable WACC, will be disallowed from recovery either through customer rates or through the issuance of securitized utility tariff bonds and such amount is reasonably estimable. An abandonment loss, if any, would equal the difference between the remaining net book value of the asset and the present value of the expected future cash flows. If the asset is still in service, the net book value is classified as plant to be abandoned, net, within “Property, Plant, and Equipment, Net” on the balance sheet. The net book value will be classified as a regulatory asset on the balance sheet when the asset is no longer in service or as required by a rate order. In relation to the NSR and Clean Air Act litigation discussed in Note 14 – Commitments and Contingencies, in December 2021, Ameren Missouri filed a motion with the United States District Court for the Eastern District of Missouri to modify a previously issued remedy order to allow the retirement of the Rush Island Energy Center in lieu of installing a flue gas desulfurization system, which was granted to establish an October 15, 2024 retirement date. As of December 31, 2023 and 2022, Ameren and Ameren Missouri determined that the Rush Island Energy Center met the criteria to be considered probable of abandonment and have classified its remaining net book value as plant to be abandoned, net, within “Property, Plant, and Equipment, Net” on Ameren’s and Ameren Missouri’s balance sheets. See Note 3 – Property, Plant, and Equipment, Net for our plant to be abandoned balance as of December 31, 2023 and 2022. Ameren Missouri concluded no abandonment loss was required for the Rush Island Energy Center as of December 31, 2023. As part of the assessment of any potential future abandonment loss, consideration will be given to rate and securitization orders issued by the MoPSC to Ameren Missouri and to orders issued to other Missouri utilities with similar facts. See Note 2 – Rate and Regulatory Matters for Ameren Missouri’s November 2023 petition filed with the MoPSC seeking securitization of the Rush Island Energy Center. Depreciation Depreciation is provided over the estimated lives of the various classes of depreciable property by applying composite rates on a straight-line basis to the cost basis of such property. The composite rates include a provision for the estimated removal cost of property, plant, and equipment retired from service, net of salvage. See Asset Retirement Obligation and Removal Costs section below for additional information. The provision for depreciation for the Ameren Companies in 2023, 2022, and 2021 ranged from 3% to 4% of the average depreciable cost. See Note 3 – Property, Plant, and Equipment, Net for additional information on estimated depreciable lives. Allowance for Funds Used During Construction As a part of “Property, Plant, and Equipment, Net” on the balance sheet, we capitalize allowance for funds used during construction, which is the cost of borrowed funds and the cost of equity funds (preferred and common shareholders’ equity) applicable to eligible rate-regulated construction work in progress, in accordance with the utility industry’s accounting practice and GAAP. The amount of allowance for funds used during construction is calculated using a FERC-prescribed formula based on a rate, which incorporates the average cost of short-term debt, the average cost of long-term debt, and the cost of equity funds. The portion attributable to borrowed funds is recorded as a reduction of “Interest Charges” on the statements of income. The portion attributable to equity funds is recorded within “Other Income, Net” on the statements of income. This accounting practice offsets the effect on earnings of the cost of financing during construction. See Note 15 – Supplemental Information for the amount of allowance for funds used during construction capitalized and the average rate applied to eligible construction work in progress. Allowance for funds used during construction does not represent a current source of cash funds. Under accepted ratemaking practice, cash recovery of allowance for funds used during construction and other construction costs occurs when completed projects are placed in service and reflected in customer rates. Goodwill Goodwill represents the excess of the purchase price of an acquisition over the fair value of the net assets acquired. Ameren and Ameren Illinois had goodwill of $411 million at December 31, 2023 and 2022. Ameren has four reporting units: Ameren Missouri, Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Transmission. Ameren Illinois has three reporting units: Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission. Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission had goodwill of $238 million, $80 million, and $93 million, respectively, at December 31, 2023 and 2022. The Ameren Transmission reporting unit had the same $93 million of goodwill as the Ameren Illinois Transmission reporting unit at December 31, 2023 and 2022. Ameren and Ameren Illinois evaluate goodwill for impairment in each of their reporting units as of October 31 each year, or more frequently if events occur or circumstances change that would more likely than not reduce the fair value of their reporting units below their carrying amounts. To determine whether the fair value of a reporting unit is more likely than not greater than its carrying amount, Ameren and Ameren Illinois elect to perform either a qualitative assessment or to bypass the qualitative assessment and perform a quantitative test. Ameren and Ameren Illinois elected to perform a qualitative assessment for their annual goodwill impairment test conducted as of October 31, 2023. As part of this qualitative assessment, Ameren and Ameren Illinois evaluated, among other things, macroeconomic conditions, industry and market considerations such as observable industry market multiples, regulatory frameworks, cost factors, overall financial performance, and entity-specific events. The results of Ameren’s and Ameren Illinois’ qualitative assessment indicated that it was more likely than not that the fair value of each reporting unit exceeded its carrying value as of October 31, 2023, resulting in no impairment of Ameren’s or Ameren Illinois’ goodwill. Impairment of Long-lived Assets We evaluate long-lived assets classified as held and used for impairment when events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. Whether an impairment has occurred is determined by comparing the estimated undiscounted cash flows attributable to the assets to the carrying value of the assets. If the carrying value exceeds the undiscounted cash flows, we recognize an impairment charge equal to the amount by which the carrying value exceeds the estimated fair value of the assets. In the period in which we determine that an asset meets held for sale criteria, we record an impairment charge to the extent the book value exceeds its estimated fair value less cost to sell. We did not identify any events or changes in circumstances that indicated that the carrying value of material long-lived assets may not be recoverable in 2023, 2022, or 2021. Variable Interest Entities As of December 31, 2023 and 2022, Ameren had unconsolidated variable interests in various equity method investments, primarily to advance clean and resilient energy technologies, totaling $73 million and $68 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 December 31, 2023, the maximum exposure to loss related to these variable interest entities is limited to the investment in these partnerships of $73 million plus associated outstanding funding commitments of $14 million. Environmental Costs Liabilities for environmental costs are recorded on an undiscounted basis when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated. Costs are expensed or deferred as a regulatory asset when it is expected that the costs will be recovered from customers in future rates. See Note 14 – Commitments and Contingencies for additional information on liabilities for environmental costs. Asset Retirement Obligations and Removal Costs We record the estimated fair value of legal obligations associated with the retirement of tangible long-lived assets in the period in which the liabilities are incurred and capitalize a corresponding amount as part of the book value of the related long-lived asset. In subsequent periods, we adjust AROs for accretion and changes in the estimated fair values of the obligations, with a corresponding increase or decrease in the asset book value for the fair value changes. Asset book values, reflected within “Property, Plant, and Equipment, Net” on the balance sheet, are depreciated over the remaining useful life of the related asset. Depreciation is deferred as a regulatory balance. The depreciation of the asset book values at Ameren Missouri was $9 million, $7 million, and $14 million for the years ended December 31, 2023, 2022, and 2021, respectively, which was deferred as a reduction to the net regulatory liability. The net regulatory liability also reflects a deferral for the nuclear decommissioning trust fund balance for the Callaway Energy Center. The depreciation deferred to the regulatory asset at Ameren Illinois was immaterial in each respective period. Uncertainties as to the probability, timing, or amount of cash expenditures associated with AROs affect our estimates of fair value. Ameren and Ameren Missouri have recorded AROs for retirement costs associated with decommissioning of Ameren Missouri’s Callaway and wind renewable energy centers, certain Ameren Missouri solar energy centers, CCR facilities, and river structures at certain energy centers used for unloading coal and circulating water systems. Additionally, Ameren, Ameren Missouri, and Ameren Illinois have recorded AROs for retirement costs associated with asbestos removal and the disposal of certain transformers. See Note 15 – Supplemental Information for a reconciliation of the beginning and ending carrying amounts of AROs. Estimated funds collected from customers to pay for the future removal cost of property, plant, and equipment retired from service, net of salvage, represent a cost of removal regulatory liability. See the cost of removal regulatory liability balance in Note 2 – Rate and Regulatory Matters. COLI Ameren (parent) and Ameren Illinois have COLI, 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 December 31, 2023, the cash surrender value of COLI at Ameren and Ameren Illinois was $248 million (December 31, 2022 – $246 million) and $111 million (December 31, 2022 – $118 million), respectively, while total borrowings against the policies were $104 million (December 31, 2022 – $110 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 COLI is affected by the investment performance of a separate account in which Ameren holds a beneficial interest. Operating Revenues We record revenues from contracts with customers for various electric and natural gas services, which primarily consist of retail distribution, electric transmission, and off-system arrangements. When more than one performance obligation exists in a contract, the consideration under the contract is allocated to the performance obligations based on the relative standalone selling price. Electric and natural gas retail distribution revenues are earned when the commodity is delivered to our customers. We accrue an estimate of electric and natural gas retail distribution revenues for service provided but unbilled at the end of each accounting period. Electric transmission revenues are earned as electric transmission services are provided. Off-system revenues are primarily comprised of MISO revenues and wholesale bilateral revenues. MISO revenues include the sale of electricity, capacity, and ancillary services. Wholesale bilateral revenues include the sale of electricity and capacity. MISO-related electricity and wholesale bilateral electricity revenues are earned as electricity is delivered. Capacity and ancillary service revenues are earned as services are provided. Retail distribution, electric transmission, and off-system revenues, including the underlying components described above, represent a series of goods or services that are substantially the same and have the same pattern of transfer over time to our customers. Revenues from contracts with customers are equal to the amounts billed and our estimate of electric and natural gas retail distribution services provided but unbilled at the end of each accounting period. Customers are billed at least monthly, and payments are due less than one month after goods and/or services are provided. See Note 16 – Segment Information for disaggregated revenue information. For certain regulatory recovery mechanisms that are alternative revenue programs rather than revenues from contracts with customers, we recognize revenues that have been authorized for rate recovery, are objectively determinable and probable of recovery, and are expected to be collected from customers within two years from the end of the year. Our alternative revenue programs include revenue requirement reconciliations, the MEEIA, the VBA, and the WNAR. These revenues are subsequently recognized as revenues from contracts with customers when billed, with an offset to alternative revenue program revenues. As of December 31, 2023 and 2022, our remaining performance obligations 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. Accounting for MISO Transactions MISO-related purchase and sale transactions are recorded by Ameren, Ameren Missouri, and Ameren Illinois using settlement information provided by the MISO. Ameren Missouri records these purchase and sale transactions on a net hourly position. Ameren Missouri records net purchases in a single hour in “Operating Expenses – Purchased power” and net sales in a single hour in “Operating Revenues – Electric” in its statement of income. Ameren Illinois records net purchases in “Operating Expenses – Purchased power” in its statement of income to reflect all of its MISO transactions relating to the procurement of power for its customers. On occasion, Ameren Missouri’s and Ameren Illinois’ prior-period transactions will be resettled outside the routine settlement process because of a change in the MISO’s tariff or a material interpretation thereof. In these cases, Ameren Missouri and Ameren Illinois recognize revenues and expenses associated with resettlements once the resettlement is probable and the resettlement amount can be estimated. There were no material MISO resettlements in 2023, 2022, or 2021. Stock-based Compensation Stock-based compensation cost is measured at the grant date based on the fair value of the award, net of an assumed forfeiture rate. Ameren recognizes as compensation expense the estimated fair value of stock-based compensation on a straight-line basis over the requisite vesting period. To the extent that actual forfeitures differ from estimated forfeitures, such differences are accounted for as an adjustment to compensation expense and recorded in the period that estimates are revised. Compensation cost is ultimately recognized only for awards for which the requisite service was provided. See Note 11 – Stock-based Compensation for additional information. Unamortized Debt Discounts, Premiums, and Issuance Costs Long-term debt discounts, premiums, and issuance costs are amortized over the lives of the related issuances. Credit agreement fees are amortized over the term of the agreement. Income Taxes Ameren uses an asset and liability approach for its financial accounting and reporting of income taxes. Deferred tax assets and liabilities are recognized for transactions that are treated differently for financial reporting and income tax return purposes. These deferred tax assets and liabilities are based on statutory tax rates. We expect that regulators will reduce future revenues for deferred tax liabilities that were initially recorded at rates in excess of the current statutory rate. Therefore, reductions in certain excess deferred tax liabilities that were recorded because of decreases in the statutory rate have been credited to a regulatory liability. A regulatory asset has been established to recognize the probable recovery through future customer rates of tax benefits related to the equity component of allowance for funds used during construction, as well as the effects of tax rate increases. To the extent deferred tax balances are included in rate base, the revaluation of deferred taxes is recorded as a regulatory asset or liability on the balance sheet and will be collected from, or refunded to, customers. For deferred tax balances not included in rate base, the revaluation of deferred taxes is recorded as an adjustment to income tax expense on the income statement. Ameren Missouri, Ameren Illinois, and all the other Ameren subsidiary companies are parties to a tax allocation agreement with Ameren (parent) that provides for the allocation of consolidated tax liabilities. The tax allocation agreement specifies that each subsidiary be allocated an amount of tax using a stand-alone calculation ratio to the total amount of tax owed by the consolidated group. Any net benefit attributable to Ameren (parent) is reallocated to the other subsidiaries. This reallocation is treated as a capital contribution to the subsidiary receiving the benefit. See Note 13 – Related-party Transactions for information regarding capital contributions under the tax allocation agreement.

Rate And Regulatory Matters

12 Months Ended

Dec. 31, 2023

Public Utilities, General Disclosures [Abstract]

Rate and Regulatory Matters

RATE AND REGULATORY MATTERS

Below is a summary of our regulatory frameworks and significant regulatory proceedings and related lawsuits. We are unable to predict the ultimate outcome of these matters, the timing of final decisions of the various agencies and courts, or the effect on our results of operations, financial position, or liquidity.

Regulatory Frameworks

The following table presents the regulatory frameworks and significant regulatory recovery mechanisms for each of Ameren’s rate-regulated businesses, which are discussed in more detail below:

Ameren Missouri

Ameren Illinois’ electric distribution business

Ameren Illinois’ natural gas delivery business

Ameren Illinois’ and ATXI’s electric transmission businesses

Regulatory framework

•Historical test year ratemaking

•Natural gas revenues for residential customers adjusted for sales volume deviations resulting from weather through the WNAR

•MYRP(a)

•Initial rates based on future test years

•Revenues decoupled from sales volumes

•Future test year ratemaking

•Revenues for residential and small nonresidential customers decoupled from sales volumes through the VBA

•Formula ratemaking

•Initial rates based on future test year

•Revenues decoupled from sales volumes

Regulatory mechanisms

•PISA

Riders:

•RESRAM

•FAC

•MEEIA

•PGA

•WNAR

Trackers:

•Pension and postretirement benefit costs

•Certain excess deferred income taxes

•Renewable energy standard costs

•Property taxes

•Production and investment tax credits or proceeds from the sale of certain tax credits allowed under the IRA

•Electric distribution service and energy-efficiency revenue requirement reconciliation adjustments(b)

Riders:

•Power procurement

•Transmission services

•Renewable energy credit compliance

•Zero emission credits

•Certain environmental costs

•Bad debt write-offs

•Costs of certain asbestos-related claims

Riders:

•QIP(c)

•PGA

•VBA

•Energy-efficiency program costs

•Certain environmental costs

•Bad debt write-offs

•Invested capital taxes

•Revenue requirement reconciliation adjustment

(a)Ameren Illinois used the IEIMA performance-based formula ratemaking framework to establish annual electric distribution customer rates effective through 2023. In December 2023, the ICC approved an MYRP to establish rates effective 2024 through 2027. See below for additional information regarding the MYRP approved in December 2023.

(b)Reconciliation adjustments under an MYRP are subject to a reconciliation cap which limits annual adjustment to 105%. See below for additional information regarding the reconciliation cap.

(c)The QIP expired in December 2023. Reconciliation hearings to determine the accuracy and prudence of natural gas capital investments recovered under the QIP from 2020 to 2023 are ongoing.

Missouri

The MoPSC regulates rates and other matters for Ameren Missouri’s electric service and natural gas distribution businesses. The rates Ameren Missouri charges customers for these services are established in a traditional regulatory rate review, which takes up to 11 months to complete, based on a historical test year and the revenue requirement established in the review.

Ameren Missouri has recovery mechanisms, including the RESRAM, FAC, MEEIA, PGA, and WNAR, that allow customer rates to be adjusted without a traditional regulatory rate review. These riders, along with the PISA, each described in more detail below, partially mitigate the effects of regulatory lag. Ameren Missouri also employs other recovery mechanisms, including a renewable energy standard cost tracker, as well as electric and natural gas trackers for uncertain income tax positions, certain excess deferred income taxes, property taxes, and pension and postretirement benefit costs. Each of these trackers allows Ameren Missouri to defer the difference between actual costs incurred and costs included in customer rates as a regulatory asset or regulatory liability, with the difference expected to be reflected in base rates in a subsequent MoPSC rate order. Ameren Missouri also employs a tracker for the utilization of production and investment tax credits or proceeds from the sale of such tax credits allowed under the IRA. Production and investment tax credits produced by renewable energy centers that support compliance with the state of Missouri’s renewable energy standard, such as the High Prairie Renewable and Atchison Renewable energy centers, are not eligible for tracking under this mechanism as they are included in the RESRAM. Ameren Missouri’s cost recovery under any of its recovery mechanisms is subject to MoPSC prudence reviews.

The PISA permits Ameren Missouri to defer and recover 85% of the depreciation expense for investments in qualifying property, plant, and equipment placed in service and not included in base rates. Investments not eligible for recovery under the PISA include amounts related to new nuclear and natural gas generating units and service to new customer premises. Additionally, the PISA permits Ameren Missouri to earn a return at the applicable WACC on rate base that incorporates those qualifying investments, as well as changes in total accumulated depreciation excluding retirements and plant-related deferred income taxes since the previous regulatory rate review. The regulatory asset for accumulated PISA deferrals also earns a return at the applicable WACC until added to rate base prospectively. Ameren Missouri recognizes an offset to “Interest Charges” on its consolidated statement of income for its carrying cost of debt relating to each return allowed under the PISA, with the difference between the applicable WACC and its carrying cost of debt recognized in revenues when recovery of PISA deferrals is reflected in customer rates. Approved PISA deferrals are recovered over a period of 20 years following a regulatory rate review. Additionally, under the RESRAM, Ameren Missouri is permitted to recover the 15% of depreciation expense not recovered under the PISA, and earn a return at the applicable WACC for investments in renewable generation plant placed in service to comply with Missouri’s renewable energy standard. The RESRAM deferrals are a regulatory asset until they are included in customer rates and collected in a subsequent period. Those investments not eligible for recovery under the PISA and the remaining 15% of certain property, plant, and equipment placed in service, unless eligible for recovery under the RESRAM, remain subject to regulatory lag. As a result of the PISA election, additional provisions of the law apply to Ameren Missouri, including limitations on electric customer rate increases. The rate increase approved by the June 2023 MoPSC electric rate order discussed below did not exceed the rate increase limitation applicable through 2023. Pursuant to a Missouri law that became effective in August 2022, Ameren Missouri’s PISA election was extended through December 2028 and an additional extension through December 2033 is allowed if requested by Ameren Missouri and approved by the MoPSC, among other things. This law also established a 2.5% annual limit on increases to the electric service revenue requirement used to set customer rates, compared to the revenue requirement established in the immediately preceding rate order, due to the inclusion of incremental PISA deferrals in the revenue requirement. The limitation will be effective for revenue requirements approved by the MoPSC after January 1, 2024.

The RESRAM permits Ameren Missouri to recover or refund, through customer rates, the difference between the cost of compliance, net of federal production and investment tax credits, with Missouri’s renewable energy standard and the amount set in base rates. Effective February 28, 2022, all sales from the High Prairie Renewable and Atchison Renewable energy centers are included in the RESRAM. Previously, 95% of these sales were included in the FAC and 5% were included in the RESRAM. Customer rates are adjusted for the RESRAM on an annual basis without a traditional regulatory rate review, subject to MoPSC prudence reviews. The difference between actual compliance costs and costs billed to customers in a given period is deferred as a regulatory asset or liability. The deferred amount is either billed or refunded to customers in a subsequent period. RESRAM regulatory assets earn carrying costs at short-term interest rates. The RESRAM permits Ameren Missouri to recover investments in wind generation and other renewables related to compliance with Missouri’s renewable energy standard, and earn a return at the applicable WACC on those investments not already provided for in customer rates or any other recovery mechanism, such as the renewable energy standard cost tracker. The renewable energy standard cost tracker allows Ameren Missouri to defer differences between actual costs primarily associated with the Maryland Heights Energy Center and renewable energy credits obtained through a 102-MW power purchase agreement with a wind farm operator, which expires in August 2024, and those costs included in customer rates.

The FAC permits Ameren Missouri to recover or refund, through customer rates, 95% of the variance in net energy costs from the amount set in base rates without a traditional regulatory rate review, subject to MoPSC prudence reviews, with the remaining 5% of changes retained by Ameren Missouri. As such, Ameren Missouri’s results of operations are affected by the 5% not recovered or refunded under the FAC. The 95% variance in net energy costs in a given period is deferred as a regulatory asset or liability, and either billed or refunded to customers in a subsequent period. FAC regulatory assets earn carrying costs at short-term interest rates. Ameren Missouri’s base rates for electric service are required to be reset at least every four years to allow for continued use of the FAC.

The MEEIA permits Ameren Missouri to recover customer energy-efficiency program costs, the related lost electric margins, and any performance incentive through the MEEIA without a traditional regulatory rate review, subject to MoPSC prudence reviews. MEEIA assets earn carrying costs at short-term interest rates.

Ameren Missouri is a member of the MISO, and its transmission rate is calculated in accordance with the MISO Open Access Transmission, Energy, and Operating Reserve Markets Tariff. The FERC regulates the rates charged and the terms and conditions for wholesale electric transmission service. The transmission rate update each June is based on Ameren Missouri’s actual historical cost from the prior calendar year. This rate is not directly charged to Missouri retail customers because, in Missouri, the revenue requirement used to set bundled retail base rates includes an amount for transmission-related costs and revenues.

The PGA allows Ameren Missouri to recover costs of natural gas purchased on behalf of its customers without a traditional regulatory rate review, subject to MoPSC prudence reviews. These pass-through purchased gas costs do not affect Ameren Missouri’s natural gas margins, as any change in costs is offset by a corresponding change in revenues. The difference between actual natural gas costs and costs billed to customers in a given period is deferred as a regulatory asset or liability. The deferred amount is either billed or refunded to customers in a subsequent period. PGA regulatory assets earn carrying costs at short-term interest rates. The WNAR allows Ameren Missouri to adjust natural gas delivery service rates charged to residential customers without a traditional regulatory rate review when

deviations from normal weather conditions cause natural gas revenues to vary from the related revenue requirement approved by the MoPSC in the previous regulatory rate review. The impact of deviations from normal weather on natural gas delivery service revenues billed to residential customers in a given period are deferred as a regulatory asset or liability. WNAR regulatory assets earn carrying costs at short-term interest rates. The deferred amount is either billed or refunded to residential customers in a subsequent period.

Illinois

The ICC regulates rates and other matters for Ameren Illinois’ electric distribution service and natural gas distribution businesses. Ameren Illinois used the IEIMA formula framework to establish annual customer electric distribution service rates effective through 2023. Under the framework, Ameren Illinois is allowed to reconcile its revenue requirement for customer rates established through 2023. Ameren Illinois’ 2021, 2022, and 2023 revenues reflected each year’s actual recoverable costs, year-end rate base, and a return at the applicable WACC, with the ROE component based on the annual average of the monthly yields of the 30-year United States Treasury bonds plus 580 basis points. The 2022 and 2023 revenue requirement reconciliation adjustments will be collected from customers within two years from the end of the reconciled year. By law, the decoupling provisions extend beyond 2023, which ensures that Ameren Illinois’ electric distribution revenues authorized in a regulatory rate review are not affected by changes in sales volumes. The rates Ameren Illinois charges customers for natural gas distribution service are established in a traditional regulatory rate review, which takes up to 11 months to complete, based on a future test year and the revenue requirement established in the review.

Ameren Illinois’ electric distribution service has cost recovery mechanisms in place that allow customer rates to be adjusted without an MYRP or a traditional regulatory rate review. Ameren Illinois’ electric distribution service business has riders for power procurement and transmission services incurred on behalf of its customers, renewable energy credit compliance, zero emission credits, and certain environmental costs, as well as bad debt write-offs and the costs of certain asbestos-related claims not recovered in base rates. These pass-through costs do not affect Ameren Illinois’ net income, as any change in costs is offset by a corresponding change in revenues. Ameren Illinois’ cost recovery under any of its recovery mechanisms is subject to ICC prudence reviews.

Pursuant to the CEJA, Ameren Illinois may elect to establish electric distribution service rates through either an MYRP or a traditional regulatory rate review for 2024 and beyond. See below for additional information regarding the MYRP approved by the ICC in December 2023, which established rates effective 2024 through 2027. Under the MYRP, Ameren Illinois will reconcile its actual revenue requirement, as adjusted for certain cost variations, to ICC-approved electric distribution service rates on an annual basis, subject to a reconciliation cap. The reconciliation cap limits the annual adjustment to 105% of the annual revenue requirement approved by the ICC. Certain variations from forecasted costs are excluded from the reconciliation cap, including those associated with major storms; new business and facility relocations; changes in the timing of certain expenditures or investments into or out of the applicable calendar year; and changes in interest rates, income taxes, taxes other than income taxes, pension and other post-retirement benefits costs, and amortization of certain assets. The reconciliation cap also excludes costs recovered outside of base rates through riders, such as those described above and the electric energy-efficiency rider discussed below, among others. Ameren Illinois’ existing riders remain effective and electric distribution service revenues continue to be decoupled from sales volumes under the MYRP. The actual revenue requirement for a particular year incorporates Ameren Illinois’ year-end rate base and actual capital structure for such year, provided that the resulting revenue requirement does not exceed the 105% reconciliation cap and the common equity ratio in such capital structure may not exceed that approved by the ICC in the MYRP. Subject to the reconciliation cap, if a given year’s revenue amount collected from customers varies from the approved revenue requirement, an adjustment is made to electric operating revenues with an offset to a regulatory asset or liability to reflect that year’s actual revenue requirement, independent of actual sales volumes. The regulatory balance is then collected from, or refunded to, customers within two years from the end of the applicable annual period. Regulatory assets applicable to the MYRP earn a return at the applicable WACC. However, Ameren Illinois recognizes the carrying cost of debt on these regulatory assets in revenue, instead of the applicable WACC, with the difference recognized in revenues when recovery of such regulatory assets is reflected in customer rates.

