Ameren Illinois Company PFD 4.26% (AILIO) 10-Q 9 Nov 23 2023 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2023	Oct. 31, 2023
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
Document Transition Report	false
Entity File Number	1-14756
Entity Registrant Name	Ameren Corporation
Entity Tax Identification Number	43-1723446
Entity Incorporation, State or Country Code	MO
Entity Address, Address Line One	1901 Chouteau Avenue
Entity Address, City or Town	St. Louis
Entity Address, State or Province	MO
Entity Address, Postal Zip Code	63103
City Area Code	(314)
Local Phone Number	621-3222
Title of 12(b) Security	Common Stock, $0.01 par value per share
Trading Symbol(s)	AEE
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Emerging growth company	false
Entity Shell Company	false
Shares outstanding		262,945,048
Entity Central Index Key	0001002910
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Amendment Flag	false
Union Electric Company
Entity Information [Line Items]
Entity File Number	1-2967
Entity Registrant Name	Union Electric Company
Entity Tax Identification Number	43-0559760
Entity Incorporation, State or Country Code	MO
Entity Address, Address Line One	1901 Chouteau Avenue
Entity Address, City or Town	St. Louis
Entity Address, State or Province	MO
Entity Address, Postal Zip Code	63103
City Area Code	(314)
Local Phone Number	621-3222
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Emerging growth company	false
Entity Shell Company	false
Shares outstanding		102,123,834
Entity Central Index Key	0000100826
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Amendment Flag	false
Ameren Illinois Company
Entity Information [Line Items]
Entity File Number	1-3672
Entity Registrant Name	Ameren Illinois Company
Entity Tax Identification Number	37-0211380
Entity Incorporation, State or Country Code	IL
Entity Address, Address Line One	10 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
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
Shares outstanding		25,452,373
Entity Central Index Key	0000018654
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Amendment Flag	false

Consolidated Statement of Incom

Consolidated Statement of Income (Loss) and Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Operating Revenues:
Total operating revenues	$ 2,060	$ 2,306	$ 5,882	$ 5,911
Operating Expenses:
Fuel	158	117	423	376
Purchased Power	272	563	1,095	1,058
Natural gas purchased for resale	30	58	280	431
Other operations and maintenance	470	475	1,368	1,427
Depreciation and amortization	369	350	1,024	965
Taxes other than income taxes	147	144	398	415
Total operating expenses	1,446	1,707	4,588	4,672
Operating Income	614	599	1,294	1,239
Other Income, Net	101	58	261	180
Interest Charges	152	126	413	356
Income Before Income Taxes	563	531	1,142	1,063
Income Taxes	69	78	144	148
Net Income	494	453	998	915
Less: Net Income Attributable to Noncontrolling Interests	1	1	4	4
Net Income Attributable to Ameren Common Shareholders	493	452	994	911
Pension and other postretirement benefit plan activity, net of income taxes (benefit)	(1)	0	(3)	1
Comprehensive Income	493	453	995	916
Less: Comprehensive Income Attributable to Noncontrolling Interests	1	1	4	4
Comprehensive Income Attributable to Ameren Common Shareholders	$ 492	$ 452	$ 991	$ 912
Earnings Per Share, Basic [Abstract]
Earnings per Common Share – Basic	$ 1.88	$ 1.75	$ 3.79	$ 3.53
Earnings Per Share, Diluted [Abstract]
Earnings per Common Share – Diluted	$ 1.87	$ 1.74	$ 3.78	$ 3.51
Weighted-average Common Shares Outstanding – Basic	262.8	258.4	262.5	258.2
Weighted-average Common Shares Outstanding – Diluted	263.4	259.5	263.2	259.3
Electric
Operating Revenues:
Total operating revenues	$ 1,921	$ 2,140	$ 5,096	$ 4,971
Natural gas
Operating Revenues:
Total operating revenues	139	166	786	940
Union Electric Company
Operating Revenues:
Total operating revenues	1,237	1,359	3,101	3,096
Operating Expenses:
Fuel	158	117	423	376
Purchased Power	75	247	420	458
Natural gas purchased for resale	4	7	60	65
Other operations and maintenance	256	252	732	744
Depreciation and amortization	217	208	579	550
Taxes other than income taxes	108	106	276	281
Total operating expenses	818	937	2,490	2,474
Operating Income	419	422	611	622
Other Income, Net	44	25	85	72
Interest Charges	63	58	166	157
Income Before Income Taxes	400	389	530	537
Income Taxes	(12)	(9)	(14)	(13)
Net Income	412	398	544	550
Preferred Stock Dividends	1	1	3	3
Net Income Attributable to Parent	411	397	541	547
Union Electric Company | Electric
Operating Revenues:
Total operating revenues	1,219	1,338	2,978	2,966
Union Electric Company | Natural gas
Operating Revenues:
Total operating revenues	18	21	123	130
Ameren Illinois Company
Operating Revenues:
Total operating revenues	783	904	2,663	2,697
Operating Expenses:
Purchased Power	200	319	679	608
Natural gas purchased for resale	26	51	220	366
Other operations and maintenance	200	215	603	663
Depreciation and amortization	139	130	410	382
Taxes other than income taxes	34	34	108	122
Total operating expenses	599	749	2,020	2,141
Operating Income	184	155	643	556
Other Income, Net	37	26	115	75
Interest Charges	54	42	151	125
Income Before Income Taxes	167	139	607	506
Income Taxes	42	36	154	130
Net Income	125	103	453	376
Preferred Stock Dividends	0	0	1	1
Net Income Attributable to Parent	125	103	452	375
Ameren Illinois Company | Electric
Operating Revenues:
Total operating revenues	661	758	1,998	1,886
Ameren Illinois Company | Natural gas
Operating Revenues:
Total operating revenues	$ 122	$ 146	$ 665	$ 811