Ameren Illinois’ electric customer energy-efficiency rider provides Ameren Illinois’ electric distribution service business with recovery of, and return on, energy-efficiency investments. Under formula ratemaking for its electric energy-efficiency investments, the revenue requirements are based on recoverable costs, year-end rate base, and a year-end ratemaking capital structure, and earn a return at the applicable WACC. The ROE component of the applicable WACC is based on the annual average of the monthly yields of the 30-year United States Treasury bonds plus 580 basis points and any performance-related basis-point adjustments, described in more detail below. Therefore, Ameren Illinois’ annual ROE for its electric energy-efficiency investments is directly correlated to the yields on such bonds. Regulatory assets applicable to formula ratemaking for electric energy-efficiency investments earn a return at the applicable WACC. However, Ameren Illinois recognizes the carrying cost of debt on these regulatory assets in revenue, instead of the applicable WACC, with the difference recognized in revenues when recovery of such regulatory assets is reflected in customer rates.

Ameren Illinois’ electric distribution service business is also subject to performance metrics. Failure to achieve the metrics would result in a reduction in the company’s allowed ROE calculated under the MYRP. In 2022, the ICC issued an order approving total ROE incentives and penalties of 24 basis points under the MYRP, allocated among seven performance metrics. These performance metrics include improvements in service reliability in both the frequency and duration of outages, a reduction in peak loads, an increased percentage of

spend with diverse suppliers, a reduction in disconnections for certain customers, and improved timeliness in response to customer requests for interconnection of distributed energy resources. These performance metrics apply annually from 2024 through 2027 under the MYRP, and the impact of any incentives and penalties will be excluded from the reconciliation cap described above. In addition, the allowed ROE on energy-efficiency investments can be increased or decreased up to 200 basis points, depending on the achievement of annual energy savings goals. Any adjustments to the allowed ROE for energy-efficiency investments will depend on annual performance for a historical period relative to energy savings goals. In 2023, 2022, and 2021, there were no performance-related basis-point adjustments that materially affected financial results.

Ameren Illinois’ natural gas distribution business has recovery mechanisms, including the PGA and VBA, that allow customer rates to be adjusted without a traditional regulatory rate review. These riders, described in more detail below, mitigate the effects of regulatory lag. Ameren Illinois employs other riders for natural gas customer energy-efficiency program costs and certain environmental costs, as well as bad debt write-offs and invested capital taxes not recovered in base rates. Pass-through costs under the riders do not affect Ameren Illinois’ net income, as any change in costs is offset by a corresponding change in revenues. Ameren Illinois’ cost recovery under any of its recovery mechanisms is subject to ICC prudence reviews.

The PGA allows Ameren Illinois to recover costs of natural gas purchased on behalf of its customers without a traditional regulatory rate review, subject to ICC prudence reviews. These pass-through purchased gas costs do not affect Ameren Illinois natural gas margins, as any change in costs is offset by a corresponding change in revenues. The difference between actual natural gas costs and costs billed to customers in a given period is deferred as a regulatory asset or liability. The deferred amount is either billed or refunded to customers in a subsequent period. PGA regulatory assets earn carrying costs at short-term interest rates. The VBA ensures recoverability of the natural gas distribution service revenue requirement that is dependent on sales volumes for residential and small nonresidential customers. For these rate classes, the VBA allows Ameren Illinois to adjust natural gas distribution service rates without a traditional regulatory rate review when changes occur in sales volumes from those volumes approved by the ICC in a previous regulatory rate review. The difference between allowed sales revenues and amounts billed to customers in a given period is deferred as a regulatory asset or liability. The deferred amount is collected from, or refunded to, customers in a subsequent period. VBA regulatory assets for a given year that are not fully collected by the end of the following year begin earning carrying costs at short-term interest rates.

The QIP expired in December 2023. Previously, it provided Ameren Illinois with recovery of, and a return on, qualifying natural gas infrastructure investments that were placed in service between regulatory rate reviews. Infrastructure investments under the QIP earned a return at the applicable WACC. Eligible natural gas investments included projects to improve safety and reliability and modernization investments, such as smart meters. The deferrals were recorded as a regulatory asset, with recovery beginning two months after the qualifying natural gas plant was placed in service and continuing until such plant was included in base rates in a natural gas delivery service rate order. Ameren Illinois’ QIP was subject to a rate impact limitation of a cumulative 4% per year since the most recent delivery service rate order, with no single year exceeding 5.5%. Ameren Illinois did not exceed the rate impact limitation in 2023. Upon issuance of a natural gas delivery service rate order, QIP rate base was transferred to base rates and the QIP was reset to zero. Reconciliation hearings to determine the accuracy and prudence of natural gas capital investments recovered under the QIP are still ongoing. See below for additional information on the recovery of capital investments that were made during 2020.

Federal

The FERC regulates rates and other matters for Ameren Illinois’ transmission business and ATXI, as well as for Ameren Missouri. See the discussion above related to Ameren Missouri. Both Ameren Illinois and ATXI are members of the MISO, and their transmission rates are calculated in accordance with the MISO Open Access Transmission, Energy, and Operating Reserve Markets Tariff. Ameren Illinois and ATXI have received FERC approval to use a company-specific, forward-looking formula ratemaking framework in setting their transmission rates. These forward-looking rates are updated annually and become effective each January with forecasted information. The formula rate framework provides for an annual reconciliation of the electric transmission service revenue requirement, which reflects the actual recoverable costs incurred and the 13-month average rate base for a given year, with the revenue requirement in customer rates, including an allowed ROE. If a given year’s revenue requirement varies from the amount collected from customers, an adjustment is made to electric operating revenues with an offset to a regulatory asset or liability to reflect that year’s actual revenue requirement, independent of actual sales volumes. The regulatory balance is collected from, or refunded to, customers within two years from the end of the year. FERC revenue requirement reconciliation adjustment regulatory assets earn carrying costs at each company’s short-term interest rates. In addition, the FERC has approved transmission rate incentives, including a 50-basis-point incentive adder to the allowed base ROE for Ameren Illinois and ATXI for participation in an RTO.

Proceedings and Updates

Missouri

June 2023 MoPSC Electric Rate Order

In June 2023, the MoPSC issued an order in Ameren Missouri’s 2022 electric service regulatory rate review, approving a nonunanimous stipulation and agreement. The order resulted in an increase of $140 million to Ameren Missouri’s annual revenue requirement for electric retail service. The approved revenue requirement was based on infrastructure investments as of December 31, 2022, and included an extension of the depreciable lives of the Sioux Energy Center’s assets from 2028 to 2030. The order did not explicitly specify an ROE, capital structure, or rate base. The order provides for the continued use of the FAC and trackers for pension and postretirement benefits, uncertain income tax positions, certain excess deferred income taxes, and renewable energy standard compliance costs that the MoPSC previously authorized in earlier electric rate orders, as well as the use of an electric property tax tracker. It also includes a tracker for the utilization of production and investment tax credits or proceeds from the sale of such tax credits allowed under the IRA. Production and investment tax credits produced by renewable energy centers that support compliance with the state of Missouri’s renewable energy standard, such as the High Prairie Renewable and Atchison Renewable energy centers, are not eligible for tracking under this mechanism as they are included in the RESRAM. The order increased the annualized base level of net energy costs pursuant to the FAC by approximately $40 million from the base level established in the MoPSC’s December 2021 electric rate order. The order also changed annualized depreciation, regulatory asset and liability amortization amounts, and the base level of expenses for trackers. On an annualized basis, these changes reflect approximate increases in “Depreciation and amortization” of $90 million and “Other income, net”, of $100 million, related to non-service pension and postretirement benefit income, on Ameren’s and Ameren Missouri’s consolidated statements of income. The new rates became effective on July 9, 2023.

Solar Generation Facilities

During 2022 and 2023, Ameren Missouri, and certain subsidiaries of Ameren Missouri, entered into agreements to acquire and/or construct various solar generation facilities, which, if placed in-service, would be eligible for recovery under the PISA. The following table provides information with respect to each agreement:

Huck Finn

Solar Project(a)(b)

Boomtown

Solar Project(b)(c)

Split Rail

Solar Project(d)

Cass County

Solar Project(c)

Vandalia

Solar Project(d)

Bowling Green

Solar Project(d)

Agreement type

Build-transfer

Build-transfer(e)

Development-transfer(e)(f)

Self-build(e)(g)

Facility size

200-MW

150-MW

300-MW

150-MW

50-MW

Status of MoPSC CCN

Approved February 2023

Approved April 2023

Filed June 2023(h)

Status of FERC approval of acquisition

Received March 2023

Received October 2023

Expect to request by mid-2024

Not applicable

Earliest completion date(i)

Fourth quarter 2024

Mid-2026

Fourth quarter 2024

Fourth quarter 2025

First quarter 2026

(a)The Huck Finn Solar Project is expected to support Ameren Missouri’s compliance with the state of Missouri’s renewable energy standard. Investments in the project will be eligible for recovery under the RESRAM.

(b)These projects collectively represent approximately $0.65 billion of expected capital expenditures.

(c)The Boomtown and Cass County solar projects are expected to support Ameren Missouri’s transition to renewable energy generation and serve customers under the Renewable Solutions Program discussed below.

(d)These solar projects are expected to support Ameren Missouri’s transition to renewable energy generation.

(e)These projects, and applicable agreements, are subject to the issuance of a CCN by the MoPSC.

(f)Ameren Missouri entered into an agreement to acquire the Cass County Solar Project, which includes project design, land rights, and engineering, procurement, and construction agreements for a solar generation facility. Ameren Missouri will construct the facility after obtaining a CCN from the MoPSC and acquiring the project. Acquisition of the project is expected by mid-2024.

(g)Ameren Missouri entered into engineering, procurement, and construction agreements to construct these solar projects.

(h)In February 2024, Ameren Missouri, the MoPSC staff, and the MoOPC filed a nonunanimous stipulation and agreement requesting the MoPSC approve Ameren Missouri’s requests for CCNs for the Split Rail, Vandalia, and Bowling Green solar projects. The stipulation and agreement also requests MoPSC approval of the CCN request for the Cass County Solar Project conditioned upon the facility supporting the Renewable Solutions Program discussed below and full subscription of the portion of the program supported by this facility, subject to certain other terms and conditions. The remaining intervenors did not object to the agreement. Ameren Missouri expects a decision by the MoPSC in March 2024.

(i)Expected completion dates are dependent on the timing of regulatory approvals, among other things.

Renewable Solutions Program

The April 2023 MoPSC order approving the CCN for the Boomtown Solar Project also approved Ameren Missouri’s Renewable Solutions Program and a tariff related to participation in the program. The program allows certain commercial, industrial, and governmental customers who enroll in the program to receive up to 100% of their energy from renewable resources. Separate enrollment occurs for each

renewable resource serving customers under the program. Collection under the tariff will not begin until the Boomtown Solar Project is placed in service.

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 14 – Commitments and Contingencies. The MoPSC staff’s review includes 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. Results of the review could be used in the securitization proceeding discussed below, which could have a material adverse effect on the results of operations, financial position, and liquidity of Ameren and Ameren Missouri if Ameren Missouri is not allowed to recover Rush Island costs through securitization.

Securitization of Rush Island Energy Center Costs

In November 2023, Ameren Missouri petitioned the MoPSC for a financing order to authorize the issuance of securitized utility tariff bonds to finance $519 million of costs related to the planned accelerated retirement of the Rush Island Energy Center, which includes the expected remaining unrecovered net plant balance associated with the facility. Ameren Missouri requested to collect the amounts necessary to repay the bonds over approximately 15 years from the date of bond issuance. In February 2024, the MoPSC staff filed a response to Ameren Missouri’s petition that stated Ameren Missouri’s decision to accelerate the retirement of the Rush Island Energy Center was prudent and largely supported Ameren Missouri’s securitization request. However, the MoPSC staff claimed Ameren Missouri’s prior actions that resulted in the adverse ruling in the NSR and Clean Air Act Litigation discussed in Note 14 – Commitments and Contingencies were imprudent and recommended that the impact of those actions on customers be considered in future rate reviews. If Ameren Missouri is not allowed to recover Rush Island Energy Center costs through securitization or if future rate reviews result in revenue reductions based on Ameren Missouri’s prior actions that resulted in the adverse ruling in the NSR and Clean Air Act Litigation, it could have a material adverse effect on the results of operations, financial position, and liquidity of Ameren and Ameren Missouri. Ameren Missouri expects a decision by the MoPSC by the end of June 2024, but cannot predict the ultimate outcome of this regulatory proceeding.

MEEIA

In August 2023, the MoPSC issued an order approving a nonunanimous stipulation and agreement to extend Ameren Missouri’s MEEIA 2019 program for an additional year through 2024. For 2024, the order approved the establishment of a portfolio of customer energy-efficiency programs and performance incentives that will provide Ameren Missouri an opportunity to earn revenues, including $12 million of performance incentive revenues if Ameren Missouri achieves certain program spending goals. In 2024, Ameren Missouri expects to invest $76 million in energy-efficiency programs.

In December 2023 and 2022, Ameren Missouri achieved certain energy-efficiency spending goals for the MEEIA 2019 program. As a result of achieving these spending goals and MoPSC orders issued in August 2022 and September 2021, Ameren Missouri recognized performance incentive revenues of $12 million, $22 million, and $9 million in 2023, 2022, and 2021, respectively.

In January 2024, Ameren Missouri filed a proposed customer energy-efficiency plan with the MoPSC under the MEEIA. This filing proposed a three-year plan, which includes a portfolio of customer energy-efficiency programs, along with the continued use of the MEEIA rider, which allows Ameren Missouri to collect from, or refund to, customers any difference in actual MEEIA program costs and related lost electric margins and the amounts collected from customers. If the plan is approved, Ameren Missouri intends to invest $123 million annually in the proposed customer energy-efficiency programs from 2025 to 2027. In addition, Ameren Missouri requested performance incentives applicable to each plan year to earn revenues by achieving certain customer energy-efficiency savings and target spending goals. If 100% of the goals are achieved, Ameren Missouri would earn performance incentive revenues totaling $56 million over the three-year plan. Ameren Missouri also requested additional performance incentives applicable to each plan year totaling up to $14 million over the three-year plan, if Ameren Missouri exceeds 100% of the goals. Ameren Missouri expects a decision by the MoPSC by October 2024 but cannot predict the ultimate outcome of this regulatory proceeding.

Illinois

MYRP

In December 2023, the ICC issued an order in Ameren Illinois' MYRP proceeding, approving base rates for electric distribution services for 2024 through 2027 and rejecting Ameren Illinois' Grid Plan, which was addressed as part of the MYRP proceeding. Rate changes consistent with the order became effective in January 2024. The ICC concluded that the proposed Grid Plan did not meet certain statutory

requirements and directed Ameren Illinois to file a revised Grid Plan within three months. Ameren Illinois expects to file a revised Grid Plan with the ICC in March 2024, and also expects to file a request to update the associated MYRP revenue requirements for 2024 through 2027 in the first half of 2024. The ICC will be under no deadline to act on the revised Grid Plan when filed. The December 2023 order adopted an alternative methodology to establish a rate base and revenue requirements for the years 2024 through 2027, using the 2022 year-end rate base approved by the ICC in its 2022 electric distribution service revenue requirement reconciliation adjustment order discussed below. This rate base will remain in effect through 2027, unless subsequently changed by the ICC in the rehearing discussed below or if approval of a revised Grid Plan results in an update of each year’s revenue requirement.

In January 2024, Ameren Illinois filed a request for rehearing of the ICC's December 2023 order. The filing contended that the use of the 2022 year-end rate base for each year of the MYRP, until a revised Grid Plan is approved, is unlawful and not in compliance with the CEJA. In addition, the filing requested the ICC revise the order to include an allowed ROE of at least 9.82% for each year of the MYRP and include a base level of investments to maintain grid reliability in each year of the MYRP, among other things. In January 2024, the ICC partially denied Ameren Illinois’ rehearing request by denying Ameren Illinois’ request regarding the allowed ROE, and granting Ameren Illinois’ request to consider whether it is appropriate to use the 2022 year-end rate base for each year of the MYRP and to include a base level of investments to maintain grid reliability in each year of the MYRP. Additionally, the scope of the rehearing will include a review of certain operations and maintenance expenses in each year of the MYRP. In February 2024, Ameren Illinois filed its request in the rehearing proceeding, which proposed updated revenue requirements and annual rate base amounts to reflect a base level of investments to maintain grid reliability for 2024 through 2027. An ICC decision in this rehearing is expected by late June 2024. Also, in January 2024, Ameren Illinois filed an appeal of the December 2023 ICC order and the partial denial of Ameren Illinois’ request for rehearing to the Illinois Appellate Court for the Fifth Judicial District. The court is under no deadline to address the appeal. Ameren Illinois cannot predict the ultimate outcome of the revised Grid Plan filing, its request to update the associated MYRP revenue requirements for 2024 through 2027, the rehearing proceeding, or the appeal to the Illinois Appellate Court for the Fifth Judicial District.

The following table presents the approved revenue requirements, ROE, capital structure common equity percentage, and annual rate base in the ICC’s December 2023 order, as well as the proposed revenue requirements and annual rate base amounts in Ameren Illinois’ February 2024 rehearing request filing:


Year	Revenue Requirement (in millions)	ROE	Capital Structure Common Equity Percentage	Annual Rate Base (in billions)
ICC’s December 2023 MYRP Order:
2024	$1,162	8.72%	50%	$3.9
2025	$1,210	8.72%	50%	$3.9
2026	$1,242	8.72%	50%	$3.9
2027	$1,255	8.72%	50%	$3.9
Ameren Illinois’ February 2024 Rehearing Request Filing:
2024	$1,214	(a)	50%	$4.2
2025	$1,300	(a)	50%	$4.5
2026	$1,371	(a)	50%	$4.7
2027	$1,420	(a)	50%	$4.9

(a)The ROE is under appeal as discussed above.

The approved revenue requirements in the ICC’s December 2023 order represent a cumulative increase of $142 million compared to a cumulative increase of $444 million requested by Ameren Illinois in its revised September 2023 MYRP filing. The ICC’s December 2023 order did not utilize a phase-in provision that is permitted by the CEJA for any initial rate increase.

2022 Electric Distribution Revenue Requirement Reconciliation Adjustment Order

In November 2023, the ICC issued an order approving Ameren Illinois’ 2022 electric distribution service revenue requirement reconciliation adjustment filing. This order approved a reconciliation adjustment of $110 million, which reflected Ameren Illinois’ actual 2022 recoverable costs, year-end rate base of $3.9 billion, and a capital structure composed of 50% common equity. The approved reconciliation adjustment will be collected from customers in 2024. In addition, Ameren Illinois will file its 2023 electric distribution service revenue requirement reconciliation with the ICC by May 2024, which will reflect its 2023 year-end rate base. The 2023 reconciliation adjustment, if approved by the ICC, will be collected from customers in 2025.

Electric Customer Energy-Efficiency Investments

In November 2023, the ICC issued an order in Ameren Illinois’ annual update filing that approved electric customer energy-efficiency rates of $100 million beginning in January 2024, which represents an increase of $24 million from 2023 rates. The order was based on a projected 2024 year-end rate base of $394 million.

2023 Natural Gas Delivery Service Rate Order

In November 2023, the ICC issued an order in Ameren Illinois’ January 2023 natural gas delivery service regulatory rate review, which resulted in an increase to its annual revenues for natural gas delivery service of $112 million based on a 9.44% allowed ROE, a capital structure composed of 50% common equity, and a rate base of approximately $2.85 billion. The order reflected a reduction of approximately $93 million of planned distribution and transmission capital investments included in Ameren Illinois’ requested revenue increase, which used a 2024 future test year. The new rates became effective on November 28, 2023.

In December 2023, Ameren Illinois filed a request for rehearing of the ICC's November 2023 order. The filing requested the ICC revise the order to include an allowed ROE of at least 9.89%, a capital structure composed of 52% common equity, and a reversal of the approximately $93 million reduction of planned distribution and transmission capital investments included in the order, among other things. In January 2024, the ICC denied Ameren Illinois’ rehearing request. Subsequently, in January 2024, Ameren Illinois filed an appeal of the November 2023 ICC order and the January 2024 ICC denial of Ameren Illinois’ request for rehearing to the Illinois Appellate Court for the Fifth Judicial District. The court is under no deadline to address the appeal. Ameren Illinois cannot predict the ultimate outcome of this appeal.

The ICC’s November 2023 natural gas delivery service rate order also required Ameren Illinois to submit a plan outlining how it expects to comply with new PHMSA rules for natural gas transmission pipelines, including proposing a capital expenditures plan necessary to meet the new rules. In February 2024, Ameren Illinois filed its plan with the ICC, which included its proposal of natural gas transmission capital expenditures necessary to achieve compliance with the PHMSA rules. The plan includes delays to certain natural gas transmission capital expenditures from 2024 to subsequent years to align with the November 2023 ICC order. The ICC is under no obligation to issue an order regarding Ameren Illinois’ plan.

Future of Gas Proceeding

The ICC’s November 2023 natural gas delivery service rate order discussed above directed the ICC staff to develop a plan for a future of gas proceeding. All of the Illinois natural gas utilities subject to ICC regulation will be included in this proceeding, which will explore issues involved with decarbonization of the natural gas distribution system in light of the state of Illinois’ goal of economy-wide 100% clean energy by 2050, pursuant to the CEJA. Some of the issues expected to be addressed include the mitigation of any natural gas distribution stranded assets, the role of energy efficiency in decarbonization, and the associated impacts of natural gas decarbonization to the electric distribution system, among others.

QIP Reconciliation Hearing

In March 2021, 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 2020. In October 2023, the Illinois Attorney General’s office challenged the recovery of capital investments that were made during 2020, alleging that the ICC should disallow approximately $53 million in natural gas capital investments as improper and imprudent, providing a potential over-recovery of approximately $3 million in 2020. In October 2023, the ICC staff filed testimony that supports the prudence and reasonableness of the capital investments made during 2020. Ameren Illinois’ 2020 QIP rate recovery request under review by the ICC was within the rate increase limitations allowed by law. The ICC is under no deadline to issue an order in this proceeding. Ameren Illinois cannot predict the ultimate outcome of this regulatory proceeding.

RTO Cost-Benefit Study

In July 2022, an Illinois law prohibiting the state’s oversight of certain electric utilities’ choice of RTO membership ceased to be effective. Given the change in law and the high prices resulting from the MISO’s April 2022 capacity auction, the ICC issued an order requiring Ameren Illinois to perform a cost-benefit study of continued participation in the MISO compared to participation in PJM Interconnection LLC, another RTO. In July 2023, Ameren Illinois filed its cost-benefit study with the ICC. The cost-benefit study examined the impacts of participation in each RTO, including reliability, resiliency, affordability, and environmental impacts, among other things, for a period of five to 10 years beginning June 2024. The study concluded that continued participation in the MISO was prudent and more cost-beneficial than participation in PJM Interconnection LLC. Intervenor comments on the study were filed in October 2023 and reply comments were filed in November 2023. In January 2024, the ICC staff submitted a report recommending the ICC not take any action with regard to changing Ameren Illinois’ RTO membership. The ICC is under no obligation to issue an order related to the cost-benefit study.

MISO Long-Range Transmission Projects CCN

In February 2024, Ameren Illinois and ATXI filed a request for a CCN with the ICC related to the portion of the MISO long-range transmission projects discussed below that are expected to be constructed within the ICC’s jurisdiction. A decision by the ICC is expected by February 2025.

Federal

MISO Transmission Rate Incentives

In July 2022, the MISO approved the first tranche of projects related to a preliminary long-range transmission planning roadmap of projects through 2039. A portion of these projects were assigned to various utilities, including Ameren. The projects assigned to Ameren are estimated to cost approximately $1.8 billion, based on the MISO’s cost estimate. In October 2023, the FERC issued an order that approved transmission rate incentives relating to the projects assigned to Ameren. The incentives will allow construction work in progress to be included in rate base for projects constructed by ATXI, thereby improving the timeliness of cash recovery, and would allow recovery of prudently incurred costs, subject to FERC approval, for any portion of the projects if they are abandoned for reasons beyond the control of Ameren. As a result of the order, ATXI will not capitalize allowance for funds used during construction on the related projects.

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. Ameren and Ameren Illinois paid these refunds, including interest, by March 31, 2022. In June and July 2020, Ameren Missouri, Ameren Illinois, and ATXI, as well as various customers, petitioned the United States Court of Appeals for the District of Columbia Circuit for review of the May 2020 order, challenging certain aspects of the new ROE methodology established. The petition filed by Ameren Missouri, Ameren Illinois, and ATXI challenged the refunds required for the period from September 2016 to May 2020. In August 2022, the court issued a ruling that granted the customers’ petition for review, vacated the FERC’s previous MISO ROE-determining orders, and remanded the proceedings to the FERC. The court elected not to rule on the issues raised by Ameren Missouri, Ameren Illinois, and ATXI. The currently allowed base ROE of 10.02% will remain effective for customer billings, but the transmission rates charged during previous periods and the currently effective rates may be subject to refund if the base ROE is changed by the FERC in a future order. The FERC is under no deadline to issue an order related to these proceedings. A 50-basis-point change in the FERC-allowed ROE would affect Ameren’s and Ameren Illinois’ annual revenue by an estimated $21 million and $15 million, respectively, based on each company’s 2024 projected rate base.

Regulatory Assets and Liabilities

The following table presents our regulatory assets and regulatory liabilities at December 31, 2023 and 2022:


	2023						2022
	Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois		Ameren
Regulatory assets:
Under-recovered FAC(a)	$	72	$	—	$	72	$	140	$	—	$	140
Under-recovered Illinois electric power costs(b)	—		10		10		—		33		33
Under-recovered PGA(b)(c)	6		—		6		23		—		23
MTM derivative losses(d)	25		143		168		68		68		136

IEIMA revenue requirement reconciliation adjustment(e)(f)	—		239		239		—		134		134
FERC revenue requirement reconciliation adjustment(g)	—		25		54		—		11		33
Under-recovered VBA(h)	—		49		49		—		—		—

Income taxes(i)	126		78		207		111		72		185


Bad debt rider(j)	—		43		43		—		5		5

Callaway refueling and maintenance outage costs(k)	37		—		37		33		—		33
Unamortized loss on reacquired debt(l)	45		5		50		47		7		54
Environmental cost riders(m)	—		50		50		—		64		64
Storm costs(f)(n)	—		27		27		—		14		14




Allowance for funds used during construction for pollution control equipment(f)(o)	10		—		10		11		—		11
Customer generation rebate program(f)(p)	—		54		54		—		50		50


PISA(f)(q)	386		—		386		320		—		320
RESRAM(r)	48		—		48		6		—		6
Certain Meramec Energy Center costs(s)	39		—		39		51		—		51
FEJA energy-efficiency rider(f)(t)	—		500		500		—		416		416
Property tax tracker(u)	13		—		13		3		—		3
Other	49		64		113		35		34		69
Total regulatory assets	$	856	$	1,287	$	2,175	$	848	$	908	$	1,780
Less: current regulatory assets	(101)		(252)		(365)		(254)		(87)		(354)
Noncurrent regulatory assets	$	755	$	1,035	$	1,810	$	594	$	821	$	1,426
Regulatory liabilities:

Over-recovered Illinois electric power costs(b)	—		36		36		—		—		—
Over-recovered PGA(b)	7		33		40		—		10		10

MTM derivative gains(d)	19		3		22		51		40		91





Income taxes(i)	999		724		1,809		1,095		749		1,931



Cost of removal(v)	1,098		1,038		2,186		1,064		989		2,091
AROs(w)	524		—		524		365		—		365

Bad debt rider(j)	—		7		7		—		21		21
Pension and postretirement benefit costs(x)	202		144		346		242		162		404
Pension and postretirement benefit costs tracker(y)	111		—		111		60		—		60


Renewable energy credits and zero emission credits(z)	—		489		489		—		373		373



Other	14		15		29		64		33		99
Total regulatory liabilities	$	2,974	$	2,489	$	5,599	$	2,941	$	2,377	$	5,445
Less: current regulatory liabilities	(15)		(71)		(87)		(70)		(64)		(136)
Noncurrent regulatory liabilities	$	2,959	$	2,418	$	5,512	$	2,871	$	2,313	$	5,309

(a)Under-recovered fuel and purchased power costs to be recovered through the FAC. Specific accumulation periods aggregate the under-recovered costs over four months, any related adjustments that occur over the following four months, and the recovery from customers that occurs over the next eight months.

(b)Under-recovered or over-recovered costs from utility customers. Amounts will be recovered from, or refunded to, customers within one year of the deferral.

(c)As a result of the significant increase in customer demand and prices for natural gas and electricity experienced in mid-February 2021 due to extremely cold weather, for the month of February 2021, Ameren Missouri had under-recovered costs under its PGA clause of $53 million. Pursuant to an October 2021 MoPSC order, the collection period for Ameren Missouri’s cumulative PGA under-recovery as of August 2021, which included the February 2021 under-recovery, was extended from 12 months to 36 months, beginning November 2021.

(d)Deferral of commodity-related derivative MTM losses or gains. See Note 7 – Derivative Financial Instruments for additional information.

(e)The difference between Ameren Illinois’ electric distribution service annual revenue requirement calculated under the IEIMA performance-based formula ratemaking framework and the revenue requirement included in customer rates for that year. The under-recovery will be recovered from customers with a return at the applicable WACC within two years.

(f)These assets earn a return at the applicable WACC.

(g)Ameren Illinois’ and ATXI’s annual revenue requirement reconciliation calculated pursuant to the FERC’s electric transmission formula ratemaking framework. Any under-recovery or over-recovery will be recovered from, or refunded to, customers within two years.

(h)Under-recovered natural gas revenue caused by sales volume deviations from weather normalized sales approved by the ICC in rate regulatory reviews. Each year’s amount will be recovered from customers from April through December of the following year.

(i)The regulatory assets represent amounts that will be recovered from customers for deferred income taxes related to the equity component of allowance for funds used during construction and the effects of tax rate increases. The regulatory liabilities represent amounts that will be refunded to customers for excess deferred income taxes related to depreciation differences, other tax liabilities, and the unamortized portion of investment tax credits all recorded at rates in excess of current statutory rates. Amounts associated with the equity component of allowance for funds used during construction and the unamortized portion of investment tax credits will be amortized over the expected life of the related assets. For net regulatory liabilities related to deferred income taxes recorded at rates other than the current statutory rate, the weighted-average remaining amortization periods at Ameren, Ameren Missouri, and Ameren Illinois are 36, 28, and 43 years.

(j)A rider for the difference between the level of bad debt write-offs, net of any subsequent recoveries, incurred by Ameren Illinois and the level of such costs included in electric distribution and natural gas delivery service rates. Under-recovered or over-recovered costs for each year are collected from, or refunded to, customers over a twelve-month period beginning in June of the following year.

(k)Maintenance expenses related to scheduled refueling and maintenance outages at Ameren Missouri’s Callaway Energy Center. Amounts are amortized over the period between refueling and maintenance outages, which has historically been approximately 18 months.

(l)Losses related to reacquired debt. These amounts are being amortized over the lives of the related new debt issuances or the original lives of the old debt issuances if no new debt was issued.

(m)The recoverable portion of accrued environmental site liabilities that will be collected from electric and natural gas customers through ICC-approved cost recovery riders. The period of recovery will depend on the timing of remediation expenditures. See Note 14 – Commitments and Contingencies for additional information.

(n)Storm costs from 2020 through 2023 deferred in accordance with the IEIMA. These costs are being amortized over five-year periods beginning in the year the storm occurred.

(o)The MoPSC’s May 2010 electric rate order allowed Ameren Missouri to record an allowance for funds used during construction for pollution control equipment at its Sioux Energy Center until the cost of that equipment was included in customer rates beginning in 2011. These costs are being amortized over the expected life of the Sioux Energy Center, currently through 2030.

(p)Costs associated with Ameren Illinois’ customer generation rebate program. Costs are amortized over a 15-year period, beginning in the year rebates are paid.

(q)Under the PISA, Ameren Missouri is permitted to defer and recover 85% of the depreciation expense and earn a return at the applicable WACC on investments in certain property, plant, and equipment placed in service and not included in base rates. Accumulated PISA deferrals, which also earn a return at the applicable WACC, are added to rate base prospectively and amortized over a period of 20 years following a regulatory rate review.

(r)Under-recovered costs associated with Ameren Missouri’s compliance with the state of Missouri’s renewable energy standard. Under-recovered or over-recovered costs are aggregated over a twelve-month period beginning each August and are amortized over a twelve-month period beginning in February of the following year.

(s)Certain costs associated with the Meramec Energy Center, which were authorized for recovery by a December 2021 MoPSC electric rate order. These costs are being collected over five years beginning in February 2022.

(t)The electric energy-efficiency investments are being amortized over their weighted-average useful lives beginning in the period in which they were made, with current remaining amortization periods ranging from three to 12 years.

(u)A regulatory recovery mechanism for the difference between actual property taxes incurred by Ameren Missouri and the related taxes included in customer rates. The period of recovery, or refund, varies based on MoPSC approval in a regulatory rate review. Amounts accumulated through 2022 are being collected over two years beginning July 2023. The amortization period for amounts accumulated after 2022 will be determined in a future regulatory rate review.

(v)Estimated funds collected from customers to pay for the future removal cost of property, plant, and equipment when retired from service, net of salvage.

(w)The ARO regulatory liability includes the nuclear decommissioning trust fund balance ($1,150 million and $958 million at December 31, 2023 and 2022, respectively), net of recoverable removal costs for AROs ($626 million and $593 million at December 31, 2023 and 2022, respectively). See Note 1 – Summary of Significant Accounting Policies – Asset Retirement Obligations and Removal Costs.

(x)Over-recovered costs are being amortized in proportion to the recognition of prior service costs (credits) and actuarial losses (gains) attributable to Ameren’s pension plan and postretirement benefit plans. See Note 10 – Retirement Benefits for additional information.

(y)A regulatory recovery mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri and the level of such costs included in customer rates. The period of refund varies based on MoPSC approval in a regulatory rate review. For electric and natural gas related costs incurred prior to 2023 and 2022, respectively, the weighted-average remaining amortization period is three years. For electric and natural gas related costs incurred after 2023 and 2022, respectively, the amortization period will be determined in a future regulatory rate review.

(z)Funds collected for the purchase of renewable energy credits and zero emission credits through IPA procurements. The balance will be amortized as the credits are purchased. Pursuant to the CEJA, if funds collected from customers are not used to procure renewable energy credits, they would be refunded to customers pursuant to a reconciliation proceeding, the first of which was initiated in August 2023. Based on amounts collected from customers and renewable energy credit purchases under contract, the August 2023 reconciliation proceeding did not result in refunds to customers.

Property And Plant, Net

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

PROPERTY AND PLANT, NET

PROPERTY, PLANT, AND EQUIPMENT, NET

The following table presents components of “Property, plant, and equipment, net” at December 31, 2023 and 2022:


	Ameren Missouri		Ameren Illinois		Other		Ameren
2023
Property, plant, and equipment at original cost(a):
Electric generation:
Coal(b)	$	3,452	$	—	$	—	$	3,452
Natural gas	921		—		—		921
Nuclear	5,879		—		—		5,879
Renewable(c)	1,973		11		—		1,984
Electric distribution	8,638		7,820		—		16,458
Electric transmission	2,134		5,381		1,993		9,508
Natural gas	688		4,186		—		4,874
Other(d)	2,191		1,657		255		4,103
	25,876		19,055		2,248		47,179
Less: Accumulated depreciation and amortization	10,243		4,783		400		15,426
	15,633		14,272		1,848		31,753
Construction work in progress:
Nuclear fuel in progress	173		—		—		173
Other	914		360		46		1,320
Plant to be abandoned, net(e)	530		—		—		530
Property, plant, and equipment, net	$	17,250	$	14,632	$	1,894	$	33,776
2022
Property, plant, and equipment at original cost(a):
Electric generation:
Coal(b)(f)	$	3,454	$	—	$	—	$	3,454
Natural gas	961		—		—		961
Nuclear	5,725		—		—		5,725
Renewable(c)	1,957		11		—		1,968
Electric distribution	7,993		7,351		—		15,344
Electric transmission	1,884		4,617		1,815		8,316
Natural gas	640		3,883		—		4,523
Other(d)	1,904		1,395		249		3,548
	24,518		17,257		2,064		43,839
Less: Accumulated depreciation and amortization(f)	9,682		4,418		365		14,465
	14,836		12,839		1,699		29,374
Construction work in progress:
Nuclear fuel in progress	108		—		—		108
Other	598		514		86		1,198
Plant to be abandoned, net(e)	582		—		—		582
Property, plant, and equipment, net	$	16,124	$	13,353	$	1,785	$	31,262

(a)The estimated lives for each asset group are as follows: 5 to 72 years for electric generation, excluding Ameren Missouri’s hydroelectric generating assets, which have useful lives of up to 150 years; 20 to 80 years for electric distribution; 50 to 75 years for electric transmission; 20 to 80 years for natural gas; and 2 to 55 years for other.

(b)Includes $29 million of oil-fired generation at December 31, 2023 and 2022.

(c)Renewable includes hydroelectric, wind, solar, and methane gas generation facilities.

(d)Other property, plant, and equipment includes assets used to support electric and natural gas services.

(e)Represents the net book value of the Rush Island Energy Center as Ameren Missouri expects to retire the energy center significantly in advance of its previously expected useful life and in the near term. See Plant to be Abandoned, Net under Note 1 – Summary of Significant Accounting Policies, NSR and Clean Air Act Litigation under Note 14 – Commitments and Contingencies, and Securitization of the Rush Island Energy Center under Note 2 – Rate and Regulatory Matters for additional information on the planned accelerated retirement of the Rush Island Energy Center.

(f)Original cost amounts include two CTs that had related financing obligations. The financing obligation for the Peno Creek CT Energy Center was settled in December 2022, while the financing obligation for the Audrain CT Energy Center was settled in January 2023. The gross cumulative plant asset values related to outstanding financing obligations as of December 31, 2022 was $125 million and the related accumulated depreciation was $54 million. See Note 5 – Long-term Debt and Equity Financings for additional information on these agreements.

Capitalized software costs are classified within “Property, Plant, and Equipment, Net” on the balance sheet and are amortized on a straight-line basis over the expected period of benefit, ranging from 2 to 15 years, with the amortization expense included in “Depreciation and amortization” on the statement of income. Deferred cloud implementation costs are classified within “Other Assets” on the balance sheet and are amortized on a straight-line basis over the term of the associated hosting arrangement, ranging from 5 to 15 years, with the amortization expense included in “Other operations and maintenance” on the statement of income. The following table presents the amortization expense, gross carrying value, and related accumulated amortization of capitalized software and deferred cloud implementation costs by year:


	Amortization Expense						Gross Carrying Value				Accumulated Amortization
	2023		2022		2021		2023		2022		2023		2022
Capitalized software costs:
Ameren	$	212	$	159	$	125	$	1,823	$	1,443	$	(1,126)	$	(914)
Ameren Missouri	114		85		66		795		613		(453)		(339)
Ameren Illinois	92		69		53		786		601		(452)		(360)
Deferred cloud implementation costs:
Ameren	$	17	$	15	$	13	$	142	$	106	$	(51)	$	(34)
Ameren Missouri	8		7		6		63		48		(23)		(15)
Ameren Illinois	9		8		6		76		54		(26)		(17)

Annual amortization expense for capitalized software placed in service as of December 31, 2023, is estimated to be as follows:


	2024		2025		2026		2027		2028
Ameren	$	202	$	147	$	106	$	79	$	45
Ameren Missouri	106		76		52		38		22
Ameren Illinois	90		65		51		38		23

Short-Term Debt And Liquidity

12 Months Ended

Dec. 31, 2023

Line of Credit Facility [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/or, in the case of Ameren Missouri and Ameren Illinois, short-term affiliate borrowings.

Short-Term Borrowings

The Credit Agreements provide $2.6 billion of credit cumulatively through maturity in December 2027. The total facility size of the Missouri Credit Agreement and Illinois Credit Agreement is $1.4 billion and $1.2 billion, respectively. The maturity date of each Credit Agreement may be extended for two additional one-year periods upon the mutual consent of the respective borrowers and the lenders. Credit available under the agreements is provided by 21 international, national, and regional lenders, with no single lender providing more than $156 million of credit in aggregate.

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


	Missouri Credit Agreement		Illinois Credit Agreement
Ameren (parent)	$	1,000	$	700
Ameren Missouri	1,000		(a)
Ameren Illinois	(a)		1,000

(a)Not applicable.

The borrowers have the option to seek additional commitments from existing or new lenders to increase the total facility size of the Credit Agreements to a maximum of $1.7 billion for the Missouri Credit Agreement and $1.5 billion for the Illinois Credit Agreement. Ameren (parent) borrowings are due and payable no later than the maturity date of the Credit Agreements. Ameren Missouri and Ameren Illinois borrowings under the applicable Credit Agreement are due and payable no later than the earlier of the maturity date or 364 days after the date of the borrowing.

The obligations of the borrowers under the Credit Agreements are unsecured. Loans are available on a revolving basis under each of the Credit Agreements. Funds borrowed may be repaid and, subject to satisfaction of the conditions to borrowing, reborrowed from time to time. At the election of each borrower, the interest rates on such loans will be the alternate base rate plus the margin applicable to the

particular borrower and/or the eurodollar rate plus the margin applicable to the particular borrower. The applicable margins will be determined by the borrower’s long-term unsecured credit ratings or, if no such ratings are in effect, the borrower’s corporate/issuer ratings then in effect. The borrowers have received commitments from the lenders to issue letters of credit up to $100 million under each of the Credit Agreements. In addition, the issuance of letters of credit is subject to the $2.6 billion overall combined facility borrowing limitations of the Credit Agreements.

The borrowers will use the proceeds from any borrowings under the Credit Agreements for general corporate purposes, including working capital, commercial paper liquidity support, loan funding under the Ameren money pool arrangements, and other short-term affiliate loan arrangements. 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, as well as to support issuance of letters of credit for the borrowers. As of December 31, 2023, based on credit capacity available under the Credit Agreements, along with cash and cash equivalents, the net liquidity available to Ameren (parent), Ameren Missouri, and Ameren Illinois, collectively, was $2.1 billion.

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 years ended December 31, 2023 and 2022:


	Ameren (parent)			Ameren Missouri			Ameren Illinois			Ameren Consolidated
2023
Average daily amount outstanding	$	726		$	274		$	166		$	1,166
Commercial paper issuances outstanding at period-end	—			170			366			536
Weighted-average interest rate	5.38		%	5.22		%	5.23		%	5.32		%
Peak amount outstanding during period(a)	$	1,298		$	592		$	450		$	1,526
Peak interest rate	5.65		%	5.68		%	5.68		%	5.68		%
2022
Average daily amount outstanding	$	485		$	229		$	138		$	852
Commercial paper issuances outstanding at period-end	477			329			264			1,070
Weighted-average interest rate	2.41		%	1.71		%	2.79		%	2.28		%
Peak amount outstanding during period(a)	$	718		$	539		$	404		$	1,267
Peak interest rate	4.80		%	4.95		%	4.80		%	4.95		%

(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 amount for the period.

Indebtedness Provisions and Other Covenants

The information below is a summary of the Ameren Companies’ compliance with indebtedness provisions and other covenants.

The Credit Agreements contain conditions for borrowings and issuances of letters of credit. These conditions include the absence of default or unmatured default, material accuracy of representations and warranties (excluding any representation after the closing date as to the absence of material adverse change and material litigation, and the absence of any notice of violation, liability, or requirement under any environmental laws that could have a material adverse effect), and obtaining required regulatory authorizations. In addition, it is a condition for any Ameren Illinois borrowing that, at the time of and after giving effect to such borrowing, Ameren Illinois not be in violation of any limitation on its ability to incur unsecured indebtedness contained in its articles of incorporation.

The Credit Agreements also contain nonfinancial covenants, including restrictions on the ability to incur certain liens, to transact with affiliates, to dispose of assets, to make investments in or transfer assets to its affiliates, and to merge with other entities. The Credit Agreements require each of Ameren, Ameren Missouri, and Ameren Illinois to maintain consolidated indebtedness of not more than 65% of its consolidated total capitalization pursuant to a defined calculation set forth in the agreements. As of December 31, 2023, the ratios of consolidated indebtedness to total consolidated capitalization, calculated in accordance with the provisions of the Credit Agreements, were 59%, 50%, and 46%, for Ameren, Ameren Missouri, and Ameren Illinois, respectively.

The Credit Agreements contain default provisions that apply separately to each borrower. However, a default of Ameren Missouri or Ameren Illinois under the applicable credit agreement is also deemed to constitute a default of Ameren (parent) under such agreement. Defaults include a cross-default resulting from a default of such borrower under any other agreement covering outstanding indebtedness of such borrower and certain subsidiaries (other than project finance subsidiaries and nonmaterial subsidiaries) in excess of $100 million in the aggregate (including under the other credit agreement). However, under the default provisions of the Credit Agreements, any default of Ameren (parent) under either credit agreement that results solely from a default of Ameren Missouri or Ameren Illinois does not result in a

cross-default of Ameren (parent) under the other credit agreement. Further, the Credit Agreements default provisions provide that an Ameren (parent) default under either of the Credit Agreements does not constitute a default by Ameren Missouri or Ameren Illinois.

None of the Credit Agreements or financing agreements contain credit rating triggers that would cause a default or acceleration of repayment of outstanding balances. The Ameren Companies were in compliance with the provisions and covenants of the Credit Agreements at December 31, 2023.

Money Pools

Ameren (parent) has money pool agreements with and among its subsidiaries to coordinate and provide for certain short-term cash and working capital requirements.

Ameren Missouri, Ameren Illinois, and ATXI may participate in the utility money pool as both lenders and borrowers. Ameren (parent) and Ameren Services may participate in the utility money pool only as lenders. Surplus internal funds are contributed to the money pool from participants. The primary sources of external funds for the utility money pool are the Credit Agreements and the commercial paper programs. The total amount available to the pool participants from the utility money pool at any given time is reduced by the amount of borrowings made by participants, but it is increased to the extent that the pool participants advance surplus funds to the utility money pool or remit funds from other external sources. The availability of funds is also determined by funding requirement limits established by regulatory authorizations. Participants receiving a loan under the utility money pool agreement must repay the principal amount of such loan, together with accrued interest. The rate of interest depends on the composition of internal and external funds in the utility money pool. The average interest rate for borrowing under the utility money pool for the year ended December 31, 2023, was 5.29% (2022 – 1.95%).

See Note 13 – Related-party Transactions for the amount of interest income and expense from the utility money pool agreement recorded by Ameren Missouri and Ameren Illinois for the years ended December 31, 2023, 2022, and 2021.

Long-Term Debt And Equity Financings

12 Months Ended

Dec. 31, 2023

Long-Term Debt And Equity Financings [Abstract]

LONG-TERM DEBT AND EQUITY FINANCINGS

The following table presents long-term debt outstanding, including maturities due within one year, as of December 31, 2023 and 2022:


	2023		2022
Ameren (Parent):

2.50% Senior unsecured notes due 2024	$	450	$	450
3.65% Senior unsecured notes due 2026	350		350
5.70% Senior unsecured notes due 2026	600		—
1.95% Senior unsecured notes due 2027	500		500
1.75% Senior unsecured notes due 2028	450		450
5.00% Senior unsecured notes due 2029	700		—
3.50% Senior unsecured notes due 2031	800		800
Total long-term debt, gross	3,850		2,550
Less: Unamortized discount and premium	(4)		(2)
Less: Unamortized debt issuance costs	(17)		(12)
Less: Maturities due within one year	(450)		—
Long-term debt, net	$	3,379	$	2,536
Ameren Missouri:
Bonds and notes:
3.50% Senior secured notes due 2024(a)	$	350	$	350
2.95% Senior secured notes due 2027(a)	400		400
3.50% First mortgage bonds due 2029(b)	450		450
2.95% First mortgage bonds due 2030(b)	465		465
2.15% First mortgage bonds due 2032(b)	525		525
2.90% 1998 Series A bonds due 2033(c)	60		60
2.90% 1998 Series B bonds due 2033(c)	50		50
2.75% 1998 Series C bonds due 2033(c)	50		50
5.50% Senior secured notes due 2034(a)	184		184
5.30% Senior secured notes due 2037(a)	300		300
8.45% Senior secured notes due 2039(a)(d)	350		350
3.90% Senior secured notes due 2042(a)(d)	485		485
3.65% Senior secured notes due 2045(a)	400		400
4.00% First mortgage bonds due 2048(b)	425		425
3.25% First mortgage bonds due 2049(b)	330		330
2.625% First mortgage bonds due 2051(b)	550		550
3.90% First mortgage bonds due 2052(b)	525		525
5.45% First mortgage bonds due 2053(b)	500		—
Finance obligations:
Audrain County agreement (Audrain County CT) due 2023(e)	—		240
Total long-term debt, gross	6,399		6,139
Less: Unamortized discount and premium	(13)		(12)
Less: Unamortized debt issuance costs	(45)		(41)
Less: Maturities due within one year	(350)		(240)
Long-term debt, net	$	5,991	$	5,846


	2023		2022
Ameren Illinois:
Bonds and notes:
0.375% First mortgage bonds due 2023(f)	$	—	$	100
3.25% Senior secured notes due 2025(g)	300		300
6.125% Senior secured notes due 2028(g)	60		60
3.80% First mortgage bonds due 2028(f)	430		430
1.55% First mortgage bonds due 2030(f)	375		375
3.85% First mortgage bonds due 2032(f)	500		500
4.95% First mortgage bonds due 2033(f)	500		—
6.70% Senior secured notes due 2036(g)	61		61
6.70% Senior secured notes due 2036(g)	42		42
4.80% Senior secured notes due 2043(g)	280		280
4.30% Senior secured notes due 2044(g)	250		250
4.15% Senior secured notes due 2046(g)	490		490
3.70% First mortgage bonds due 2047(f)	500		500
4.50% First mortgage bonds due 2049(f)	500		500
3.25% First mortgage bonds due 2050(f)	300		300
2.90% First mortgage bonds due 2051(f)	350		350
5.90% First mortgage bonds due 2052(f)	350		350
Total long-term debt, gross	5,288		4,888
Less: Unamortized discount and premium	(9)		(9)
Less: Unamortized debt issuance costs	(47)		(44)
Less: Maturities due within one year	—		(100)
Long-term debt, net	$	5,232	$	4,735
ATXI:
2.45% Senior unsecured notes due 2036(h)	$	75	$	75
3.43% Senior unsecured notes due 2050(i)	400		400
2.96% Senior unsecured notes due 2052(j)	95		95
Total long-term debt, gross	570		570

Less: Unamortized debt issuance costs	(2)		(2)
Less: Maturities due within one year	(49)		—
Long-term debt, net	$	519	$	568
Ameren consolidated long-term debt, net	$	15,121	$	13,685

(a)These notes are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any first mortgage bonds issued under the Ameren Missouri mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the 2053 maturity of the 5.45% first mortgage bonds and the restrictions preventing a release date to occur that are attached to certain senior secured notes described in footnote (d) below, Ameren Missouri does not expect the first mortgage lien protection associated with these notes to fall away.

(b)These bonds are first mortgage bonds issued by Ameren Missouri under the Ameren Missouri bond indenture. They are secured by substantially all Ameren Missouri property and franchises.

(c)These bonds are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture and have a fall-away lien provision similar to that of Ameren Missouri’s senior secured notes.

(d)Ameren Missouri has agreed that so long as any of the 3.90% senior secured notes due 2042 are outstanding, Ameren Missouri will not permit a release date to occur, and so long as any of the 8.45% senior secured notes due 2039 are outstanding, Ameren Missouri will not optionally redeem, purchase, or otherwise retire in full the outstanding first mortgage bonds not subject to release provisions.

(e)No cash was exchanged associated with the termination of the Audrain County agreement as the $240 million principal amount of the financing obligation due from Ameren Missouri was equal to the amount of bond service payments due to Ameren Missouri. The balance of the financing obligation and the related investment in debt securities was $240 million as of December 31, 2022. The investment was recorded in “Investments in industrial development revenue bonds” as of December 31, 2022. See below for additional information on this financing obligation.

(f)These bonds are first mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture. They are secured by substantially all Ameren Illinois property and franchises.

(g)These notes are collaterally secured by first mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any first mortgage bonds issued under its mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the 2052 maturity date of the 5.90% first mortgage bonds, Ameren Illinois does not expect the first mortgage lien protection associated with these notes to fall away.

(h)The following table presents the principal maturities schedule for the 2.45% senior unsecured notes due 2036:


Payment Date		Principal Payment
November 2029	$	30
November 2036		45
Total	$	75

(i)The following table presents the principal maturities schedule for the 3.43% senior unsecured notes due 2050:


Payment Date		Principal Payment
August 2024	$	49
August 2027		50
August 2030		49
August 2032		50
August 2038		49
August 2043		77
August 2050		76
Total	$	400

(j)The following table presents the principal maturities schedule for the 2.96% senior unsecured notes due 2052:


Payment Date		Principal Payment
August 2040	$	45
August 2052		50
Total	$	95

The following table presents the aggregate maturities of long-term debt, including current maturities, at December 31, 2023:


	Ameren (parent)(a)		Ameren Missouri(a)		Ameren Illinois(a)		ATXI(a)		Ameren Consolidated(a)
2024	$	450	$	350	$	—	$	49	$	849
2025	—		—		300		—		300
2026	950		—		—		—		950
2027	500		400		—		50		950
2028	450		—		490		—		940
Thereafter	1,500		5,649		4,498		471		12,118
Total	$	3,850	$	6,399	$	5,288	$	570	$	16,107

(a)Excludes unamortized discount, premium, and debt issuance costs of $21 million, $58 million, $56 million, and $2 million at Ameren (parent), Ameren Missouri, Ameren Illinois, and ATXI, respectively.