Consolidated Statement of Inc_2

Consolidated Statement of Income (Loss) and Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Income Statement [Abstract]
Pension and other postretirement benefit plan activity, tax	$ (1)	$ 0	$ (1)	$ 0

Consolidated Balance Sheet

Consolidated Balance Sheet - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Current Assets:
Cash and cash equivalents	$ 8	$ 10
Accounts receivable - trade (less allowance for doubtful accounts)	597	600
Unbilled revenue	360	446
Miscellaneous accounts receivable	65	54
Inventories	760	667
Current regulatory assets	157	354
Investment in industrial development revenue bonds	0	240
Current collateral assets	13	142
Other current assets	124	155
Total current assets	2,084	2,668
Property, Plant, and Equipment, Net	32,938	31,262
Investments and Other Assets:
Nuclear decommissioning trust fund	1,042	958
Goodwill	411	411
Regulatory assets	1,772	1,426
Pension and other postretirement benefits	470	411
Other assets	882	768
Total investments and other assets	4,577	3,974
TOTAL ASSETS	39,599	37,904
Current Liabilities:
Current maturities of long-term debt	849	340
Short-term debt	1,340	1,070
Accounts and wages payable	955	1,159
Taxes accrued	209	59
Other current liabilities	664	738
Total current liabilities	4,017	3,366
Long-term Debt, Net	13,829	13,685
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and tax credits, net	4,068	3,804
Regulatory liabilities	5,336	5,309
Asset retirement obligations	761	763
Other deferred credits and liabilities	416	340
Total deferred credits and other liabilities	10,581	10,216
Commitments and Contingencies
Shareholders’ Equity:
Common Stock	3	3
Other paid-in capital, principally premium on common stock	6,900	6,860
Retained earnings	4,144	3,646
Accumulated other comprehensive loss	(4)	(1)
Total shareholders’ equity	11,043	10,508
Noncontrolling Interests	129	129
Total equity	11,172	10,637
TOTAL LIABILITIES AND EQUITY	39,599	37,904
Union Electric Company
Current Assets:
Cash and cash equivalents	3	0
Unbilled revenue	240	184
Miscellaneous accounts receivable	24	18
Inventories	512	434
Current regulatory assets	91	254
Investment in industrial development revenue bonds	0	240
Current collateral assets	12	101
Other current assets	41	66
Total current assets	1,228	1,592
Property, Plant, and Equipment, Net	16,797	16,124
Investments and Other Assets:
Nuclear decommissioning trust fund	1,042	958
Regulatory assets	700	594
Pension and other postretirement benefits	120	98
Other assets	137	140
Total investments and other assets	1,999	1,790
TOTAL ASSETS	20,024	19,506
Current Liabilities:
Current maturities of long-term debt	350	240
Short-term debt	157	329
Taxes accrued	181	29
Other current liabilities	213	323
Total current liabilities	1,382	1,570
Long-term Debt, Net	5,991	5,846
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and tax credits, net	2,018	1,982
Regulatory liabilities	2,851	2,871
Asset retirement obligations	757	759
Other deferred credits and liabilities	57	51
Total deferred credits and other liabilities	5,683	5,663