All classes of Ameren Missouri’s and Ameren Illinois’ preferred stock are entitled to cumulative dividends, have voting rights, and are not subject to mandatory redemption. The preferred stock of Ameren’s subsidiaries is included in “Noncontrolling Interests” on Ameren’s consolidated balance sheet. The following table presents the outstanding preferred stock of Ameren Missouri and Ameren Illinois, which is redeemable at the option of the issuer, at the prices shown below as of December 31, 2023 and 2022:


	Shares Outstanding	Redemption Price (per share)			2023		2022
Ameren Missouri:
Without par value and stated value of $100 per share, 25 million shares authorized
$3.50 Series	130,000 shares	$	110.00		$	13	$	13
$3.70 Series	40,000 shares	104.75			4		4
$4.00 Series	150,000 shares	105.625			15		15
$4.30 Series	40,000 shares	105.00			4		4
$4.50 Series	213,595 shares	110.00		(a)	21		21
$4.56 Series	200,000 shares	102.47			20		20
$4.75 Series	20,000 shares	102.176			2		2
$5.50 Series A	14,000 shares	110.00			1		1
Total					$	80	$	80
Ameren Illinois:
With par value of $100 per share, 2 million shares authorized
4.00% Series	144,275 shares	$	101.00		$	14	$	14
4.08% Series	45,224 shares	103.00			5		5
4.20% Series	23,655 shares	104.00			2		2
4.25% Series	50,000 shares	102.00			5		5
4.26% Series	16,621 shares	103.00			2		2
4.42% Series	16,190 shares	103.00			2		2
4.70% Series	18,429 shares	104.30			2		2
4.90% Series	73,825 shares	102.00			7		7
4.92% Series	49,289 shares	103.50			5		5
5.16% Series	50,000 shares	102.00			5		5


Total					$	49	$	49
Total Ameren					$	129	$	129

(a)In the event of voluntary liquidation, $105.50.

Ameren has 100 million shares of $0.01 par value preferred stock authorized, with no such shares outstanding. Ameren Missouri has 7.5 million shares of $1 par value preference stock authorized, with no such shares outstanding. Ameren Illinois has 2.6 million shares of no par value preferred stock authorized, with no such shares outstanding.

Ameren

Under the DRPlus and its 401(k) plan, Ameren issued 0.6 million, 0.5 million, and 0.5 million shares of common stock in 2023, 2022, and 2021, respectively, received proceeds of $39 million, $41 million, and $47 million for the respective years, and had a receivable of $7 million and $8 million as of December 31, 2023 and 2022. In addition, Ameren issued 0.5 million, 0.4 million, and 0.5 million shares of common stock valued at $40 million, $31 million, and $33 million in 2023, 2022, 2021, respectively, for no cash consideration in connection with stock-based compensation.

In May 2023, Ameren filed a Form S-3 registration statement with the SEC, authorizing the offering of 3 million additional shares of its common stock under the DRPlus, which expires in May 2026. Shares of common stock sold under the DRPlus are, at Ameren’s option, newly issued shares, treasury shares, or shares purchased in the open market or in privately negotiated contracts.

In October 2023, Ameren, Ameren Missouri, and Ameren Illinois filed a Form S-3 shelf registration statement with the SEC, registering the issuance of an unspecified amount of certain types of securities. This registration statement expires in October 2026.

In May 2022, Ameren filed a Form S-8 registration statement with the SEC, authorizing the offering of 7.5 million additional shares of its common stock under its 401(k) plan. Shares of common stock issuable under the 401(k) plan are, at Ameren’s option, newly issued shares, treasury shares, or shares purchased in the open market or in privately negotiated contracts.

Ameren has entered into an equity distribution sales agreement pursuant to which Ameren may offer and sell from time to time up to $1.75 billion of its common stock through an ATM program, which includes the ability to enter into forward sale agreements. Under the ATM, Ameren issued 3.2 million, 3.4 million, and 1.8 million shares of common stock and received proceeds of $299 million, $292 million, and $148 million in 2023, 2022 and 2021, respectively. These proceeds were net of $3 million, $3 million and $2 million, respectively, in compensation paid to selling agents. As of December 31, 2023, Ameren had approximately $770 million of common stock available for sale under the ATM program, which takes into account the forward sale agreements in effect as of December 31, 2023, discussed below.

The forward sale agreements outstanding as of December 31, 2023, can be settled at Ameren’s discretion on or prior to dates ranging from October 3, 2024 to February 28, 2025. On a settlement date or dates, if Ameren elects to physically settle a 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 $76.69 to $89.31, with an average initial forward sale price of $80.45. Each 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 December 31, 2023, Ameren could have settled the forward sale agreements with physical delivery of 2.9 million shares of common stock to the respective counterparties in exchange for cash of $230 million. Alternatively, the forward sale agreements could have also been settled at December 31, 2023, with the counterparties delivering approximately $24 million of cash or approximately 0.3 million shares of common stock to Ameren. In connection to the forward sale agreements, the various counterparties, or their affiliates, borrowed from third parties and sold 2.9 million shares of common stock. The gross sales price of these shares totaled $232 million. Ameren has not received any proceeds from such sales of borrowed shares. The forward sale agreements have been classified as equity transactions.

In February 2021, Ameren settled the remainder of a forward sale agreement entered into in August 2019, by physically delivering 1.6 million shares of common stock for cash proceeds of $113 million. The proceeds were used to fund a portion of Ameren Missouri’s wind generation investments.

In November 2023, Ameren (parent) issued $600 million of 5.70% senior unsecured notes due December 2026, with interest payable semiannually on June 1 and December 1 of each year, beginning June 1, 2024. Net proceeds from this issuance were used to repay short-term debt.

In December 2023, Ameren (parent) issued $700 million of 5.00% senior unsecured notes due January 2029, with interest payable semiannually on January 15 and July 15 of each year, beginning July 15, 2024. Net proceeds from this issuance were used for general corporate purposes, including the repayment of short-term debt.

Ameren Missouri

In January 2024, Ameren Missouri issued $350 million of 5.25% first mortgage bonds due January 2054, with interest payable semiannually on January 15 and July 15 of each year, beginning July 15, 2024. Net proceeds from this issuance were used for capital expenditures and to repay short-term debt.

In January 2023, Ameren Missouri and Audrain County mutually agreed to terminate a financing obligation agreement related to the CT energy center in Audrain County, which was scheduled to expire in December 2023. No cash was exchanged in connection with the termination of the agreement as the $240 million principal amount of the financing obligation due from Ameren Missouri was equal to the amount of bond service payments due to Ameren Missouri. Ownership of the energy center was transferred to Ameren Missouri in January 2023, at which time the property, plant, and equipment became subject to the lien of the Ameren Missouri mortgage bond indenture.

In March 2023, Ameren Missouri issued $500 million of 5.45% first mortgage bonds due March 2053, with interest payable semiannually on March 15 and September 15 of each year, beginning September 15, 2023. Net proceeds from this issuance were used for capital expenditures and to repay short-term debt.

In April 2022, Ameren Missouri issued $525 million of 3.90% green first mortgage bonds due April 2052, with interest payable semiannually on April 1 and October 1 of each year, beginning October 1, 2022. Net proceeds from this issuance were used for capital expenditures and to repay short-term debt. Ameren Missouri intends to allocate an amount equal to the net proceeds to sustainability projects meeting certain eligibility criteria.

In November 2022, $47 million principal amount of Ameren Missouri’s 1.60% 1992 Series bonds matured and were repaid with commercial paper borrowings.

In December 2022, Ameren Missouri repaid $8 million of the remaining principal amount of the financing obligation related to the Peno Creek CT Energy Center to a trustee, which is authorized to utilize the cash only to pay equal amounts due to Ameren Missouri under related bonds issued by the city of Bowling Green and held by Ameren Missouri. The timing and amounts of payments due from Ameren Missouri under the agreement were equal to the timing and amount of bond service payments due to Ameren Missouri, resulting in no net cash flow. Under the terms of this agreement, Ameren Missouri was responsible for all operation and maintenance for the energy center. Ownership of the energy center transferred to Ameren Missouri in December 2022, at which time the property, plant, and equipment became subject to the lien of the Ameren Missouri mortgage bond indenture.

For information on Ameren Missouri’s capital contributions, refer to Capital Contributions in Note 13 – Related-party Transactions.

Ameren Illinois

In May 2023, Ameren Illinois issued $500 million of 4.95% first mortgage bonds due June 2033, with interest payable semiannually on June 1 and December 1 of each year, beginning December 1, 2023. Net proceeds from this issuance were used to repay $100 million principal amount of its 0.375% first mortgage bonds that matured in June 2023 and short-term debt.

In August 2022, Ameren Illinois issued $500 million of 3.85% first mortgage bonds due September 2032, with interest payable semiannually on March 1 and September 1 of each year, beginning March 1, 2023. Net proceeds from this issuance were used to repay $400 million principal amount of its 2.70% senior secured notes that matured in September 2022 and short-term debt.

In November 2022, Ameren Illinois issued $350 million of 5.90% first mortgage bonds due December 2052, with interest payable semiannually on June 1 and December 1 of each year, beginning June 1, 2023. Net proceeds from this issuance were used to repay short-term debt. Ameren Illinois intends to allocate an amount equal to the net proceeds to sustainability projects meeting certain eligibility criteria.

For information on Ameren Illinois’ capital contributions, refer to Capital Contributions in Note 13 – Related-party Transactions.

ATXI

In August 2022, ATXI issued $95 million of its 2.96% senior unsecured notes due 2052 pursuant to a November 2021 note purchase agreement, 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. Net proceeds from this issuance were 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 in August 2022, and to repay short-term debt.

Indenture Provisions and Other Covenants

Ameren Missouri’s and Ameren Illinois’ indentures and articles of incorporation include covenants and provisions related to issuances of first mortgage bonds and preferred stock. Ameren Missouri and Ameren Illinois are required to meet certain ratios to issue additional first mortgage bonds and preferred stock. A failure to achieve these ratios would not result in a default under these covenants and provisions but would restrict the companies’ ability to issue bonds or preferred stock. The following table summarizes the required and actual interest coverage ratios for interest charges, dividend coverage ratios, and bonds and preferred stock issuable as of December 31, 2023, at an assumed interest rate of 7% and dividend rate of 8%.

Required Interest

Coverage Ratio(a)

Actual Interest
Coverage Ratio

Bonds Issuable(b)

Required Dividend

Coverage Ratio(c)

Actual Dividend
Coverage Ratio

Preferred Stock
Issuable

Ameren Missouri

>2.0

3.3

$4,209

>2.5

160.5

$2,701

Ameren Illinois

>2.0

6.9

8,517

>1.5

3.8

203

(d)

(a)Coverage required on the annual interest charges on first mortgage bonds outstanding and to be issued. Coverage is not required in certain cases when additional first mortgage bonds are issued on the basis of retired bonds.

(b)Amount of bonds issuable based either on required coverage ratios or unfunded property additions, whichever is more restrictive. The amounts shown also include bonds issuable based on retired bond capacity of $1,959 million and $1,143 million at Ameren Missouri and Ameren Illinois, respectively.

(c)Coverage required on the annual dividend on preferred stock outstanding and to be issued, as required in the respective company’s articles of incorporation.

(d)Preferred stock issuable is restricted by the amount of preferred stock that is currently authorized by Ameren Illinois’ articles of incorporation.

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

Ameren Missouri and Ameren Illinois and certain other nonregistrant Ameren subsidiaries are subject to Section 305(a) of the Federal Power Act, which makes it unlawful for any officer or director of a public utility, as defined in the Federal Power Act, to participate in the making or paying of any dividend from any funds “properly included in capital account.” The FERC has consistently interpreted the provision to allow dividends to be paid as long as (1) the source of the dividends is clearly disclosed, (2) the dividends are not excessive, and (3) there is no self-dealing on the part of corporate officials. At a minimum, Ameren believes that dividends can be paid by its subsidiaries that are public utilities from net income and retained earnings. In addition, under Illinois law, Ameren Illinois and ATXI may not pay any dividend on their respective stock unless, among other things, their respective earnings and earned surplus are sufficient to declare and pay a dividend after provisions are made for reasonable and proper reserves, or unless Ameren Illinois or ATXI has specific authorization from the ICC.

Ameren Illinois’ articles of incorporation require dividend payments on its common stock to be based on ratios of common stock to total capitalization and other provisions related to certain operating expenses and accumulations of earned surplus. Ameren Illinois has made a commitment to the FERC to maintain a minimum 30% ratio of common stock equity to total capitalization. As of December 31, 2023, using the FERC-agreed upon calculation method, Ameren Illinois’ ratio of common stock equity to total capitalization was 53%.

ATXI’s note purchase agreements includes financial covenants that require ATXI not to permit at any time (1) debt to exceed 70% of total capitalization or (2) secured debt to exceed 10% of total assets.

At December 31, 2023, 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. In order for the Ameren Companies to issue securities in the future, they will have to comply with all applicable requirements in effect at the time of any such issuances.

Off-Balance-Sheet Arrangements

At December 31, 2023, none of the Ameren Companies had any material off-balance-sheet financing arrangements, other than their investments in 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

12 Months Ended

Dec. 31, 2023

Other Nonoperating Income (Expense) [Abstract]

OTHER INCOME AND EXPENSES

OTHER INCOME, NET

The following table presents the components of “Other Income, Net” in the Ameren Companies’ statements of income for the years ended December 31, 2023, 2022, and 2021:


	2023		2022		2021
Ameren:
Other Income, Net
Allowance for equity funds used during construction	$	54	$	43	$	43
Interest income on industrial development revenue bonds	1		24		25
Other interest income	32		11		2
Non-service cost components of net periodic benefit income(a)	295		184		136
Miscellaneous income	7		10		10
Earnings related to equity method investments	1		2		12
Donations	(24)		(26)		(9)
Miscellaneous expense	(18)		(22)		(17)
Total Other Income, Net	$	348	$	226	$	202
Ameren Missouri:
Other Income, Net
Allowance for equity funds used during construction	$	30	$	24	$	26
Interest income on industrial development revenue bonds	1		24		25
Other interest income	10		4		1
Non-service cost components of net periodic benefit income(a)	97		55		55
Miscellaneous income	3		4		3
Donations	(2)		(3)		(4)
Miscellaneous expense	(9)		(9)		(7)
Total Other Income, Net	$	130	$	99	$	99
Ameren Illinois:
Other Income, Net
Allowance for equity funds used during construction	$	19	$	18	$	17
Interest income	21		7		1
Non-service cost components of net periodic benefit income	124		84		55
Miscellaneous income	4		5		6
Donations	(4)		(8)		(5)
Miscellaneous expense	(8)		(10)		(8)
Total Other Income, Net	$	156	$	96	$	66

(a)For the years ended December 31, 2023, 2022, and 2021, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $27 million, $22 million, and $(7) 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

12 Months Ended

Dec. 31, 2023

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. See Note 8 – Fair Value Measurements for discussion of our methods of assessing the fair value of derivative instruments. Many of our physical contracts, such as our purchased power contracts, qualify for the NPNS exception to derivative accounting rules. The revenue or expense on NPNS contracts is recognized at the contract price upon physical delivery. 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 December 31, 2023 and 2022, all contracts that met the definition of a derivative and were not eligible for the NPNS exception received regulatory deferral. The cash flows from our derivative financial instruments follow the cash flow classification of the hedged item.

The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of December 31, 2023 and 2022. As of December 31, 2023, these contracts extended through October 2026, October 2029, May 2032, and March 2024 for fuel oils, natural gas, power, and uranium, respectively.


	Quantity (in millions, except as indicated)
	2023			2022
Commodity	Ameren Missouri	Ameren Illinois	Ameren	Ameren Missouri	Ameren Illinois	Ameren
Fuel oils (in gallons)	17	—	17	18	—	18
Natural gas (in mmbtu)	53	218	271	48	157	205
Power (in MWhs)	—	5	5	1	6	7
Uranium (pounds in thousands)	186	—	186	514	—	514

The following table presents the carrying value and balance sheet location of all derivative commodity contracts, none of which were designated as hedging instruments, as of December 31, 2023 and 2022:


		2023						2022
Commodity	Balance Sheet Location	Ameren Missouri		Ameren Illinois		Ameren			Ameren Missouri		Ameren Illinois		Ameren
Fuel oils	Other current assets	$	2	$	—	$	2		$	13	$	—	$	13
	Other assets	—		—		—			3		—		3

Natural gas	Other current assets	—		—		—			7		23		30
	Other assets	3		3		6			9		11		20

Power	Other current assets	5		—		5			14		2		16
	Other assets	—		—		—			—		4		4
Uranium	Other current assets	9		—		9			2		—		2
	Other assets	—		—		—			1		—		1
	Total assets	$	19	$	3	$	22		$	49	$	40	$	89

Fuel oils	Other current liabilities	$	1	$	—	$	1		$	—	$	—	$	—
	Other deferred credits and liabilities	1		—		1			—		—		—

Natural gas	Other current liabilities	12		45		57			7		20		27
	Other deferred credits and liabilities	10		30		40			2		9		11

Power	Other current liabilities	1		12		13			59		2		61
	Other deferred credits and liabilities	—		56		56			—		37		37



	Total liabilities	$	25	$	143	$	168		$	68	$	68	$	136

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 December 31, 2023 and 2022:


			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
2023
Assets:
Ameren Missouri	$	19	$	6	$	—	$	13
Ameren Illinois	3		1		—		2
Ameren	$	22	$	7	$	—	$	15
Liabilities:
Ameren Missouri	$	25	$	6	$	—	$	19
Ameren Illinois	143		1		6		136
Ameren	$	168	$	7	$	6	$	155
2022
Assets:
Ameren Missouri	$	49	$	9	$	—	$	40
Ameren Illinois	40		20		—		20
Ameren	$	89	$	29	$	—	$	60
Liabilities:
Ameren Missouri	$	68	$	9	$	56	$	3
Ameren Illinois	68		20		—		48
Ameren	$	136	$	29	$	56	$	51

(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 “Current collateral assets” and “Other assets” on the balance sheet for Ameren and Ameren Missouri and “Other current assets” and “Other assets” for Ameren Illinois.

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 December 31, 2023, if counterparty groups were to fail completely to perform on contracts, the Ameren Companies’ maximum exposure related to derivative assets, predominantly from financial institutions, would have been immaterial with or without consideration of the application of master netting arrangements or similar agreements and collateral held.

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 the 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 December 31, 2023, 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	$	24	$	—	$	19
Ameren Illinois	74		6		66
Ameren	$	98	$	6	$	85

(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

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

FAIR VALUE MEASUREMENTS

Fair value is defined as the price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. We use various methods to determine fair value, including market, income, and cost approaches. With these approaches, we adopt certain assumptions that market participants would use in pricing the asset or liability, including assumptions about market risk or the risks inherent in the inputs to the valuation. Inputs to valuation can be readily observable, market-corroborated, or unobservable. We use valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs. Authoritative accounting guidance established a fair value hierarchy that prioritizes the inputs used to measure fair value. All financial assets and liabilities carried at fair value are classified and disclosed in one of the following three hierarchy levels:

Level 1 (quoted prices in active markets for identical assets or liabilities): Inputs based on quoted prices in active markets for identical assets or liabilities. Level 1 assets and liabilities are primarily exchange-traded derivatives, cash and cash equivalents, and listed equity securities.

The market approach is used to measure the fair value of equity securities held in Ameren Missouri’s nuclear decommissioning trust fund. Equity securities in this fund are representative of the S&P 500 index, excluding securities of Ameren Corporation, owners and/or operators of nuclear power plants, and the trustee and investment managers. The S&P 500 index comprises stocks of large-capitalization companies.

Level 2 (significant other observable inputs): Market-based inputs corroborated by third-party brokers or exchanges based on transacted market data. Level 2 assets and liabilities include certain assets held in Ameren Missouri’s nuclear decommissioning trust fund, including United States Treasury and agency securities, corporate bonds and other fixed-income securities, and certain over-the-counter derivative instruments, including natural gas and financial power transactions.

Fixed income securities are valued by using prices from independent industry-recognized data vendors who provide values that are either exchange-based or matrix-based. The fair value measurements of fixed-income securities classified as Level 2 are based on inputs other than quoted prices that are observable for the asset or liability. Examples are matrix pricing, market corroborated pricing, and inputs such as yield curves and indices.

Derivative instruments classified as Level 2 are valued by corroborated observable inputs, such as pricing services or prices from similar instruments that trade in liquid markets. Our development and corroboration process entails obtaining multiple quotes or prices from outside sources. To derive our forward view to price our derivative instruments at fair value, we average the bid/ask spreads to the midpoints. Additionally, a review of all sources is performed to identify any anomalies or potential errors. Further, we consider the volume of transactions on certain trading platforms in our reasonableness assessment of the averaged midpoints. The value of natural gas derivative contracts is based upon exchange closing prices without significant unobservable adjustments. The value of power derivative contracts is based upon exchange closing prices or the use of multiple forward prices provided by third parties.

Level 3 (significant other unobservable inputs): Unobservable inputs that are not corroborated by market data. Level 3 assets and liabilities are valued by internally developed models and assumptions or methodologies that use significant unobservable inputs. Level 3 assets and liabilities include derivative instruments that trade in less liquid markets, where pricing is largely unobservable. We value Level 3 instruments by using pricing models with inputs that are often unobservable in the market, such as certain internal assumptions, quotes or prices from outside sources not supported by a liquid market, or trend rates.

We perform an analysis each quarter to determine the appropriate hierarchy level of the assets and liabilities subject to fair value measurements. Financial assets and liabilities are classified in their entirety according to the lowest level of input that is significant to the fair value measurement. All assets and liabilities whose fair value measurement is based on significant unobservable inputs are classified as Level 3.

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 2023, 2022, or 2021. At December 31, 2023 and 2022, the counterparty default risk valuation adjustment related to derivative contracts was immaterial for Ameren, Ameren Missouri, and Ameren Illinois.

The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of December 31, 2023 and 2022:


		December 31, 2023									December 31, 2022
		Level 1		Level 2		Level 3		Total			Level 1		Level 2		Level 3		Total
Assets:
Ameren Missouri
	Derivative assets – commodity contracts:
	Fuel oils	$	2	$	—	$	—	$	2		$	16	$	—	$	—	$	16
	Natural gas	—		3		—		3			1		15		—		16
	Power	—		—		5		5			—		—		14		14
	Uranium	—		—		9		9			—		—		3		3
	Total derivative assets – commodity contracts	$	2	$	3	$	14	$	19		$	17	$	15	$	17	$	49
	Nuclear decommissioning trust fund:

	Equity securities:
	U.S. large capitalization	$	787	$	—	$	—	$	787		$	618	$	—	$	—	$	618
	Debt securities:
	U.S. Treasury and agency securities	—		150		—		150			—		137		—		137
	Corporate bonds	—		136		—		136			—		122		—		122


	Other	—		68		—		68			—		70		—		70
	Total nuclear decommissioning trust fund	$	787	$	354	$	—	$	1,141	(a)	$	618	$	329	$	—	$	947	(a)
	Total Ameren Missouri	$	789	$	357	$	14	$	1,160		$	635	$	344	$	17	$	996
Ameren Illinois
	Derivative assets – commodity contracts:
	Natural gas	$	—	$	1	$	2	$	3		$	1	$	28	$	5	$	34
	Power	—		—		—		—			—		—		6		6
	Total Ameren Illinois	$	—	$	1	$	2	$	3		$	1	$	28	$	11	$	40
Ameren
	Derivative assets – commodity contracts(b)	$	2	$	4	$	16	$	22		$	18	$	43	$	28	$	89
	Nuclear decommissioning trust fund(c)	787		354		—		1,141		(a)	618		329		—		947		(a)
	Total Ameren	$	789	$	358	$	16	$	1,163		$	636	$	372	$	28	$	1,036
Liabilities:
Ameren Missouri
	Derivative liabilities – commodity contracts:
	Fuel oils	$	2	$	—	$	—	$	2		$	—	$	—	$	—	$	—
	Natural gas	$	—	$	19	$	3	$	22		$	—	$	6	$	3	$	9
	Power	—		—		1		1			57		—		2		59

	Total Ameren Missouri	$	2	$	19	$	4	$	25		$	57	$	6	$	5	$	68
Ameren Illinois
	Derivative liabilities – commodity contracts:
	Natural gas	$	4	$	60	$	11	$	75		$	—	$	19	$	10	$	29
	Power	—		—		68		68			—		—		39		39
	Total Ameren Illinois	$	4	$	60	$	79	$	143		$	—	$	19	$	49	$	68
Ameren
	Derivative liabilities – commodity contracts(b)	$	6	$	79	$	83	$	168		$	57	$	25	$	54	$	136

(a)Balance excludes $9 million and $11 million of cash and cash equivalents, receivables, payables, and accrued income, net for December 31, 2023 and 2022, respectively.

(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 Ameren’s nuclear decommissioning trust fund by investment type.

See Note 10 – Retirement Benefits for tables that set forth, by level within the fair value hierarchy, Ameren’s pension and postretirement plan assets as of December 31, 2023 and 2022.

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 years ended December 31, 2023 and 2022:


	2023						2022
	Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois		Ameren





















Beginning balance at January 1	$	12	$	(33)	$	(21)	$	(15)	$	(117)	$	(132)
Realized and unrealized gains (losses) included in regulatory assets/liabilities	1		(48)		(47)		(45)		92		47


Settlements	(9)		13		4		72		(8)		64


Ending balance at December 31	$	4	$	(68)	$	(64)	$	12	$	(33)	$	(21)
Change in unrealized gains (losses) related to assets/liabilities held at December 31	$	4	$	(36)	$	(32)	$	12	$	75	$	87

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 December 31, 2023 and 2022:


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









2023	Power(c)	$	5	$	(69)	Discounted cash flow	Average forward peak and off-peak pricing – forwards/swaps ($/MWh)	31 – 65	43

							Nodal basis ($/MWh)	(8) – (1)	(5)














































2022	Power(d)	$	20	$	(41)	Discounted cash flow	Average forward peak and off-peak pricing – forwards/swaps ($/MWh)	38 – 89	51
							Nodal basis ($/MWh)	(10) – (1)	(4)


							Trend rate (%)	0– 1	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 use visible forward prices adjusted for nodal-to-hub basis differentials.

(d)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.