Commitments and Contingencies
Shareholders’ Equity:
Common Stock	511	511
Other paid-in capital, principally premium on common stock	2,725	2,725
Preferred stock	80	80
Retained earnings	3,652	3,111
Total shareholders’ equity	6,968	6,427
TOTAL LIABILITIES AND EQUITY	20,024	19,506
Union Electric Company | Nonrelated Party
Current Assets:
Accounts receivable - trade (less allowance for doubtful accounts)	289	244
Current Liabilities:
Accounts and wages payable	396	606
Union Electric Company | Related Party
Current Assets:
Accounts receivable - trade (less allowance for doubtful accounts)	16	51
Current Liabilities:
Accounts and wages payable	85	43
Ameren Illinois Company
Current Assets:
Cash and cash equivalents	0	0
Unbilled revenue	120	262
Miscellaneous accounts receivable	29	23
Inventories	248	233
Current regulatory assets	63	87
Other current assets	46	98
Total current assets	811	1,056
Property, Plant, and Equipment, Net	14,271	13,353
Investments and Other Assets:
Goodwill	411	411
Regulatory assets	1,046	821
Pension and other postretirement benefits	341	318
Other assets	565	482
Total investments and other assets	2,363	2,032
TOTAL ASSETS	17,445	16,441
Current Liabilities:
Current maturities of long-term debt	0	100
Short-term debt	59	264
Customer deposits	132	87
Regulatory Liability, Current	53	64
Other current liabilities	242	232
Total current liabilities	1,042	1,291
Long-term Debt, Net	5,231	4,735
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and tax credits, net	1,845	1,699
Regulatory liabilities	2,353	2,313
Other deferred credits and liabilities	304	235
Total deferred credits and other liabilities	4,502	4,247
Commitments and Contingencies
Shareholders’ Equity:
Common Stock	0	0
Other paid-in capital, principally premium on common stock	2,979	2,929
Preferred stock	49	49
Retained earnings	3,642	3,190
Total shareholders’ equity	6,670	6,168
TOTAL LIABILITIES AND EQUITY	17,445	16,441
Ameren Illinois Company | Nonrelated Party
Current Assets:
Accounts receivable - trade (less allowance for doubtful accounts)	294	341
Current Liabilities:
Accounts and wages payable	420	451
Ameren Illinois Company | Related Party
Current Assets:
Accounts receivable - trade (less allowance for doubtful accounts)	11	12
Current Liabilities:
Accounts and wages payable	$ 136	$ 93

Consolidated Balance Sheet (Par

Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Accounts Receivable, Allowance for Credit Loss, Current	$ 33	$ 31
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	400,000,000	400,000,000
Common Stock, Shares, Outstanding	262,900,000	262,000,000
Union Electric Company
Accounts Receivable, Allowance for Credit Loss, Current	$ 12	$ 13
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized (in shares)	150,000,000	150,000,000
Common Stock, Shares, Outstanding	102,100,000	102,100,000
Ameren Illinois Company
Accounts Receivable, Allowance for Credit Loss, Current	$ 21	$ 18
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	45,000,000	45,000,000
Common Stock, Shares, Outstanding	25,500,000	25,500,000

Consolidated Statement of Cash

Consolidated Statement of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash Flows From Operating Activities:
Net income	$ 998	$ 915
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	1,063	1,016
Amortization of nuclear fuel	56	46
Amortization of debt issuance costs and premium/discounts	12	17
Deferred income taxes and investment tax credits, net	128	137
Allowance for equity funds used during construction	(39)	(31)
Stock-based compensation costs	21	18
Other	12	63
Changes in assets and liabilities:
Receivables	54	(296)
Inventories	(93)	(103)
Accounts and wages payable	(287)	(128)
Taxes accrued	156	147
Regulatory assets and liabilities	15	(17)
Assets, other	(78)	(87)
Liabilities, other	51	19
Pension and other postretirement benefits	(182)	(49)
Counterparty collateral, net	144	(68)
Net cash provided by operating activities	2,031	1,599
Cash Flows From Investing Activities:
Capital expenditures	(2,571)	(2,437)
Nuclear fuel expenditures	(63)	(22)
Purchases of securities – nuclear decommissioning trust fund	(156)	(176)
Sales and maturities of securities – nuclear decommissioning trust fund	136	163
Other	(2)	14
Net cash used in investing activities	(2,656)	(2,458)
Cash Flows From Financing Activities:
Dividends on common stock	(496)	(457)
Dividends paid to noncontrolling interest holders	(4)	(4)
Short-term debt, net	272	675
Maturities of long-term debt	(100)	(450)
Issuances of long-term debt	997	1,118
Issuances of common stock	28	29
Employee payroll taxes related to stock-based compensation	(20)	(16)
Debt issuance costs	(12)	(11)
Other	(10)	0
Net cash provided by financing activities	655	884
Net change in cash, cash equivalents, and restricted cash	30	25
Cash, cash equivalents, and restricted cash at beginning of year	216	155
Cash, cash equivalents, and restricted cash at end of period	246	180
Union Electric Company
Cash Flows From Operating Activities:
Net income	544	550
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	618	603
Amortization of nuclear fuel	56	46
Amortization of debt issuance costs and premium/discounts	5	5
Deferred income taxes and investment tax credits, net	(73)	(17)
Allowance for equity funds used during construction	(20)	(17)
Other	(12)	9
Changes in assets and liabilities:
Receivables	(119)	(160)
Inventories	(78)	(19)
Accounts and wages payable	(206)	(192)
Taxes accrued	222	161
Regulatory assets and liabilities	65	(164)
Assets, other	12	(9)
Liabilities, other	(5)	14
Pension and other postretirement benefits	(67)	(12)
Counterparty collateral, net	89	(72)
Net cash provided by operating activities	1,031	726
Cash Flows From Investing Activities:
Capital expenditures	(1,255)	(1,237)
Nuclear fuel expenditures	(63)	(22)
Purchases of securities – nuclear decommissioning trust fund	(156)	(176)
Sales and maturities of securities – nuclear decommissioning trust fund	136	163
Other	0	17
Net cash used in investing activities	(1,338)	(1,255)
Cash Flows From Financing Activities:
Dividends on preferred stock	(3)	(3)
Short-term debt, net	(172)	13
Issuances of long-term debt	499	524
Debt issuance costs	(7)	(6)
Other	(10)	0
Net cash provided by financing activities	307	528
Net change in cash, cash equivalents, and restricted cash	0	(1)
Cash, cash equivalents, and restricted cash at beginning of year	13	8
Cash, cash equivalents, and restricted cash at end of period	13	7
Ameren Illinois Company
Cash Flows From Operating Activities:
Net income	453	376
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	410	381
Amortization of debt issuance costs and premium/discounts	3	9
Deferred income taxes and investment tax credits, net	123	92
Allowance for equity funds used during construction	(15)	(14)
Other	31	19
Changes in assets and liabilities:
Receivables	164	(138)
Inventories	(15)	(84)
Accounts and wages payable	(77)	62
Taxes accrued	19	54
Regulatory assets and liabilities	(45)	147
Assets, other	(80)	(70)
Liabilities, other	74	25
Pension and other postretirement benefits	(74)	(29)
Counterparty collateral, net	55	5
Net cash provided by operating activities	1,026	835
Cash Flows From Investing Activities:
Capital expenditures	(1,226)	(1,145)
Other	(3)	0
Net cash used in investing activities	(1,229)	(1,145)
Cash Flows From Financing Activities:
Dividends on preferred stock	(1)	(1)
Short-term debt, net	(205)	250
Maturities of long-term debt	(100)	(400)
Issuances of long-term debt	498	499
Capital contributions from parent	50	0
Debt issuance costs	(5)	(5)
Net cash provided by financing activities	237	343
Net change in cash, cash equivalents, and restricted cash	34	33
Cash, cash equivalents, and restricted cash at beginning of year	191	133
Cash, cash equivalents, and restricted cash at end of period	$ 225	$ 166

Consolidated Statement of Stock

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 Shareholders’ Equity	Noncontrolling Interests:	Union Electric Company	Union Electric Company Common Stock	Union Electric Company Other Paid-in Capital:	Union Electric Company Preferred Stock	Union Electric Company Retained Earnings:	Ameren Illinois Company	Ameren Illinois Company Common Stock	Ameren Illinois Company Other Paid-in Capital:	Ameren Illinois Company Preferred Stock