The following table sets forth, by level within the fair value hierarchy, the carrying amount and fair value of financial assets and liabilities disclosed, but not carried, at fair value as of December 31, 2023 and 2022:


	Carrying Amount			Fair Value
				Level 1		Level 2		Level 3			Total
	December 31, 2023
Ameren:
Cash, cash equivalents, and restricted cash	$	272		$	272	$	—	$	—		$	272

Short-term debt	536			—		536		—			536
Long-term debt (including current portion)	15,970		(a)	—		14,366		467		(b)	14,833
Ameren Missouri:
Cash, cash equivalents, and restricted cash	$	10		$	10	$	—	$	—		$	10


Short-term debt	170			—		170		—			170
Borrowings from money pool	306			—		306		—			306
Long-term debt (including current portion)	6,341		(a)	—		5,800		—			5,800
Ameren Illinois:
Cash, cash equivalents, and restricted cash	$	234		$	234	$	—	$	—		$	234

Short-term debt	366			—		366		—			366
Borrowings from money pool	135			—		135		—			135
Long-term debt (including current portion)	5,232		(a)	—		4,867		—			4,867
	December 31, 2022
Ameren:
Cash, cash equivalents, and restricted cash	$	216		$	216	$	—	$	—		$	216
Investments in industrial development revenue bonds(c)	240			—		240		—			240
Short-term debt	1,070			—		1,070		—			1,070
Long-term debt (including current portion)(c)	14,025		(a)	—		11,989		464		(b)	12,453
Ameren Missouri:
Cash, cash equivalents, and restricted cash	$	13		$	13	$	—	$	—		$	13

Investments in industrial development revenue bonds(c)	240			—		240		—			240
Short-term debt	329			—		329		—			329

Long-term debt (including current portion)(c)	6,086		(a)	—		5,365		—			5,365
Ameren Illinois:
Cash, cash equivalents, and restricted cash	$	191		$	191	$	—	$	—		$	191

Short-term debt	264			—		264		—			264

Long-term debt (including current portion)	4,835		(a)	—		4,320		—			4,320

(a)Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $111 million, $45 million, and $47 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2023. Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $99 million, $41 million, and $44 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2022.

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

(c)Ameren and Ameren Missouri had investments in industrial development revenue bonds, classified as held-to-maturity and recorded in “Investments in industrial development revenue bonds,” as of December 31, 2022, respectively, that were equal to the finance obligation for the Audrain CT energy center. As of December 31, 2022, the carrying amount of the investments in industrial development revenue bonds and the finance obligations approximated fair value. The financing obligation for the Audrain CT Energy Center was settled in January 2023. See Note 5 – Long-term Debt and Equity Financings for additional information on these agreements.

- 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

Callaway Energy Center

12 Months Ended

Dec. 31, 2023

Nuclear Waste Matters [Abstract]

CALLAWAY ENERGY CENTER

Spent Nuclear Fuel

Under the Nuclear Waste Policy Act of 1982, as amended, the DOE is responsible for disposing of spent nuclear fuel from the Callaway Energy Center and other commercial nuclear energy centers. As required by the act, Ameren Missouri and other utilities have entered into standard contracts with the DOE, which stated that the DOE would begin to dispose of spent nuclear fuel by 1998. However, the DOE failed to fulfill its disposal obligations, and Ameren Missouri and other nuclear energy center owners sued the DOE to recover costs incurred for ongoing storage of their spent fuel. Ameren Missouri’s lawsuit against the DOE resulted in a settlement agreement that provides for annual reimbursement of additional spent fuel storage and related costs. Ameren Missouri received immaterial reimbursements from the DOE in the years ended December 31, 2023, 2022, and 2021. Ameren Missouri will continue to apply for reimbursement from the DOE for allowable costs associated with the ongoing storage of spent fuel. The DOE’s delay in carrying out its obligation to dispose of spent nuclear fuel from the Callaway Energy Center is not expected to adversely affect the continued operations of the energy center.

Decommissioning

Electric rates charged to customers provide for the recovery of the Callaway Energy Center’s decommissioning costs, which include decontamination, dismantling, and site restoration costs, over the expected life of the nuclear energy center. Amounts collected from customers are deposited into the external nuclear decommissioning trust fund to provide for the Callaway Energy Center’s decommissioning. It is assumed that the Callaway Energy Center site will be decommissioned after its retirement through the immediate dismantlement method and removed from service. The Callaway Energy Center’s operating license expires in 2044. Ameren and Ameren Missouri have recorded an ARO for the Callaway Energy Center decommissioning costs at fair value. 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 December 2023 and reflected within the ARO. Ameren Missouri’s filing supported no change in electric service rates for decommissioning costs. There is no deadline by which the MoPSC must issue an order regarding the filing.

Ameren and Ameren Missouri have classified the investments in debt and equity securities that are held in the nuclear decommissioning trust fund as available for sale, and have recorded all such investments at their fair market value at December 31, 2023 and 2022. Investments in the nuclear decommissioning trust fund have a target allocation of 60% to 70% in equity securities, with the balance invested in debt securities.

The 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 regulatory liability related to AROs. This reporting is consistent with the method used to account for the decommissioning costs recovered in rates. See Note 2 – Rate and Regulatory Matters for the regulatory liability recorded at December 31, 2023. If the assumed return on trust assets is not earned, Ameren Missouri believes that it is probable that any additional funding requirements resulting from such earnings deficiency will be recovered in customer rates.

The following table presents proceeds from the sales and maturities of investments in Ameren Missouri’s nuclear decommissioning trust fund and the gross realized gains and losses resulting from those sales for the years ended December 31, 2023, 2022, and 2021:


	2023		2022		2021
Proceeds from sales and maturities	$	240	$	216	$	439
Gross realized gains	6		40		32
Gross realized losses	11		10		6

The following table presents the cost and fair value of investments in debt and equity securities in Ameren’s and Ameren Missouri’s nuclear decommissioning trust fund at December 31, 2023 and 2022:


Security Type	Cost		Gross Unrealized Gain		Gross Unrealized Loss		Fair Value
2023
Debt securities	$	382	$	3	$	31	$	354
Equity securities	191		603		7		787
Cash and cash equivalents	5		—		—		5
Other(a)	4		—		—		4
Total	$	582	$	606	$	38	$	1,150
2022
Debt securities	$	374	$	—	$	45	$	329
Equity securities	177		455		14		618
Cash and cash equivalents	8		—		—		8
Other(a)	3		—		—		3
Total	$	562	$	455	$	59	$	958

(a)Represents net receivables and payables relating to pending securities sales, interest, and securities purchases.

The following table presents the costs and fair values of investments in debt securities in Ameren’s and Ameren Missouri’s nuclear decommissioning trust fund according to their contractual maturities at December 31, 2023:


	Cost		Fair Value
Less than 5 years	$	101	$	98
5 years to 10 years	163		156
Due after 10 years	118		100
Total	$	382	$	354

Insurance

The following table presents insurance coverage at Ameren Missouri’s Callaway Energy Center at January 1, 2024:


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, 2024	$	500		$	—
Pool participation	(a)	15,763		(a)	166		(b)
		$	16,263	(c)	$	166
Property damage:
NEIL and EMANI	April 1, 2023	$	3,200	(d)	$	28	(e)
Accidental outage:
NEIL	April 1, 2023	$	490	(f)	$	9	(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 $500 million in the event of an incident at any licensed United States commercial reactor, payable at $24.7 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 October 2023. 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

12 Months Ended

Dec. 31, 2023

Retirement Benefits [Abstract]

RETIREMENT BENEFITS

The primary objective of the Ameren pension and postretirement benefit plans is to provide eligible employees with pension and postretirement health care and life insurance benefits. Ameren has defined benefit pension plans covering substantially all of its employees and has a postretirement benefit plan covering non-union employees hired before October 2015 and union employees hired before January 2020. Ameren Missouri and Ameren Illinois each participate in Ameren’s single-employer pension and other postretirement plans. All non-union employees participate in a cash balance pension plan. Ameren Missouri union employees hired after June 2013, and Ameren Illinois union employees hired after mid-October 2012, participate in a cash balance pension plan. Ameren uses a measurement date of December 31 for its pension and postretirement benefit plans. Ameren’s qualified pension plan is the Ameren Retirement Plan. Ameren’s other postretirement plan is the Ameren Retiree Welfare Benefit Plan. Ameren also has an unfunded nonqualified pension plan, the Ameren Supplemental Retirement Plan, which is available to provide certain non-union employees and retirees with a supplemental benefit when their qualified pension plan benefits are capped in compliance with Internal Revenue Code limitations. Only Ameren subsidiaries participate in the plans listed above.

Ameren’s pension and other postretirement benefit plans were overfunded by $551 million and $377 million in the aggregate as of December 31, 2023 and 2022, respectively. These net assets are recorded in “Pension and other postretirement benefits,” “Other current liabilities,” and “Other deferred credits and liabilities” on Ameren’s consolidated balance sheet. The increase in the overfunded pension and postretirement benefit plans during 2023 was primarily the result of gains on plan assets of the pension and postretirement trusts during 2023 offset by a 30-basis-point decrease in the pension and other postretirement benefit plan discount rates used to determine the present value of the obligation. The overfunded pension and other postretirement benefit plans also resulted in regulatory liabilities on Ameren’s, Ameren Missouri’s, and Ameren Illinois’ balance sheets.

The following table presents the net benefit liability/(asset) recorded on the balance sheets as of December 31, 2023 and 2022:


	2023		2022
Ameren(a)	$	(551)	$	(377)
Ameren Missouri(a)	(142)		(84)
Ameren Illinois(a)	(351)		(263)

(a)Liabilities associated with pension and other postretirement benefits are recorded in “Other current liabilities” and “Other deferred credits and liabilities” on Ameren’s, Ameren Missouri’s, and Ameren Illinois’ balance sheets.

Ameren recognizes the overfunded and underfunded status of its pension and postretirement plans as an asset or a liability on its consolidated balance sheet, with offsetting entries to accumulated OCI and regulatory assets or liabilities. The following table presents the funded status of Ameren’s pension and postretirement benefit plans as of December 31, 2023 and 2022. It also provides the amounts included in regulatory assets or liabilities and accumulated OCI at December 31, 2023 and 2022, that have not been recognized in net periodic benefit costs.


	2023				2022
	Pension Benefits			Postretirement Benefits	Pension Benefits			Postretirement Benefits
Accumulated benefit obligation at end of year	$	4,102	$	(a)	$	3,911	$	(a)
Change in benefit obligation:
Net benefit obligation at beginning of year	$	4,061	$	838	$	5,457	$	1,129
Service cost	79			12	128			20
Interest cost	221			45	163			34

Participant contributions	—			7	—			8
Actuarial (gain) loss	170			17	(1,425)			(289)

Benefits paid	(273)			(63)	(262)			(64)


Net benefit obligation at end of year	4,258			856	4,061			838
Change in plan assets:
Fair value of plan assets at beginning of year	4,027			1,249	5,745			1,558
Actual return on plan assets	514			197	(1,461)			(255)
Employer contributions	4			3	5			2


Participant contributions	—			7	—			8


Benefits paid	(273)			(63)	(262)			(64)
Fair value of plan assets at end of year	4,272			1,393	4,027			1,249
Funded status – deficiency (surplus)	(14)			(537)	34			(411)
Accrued benefit cost (asset) at December 31	$	(14)	$	(537)	$	34	$	(411)
Amounts recognized in the balance sheet consist of:
Noncurrent asset	$	(44)	$	(537)	$	—	$	(411)
Current liability(b)	2			—	3			—
Noncurrent liability(c)	28			—	31			—
Net liability (asset) recognized	$	(14)	$	(537)	$	34	$	(411)
Amounts recognized in regulatory assets or liabilities consist of:
Net actuarial gain	$	(10)	$	(311)	$	(107)	$	(268)
Prior service credit	—			(25)	—			(29)

Amounts recognized in accumulated OCI (pretax) consist of:
Net actuarial (gain) loss	22			(4)	15			(4)

Total	$	12	$	(340)	$	(92)	$	(301)

(a)Not applicable.

(b)Included in “Other current liabilities” on Ameren’s consolidated balance sheet.

(c)Included in “Other deferred credits and liabilities” on Ameren’s consolidated balance sheet.

The following table presents the assumptions used to determine our benefit obligations at December 31, 2023 and 2022:


	Pension Benefits						Postretirement Benefits
	2023			2022			2023			2022
Discount rate at measurement date	5.25	%		5.55	%		5.25	%		5.55	%
Increase in future compensation	3.50		(a)	3.50		(a)	3.50		(a)	3.50		(a)
Cash balance pension plan interest crediting rate	5.50			5.00		(b)	(c)			(c)
Medical cost trend rate (initial)(d)	(c)			(c)			(e)			(e)
Medical cost trend rate (ultimate)(d)	(c)			(c)			5.00			5.00

(a)As of December 31, 2023, increase in future compensation is 4.00% in 2024, and 3.50% thereafter. As of December 31, 2022, increase in future compensation was 4.50% for 2023, 4.00% in 2024, and 3.50% thereafter.

(b)Cash balance pension plan interest crediting rate was 5.50% for 2023 and 2024, and 5.00% thereafter.

(c)Not applicable.

(d)Initial and ultimate medical cost trend rate for certain Medicare-eligible participants was 2.50% at December 31, 2023 and 2022.

(e)Initial medical cost trend rates of 6.93% and 7.25% for pre-Medicare plan participants and 6.50% and 6.75% for post-Medicare plan participants at December 31, 2023 and 2022, respectively, trend down to the ultimate rate by 2030, with a 3.00% upward adjustment to the post-Medicare trend rate in 2025.

Ameren determines discount rate assumptions by identifying a theoretical settlement portfolio of high-quality corporate bonds sufficient to provide for a plan’s projected benefit payments. The settlement portfolio of bonds is selected from a pool of approximately 860 high-quality corporate bonds. A single discount rate is then determined; that rate results in a discounted value of the plan’s benefit payments that equates to the market value of the selected bonds. In 2023, Ameren elected to continue to use the Society of Actuaries mortality table and the Society of Actuaries 2020 Mortality Improvement Scale.

Funding

Pension benefits are based on the employees’ years of service, age, and compensation. Ameren’s pension plans are funded in compliance with income tax regulations, federal funding requirements, and other regulatory requirements. As a result, Ameren expects to fund its pension plans at a level equal to the greater of the pension cost or the legally required minimum contribution. Based on its assumptions at December 31, 2023, its investment performance in 2023, and its pension funding policy, Ameren does not expect to make material contributions in 2024 and 2025, and expects to make aggregate contributions of $120 million in 2026 through 2028. Ameren Missouri and Ameren Illinois estimate that their portion of the future funding requirements will be 40% and 50%, respectively. These estimated contributions may change based on actual investment performance, changes in interest rates, changes in our assumptions, changes in government regulations, and any voluntary contributions. Our funding policy for postretirement benefits is primarily to fund the Voluntary Employee Beneficiary Association (VEBA) trusts to match the annual postretirement expense.

The following table presents the cash contributions made to our defined benefit retirement plans and to our postretirement plan during 2023, 2022, and 2021:


	Pension Benefits						Postretirement Benefits
	2023		2022		2021		2023		2022		2021
Ameren Missouri	$	1	$	1	$	22	$	2	$	1	$	1
Ameren Illinois	2		3		28		1		1		1
Ameren Services	1		1		10		—		—		—
Ameren	$	4	$	5	$	60	$	3	$	2	$	2

Investment Strategy and Policies

Ameren manages plan assets in accordance with the “prudent investor” guidelines contained in ERISA. The investment committee, which includes members of senior management, approves and implements investment strategy and asset allocation guidelines for the plan assets. The investment committee’s goals are twofold: first, to ensure that sufficient funds are available to provide the benefits at the time they are payable; and second, to maximize total return on plan assets and to minimize expense volatility consistent with its tolerance for risk. Ameren delegates the task of investment management to specialists in each asset class. As appropriate, Ameren provides each investment manager with guidelines that specify allowable and prohibited investment types. The investment committee regularly monitors manager performance and compliance with investment guidelines.

The expected return on plan assets assumption is based on historical and projected rates of return for current and planned asset classes in the investment portfolio. Projected rates of return for each asset class were estimated after an analysis of historical experience, future expectations, and the volatility of the various asset classes. After considering the target asset allocation for each asset class, we reviewed the overall expected rate of return for the portfolio for historical and expected experience of active portfolio management results compared with benchmark returns and for the effect of expenses paid from plan assets. Ameren will use an expected return on plan assets for its pension and postretirement plan assets of 6.75% in 2024.

Ameren’s investment committee strives to assemble a portfolio of diversified assets that does not create a significant concentration of risks. The investment committee develops asset allocation guidelines between asset classes, and it creates diversification through investments in assets that differ by type (equity, debt, real estate), duration, market capitalization, country, style (growth or value), and industry, among other factors. The diversification of assets is displayed in the target allocation table below. The investment committee also routinely rebalances the plan assets to adhere to the diversification goals. The investment committee’s strategy reduces the concentration of investment risk; however, Ameren is still subject to overall market risk.

Ameren’s investment committee developed and implemented a liability hedging investment strategy for its qualified pension plans designed to reduce interest rate risk as part of an objective for its long-term investment strategy. The plan invests in derivative instruments mainly consisting of interest rate futures intended to extend the duration of the pension plan assets so that the assets are more closely aligned with the duration of the liabilities. In addition, part of Ameren’s investment strategy includes participation in a securities lending program, which allows it to lend eligible securities to third party borrowers. All loans are collateralized by at least 103% of the loaned asset’s market value and the collateral is invested in the form of cash, government obligations, and U.S. agency obligations. Ameren’s fair value of securities loaned was $234 million and $239 million as of December 31, 2023 and 2022, respectively. Cash and securities obtained as collateral exceeded the fair value of the securities loaned as of December 31, 2023 and 2022.

The following table presents our target allocations and our pension and postretirement plans’ asset categories as of December 31, 2023 and 2022:


Asset Category	Target Allocation 2023	Percentage of Plan Assets at December 31,
		2023			2022
Pension Plan:
Cash and cash equivalents	0% – 5%	1	%		1	%
Equity securities:
U.S. large-capitalization	11% – 21%	15	%		15	%
U.S. small- and mid-capitalization	3% – 13%	8	%		8	%
Global	10% – 20%	16	%		12	%
International	6% – 16%	12	%		16	%
Total equity	45% – 55%	51	%		51	%
Debt securities	35% – 45%	35	%	(a)	35	%	(a)
Diversified credit	0% – 10%	7	%		7	%
Real estate	0% – 10%	6	%		6	%
Private equity	0% – 5%	(b)			(b)
Total		100	%		100	%
Postretirement Plans:
Cash and cash equivalents	0% – 7%	1	%		2	%
Equity securities:
U.S. large-capitalization	23% – 33%	32	%		29	%
U.S. small- and mid-capitalization	3% – 13%	8	%		8	%
Global	9% – 19%	15	%		10	%
International	5% – 15%	8	%		13	%
Total equity	55% – 65%	63	%		60	%
Debt securities	33% – 43%	36	%		38	%
Total		100	%		100	%

(a)Includes interest rate futures derivative instruments.

(b)Less than 1% of plan assets.

In general, the United States large-capitalization equity investments are passively managed or indexed, whereas the international, global, United States small-capitalization, and United States mid-capitalization equity investments are actively managed by investment managers. Debt securities include a broad range of fixed-income vehicles. Debt security investments in high-yield securities and non-United-States-dollar-denominated securities are owned by the plans, but in limited quantities to reduce risk. Most of the debt security investments are under active management by investment managers. Diversified credit investments include but are not limited to, sub-investment grade rated bonds and loans, securitized credit, and emerging market debt. Real estate investments include private real estate vehicles; however, Ameren does not, by policy, hold direct investments in real estate property. In addition to the derivative investments included in the liability hedging investment strategy described above, Ameren’s investment committee also allows investment managers to use derivatives, such as index futures, foreign exchange futures, and options, in certain situations to increase or to reduce market exposure in an efficient and timely manner.

Fair Value Measurements of Plan Assets

Investments in the pension and postretirement benefit plans were stated at fair value as of December 31, 2023. Fair value is defined as the price that would be received for an asset in the principal or most advantageous market for the asset in an orderly transaction between market participants on the measurement date. Cash and cash equivalents have initial maturities of three months or less and are recorded at cost plus accrued interest. Investments traded in active markets on national or international securities exchanges are valued at closing prices on the measurement date or, if that is not a business day, on the last business day before that date. Securities traded in over-the-counter markets are valued by quoted market prices, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency. Investments measured under NAV as a practical expedient are based on the fair values of the underlying assets provided by the funds and their administrators. The fair value of real estate investments is based on NAV; it is determined by annual appraisal reports prepared by an independent real estate appraiser. Investments measured at NAV often provide for daily, monthly, or quarterly redemptions with 60 or less days of notice depending on the fund. For some funds, redemption may also require approval from the fund’s board of directors. Derivative contracts are valued at fair value, as determined by the investment managers (or independent third parties on behalf of the investment managers), who use proprietary models and take into consideration exchange quotations on underlying instruments, dealer quotations, and other market information.

The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the pension plans’ assets measured at fair value and NAV as of December 31, 2023 and 2022:


	December 31, 2023								December 31, 2022
	Level 1		Level 2		NAV		Total			Level 1		Level 2		NAV		Total
Cash and cash equivalents	$	—	$	—	$	90	$	90		$	—	$	—	$	172	$	172
Equity securities:
U.S. large-capitalization	—		—		663		663			—		—		658		658
U.S. small- and mid-capitalization	353		—		—		353			321		—		—		321
International	316		—		229		545			266		—		395		661
Global	—		—		721		721			—		—		493		493
Debt securities:
Corporate bonds	—		479		—		479			—		397		—		397
Municipal bonds	—		43		—		43			—		41		—		41
U.S. Treasury and agency securities	—		994		—		994			—		859		—		859
Diversified credit	—		—		305		305			—		—		281		281
Other	49		13		—		62			(3)		7		—		4
Real estate	—		—		248		248			—		—		271		271
Private equity	—		—		—		—			—		—		1		1
Total	$	718	$	1,529	$	2,256	$	4,503		$	584	$	1,304	$	2,271	$	4,159
Less: Medical benefit assets(a)							(196)									(172)
Plus: Net receivables (payables)(b)							(35)									40
Fair value of pension plans’ assets							$	4,272								$	4,027

(a)Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation.

(b)Net of receivables related to pending securities sales and payables related to pending securities purchases.

The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the postretirement benefit plans’ assets measured at fair value and NAV as of December 31, 2023 and 2022:


	December 31, 2023								December 31, 2022
	Level 1		Level 2		NAV		Total			Level 1		Level 2		NAV		Total
Cash and cash equivalents	$	10	$	—	$	—	$	10		$	14	$	—	$	—	$	14
Equity securities:
U.S. large-capitalization	302		—		81		383			221		—		87		308
U.S. small- and mid-capitalization	96		—		—		96			92		—		—		92
International	51		—		49		100			43		—		98		141
Global	—		—		174		174			—		—		110		110

Debt securities:

Municipal bonds	—		161		—		161			—		123		—		123


Other	—		—		271		271			—		—		287		287
Total	$	459	$	161	$	575	$	1,195		$	370	$	123	$	582	$	1,075
Plus: Medical benefit assets(a)							196									172
Plus: Net receivables(b)							2									2
Fair value of postretirement benefit plans’ assets							$	1,393								$	1,249

(a)Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation. These 401(h) assets are included in the pension plan assets shown above.

(b)Net of receivables related to pending securities sales and payables related to pending securities purchases.

Net Periodic Benefit Cost

The following table presents the components of the net periodic benefit cost (income) of Ameren’s pension and postretirement benefit plans during 2023, 2022, and 2021:


	Pension Benefits						Postretirement Benefits
	2023		2022		2021		2023		2022		2021
Service cost(a)	$	79	$	128	$	134	$	12	$	20	$	23
Non-service cost components:
Interest cost	221		163		152		45		34		33
Expected return on plan assets(b)	(333)		(320)		(297)		(91)		(85)		(80)
Amortization of(b):

Prior service credit	—		—		—		(4)		(4)		(4)
Actuarial (gain) loss	(115)		25		73		(45)		(19)		(6)


Total non-service cost components(c)	$	(227)	$	(132)	$	(72)	$	(95)	$	(74)	$	(57)
Net periodic benefit cost (income)(d)	$	(148)	$	(4)	$	62	$	(83)	$	(54)	$	(34)

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

(b)Prior service cost is amortized on a straight-line basis over the average future service of active participants benefiting under the plan amendment. Net actuarial gains or losses related to the net benefit obligation subject to amortization are amortized on a straight-line basis over 10 years. The difference between the actual and expected return on plan assets is amortized over 4 years.

(c)Non-service cost components are reflected in “Other Income, Net” on Ameren’s consolidated statement of income. See Note 6 – Other Income, Net for additional information.

(d)Does not include the impact of the tracker for the difference between the level of pension and postretirement benefit costs (income) incurred by Ameren Missouri under GAAP and the level of such costs included in rates.

The Ameren Companies are responsible for their share of the pension and postretirement benefit costs (income). The following table presents the pension and postretirement benefit costs (income) incurred for the years ended December 31, 2023, 2022, and 2021:


	Pension Costs						Postretirement Costs
	2023		2022		2021		2023		2022		2021
Ameren Missouri(a)	$	(76)	$	(3)	$	29	$	(30)	$	(14)	$	(4)
Ameren Illinois	(62)		3		34		(54)		(41)		(31)
Other	(10)		(4)		(1)		1		1		1
Ameren	$	(148)	$	(4)	$	62	$	(83)	$	(54)	$	(34)

(a)Does not include the impact of the tracker for the difference between the level of pension and postretirement benefit costs (income) incurred by Ameren Missouri under GAAP and the level of such costs included in customer rates.

The expected pension and postretirement benefit payments from qualified trust and company funds, which reflect expected future service, as of December 31, 2023, are as follows:


	Pension Benefits				Postretirement Benefits
	Paid from Qualified Trust Funds		Paid from Company Funds		Paid from Qualified Trust Funds		Paid from Company Funds
2024	$	277	$	3	$	56	$	3
2025	281		3		58		3
2026	287		3		58		3
2027	290		3		58		3
2028	293		2		58		3
2029 – 2033	1,488		13		289		15

The following table presents the assumptions used to determine net periodic benefit cost for our pension and postretirement benefit plans for the years ended December 31, 2023, 2022, and 2021:


	Pension Benefits							Postretirement Benefits
	2023			2022		2021		2023			2022		2021
Discount rate at measurement date	5.55	%		3.00	%	2.75	%	5.55	%		3.00	%	2.75	%
Expected return on plan assets	6.75			6.50		6.50		6.75			6.50		6.50
Increase in future compensation	3.50		(a)	3.50		3.50		3.50		(a)	3.50		3.50
Cash balance pension plan interest crediting rate	5.00		(b)	5.00		5.00		(c)			(c)		(c)
Medical cost trend rate (initial)(d)	(c)			(c)		(c)		(e)			5.00		5.00
Medical cost trend rate (ultimate)(d)	(c)			(c)		(c)		5.00			5.00		5.00

(a)Increase in future compensation is 4.50% for 2023, 4.00% in 2024, and 3.50% thereafter for the year ended December 31, 2023.

(b)Cash balance pension plan interest crediting rate is 5.50% for 2023 and 2024, and 5.00% thereafter for the year ended December 31, 2023.

(c)Not applicable.

(d)Initial and ultimate medical cost trend rate for certain Medicare-eligible participants is 2.50% for the year ended December 31, 2023 and 3.00% for the years ended December 31, 2022 and 2021.

(e)Initial medical cost trend rates of 7.25% for pre-Medicare plan participants and 6.75% for post-Medicare plan participants trend down to the ultimate rate by 2030, with a 3.00% upward adjustment to the post-Medicare trend rate in 2025.

Other

Ameren sponsors a 401(k) plan for eligible employees. The Ameren 401(k) plan covered all eligible Ameren employees at December 31, 2023. The plan allows employees to contribute a portion of their compensation in accordance with specific guidelines. Ameren matches a percentage of the employee contributions up to certain limits. The following table presents the portion of the matching contribution to the Ameren 401(k) plan attributable to each of the Ameren Companies for the years ended December 31, 2023, 2022, and 2021:


	2023		2022		2021
Ameren Missouri	$	27	$	23	$	21
Ameren Illinois	21		19		16
Other	1		1		1
Ameren	$	49	$	43	$	38

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 70
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480794/715-70-50-1

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480482/715-20-55-17

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(iv)(03)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (q)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (l)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//715/tableOfContent

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(iii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (o)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (p)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (r)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (r)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480126/715-20-S99-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 60
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480266/715-60-50-3

+ Details

Stock-Based Compensation

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

STOCK-BASED COMPENSATION

The 2022 Omnibus Incentive Compensation Plan is Ameren’s long-term incentive plan available for eligible employees and directors. It provides for a maximum of 8.8 million common shares to be available for grant to eligible employees and directors. At December 31, 2023, there were 8.2 million common shares remaining for grant. Awards may be restricted stock, restricted stock units, stock options (incentive stock options and nonqualified stock options), stock appreciation rights, performance awards, cash-based awards and other stock-based awards. Ameren used newly issued shares to fulfill its stock-based compensation obligations for 2023, 2022, and 2021, and intends to use newly issued shares to fulfill its stock-based compensation obligations for 2024.

The following table summarizes Ameren’s outstanding performance share unit and restricted stock unit activity for the year ended December 31, 2023:


	Performance Share Units – Market Condition(a)			Performance Share Units – Performance Condition(b)			Restricted Stock Units
	Share Units	Weighted-average Fair Value per Share Unit		Share Units	Weighted-average Fair Value per Share Unit		Stock Units	Weighted-average Fair Value per Stock Unit
Outstanding at January 1, 2023(c)	744,273	$	87.23	119,737	$	80.65	436,812	$	80.94
Granted	311,674	88.52		40,118	84.70		130,600	84.44
Forfeitures	(45,080)	90.97		(7,389)	84.73		(22,566)	84.75
Dividend equivalents(d)	14,749	89.79		2,372	82.66		9,132	82.44
Vested and distributed	(263,904)	82.50		(42,447)	76.70		(176,114)	76.94

Outstanding at December 31, 2023(c)	761,712	$	89.22	112,391	$	83.36	377,864	$	83.82

(a)The exact number of shares issued pursuant to a share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the specified market conditions. Compensation cost on nonforfeited awards is recognized regardless of whether Ameren achieves the specified market conditions.

(b)The exact number of shares issued pursuant to a share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the performance goals. Compensation cost is recognized ratably over the requisite service period only for awards for which it is probable that the performance condition will be satisfied.

(c)Outstanding awards include awards that vest on a pro-rata basis due to attainment of retirement eligibility by certain employees, but have not yet been distributed. In these cases, the pro-rata basis awards have not yet been distributed as the entire performance period has not been completed. The number of shares issued for retirement-eligible employees will vary depending on actual performance over the three-year performance period.

(d)Dividend equivalents represent the right to receive shares measured by the dividend payable with respect to the corresponding number of outstanding share units. Dividend equivalents will accrue and be reinvested in additional share units throughout the performance period.

Performance Share Units – Market Condition

A market condition performance share unit vests and entitles an employee to receive shares of Ameren common stock (plus accumulated dividends) if, at the end of the three-year performance period, certain specified market conditions have been met and if the individual remains employed by Ameren through the required vesting period. The vesting period for share units awarded extends beyond the three-year performance period to the payout date, which is approximately 38 months after the grant date. In the event of a participant’s death or retirement at age 55 or older with five years or more of service, awards vest on a pro-rata basis over the three-year performance period. The exact number of shares issued pursuant to a share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the specified market conditions.

The fair value of each share unit is based on Ameren’s closing common share price at December 31 of the year prior to the award year and a Monte Carlo simulation. The Monte Carlo simulation is used to estimate expected share payout based on Ameren’s TSR for a three-year performance period relative to the designated peer group beginning January 1st of the award year. The simulation can produce a greater fair value for the share unit than the applicable closing common share price because it includes the weighted payout scenarios in which an increase in the share price has occurred and/or in which the payout is above 100% due to Ameren’s projected TSR performance. The key assumptions used to calculate fair value also include a three-year risk-free rate, Ameren’s common stock volatility, and volatility for the peer group. The following table presents the fair value of each share unit along with the significant assumptions used to calculate the fair value of each share unit for the years ended December 31, 2023, 2022, and 2021:


	2023	2022	2021
Fair value of share units awarded	$91.07	$92.75	$87.11

Three-year risk-free rate	4.19%	1.80%	0.17%
Ameren’s common stock volatility(a)	26%	29%	28%
Volatility range for the peer group(a)	24% – 32%	26% – 35%	26% – 36%

(a)Based on a historical period that is equal to the remaining term of the performance period as of the grant date.

In addition to the market condition performance share units described above, there are an immaterial number of market condition performance share units with different vesting conditions and target payout percentages.

Performance Share Units – Performance Condition

A performance condition share unit vests and entitles an employee to receive shares of Ameren common stock (plus accumulated dividends) if, at the end of the three-year performance period, Ameren has met the specified performance condition and if the individual remains employed by Ameren through the required vesting period. The vesting period for share units awarded extends beyond the three-year performance period to the payout date, which is approximately 38 months after the grant date. In the event of a participant’s death or retirement at age 55 or older with five years or more of service, awards vest on a pro-rata basis over the three-year performance period. The exact number of shares issued pursuant to a share unit varies from 0% to 200% of the target award, depending on actual performance conditions achieved. The specified performance condition in each award year is based on Ameren’s clean energy transition. The grant-date fair value for an individual outcome of a performance condition is determined by Ameren’s closing common share price on the grant date.

Restricted Stock Units

Restricted stock units vest and entitle an employee to receive shares of Ameren common stock (plus accumulated dividends) if the individual remains employed with Ameren through the payment date of the awards. Generally, in the event of a participant’s death or retirement at age 55 or older with five years or more of service, awards vest on a pro-rata basis. The payout date of the awards is approximately 38 months after the grant date. The fair value of each restricted stock unit is determined by Ameren’s closing common share price on the grant date.

Stock-Based Compensation Expense

The following table presents the stock-based compensation expense for the years ended December 31, 2023, 2022, and 2021:


	2023		2022		2021
Ameren Missouri	$	6	$	4	$	5
Ameren Illinois	4		2		3
Other(a)	16		18		14
Ameren	26		24		22
Less: Income tax benefit	7		6		6
Stock-based compensation expense, net	$	19	$	18	$	16

(a)Represents compensation expense for employees of Ameren Services. These amounts are not included in the Ameren Missouri and Ameren Illinois amounts above.

Ameren settled performance share units and restricted stock units of $60 million, $47 million, and $50 million for the years ended December 31, 2023, 2022, and 2021, respectively. There were no significant stock-based compensation costs capitalized during the years ended December 31, 2023, 2022, and 2021. As of December 31, 2023, total compensation cost of $41 million related to outstanding awards not yet recognized is expected to be recognized over a weighted-average period of 26 months.

For the years ended December 31, 2023, 2022, and 2021, excess tax benefits associated with the settlement of stock-based compensation awards reduced income tax expense by $6 million, $5 million, and $5 million, respectively.

Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

INCOME TAXES

IRA

The IRA was enacted in August 2022, and includes various income tax provisions, among other things. The law extends federal production and investment tax credits for projects beginning construction through 2024 and allows for a 10% adder to the production and investment tax credits for siting projects at existing energy communities as defined in the law, which includes sites previously used for coal-fired generation. The law also creates clean energy tax credits for projects placed in service after 2024. The clean energy tax credits will apply to renewable energy production and investments, along with certain nuclear energy production, and will be phased out beginning in 2033, at the earliest. The phase-out is triggered when greenhouse gas emissions from the electric generation industry are reduced by at least 75% from the annual 2022 emission rate or at the beginning of 2033, whichever is later. The law allows for transferability to an unrelated party for cash of up to 100% of certain tax credits generated after 2022. In addition, the new law imposes a 15% minimum tax on adjusted financial statement income, as defined in the law, for corporations whose average annual adjusted financial statement income exceeds $1 billion for three consecutive preceding tax years effective for tax years beginning after December 31, 2022. Once a corporation exceeds this three-year average annual adjusted financial statement income threshold, it will be subject to the minimum tax for all future tax years. Additional regulations, interpretations, amendments, or technical corrections to or in connection with the IRA have been and are expected to be issued by the IRS or United States Department of Treasury, which may impact the timing of when the 15% minimum tax becomes applicable for Ameren.

The following table presents the principal reasons for the difference between the effective income tax rate and the federal statutory corporate income tax rate for the years ended December 31, 2023, 2022, and 2021:


	Ameren Missouri		Ameren Illinois		Ameren
2023
Federal statutory corporate income tax rate	21	%	21	%	21	%
Increases (decreases) from:
Amortization of excess deferred income taxes(a)	(15)		(2)		(8)

Amortization of deferred investment tax credit	(1)		—		—
Production and other tax credits(b)	(10)		—		(4)
State tax	3		7		5


Effective income tax rate	(2)	%	26	%	14	%
2022
Federal statutory corporate income tax rate	21	%	21	%	21	%
Increases (decreases) from:
Amortization of excess deferred income taxes(a)	(15)		(2)		(8)

Amortization of deferred investment tax credit	(1)		—		—
Production and other tax credits(b)	(10)		—		(4)
State tax	3		7		5


Effective income tax rate	(2)	%	26	%	14	%
2021
Federal statutory corporate income tax rate	21	%	21	%	21	%
Increases (decreases) from:
Amortization of excess deferred income taxes(a)	(15)		(3)		(8)

Amortization of deferred investment tax credit	(1)		—		—
Production and other tax credits(b)	(7)		—		(3)
State tax	3		7		5
Stock-based compensation	—		—		(1)
Effective income tax rate	1	%	25	%	14	%

(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)The benefit of the credits associated with Missouri renewable energy standard compliance is refunded to customers through the RESRAM.

The following table presents the components of income tax expense (benefit) for the years ended December 31, 2023, 2022, and 2021:


	Ameren Missouri		Ameren Illinois		Other		Ameren
2023
Current taxes:
Federal	$	(37)	$	27	$	(37)	$	(47)
State	1		5		(5)		1
Deferred taxes:
Federal	102		123		35		260
State	9		71		(10)		70
Amortization of excess deferred income taxes	(80)		(17)		(1)		(98)
Amortization of deferred investment tax credits	(3)		—		—		(3)
Total income tax expense (benefit)	$	(8)	$	209	$	(18)	$	183
2022
Current taxes:
Federal	$	(26)	$	46	$	(15)	$	5
State	(5)		16		(10)		1
Deferred taxes:
Federal	93		82		19		194
State	18		48		14		80
Amortization of excess deferred income taxes	(86)		(13)		(1)		(100)
Amortization of deferred investment tax credits	(4)		—		—		(4)
Total income tax expense (benefit)	$	(10)	$	179	$	7	$	176
2021
Current taxes:
Federal	$	—	$	(15)	$	22	$	7
State	—		(7)		1		(6)
Deferred taxes:
Federal	65		120		(15)		170
State	23		59		4		86
Amortization of excess deferred income taxes	(81)		(14)		(1)		(96)
Amortization of deferred investment tax credits	(4)		—		—		(4)
Total income tax expense	$	3	$	143	$	11	$	157

The following table presents the accumulated deferred income tax assets and liabilities recorded as a result of temporary differences and accumulated deferred investment tax credits at December 31, 2023 and 2022:


	Ameren Missouri		Ameren Illinois		Other		Ameren
2023
Accumulated deferred income taxes, net liability (asset):
Plant-related	$	2,370	$	2,030	$	246	$	4,646
Regulatory assets and liabilities, net	(206)		(184)		(23)		(413)
Deferred employee benefit costs	(48)		55		(33)		(26)
Tax carryforwards	(124)		(33)		(61)		(218)
Other	104		38		19		161
Total net accumulated deferred income tax liabilities (assets)	2,096		1,906		148		4,150
Accumulated deferred investment tax credits	26		—		—		26
Accumulated deferred income taxes and investment tax credits	$	2,122	$	1,906	$	148	$	4,176
2022
Accumulated deferred income taxes, net liability (asset):
Plant-related	$	2,297	$	1,880	$	239	$	4,416
Regulatory assets and liabilities, net	(233)		(193)		(23)		(449)
Deferred employee benefit costs	(55)		28		(43)		(70)
Tax carryforwards	(122)		(34)		(72)		(228)
Other	70		18		22		110
Total net accumulated deferred income tax liabilities (assets)	1,957		1,699		123		3,779
Accumulated deferred investment tax credits	25		—		—		25
Accumulated deferred income taxes and investment tax credits	$	1,982	$	1,699	$	123	$	3,804

The following table presents the components of accumulated deferred income tax assets relating to net operating loss carryforwards and tax credit carryforwards at December 31, 2023 and 2022:


	Ameren Missouri		Ameren Illinois		Other		Ameren
2023
Net operating loss carryforwards:

State(a)	$	—	$	26	$	16	$	42
Total net operating loss carryforwards	$	—	$	26	$	16	$	42
Tax credit carryforwards:
Federal(b)	$	124	$	5	$	45	$	174
State(c)	—		2		—		2

Total tax credit carryforwards	$	124	$	7	$	45	$	176



2022
Net operating loss carryforwards:
Federal	$	3	$	4	$	4	$	11
State	1		26		9		36
Total net operating loss carryforwards	$	4	$	30	$	13	$	47
Tax credit carryforwards:
Federal	$	118	$	3	$	55	$	176
State	—		1		4		5

Total tax credit carryforwards	$	118	$	4	$	59	$	181

(a)Will expire between 2032 and 2043.

(b)Will expire between 2030 and 2043.

(c)Will expire between 2025 and 2028.

Uncertain Tax Positions

As of December 31, 2023 and 2022, the Ameren Companies did not record any uncertain tax positions.

Ameren is a part of the IRS’s compliance assurance process program, which involves real-time review of compliance with federal income tax law. State income tax returns are generally subject to examination for a period of three years after filing. The state impact of any federal changes remains subject to examination by various states for up to one year after formal notification to the states. Ameren’s federal tax returns for the 2020, 2021, and 2022 tax years are open, but, at the time of this filing, the Ameren Companies do not have material income tax issues under examination, administrative appeals, or litigation.

- 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
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-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

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+ Details

Related Party Transactions

12 Months Ended

Dec. 31, 2023

RELATED PARTY TRANSACTIONS

RELATED-PARTY TRANSACTIONS

In the normal course of business, Ameren Missouri and Ameren Illinois 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. Below are the material related-party agreements.

Electric Power Supply Agreements

Ameren Illinois must acquire capacity and energy sufficient to meet its obligations to customers. Ameren Illinois uses periodic RFP processes, administered by the IPA and approved by the ICC, to contract capacity and energy on behalf of its customers. Ameren Missouri participates in the RFP process and has been a winning supplier for certain periods.

Capacity Supply Agreements

In procurement events in 2021, Ameren Missouri contracted to supply a portion of Ameren Illinois’ capacity requirements for $2 million from June 2022 through May 2023.

Energy Product Agreements

Based on the outcome of IPA-administered procurement events, Ameren Missouri and Ameren Illinois have entered into energy product agreements by which Ameren Missouri agreed to sell, and Ameren Illinois agreed to purchase, a set amount of MWhs at a predetermined price over a specified period of time. The following table presents the specified performance period, average price per MWh, and amount of MWhs included in the agreements:


IPA Procurement Event	Performance Period	MWhs	Average Price per MWh
April 2019	January 2020 – December 2021	288,000	$	35
September 2019	April 2020 – November 2021	170,800	29
September 2020	September 2021 – November 2022	204,800	31
April 2021	July 2022 – November 2022	33,600	34
September 2021	January 2022 – September 2023	136,000	37

Interconnection Agreements

Ameren Missouri and Ameren Illinois are parties to an interconnection agreement that governs the connection of their respective transmission lines and other facilities used for the distribution of power. These agreements have no contractual expiration date, but may be terminated by either party with three years’ notice.

Ameren Missouri and ATXI are parties to an interconnection agreement that governs the connection of the High Prairie Renewable Energy Center to an ATXI transmission line that allows Ameren Missouri to distribute power generated from the High Prairie Renewable Energy Center.

Support Services Agreements

Ameren Services provides support services to its affiliates. The costs of support services including wages, employee benefits, professional services, and other expenses, are based on, or are an allocation of, actual costs incurred. The support services agreement can be terminated at any time by the mutual agreement of Ameren Services and that affiliate or by either party with 60 days’ notice before the end of a calendar year.

In addition, Ameren Missouri and Ameren Illinois provide affiliates with access to their facilities for administrative purposes and with use of other assets. The costs of the rent and facility services and other assets are based on, or are an allocation of, actual costs incurred.

Ameren Missouri and Ameren Illinois also provide storm-related and miscellaneous support services to each other on an as-needed basis.

Ameren Missouri and Ameren Illinois had long-term receivables included in “Other assets” from Ameren Services of $31 million and $34 million, respectively, as of December 31, 2023, and $41 million and $43 million, respectively, as of December 31, 2022, related to Ameren Services’ allocated portion of Ameren’s pension and postretirement benefit plans.

Transmission Services

Ameren Missouri and Ameren Illinois each receives transmission services from ATXI for their respective retail loads.

Electric Transmission Maintenance and Construction Agreements

ATXI entered into separate agreements with Ameren Missouri and Ameren Illinois in which Ameren Missouri or Ameren Illinois, as applicable, may perform certain maintenance and construction services related to ATXI’s electric transmission assets.

Money Pool

See Note 4 – Short-term Debt and Liquidity for a discussion of affiliate borrowing arrangements.

Tax Allocation Agreement

See Note 1 – Summary of Significant Accounting Policies for a discussion of the tax allocation agreement. The following table presents the affiliate balances related to income taxes for Ameren Missouri and Ameren Illinois as of December 31, 2023 and 2022:


	2023				2022
	Ameren Missouri		Ameren Illinois		Ameren Missouri		Ameren Illinois
Income taxes payable to parent(a)	$	—	$	2	$	—	$	50
Income taxes receivable from parent(b)	56		22		39		—

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

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

Capital Contributions

The following table presents cash capital contributions received from Ameren (parent) by Ameren Missouri and Ameren Illinois for the years ended December 31, 2023, 2022, and 2021:


	2023		2022		2021
Ameren Missouri(a)	$	—	$	—	$	207
Ameren Illinois(a)	91		15		262

(a)Includes capital contributions made as a result of the tax allocation agreement.

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 years ended December 31, 2023, 2022, and 2021. It is based primarily on the agreements discussed above and the money pool arrangements discussed in Note 4 – Short-term Debt and Liquidity.


Agreement	Income Statement Line Item			Ameren Missouri		Ameren Illinois
Ameren Missouri power supply agreements	Operating Revenues	2023	$	2	$	(a)
with Ameren Illinois		2022		9		(a)
		2021		16		(a)
Ameren Missouri and Ameren Illinois	Operating Revenues	2023		32		(b)
rent and facility services		2022		25		(b)
		2021		26		1
Ameren Missouri and Ameren Illinois	Operating Revenues	2023		(b)		2
miscellaneous support services		2022		(b)		2
		2021		(b)		5



Total Operating Revenues		2023	$	34	$	2
		2022		34		2
		2021		42		6
Ameren Illinois power supply	Purchased Power	2023	$	(a)	$	2
agreements with Ameren Missouri		2022		(a)		9
		2021		(a)		16
Ameren Missouri and Ameren Illinois	Purchased Power	2023		2		1
transmission services from ATXI		2022		1		(b)
		2021		4		1
Total Purchased Power		2023	$	2	$	3
		2022		1		9
		2021		4		17
Ameren Missouri and Ameren Illinois	Other Operations and	2023	$	(b)	$	3
rent and facility services	Maintenance	2022		(b)		3
		2021		1		4
Ameren Services support services	Other Operations and	2023		148		138
agreement	Maintenance	2022		150		141
		2021		147		137
Total Other Operations and		2023	$	148	$	141
Maintenance Expenses		2022		150		144
		2021		148		141
Money pool borrowings (advances)	(Interest Charges)	2023	$	(b)	$	(b)
	Other Income, Net	2022		(b)		(b)
		2021		(b)		(b)

(a)Not applicable.

(b)Amount less than $1 million.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

+ Details

Commitments And Contingencies	12 Months Ended
Commitments And Contingencies	Dec. 31, 2023
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, will not have a material adverse effect on our results of operations, financial position, or liquidity. See also Note 1 – Summary of Significant Accounting Policies, Note 2 – Rate and Regulatory Matters, Note 9 – Callaway Energy Center, Note 13 – Related-party Transactions, and Note 15 – Supplemental Information in 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 by 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 energy-related 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 requirements of environmental laws. 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. Regulations under the Clean Air Act 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. Regulations implementing the Clean Water Act govern both intake and discharges of water, as well as evaluation of the ecological and biological impact of those 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, capital expenditures associated with these modifications 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 surface impoundments at Ameren Missouri’s coal-fired energy centers. The individual or combined effects of compliance with 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. Additionally, Ameren Missouri’s wind generation facilities may be subject to operating restrictions to limit the impact on protected species. Since 2021, Ameren Missouri’s High Prairie Renewable Energy Center curtailed nighttime operations from April through October to limit impacts on protected species during the critical biological season. The extent and duration of future curtailments are unknown at this time as assessment of mitigation technologies is ongoing. Ameren Missouri does not anticipate these operating curtailments will have a material impact on its results of operations, financial position, or liquidity. Ameren and Ameren Missouri estimate that they will need to make capital expenditures of $90 million to $120 million from 2024 through 2028 in order to comply with existing environmental regulations. Additional capital expenditures for environmental controls beyond 2028 could be required. This estimate of capital expenditures includes surface impoundment closure and corrective action measures required by the CCR Rule and 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 2023 IRP filed with the MoPSC in September 2023 and as noted below with respect to the NSR and Clean Air Act litigation and Illinois emissions standards, Ameren Missouri’s current plan for compliance with existing air emission regulations includes 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 by state regulators and the EPA, revisions to regulatory obligations, and varying cost of potential compliance strategies, among other things. The following sections describe the more significant environmental statutes and regulations and environmental enforcement and remediation matters that affect or could affect our operations. The EPA periodically amends and revises its regulations and proposes amendments to regulations and guidelines, which could ultimately result in the revision of all or part of such regulations. Clean Air Act Federal and state laws, including the CSAPR, regulate emissions of SO2 and NOx through the reduction of emissions at their source and the use and retirement of emission allowances. In April 2022, the EPA proposed plans for additional NOx emission reductions from power plants in Missouri, Illinois, and other states through revisions to the CSAPR. In January 2023, the EPA issued its final disapproval of Missouri’s proposed state implementation plan for addressing the transport of ozone under the Good Neighbor Plan of the Clean Air Act. The disapproval of the state plan allows the EPA to implement revisions to the CSAPR through a federal implementation plan. In March 2023, the EPA announced federal implementation plan requirements, which were subsequently published to the Federal Register in June 2023, reducing the amount of NOx allowances available for state budgets and imposing NOx emission limits on electric generating units for Missouri, Illinois, and other states under the Good Neighbor Plan of the Clean Air Act. In April 2023, the Missouri Attorney General and Ameren Missouri separately filed lawsuits in the United States Court of Appeals for the Eighth Circuit challenging the EPA’s disapproval of the Missouri state plan and sought a stay of the EPA’s disapproval of the Missouri state plan. The United States Court of Appeals for the Eighth Circuit in May 2023 granted those stay motions thereby preventing the EPA from imposing the federal implementation plan until the court of appeals issues a ruling. In December 2023, the United States Supreme Court agreed to hear challenges to the Good Neighbor Plan and scheduled oral argument for February 2024, with a decision expected by June 2024. Ameren Missouri complies with the 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 existing NOx air pollution control equipment. Reducing the amount of state budget NOx allowances for compliance with NOx emission limits could result in additional controls being required on Ameren Missouri’s generating units and/or the reduction of operations. Any additional costs for compliance are expected to be recovered from customers, subject to MoPSC prudence review, through the FAC or higher base rates. CO2 Emissions Standards In June 2022, the United States Supreme Court issued its decision in West Virginia v. EPA, clarifying that there are limits on how the EPA may regulate greenhouse gases absent further direction from the United States Congress. The court concluded that the EPA’s proposed rules were designed to shift generation from fossil-fuel-fired power plants to renewable energy facilities, which was improper absent specific congressional authorization. In May 2023, the EPA issued a new proposed rule that would set CO2 emission standards for new and existing fossil-fuel-fired power plants based on the adoption of carbon capture technology, natural gas co-firing, and co-firing hydrogen fuel to reduce emissions. If the proposed rule were adopted, the affected fossil-fuel-fired power plants would be required to comply with the rule through a phased-in approach or retire. Capacity restrictions for coal-fired units could apply as early as 2030. Larger natural gas-fired power plants would be required to co-fire with hydrogen by 2032, with additional requirements by 2038. The EPA expects to issue a final rule in 2024. Legal challenges to the final rule, if adopted as proposed, are expected. Ameren and Ameren Missouri cannot predict the results of any such challenges or potential impacts of any such regulations on their results of operations, financial position, and liquidity until final regulations are adopted and the merits of such legal challenges are determined. 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 projects performed in 2007 and 2010 at the coal-fired Rush Island Energy Center 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. Following an appeal from Ameren Missouri, in August 2021, the United States Court of Appeals for the Eighth Circuit 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 September 2023, the district court granted Ameren Missouri’s request 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. In its amended remedy order, the district court established an October 15, 2024 retirement date and, in the interim, authorized Ameren Missouri to operate the energy center as directed by the MISO. The United States Department of Justice is seeking an order from the district court providing for additional mitigation relief. Ameren Missouri could be required to implement mitigation relief measures, the costs of which could be material and which Ameren Missouri would not expect to recover. Ameren Missouri is challenging such mitigation claims, noting that the scope of any such potential additional mitigation relief should be limited by the August 2021 court of appeals decision and offset by emission reductions resulting from the accelerated retirement of the Rush Island Energy Center. The MISO designated the energy center as a system support resource in 2022 and concluded that certain reliability mitigation measures, including transmission upgrades, should occur before the energy center is retired. The Rush Island Energy Center began operating as a system support resource on September 1, 2022. In 2023, the MISO extended the system support resource designation through August 2024, and in September 2023, an agreement between Ameren Missouri and the MISO was approved by the FERC that results in the Rush Island Energy Center only operating during peak demand times and emergencies. The system support resource designation and the related agreement are subject to annual renewal and revision. Construction activities are underway for the transmission upgrades approved by the MISO, with the majority of the upgrades expected to be completed in the fall of 2024. Ameren Missouri expects to complete the last of the upgrades by mid-2025. In addition, in August 2023, the FERC approved a settlement agreement for Ameren Missouri’s request for recovery of non-energy costs under the related MISO tariff between Ameren Missouri and certain intervenors, which provided for recovery of substantially all of Ameren Missouri’s requested non-energy costs through August 2023. In October 2023, Ameren Missouri received FERC approval for the recovery of non-energy costs under the related MISO tariff from September 2023 to August 2024. Revenues and costs under the MISO tariff are included in the FAC. 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 accelerated retirement of the Rush Island Energy Center, Ameren Missouri is seeking 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 Missouri’s securitization statute. See Note 2 – Rate and Regulatory Matters for additional information. As of December 31, 2023, the Rush Island Energy Center had a net plant balance of $530 million included in plant to be abandoned, net, within “Property, Plant, and Equipment, Net”. See Note 1 – Summary of Significant Accounting Policies for additional information regarding plant to be abandoned, net. 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 Among other items, the Clean Water Act requires 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 this 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. Permits for Ameren Missouri’s coal-fired and nuclear energy centers have been issued or are in the process of renewal. 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 by 2025. To comply with these guidelines, Ameren Missouri installed dry ash handling systems and wastewater treatment facilities at its coal-fired energy centers. CCR Management The EPA’s CCR Rule establishes requirements for the management and disposal of CCR from coal-fired power plants and has resulted in the closure of surface impoundments at Ameren Missouri’s energy centers, with closures of surface impoundments in process at its Sioux Energy Center and retired Meramec Energy Center. Ameren Missouri plans to substantially complete the closures of remaining surface impoundments by the end of 2026. Ameren Missouri’s CCR management compliance plan includes installation of groundwater monitoring equipment and groundwater treatment facilities. Ameren and Ameren Missouri have AROs of $40 million recorded on their respective balance sheets as of December 31, 2023, associated with CCR storage 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 December 31, 2023, Ameren Illinois has remediated the majority of the 44 former MGP sites in Illinois with an estimated remaining obligation primarily related to three of these former MGP sites at $51 million to $96 million. Ameren and Ameren Illinois recorded a liability of $51 million to represent the estimated minimum obligation for these sites, as no other amount within the range was a better estimate. Ameren cannot estimate the completion date of the estimated remaining obligation due to site accessibility, among other things. 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. The ICC allows Ameren Illinois to recover MGP 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. 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, including additional or more stringent cleanup standards, or will affect our results of operations, financial position, or liquidity. Illinois Emission Standards The CEJA established emission standards that became effective in September 2021. Ameren Missouri's natural gas-fired energy centers in Illinois are subject to annual limits on emissions, including CO2 and NOx. Further reductions to emissions limits will become effective between 2030 and 2040, resulting in the closure of the Venice Energy Center by the end of 2029. The reductions could also limit the operations of Ameren Missouri's four other natural gas-fired energy centers located in the state of Illinois, and will result in their closure by 2040. These energy centers are utilized to support peak loads. Subject to conditions in the CEJA, these energy centers may be allowed to exceed the emissions limits in order to maintain reliability of electric utility service. Ameren Missouri filed its 2023 IRP with the MoPSC in September 2023 to reflect, among other things, the updated scheduled retirement dates of the natural gas-fired energy centers located in the state of Illinois.

Supplemental Information

12 Months Ended

Dec. 31, 2023

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 as of December 31, 2023 and 2022:


	December 31, 2023						December 31, 2022
	Ameren		Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois
Cash and cash equivalents	$	25	$	—	$	—	$	10	$	—	$	—
Restricted cash included in “Other current assets”	13		5		5		13		5		6
Restricted cash included in “Other assets”	229		—		229		185		—		185
Restricted cash included in “Nuclear decommissioning trust fund”	5		5		—		8		8		—
Total cash, cash equivalents, and restricted cash	$	272	$	10	$	234	$	216	$	13	$	191

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 December 31, 2023 and 2022, “Other current liabilities” on Ameren’s and Ameren Illinois’ balance sheets included payables for purchased receivables of $42 million and $31 million, respectively.

The following table provides a reconciliation of the beginning and ending amount of the allowance for doubtful accounts for the years ended December 31, 2023 and 2022:


	December 31, 2023						December 31, 2022
	Ameren Missouri		Ameren Illinois(a)		Ameren			Ameren Missouri		Ameren Illinois(a)		Ameren
Beginning balance at January 1	$	13	$	18	$	31		$	13	$	16	$	29
Bad debt expense	11		40		51			9		25		34
Charged to other accounts(b)	—		5		5			—		4		4
Net write-offs	(12)		(45)		(57)			(9)		(27)		(36)
Ending balance at December 31	$	12	$	18	$	30		$	13	$	18	$	31

(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.

(b)Amounts associated with the allowance for doubtful accounts related to receivables purchased by Ameren Illinois from alternative retail electric suppliers, as required by the Illinois Public Utilities Act.

As of December 31, 2023, accounts receivable balances that were 30 days or greater past due or that were a part of a deferred payment arrangement represented 22%, 16%, and 27%, or $114 million, $35 million, and $79 million, of Ameren’s, Ameren Missouri’s, and Ameren Illinois’ customer trade receivables before allowance for doubtful accounts, respectively. In comparison, as of December 31, 2022, these percentages were 17%, 14%, and 20%, or $107 million, $35 million, and $71 million, for Ameren, Ameren Missouri, and Ameren Illinois, respectively.

Inventories

The following table presents the components of inventories for each of the Ameren Companies at December 31, 2023 and 2022:


	December 31, 2023						December 31, 2022
	Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois		Ameren
Fuel(a)	$	109	$	—	$	109	$	79	$	—	$	79
Natural gas stored underground	8		87		95		10		120		130
Materials, supplies, and other	391		138		529		345		113		458
Total inventories	$	508	$	225	$	733	$	434	$	233	$	667

(a)Consists of coal, oil, and propane.

Asset Retirement Obligations

The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the years ended December 31, 2023 and 2022:


	December 31, 2023									December 31, 2022
	Ameren Missouri			Ameren Illinois			Ameren			Ameren Missouri			Ameren Illinois			Ameren
Beginning balance at January 1	$	782	(a)	$	4	(b)	$	786	(a)	$	760		$	4		$	764
Liabilities incurred	—			—			—			1			—			1
Liabilities settled	(10)			—			(10)			(4)			—			(4)
Accretion(c)	33			—			33			32			—			32
Change in estimates	(18)			—			(18)			(7)			—			(7)
Ending balance at December 31	$	787	(a)(d)	$	4	(b)	$	791	(a)(d)	$	782	(a)	$	4	(b)	$	786	(a)

(a)Balance included $19 million and $23 million in “Other current liabilities” on the balance sheet as of December 31, 2023 and 2022, respectively.

(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)The balance as of December 31, 2023, included an ARO related to the decommissioning of the Callaway Enter Center of $619 million.

Deferred Compensation

As of December 31, 2023, and 2022, the present value of benefits to be paid for deferred compensation obligations was $85 million and $87 million, respectively, which was primarily reflected in “Other deferred credits and liabilities” on Ameren’s consolidated balance sheet. Deferred compensation obligations are primarily recorded on the balance sheet of Ameren (parent).

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 years ended December 31, 2023, 2022, and 2021:


	2023		2022		2021
Ameren Missouri	$	166	$	162	$	150
Ameren Illinois	121		133		125
Ameren	$	287	$	295	$	275

Allowance for Funds Used During Construction

The following table presents the average rate that was applied to eligible construction work in progress and the amounts of allowance for funds used during construction capitalized in 2023, 2022, and 2021:


	2023			2022			2021
Average rate:
Ameren Missouri	6		%	5		%	6		%
Ameren Illinois	6		%	5		%	5		%
Ameren:
Allowance for equity funds used during construction	$	54		$	43		$	43
Allowance for borrowed funds used during construction	48			26			17
Total Ameren	$	102		$	69		$	60
Ameren Missouri:
Allowance for equity funds used during construction	$	30		$	24		$	26
Allowance for borrowed funds used during construction	27			13			10
Total Ameren Missouri	$	57		$	37		$	36
Ameren Illinois:
Allowance for equity funds used during construction	$	19		$	18		$	17
Allowance for borrowed funds used during construction	17			12			7
Total Ameren Illinois	$	36		$	30		$	24

Earnings per Share

Earnings per basic and diluted share are computed by dividing “Net Income Attributable to Ameren Common Shareholders” by the weighted-average number of basic and diluted common shares outstanding, respectively, during the applicable period. The weighted-average shares outstanding for earnings per diluted share includes the incremental effects resulting from performance share units, restricted stock units, and forward sale agreements relating to common stock when the impact would be dilutive, as calculated using the treasury stock method. For information regarding performance share units and restricted stock units, see Note 11 – Stock-based Compensation. For information regarding forward sale agreements, see Note 5 – Long-term Debt and Equity Financings.

The following table reconciles the weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the years ended December 31, 2023, 2022, and 2021:


	2023	2022	2021


Weighted-average Common Shares Outstanding – Basic	262.8	258.4	256.3
Assumed settlement of performance share units and restricted stock units	0.6	1.0	1.3
Dilutive effect of forward sale agreements	—	0.1	—
Weighted-average Common Shares Outstanding – Diluted(a)	263.4	259.5	257.6

(a)There was an immaterial number of anti-dilutive securities excluded from the earnings per diluted share calculations for the years ended December 31, 2023, 2022, and 2021 related to performance share units and restricted stock units. The outstanding forward sale agreements as of December 31, 2023, were anti-dilutive for the year ended December 31, 2023, and excluded from the earnings per diluted share calculation as calculated using the treasury stock method.

Supplemental Cash Flow Information

The following table provides noncash financing and investing activity excluded from the statements of cash flows for the years ended December 31, 2023, 2022, and 2021:


	December 31, 2023						December 31, 2022							December 31, 2021
	Ameren		Ameren Missouri		Ameren Illinois			Ameren		Ameren Missouri		Ameren Illinois			Ameren		Ameren Missouri		Ameren Illinois
Investing
Accrued capital expenditures, including nuclear fuel expenditures	$	518	$	270	$	212		$	441	$	243	$	181		$	524	$	301	$	215


Net realized and unrealized gain (loss) – nuclear decommissioning trust fund	167		167		—			(218)		(218)		—			163		163		—
Return of investment in industrial development revenue bonds(a)	240		240		—			—		—		—			—		—		—
Financing
Issuance of common stock for stock-based compensation	$	40	$	—	$	—		$	31	$	—	$	—		$	33	$	—	$	—
Issuance of common stock under the DRPlus	7		—		—			8		—		—			—		—		—
Termination of a financing agreement(a)	240		240		—			—		—		—			—		—		—

(a)In January 2023, Ameren Missouri and Audrain County mutually agreed to terminate a financing obligation agreement related to the CT energy center in Audrain County, which was scheduled to expire in December 2023. No cash was exchanged in connection with the termination of the agreement as the $240 million principal amount of the financing obligation due from Ameren Missouri was equal to the amount of bond service payments due to Ameren Missouri.

Segment Information

12 Months Ended

Dec. 31, 2023

Segment Reporting [Abstract]

SEGMENT INFORMATION

Ameren has four segments: Ameren Missouri, Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Transmission. The Ameren Missouri segment includes all of the operations of Ameren Missouri. Ameren Illinois Electric Distribution consists of the electric distribution business of Ameren Illinois. Ameren Illinois Natural Gas consists of the natural gas business of Ameren Illinois. Ameren Transmission primarily consists of the aggregated electric transmission businesses of Ameren Illinois and ATXI. The category called Other primarily includes Ameren (parent) activities and Ameren Services.

Ameren Missouri has one segment. Ameren Illinois has three segments: Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission. See Note 1 – Summary of Significant Accounting Policies for additional information regarding the operations of Ameren Missouri, Ameren Illinois, and ATXI.

Segment operating revenues and a majority of operating expenses are directly recognized and incurred by Ameren Illinois to each Ameren Illinois segment. Common operating expenses, miscellaneous income and expenses, interest charges, and income tax expense are allocated by Ameren Illinois to each Ameren Illinois segment based on certain factors, which primarily relate to the nature of the cost. Additionally, Ameren Illinois Transmission earns revenue from transmission service provided to Ameren Illinois Electric Distribution, other retail electric suppliers, and wholesale customers. The transmission expense for Illinois customers who have elected to purchase their power from Ameren Illinois is recovered through a cost recovery mechanism with no net effect on Ameren Illinois Electric Distribution earnings, as costs are offset by corresponding revenues. Transmission revenues from these transactions are reflected in Ameren Transmission’s and Ameren Illinois Transmission’s operating revenues. An intersegment elimination at Ameren and Ameren Illinois occurs to eliminate these transmission revenues and expenses.

The following tables present information about the reported revenue and specified items reflected in net income attributable to common shareholders and capital expenditures by segment at Ameren and Ameren Illinois for the years ended December 31, 2023, 2022, and 2021. Ameren, Ameren Missouri, and Ameren Illinois management review segment capital expenditure information rather than any individual or total asset amount.

Ameren


	Ameren Missouri		Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission			Other		Intersegment Eliminations		Ameren
2023
External revenues	$	3,825	$	2,217	$	897	$	561		$	—	$	—	$	7,500
Intersegment revenues	34		1		—		116			—		(151)		—
Depreciation and amortization	783		351		108		138			7		—		1,387
Interest income	11		19		1		2			5		(5)		33
Interest charges	227		89		55		96		(a)	104		(5)		566
Income taxes (benefit)	(8)		82		50		106			(47)		—		183
Net income (loss) attributable to Ameren common shareholders	545		258		134		296			(81)		—		1,152
Capital expenditures	1,760		752		299		804			9		(27)		3,597

2022
External revenues	$	4,012	$	2,255	$	1,180	$	510		$	—	$	—	$	7,957
Intersegment revenues	34		1		—		105			—		(140)		—
Depreciation and amortization	732		332		98		123			4		—		1,289
Interest income	28		7		—		—			1		(1)		35
Interest charges	213		74		44		84		(a)	72		(1)		486
Income taxes (benefit)	(10)		68		46		92			(20)		—		176
Net income (loss) attributable to Ameren common shareholders	562		202		123		263			(76)		—		1,074
Capital expenditures	1,690		621		308		741			7		(16)		3,351

2021
External revenues	$	3,311	$	1,635	$	957	$	491		$	—	$	—	$	6,394
Intersegment revenues	42		4		—		71			—		(117)		—
Depreciation and amortization	632		309		90		111			4		—		1,146
Interest income	26		1		—		—			3		(3)		27
Interest charges	137		74		42		83		(a)	50		(3)		383
Income taxes (benefit)	3		53		39		82			(20)		—		157
Net income (loss) attributable to Ameren common shareholders	518		165		108		230			(31)		—		990
Capital expenditures	2,015		579		278		616			4		(13)		3,479

(a)Ameren Transmission interest charges include an allocation of financing costs from Ameren (parent).

Ameren Illinois


	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Intersegment Eliminations		Ameren Illinois
2023
External revenues	$	2,218	$	897	$	367	$	—	$	3,482
Intersegment revenues	—		—		113		(113)		—
Depreciation and amortization	351		108		97		—		556
Interest income	19		1		1		—		21
Interest charges	89		55		60		—		204
Income taxes	82		50		77		—		209
Net income available to common shareholder	258		134		215		—		607
Capital expenditures	752		299		680		—		1,731

2022
External revenues	$	2,256	$	1,180	$	320	$	—	$	3,756
Intersegment revenues	—		—		104		(104)		—
Depreciation and amortization	332		98		84		—		514
Interest income	7		—		—		—		7
Interest charges	74		44		50		—		168
Income taxes	68		46		65		—		179
Net income available to common shareholder	202		123		188		—		513
Capital expenditures	621		308		672		—		1,601

2021
External revenues	$	1,639	$	957	$	299	$	—	$	2,895
Intersegment revenues	—		—		66		(66)		—
Depreciation and amortization	309		90		73		—		472
Interest income	1		—		—		—		1
Interest charges	74		42		48		—		164
Income taxes	53		39		51		—		143
Net income available to common shareholder	165		108		152		—		425
Capital expenditures	579		278		575		—		1,432

The following tables present disaggregated revenues by segment at Ameren and Ameren Illinois for the years ended December 31, 2023, 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 sales and capacity revenues.

Ameren


	Ameren Missouri		Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission		Intersegment Eliminations		Ameren
2023
Residential	$	1,577	$	1,344	$	—	$	—	$	—	$	2,921
Commercial	1,280		747		—		—		—		2,027
Industrial	306		186		—		—		—		492
Other	531		(59)		—		677		(150)		999
Total electric revenues	$	3,694	$	2,218	$	—	$	677	$	(150)	$	6,439
Residential	$	100	$	—	$	657	$	—	$	—	$	757
Commercial	46		—		164		—		—		210
Industrial	5		—		14		—		—		19
Other	14		—		62		—		(1)		75
Total gas revenues	$	165	$	—	$	897	$	—	$	(1)	$	1,061
Total revenues(a)	$	3,859	$	2,218	$	897	$	677	$	(151)	$	7,500
2022
Residential	$	1,578	$	1,325	$	—	$	—	$	—	$	2,903
Commercial	1,219		768		—		—		—		1,987
Industrial	290		199		—		—		—		489
Other	762		(36)		—		615		(139)		1,202
Total electric revenues	$	3,849	$	2,256	$	—	$	615	$	(139)	$	6,581
Residential	$	119	$	—	$	846	$	—	$	—	$	965
Commercial	56		—		221		—		—		277
Industrial	7		—		41		—		—		48
Other	15		—		72		—		(1)		86
Total gas revenues	$	197	$	—	$	1,180	$	—	$	(1)	$	1,376
Total revenues(a)	$	4,046	$	2,256	$	1,180	$	615	$	(140)	$	7,957
2021
Residential	$	1,445	$	933	$	—	$	—	$	—	$	2,378
Commercial	1,126		545		—		—		—		1,671
Industrial	280		135		—		—		—		415
Other	361		26		—		562		(116)		833
Total electric revenues	$	3,212	$	1,639	$	—	$	562	$	(116)	$	5,297
Residential	$	79	$	—	$	657	$	—	$	—	$	736
Commercial	34		—		172		—		—		206
Industrial	4		—		35		—		—		39
Other	24		—		93		—		(1)		116
Total gas revenues	$	141	$	—	$	957	$	—	$	(1)	$	1,097
Total revenues(a)	$	3,353	$	1,639	$	957	$	562	$	(117)	$	6,394

(a)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the years ended December 31, 2023, 2022, and 2021:


	Ameren Missouri			Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Transmission		Ameren
2023
Revenues from alternative revenue programs	$	(5)		$	116	$	49	$	19	$	179
Other revenues not from contracts with customers	(9)		(a)	7		2		—		—		(a)
2022
Revenues from alternative revenue programs	$	17		$	89	$	(19)	$	(9)	$	78
Other revenues not from contracts with customers	(103)		(a)(b)	6		3		—		(94)		(a)(b)
2021
Revenues from alternative revenue programs	$	(16)		$	77	$	5	$	11	$	77
Other revenues not from contracts with customers	56		(a)(b)	10		2		—		68		(a)(b)

(a)Includes net realized gains and losses on derivative power contracts.

(b)Includes $10 million and $78 million for insurance recoveries related to lost sales associated with the Callaway Energy Center maintenance outage for the years ended December 31, 2022 and 2021, respectively.

Ameren Illinois


	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Intersegment Eliminations		Ameren Illinois
2023
Residential	$	1,344	$	657	$	—	$	—	$	2,001
Commercial	747		164		—		—		911
Industrial	186		14		—		—		200
Other	(59)		62		480		(113)		370
Total revenues(a)	$	2,218	$	897	$	480	$	(113)	$	3,482
2022
Residential	$	1,325	$	846	$	—	$	—	$	2,171
Commercial	768		221		—		—		989
Industrial	199		41		—		—		240
Other	(36)		72		424		(104)		356
Total revenues(a)	$	2,256	$	1,180	$	424	$	(104)	$	3,756
2021
Residential	$	933	$	657	$	—	$	—	$	1,590
Commercial	545		172		—		—		717
Industrial	135		35		—		—		170
Other	26		93		365		(66)		418
Total revenues(a)	$	1,639	$	957	$	365	$	(66)	$	2,895

(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 years ended December 31, 2023, 2022, and 2021:


	Ameren Illinois Electric Distribution		Ameren Illinois Natural Gas		Ameren Illinois Transmission		Ameren Illinois
2023
Revenues from alternative revenue programs	$	116	$	49	$	12	$	177
Other revenues not from contracts with customers	7		2		—		9
2022
Revenues from alternative revenue programs	$	89	$	(19)	$	(7)	$	63
Other revenues not from contracts with customers	6		3		—		9
2021
Revenues from alternative revenue programs	$	77	$	5	$	9	$	91
Other revenues not from contracts with customers	10		2		—		12

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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+ Details

Schedule I - Condensed Financial Information Of Parent

12 Months Ended

Dec. 31, 2023

Condensed Financial Information Disclosure [Abstract]

Condensed Financial Information Of Parent


SCHEDULE I – CONDENSED FINANCIAL INFORMATION OF PARENT AMEREN CORPORATION CONDENSED STATEMENT OF INCOME AND COMPREHENSIVE INCOME For the Years Ended December 31, 2023, 2022, and 2021
(In millions)	2023		2022		2021
Operating revenues	$	—	$	—	$	—
Operating expenses	22		15		13
Operating loss	(22)		(15)		(13)
Equity in earnings of subsidiaries	1,245		1,161		1,039
Interest income from affiliates	10		2		3
Total other expense, net	(11)		(13)		—
Interest charges	(119)		(86)		(64)
Income tax benefit	49		25		25


Net Income Attributable to Ameren Common Shareholders	$	1,152	$	1,074	$	990

Net Income Attributable to Ameren Common Shareholders	$	1,152	$	1,074	$	990
Other Comprehensive Income (Loss), Net of Taxes:
Pension and other postretirement benefit plan activity, net of income taxes (benefit) of $(2), $(4), and $4, respectively	(5)		(14)		14




Comprehensive Income Attributable to Ameren Common Shareholders	$	1,147	$	1,060	$	1,004


SCHEDULE I – CONDENSED FINANCIAL INFORMATION OF PARENT AMEREN CORPORATION CONDENSED BALANCE SHEET
(In millions, except per share amounts)	December 31, 2023		December 31, 2022
Assets:
Cash and cash equivalents	$	16	$	—
Advances to money pool	598		68
Accounts receivable – affiliates	20		59

Miscellaneous accounts and notes receivable	31		11


Total current assets	665		138

Investments in subsidiaries	14,573		13,394


Accumulated deferred income taxes, net	44		46
Other assets	149		137
Total assets	$	15,431	$	13,715
Liabilities and Shareholders’ Equity:
Current maturities of long-term debt	$	450	$	—
Short-term debt	—		477

Accounts payable	2		—
Taxes accrued	10		5
Accounts payable – affiliates	100		52
Other current liabilities	45		41
Total current liabilities	607		575
Long-term debt, net	3,379		2,536
Pension and other postretirement benefits	19		19
Other deferred credits and liabilities	77		77
Total liabilities	4,082		3,207
Commitments and Contingencies (Note 4)
Shareholders’ Equity:
Common stock, $.01 par value, 400.0 shares authorized – shares outstanding of 266.3 and 262.0, respectively	3		3
Other paid-in capital, principally premium on common stock	7,216		6,860
Retained earnings	4,136		3,646
Accumulated other comprehensive income (loss)	(6)		(1)
Total shareholders’ equity	11,349		10,508
Total liabilities and shareholders’ equity	$	15,431	$	13,715


SCHEDULE I – CONDENSED FINANCIAL INFORMATION OF PARENT AMEREN CORPORATION CONDENSED STATEMENT OF CASH FLOWS For the Years Ended December 31, 2023, 2022, and 2021
(In millions)	2023		2022		2021
Net cash flows provided by operating activities	$	171	$	44	$	79
Cash flows from investing activities:
Money pool advances, net	(530)		40		(92)
Notes receivable – ATXI	—		35		40
Investments in subsidiaries	(109)		(30)		(489)



Other	5		3		7
Net cash flows provided by (used in) investing activities	(634)		48		(534)
Cash flows from financing activities:
Dividends on common stock	(662)		(610)		(565)
Short-term debt, net	(475)		198		(213)


Issuances of long-term debt	1,298		—		949
Issuances of common stock	346		333		308

Employee payroll taxes related to stock-based compensation	(20)		(16)		(17)
Debt issuance costs	(8)		(1)		(7)

Net cash flows provided by (used in) financing activities	479		(96)		455
Net change in cash, cash equivalents, and restricted cash	$	16	$	(4)	$	—
Cash, cash equivalents, and restricted cash at beginning of year	—		4		4
Cash, cash equivalents, and restricted cash at end of year	$	16	$	—	$	4
Supplemental information:
Cash dividends received from consolidated subsidiaries	$	173	$	76	$	123


Noncash financing activity – Issuance of common stock for stock-based compensation	40		31		33
Noncash financing activity – Issuance of common stock under the DRPlus	7		8		—

AMEREN CORPORATION (parent company only)

NOTES TO CONDENSED FINANCIAL STATEMENTS December 31, 2023

NOTE 1 – BASIS OF PRESENTATION

Ameren Corporation (parent company only) is a public utility holding company that conducts substantially all of its business operations through its subsidiaries. Ameren Corporation (parent company only) has accounted for its subsidiaries using the equity method. These financial statements are presented on a condensed basis.

See Note 1 – Summary of Significant Accounting Policies and Note 15 – Supplemental Information under Part II, Item 8, of this report for additional information.

NOTE 2 – SHORT-TERM DEBT AND LIQUIDITY

Ameren, Ameren Services, and other non-state-regulated Ameren subsidiaries have the ability, subject to Ameren parent company and applicable regulatory short-term borrowing authorizations, to access funding from the Credit Agreements and the commercial paper programs through a non-state-regulated subsidiary money pool agreement. All participants may borrow from or lend to the non-state-regulated money pool. The total amount available to pool participants from the non-state-regulated subsidiary money pool at any given time is reduced by the amount of borrowings made by participants, but is increased to the extent that the pool participants advance surplus funds to the non-state-regulated subsidiary money pool or remit funds from other external sources. The non-state-regulated subsidiary money pool was established to coordinate and to provide short-term cash and working capital for the participants. Participants receiving a loan under the non-state-regulated subsidiary money pool agreement must repay the principal amount of such loan, together with accrued interest. The rate of interest depends on the composition of internal and external funds in the non-state-regulated subsidiary money pool. Interest revenues related to non-state-regulated money pool advances were $10 million in 2023 and immaterial in 2022 and 2021. Interest charges related to non-state-regulated money pool borrowings were immaterial in 2021, 2022, and 2023.

See Note 4 – Short-term Debt and Liquidity under Part II, Item 8, of this report for a description and details of short-term debt and liquidity needs of Ameren Corporation (parent company only).

NOTE 3 – LONG-TERM OBLIGATIONS

See Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, of this report for additional information on Ameren Corporation’s (parent company only) long-term debt, indenture provisions, forward sale agreements related to common stock, and ATM program.

NOTE 4 – COMMITMENTS AND CONTINGENCIES

See Note 14 – Commitments and Contingencies under Part II, Item 8, of this report for a description of all material contingencies of Ameren Corporation (parent company only).

NOTE 5 – TOTAL OTHER EXPENSE, NET

The following table presents the components of “Total Other Expense, Net” in the Condensed Statement of Income and Comprehensive Income for the years ended December 31, 2023, 2022, and 2021:


(In millions)	2023		2022		2021
Total Other Expense, Net
Non-service cost components of net periodic benefit income	$	8	$	3	$	1
Donations	(18)		(15)		—
Other expense, net	(1)		(1)		(1)
Total Other Expense, Net	$	(11)	$	(13)	$	—

Other Income And Expenses

The following table presents the components of “Other Income, Net” in the Ameren Companies’ statements of income for the years ended December 31, 2023, 2022, and 2021:


	2023		2022		2021
Ameren:
Other Income, Net
Allowance for equity funds used during construction	$	54	$	43	$	43
Interest income on industrial development revenue bonds	1		24		25
Other interest income	32		11		2
Non-service cost components of net periodic benefit income(a)	295		184		136
Miscellaneous income	7		10		10
Earnings related to equity method investments	1		2		12
Donations	(24)		(26)		(9)
Miscellaneous expense	(18)		(22)		(17)
Total Other Income, Net	$	348	$	226	$	202
Ameren Missouri:
Other Income, Net
Allowance for equity funds used during construction	$	30	$	24	$	26
Interest income on industrial development revenue bonds	1		24		25
Other interest income	10		4		1
Non-service cost components of net periodic benefit income(a)	97		55		55
Miscellaneous income	3		4		3
Donations	(2)		(3)		(4)
Miscellaneous expense	(9)		(9)		(7)
Total Other Income, Net	$	130	$	99	$	99
Ameren Illinois:
Other Income, Net
Allowance for equity funds used during construction	$	19	$	18	$	17
Interest income	21		7		1
Non-service cost components of net periodic benefit income	124		84		55
Miscellaneous income	4		5		6
Donations	(4)		(8)		(5)
Miscellaneous expense	(8)		(10)		(8)
Total Other Income, Net	$	156	$	96	$	66

(a)For the years ended December 31, 2023, 2022, and 2021, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $27 million, $22 million, and $(7) 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.

The following table presents the components of “Total Other Expense, Net” in the Condensed Statement of Income and Comprehensive Income for the years ended December 31, 2023, 2022, and 2021:


(In millions)	2023		2022		2021
Total Other Expense, Net
Non-service cost components of net periodic benefit income	$	8	$	3	$	1
Donations	(18)		(15)		—
Other expense, net	(1)		(1)		(1)
Total Other Expense, Net	$	(11)	$	(13)	$	—

Schedule II - Valuation And Qualifying Accounts

12 Months Ended

Dec. 31, 2023

SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]

Valuation And Qualifying Accounts


SCHEDULE II – VALUATION AND QUALIFYING ACCOUNTS FOR THE YEARS ENDED DECEMBER 31, 2023, 2022, AND 2021
(In millions)
Column A	Column B		Column C				Column D		Column E
Description	Balance at Beginning of Period		(1) Charged to Costs and Expenses		(2) Charged to Other Accounts(a)		Deductions(b)		Balance at End of Period
Ameren:
Deducted from assets – allowance for doubtful accounts:
2023	$	31	$	51	$	5	$	57	$	30
2022	29		34		4		36		31
2021	50		9		—		30		29




Ameren Missouri:
Deducted from assets – allowance for doubtful accounts:
2023	$	13	$	11	$	—	$	12	$	12
2022	13		9		—		9		13
2021	16		5		—		8		13




Ameren Illinois:
Deducted from assets – allowance for doubtful accounts:
2023	$	18	$	40	$	5	$	45	$	18
2022	16		25		4		27		18
2021	34		4		—		22		16

(a)Amounts associated with the allowance for doubtful accounts relate to the uncollectible account reserve associated with receivables purchased by Ameren Illinois from alternative retail electric suppliers, as required by the Illinois Public Utilities Act.

(b)Uncollectible accounts charged off, less recoveries.

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Dec. 31, 2023
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Summary Of Significant Accounting Policies (Policies)	12 Months Ended
Summary Of Significant Accounting Policies (Policies)	Dec. 31, 2023
Accounting Policies [Abstract]
Nature of Operations	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 also 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 Missouri was incorporated in Missouri in 1922 and is successor to a number of companies, the oldest of which was organized in 1881. It is the largest electric utility in the state of Missouri. It supplies electric and natural gas service to a 24,000-square-mile area in central and eastern Missouri, which includes the Greater St. Louis area. Ameren Missouri supplies electric service to 1.2 million customers and natural gas service to 0.1 million customers. •Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois. Ameren Illinois was incorporated in Illinois in 1923 and is the successor to a number of companies, the oldest of which was organized in 1902. Ameren Illinois supplies electric and natural gas utility service to a 43,700 square mile area in central and southern Illinois. Ameren Illinois supplies electric service to 1.2 million customers and natural gas service to 0.8 million customers. •ATXI operates a FERC rate-regulated electric transmission business in the MISO. ATXI was incorporated in Illinois in 2006. ATXI operates, among other assets, the Spoon River, Mark Twain, and Illinois Rivers transmission lines.
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 the reported amounts of revenues and expenses during the reported periods. Actual results could differ from those estimates.
Public Utilities	Regulation Our customer rates are regulated by the MoPSC, the ICC, and the FERC. We defer certain costs as assets pursuant to actions of rate regulators or because of expectations that we will be able to recover such costs in future rates charged to customers. We also defer certain amounts as liabilities pursuant to actions of rate regulators or based on the expectation that such amounts will be refunded to customers in future rates. Regulatory assets and liabilities are amortized consistent with the period of expected regulatory treatment. See Note 2 – Rate and Regulatory Matters for additional information on our regulatory frameworks, regulatory recovery mechanisms, and regulatory assets and liabilities recorded at December 31, 2023 and 2022. We continually assess the recoverability of our regulatory assets and probability of refund of our regulatory liabilities. Regulatory assets are charged to earnings when it is no longer probable that such amounts will be recovered through future revenues. To the extent that refunds to customers related to regulatory liabilities are no longer probable, the amounts are credited to earnings. Environmental Costs Liabilities for environmental costs are recorded on an undiscounted basis when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated. Costs are expensed or deferred as a regulatory asset when it is expected that the costs will be recovered from customers in future rates. See Note 14 – Commitments and Contingencies for additional information on liabilities for environmental costs.
Cash and Cash Equivalents	Cash, Cash Equivalents, and Restricted Cash Cash and cash equivalents include short-term, highly liquid investments purchased with an original maturity of three months or less. Cash and cash equivalents subject to legal or contractual restrictions and not readily available for use for general corporate purposes are classified as restricted cash. See Note 15 – Supplemental Information for a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows.
Allowance for Doubtful Accounts Receivable	Allowance for Doubtful Accounts Receivable The allowance for doubtful accounts represents our estimate of existing accounts receivable that will ultimately be uncollectible. The allowance is calculated by applying estimated loss factors to various classes of outstanding receivables, including unbilled revenue. The loss factors used to estimate uncollectible accounts are based upon both historical collections experience and management’s estimate of future collections success given the existing and anticipated future collections environment. Ameren Illinois has bad debt riders that adjust rates for net write-offs of customer accounts receivable above or below those being collected in rates.
Inventories	Inventories Inventories are recorded at the lower of weighted-average cost or net realizable value. Inventories are capitalized when purchased and then expensed as consumed or capitalized as property, plant, and equipment when installed, as appropriate using the weighted-average cost method. See Note 15 – Supplemental Information for the components of inventories.
Property and Plant	Property, Plant, and Equipment, Net We capitalize the cost of additions to, and betterments of, units of property, plant, and equipment. The cost includes labor, material, applicable taxes, and overhead. An allowance for funds used during construction, as discussed below, is also capitalized as a cost of our rate-regulated assets. Maintenance expenses related to scheduled Callaway nuclear refueling and maintenance outages are deferred and amortized over the number of expected months until the completion of the next refueling outage, which historically has been approximately 18 months. Other maintenance expenditures are expensed as incurred. When units of depreciable property are retired, the original costs, and the associated removal cost, net of salvage, are charged to accumulated depreciation. If environmental expenditures are related to assets currently in use, as in the case of the installation of pollution control equipment, the cost is capitalized and depreciated over the expected life of the asset. See Asset Retirement Obligations and Removal Costs section below and Note 3 – Property, Plant, and Equipment, Net for additional information. Ameren Missouri’s cost of nuclear fuel is capitalized as a part of “Property, Plant, and Equipment, Net” on Ameren and Ameren Missouri’s balance sheets and then amortized to “Operating Expenses – Fuel” in their respective statements of income on a unit-of-production basis. Nuclear fuel amortization is reflected as a part of “Depreciation and amortization” on their respective statements of cash flow. Plant to be Abandoned, Net When it becomes probable an asset will be retired significantly in advance of its previously expected useful life and in the near term, the Ameren Companies must assess the probability of recovery of the remaining net book value of the asset to be abandoned. We recognize a loss on abandonment when it becomes probable that all or part of the cost of an asset, including a return at the applicable WACC, will be disallowed from recovery either through customer rates or through the issuance of securitized utility tariff bonds and such amount is reasonably estimable. An abandonment loss, if any, would equal the difference between the remaining net book value of the asset and the present value of the expected future cash flows. If the asset is still in service, the net book value is classified as plant to be abandoned, net, within “Property, Plant, and Equipment, Net” on the balance sheet. The net book value will be classified as a regulatory asset on the balance sheet when the asset is no longer in service or as required by a rate order. In relation to the NSR and Clean Air Act litigation discussed in Note 14 – Commitments and Contingencies, in December 2021, Ameren Missouri filed a motion with the United States District Court for the Eastern District of Missouri to modify a previously issued remedy order to allow the retirement of the Rush Island Energy Center in lieu of installing a flue gas desulfurization system, which was granted to establish an October 15, 2024 retirement date. As of December 31, 2023 and 2022, Ameren and Ameren Missouri determined that the Rush Island Energy Center met the criteria to be considered probable of abandonment and have classified its remaining net book value as plant to be abandoned, net, within “Property, Plant, and Equipment, Net” on Ameren’s and Ameren Missouri’s balance sheets. See Note 3 – Property, Plant, and Equipment, Net for our plant to be abandoned balance as of December 31, 2023 and 2022. Ameren Missouri concluded no abandonment loss was required for the Rush Island Energy Center as of December 31, 2023. As part of the assessment of any potential future abandonment loss, consideration will be given to rate and securitization orders issued by the MoPSC to Ameren Missouri and to orders issued to other Missouri utilities with similar facts. See Note 2 – Rate and Regulatory Matters for Ameren Missouri’s November 2023 petition filed with the MoPSC seeking securitization of the Rush Island Energy Center. Depreciation Depreciation is provided over the estimated lives of the various classes of depreciable property by applying composite rates on a straight-line basis to the cost basis of such property. The composite rates include a provision for the estimated removal cost of property, plant, and equipment retired from service, net of salvage. See Asset Retirement Obligation and Removal Costs section below for additional information. The provision for depreciation for the Ameren Companies in 2023, 2022, and 2021 ranged from 3% to 4% of the average depreciable cost. See Note 3 – Property, Plant, and Equipment, Net for additional information on estimated depreciable lives.
Allowance for Funds Used During Construction	Allowance for Funds Used During Construction As a part of “Property, Plant, and Equipment, Net” on the balance sheet, we capitalize allowance for funds used during construction, which is the cost of borrowed funds and the cost of equity funds (preferred and common shareholders’ equity) applicable to eligible rate-regulated construction work in progress, in accordance with the utility industry’s accounting practice and GAAP. The amount of allowance for funds used during construction is calculated using a FERC-prescribed formula based on a rate, which incorporates the average cost of short-term debt, the average cost of long-term debt, and the cost of equity funds. The portion attributable to borrowed funds is recorded as a reduction of “Interest Charges” on the statements of income. The portion attributable to equity funds is recorded within “Other Income, Net” on the statements of income. This accounting practice offsets the effect on earnings of the cost of financing during construction. See Note 15 – Supplemental Information for the amount of allowance for funds used during construction capitalized and the average rate applied to eligible construction work in progress. Allowance for funds used during construction does not represent a current source of cash funds. Under accepted ratemaking practice, cash recovery of allowance for funds used during construction and other construction costs occurs when completed projects are placed in service and reflected in customer rates.
Goodwill	Goodwill Goodwill represents the excess of the purchase price of an acquisition over the fair value of the net assets acquired. Ameren and Ameren Illinois had goodwill of $411 million at December 31, 2023 and 2022. Ameren has four reporting units: Ameren Missouri, Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Transmission. Ameren Illinois has three reporting units: Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission. Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission had goodwill of $238 million, $80 million, and $93 million, respectively, at December 31, 2023 and 2022. The Ameren Transmission reporting unit had the same $93 million of goodwill as the Ameren Illinois Transmission reporting unit at December 31, 2023 and 2022. Ameren and Ameren Illinois evaluate goodwill for impairment in each of their reporting units as of October 31 each year, or more frequently if events occur or circumstances change that would more likely than not reduce the fair value of their reporting units below their carrying amounts. To determine whether the fair value of a reporting unit is more likely than not greater than its carrying amount, Ameren and Ameren Illinois elect to perform either a qualitative assessment or to bypass the qualitative assessment and perform a quantitative test. Ameren and Ameren Illinois elected to perform a qualitative assessment for their annual goodwill impairment test conducted as of October 31, 2023. As part of this qualitative assessment, Ameren and Ameren Illinois evaluated, among other things, macroeconomic conditions, industry and market considerations such as observable industry market multiples, regulatory frameworks, cost factors, overall financial performance, and entity-specific events. The results of Ameren’s and Ameren Illinois’ qualitative assessment indicated that it was more likely than not that the fair value of each reporting unit exceeded its carrying value as of October 31, 2023, resulting in no impairment of Ameren’s or Ameren Illinois’ goodwill.
Impairment of Long-lived Assets	Impairment of Long-lived Assets We evaluate long-lived assets classified as held and used for impairment when events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. Whether an impairment has occurred is determined by comparing the estimated undiscounted cash flows attributable to the assets to the carrying value of the assets. If the carrying value exceeds the undiscounted cash flows, we recognize an impairment charge equal to the amount by which the carrying value exceeds the estimated fair value of the assets. In the period in which we determine that an asset meets held for sale criteria, we record an impairment charge to the extent the book value exceeds its estimated fair value less cost to sell. We did not identify any events or changes in circumstances that indicated that the carrying value of material long-lived assets may not be recoverable in 2023, 2022, or 2021.
Variable Interest Entities	Variable Interest Entities As of December 31, 2023 and 2022, Ameren had unconsolidated variable interests in various equity method investments, primarily to advance clean and resilient energy technologies, totaling $73 million and $68 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 December 31, 2023, the maximum exposure to loss related to these variable interest entities is limited to the investment in these partnerships of $73 million plus associated outstanding funding commitments of $14 million.
Asset Retirement Obligations	Asset Retirement Obligations and Removal Costs We record the estimated fair value of legal obligations associated with the retirement of tangible long-lived assets in the period in which the liabilities are incurred and capitalize a corresponding amount as part of the book value of the related long-lived asset. In subsequent periods, we adjust AROs for accretion and changes in the estimated fair values of the obligations, with a corresponding increase or decrease in the asset book value for the fair value changes. Asset book values, reflected within “Property, Plant, and Equipment, Net” on the balance sheet, are depreciated over the remaining useful life of the related asset. Depreciation is deferred as a regulatory balance. The depreciation of the asset book values at Ameren Missouri was $9 million, $7 million, and $14 million for the years ended December 31, 2023, 2022, and 2021, respectively, which was deferred as a reduction to the net regulatory liability. The net regulatory liability also reflects a deferral for the nuclear decommissioning trust fund balance for the Callaway Energy Center. The depreciation deferred to the regulatory asset at Ameren Illinois was immaterial in each respective period. Uncertainties as to the probability, timing, or amount of cash expenditures associated with AROs affect our estimates of fair value. Ameren and Ameren Missouri have recorded AROs for retirement costs associated with decommissioning of Ameren Missouri’s Callaway and wind renewable energy centers, certain Ameren Missouri solar energy centers, CCR facilities, and river structures at certain energy centers used for unloading coal and circulating water systems. Additionally, Ameren, Ameren Missouri, and Ameren Illinois have recorded AROs for retirement costs associated with asbestos removal and the disposal of certain transformers. See Note 15 – Supplemental Information for a reconciliation of the beginning and ending carrying amounts of AROs. Estimated funds collected from customers to pay for the future removal cost of property, plant, and equipment retired from service, net of salvage, represent a cost of removal regulatory liability. See the cost of removal regulatory liability balance in Note 2 – Rate and Regulatory Matters.
Company-owned Life Insurance	COLI Ameren (parent) and Ameren Illinois have COLI, 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 December 31, 2023, the cash surrender value of COLI at Ameren and Ameren Illinois was $248 million (December 31, 2022 – $246 million) and $111 million (December 31, 2022 – $118 million), respectively, while total borrowings against the policies were $104 million (December 31, 2022 – $110 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 COLI is affected by the investment performance of a separate account in which Ameren holds a beneficial interest.
Operating Revenues	Operating Revenues We record revenues from contracts with customers for various electric and natural gas services, which primarily consist of retail distribution, electric transmission, and off-system arrangements. When more than one performance obligation exists in a contract, the consideration under the contract is allocated to the performance obligations based on the relative standalone selling price. Electric and natural gas retail distribution revenues are earned when the commodity is delivered to our customers. We accrue an estimate of electric and natural gas retail distribution revenues for service provided but unbilled at the end of each accounting period. Electric transmission revenues are earned as electric transmission services are provided. Off-system revenues are primarily comprised of MISO revenues and wholesale bilateral revenues. MISO revenues include the sale of electricity, capacity, and ancillary services. Wholesale bilateral revenues include the sale of electricity and capacity. MISO-related electricity and wholesale bilateral electricity revenues are earned as electricity is delivered. Capacity and ancillary service revenues are earned as services are provided. Retail distribution, electric transmission, and off-system revenues, including the underlying components described above, represent a series of goods or services that are substantially the same and have the same pattern of transfer over time to our customers. Revenues from contracts with customers are equal to the amounts billed and our estimate of electric and natural gas retail distribution services provided but unbilled at the end of each accounting period. Customers are billed at least monthly, and payments are due less than one month after goods and/or services are provided. See Note 16 – Segment Information for disaggregated revenue information. For certain regulatory recovery mechanisms that are alternative revenue programs rather than revenues from contracts with customers, we recognize revenues that have been authorized for rate recovery, are objectively determinable and probable of recovery, and are expected to be collected from customers within two years from the end of the year. Our alternative revenue programs include revenue requirement reconciliations, the MEEIA, the VBA, and the WNAR. These revenues are subsequently recognized as revenues from contracts with customers when billed, with an offset to alternative revenue program revenues. As of December 31, 2023 and 2022, our remaining performance obligations 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.
Cost Of Sales	Accounting for MISO Transactions MISO-related purchase and sale transactions are recorded by Ameren, Ameren Missouri, and Ameren Illinois using settlement information provided by the MISO. Ameren Missouri records these purchase and sale transactions on a net hourly position. Ameren Missouri records net purchases in a single hour in “Operating Expenses – Purchased power” and net sales in a single hour in “Operating Revenues – Electric” in its statement of income. Ameren Illinois records net purchases in “Operating Expenses – Purchased power” in its statement of income to reflect all of its MISO transactions relating to the procurement of power for its customers. On occasion, Ameren Missouri’s and Ameren Illinois’ prior-period transactions will be resettled outside the routine settlement process because of a change in the MISO’s tariff or a material interpretation thereof. In these cases, Ameren Missouri and Ameren Illinois recognize revenues and expenses associated with resettlements once the resettlement is probable and the resettlement amount can be estimated. There were no material MISO resettlements in 2023, 2022, or 2021.
Stock-Based Compensation	Stock-based Compensation Stock-based compensation cost is measured at the grant date based on the fair value of the award, net of an assumed forfeiture rate. Ameren recognizes as compensation expense the estimated fair value of stock-based compensation on a straight-line basis over the requisite vesting period. To the extent that actual forfeitures differ from estimated forfeitures, such differences are accounted for as an adjustment to compensation expense and recorded in the period that estimates are revised. Compensation cost is ultimately recognized only for awards for which the requisite service was provided. See Note 11 – Stock-based Compensation for additional information.
Unamortized Debt Discount, Premium, And Expense	Unamortized Debt Discounts, Premiums, and Issuance Costs Long-term debt discounts, premiums, and issuance costs are amortized over the lives of the related issuances. Credit agreement fees are amortized over the term of the agreement.
Income Taxes	Income Taxes Ameren uses an asset and liability approach for its financial accounting and reporting of income taxes. Deferred tax assets and liabilities are recognized for transactions that are treated differently for financial reporting and income tax return purposes. These deferred tax assets and liabilities are based on statutory tax rates. We expect that regulators will reduce future revenues for deferred tax liabilities that were initially recorded at rates in excess of the current statutory rate. Therefore, reductions in certain excess deferred tax liabilities that were recorded because of decreases in the statutory rate have been credited to a regulatory liability. A regulatory asset has been established to recognize the probable recovery through future customer rates of tax benefits related to the equity component of allowance for funds used during construction, as well as the effects of tax rate increases. To the extent deferred tax balances are included in rate base, the revaluation of deferred taxes is recorded as a regulatory asset or liability on the balance sheet and will be collected from, or refunded to, customers. For deferred tax balances not included in rate base, the revaluation of deferred taxes is recorded as an adjustment to income tax expense on the income statement. Ameren Missouri, Ameren Illinois, and all the other Ameren subsidiary companies are parties to a tax allocation agreement with Ameren (parent) that provides for the allocation of consolidated tax liabilities. The tax allocation agreement specifies that each subsidiary be allocated an amount of tax using a stand-alone calculation ratio to the total amount of tax owed by the consolidated group. Any net benefit attributable to Ameren (parent) is reallocated to the other subsidiaries. This reallocation is treated as a capital contribution to the subsidiary receiving the benefit. See Note 13 – Related-party Transactions for information regarding capital contributions under the tax allocation agreement.
Noncontrolling Interests	The preferred stock of Ameren’s subsidiaries is included in “Noncontrolling Interests” on Ameren’s consolidated balance sheet
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. 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.
Excise Taxes	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.
Earnings Per Share, Policy	Earnings per Share Earnings per basic and diluted share are computed by dividing “Net Income Attributable to Ameren Common Shareholders” by the weighted-average number of basic and diluted common shares outstanding, respectively, during the applicable period. The weighted-average shares outstanding for earnings per diluted share includes the incremental effects resulting from performance share units, restricted stock units, and forward sale agreements relating to common stock when the impact would be dilutive, as calculated using the treasury stock method.

Rate And Regulatory Matters (Tables)

12 Months Ended

Dec. 31, 2023

Public Utilities, General Disclosures [Abstract]

Schedule of Regulatory Frameworks and Significant Recovery Mechanisms

The following table presents the regulatory frameworks and significant regulatory recovery mechanisms for each of Ameren’s rate-regulated businesses, which are discussed in more detail below:

Ameren Missouri

Ameren Illinois’ electric distribution business

Ameren Illinois’ natural gas delivery business

Ameren Illinois’ and ATXI’s electric transmission businesses

Regulatory framework

•Historical test year ratemaking

•Natural gas revenues for residential customers adjusted for sales volume deviations resulting from weather through the WNAR

•MYRP(a)

•Initial rates based on future test years

•Revenues decoupled from sales volumes

•Future test year ratemaking

•Revenues for residential and small nonresidential customers decoupled from sales volumes through the VBA

•Formula ratemaking

•Initial rates based on future test year

•Revenues decoupled from sales volumes

Regulatory mechanisms

•PISA

Riders:

•RESRAM

•FAC

•MEEIA

•PGA

•WNAR

Trackers:

•Pension and postretirement benefit costs

•Certain excess deferred income taxes

•Renewable energy standard costs

•Property taxes

•Production and investment tax credits or proceeds from the sale of certain tax credits allowed under the IRA

•Electric distribution service and energy-efficiency revenue requirement reconciliation adjustments(b)

Riders:

•Power procurement

•Transmission services

•Renewable energy credit compliance

•Zero emission credits

•Certain environmental costs

•Bad debt write-offs

•Costs of certain asbestos-related claims

Riders:

•QIP(c)

•PGA

•VBA

•Energy-efficiency program costs

•Certain environmental costs

•Bad debt write-offs

•Invested capital taxes

•Revenue requirement reconciliation adjustment

(a)Ameren Illinois used the IEIMA performance-based formula ratemaking framework to establish annual electric distribution customer rates effective through 2023. In December 2023, the ICC approved an MYRP to establish rates effective 2024 through 2027. See below for additional information regarding the MYRP approved in December 2023.

(b)Reconciliation adjustments under an MYRP are subject to a reconciliation cap which limits annual adjustment to 105%. See below for additional information regarding the reconciliation cap.

(c)The QIP expired in December 2023. Reconciliation hearings to determine the accuracy and prudence of natural gas capital investments recovered under the QIP from 2020 to 2023 are ongoing.

Schedule of Solar Projects

The following table provides information with respect to each agreement: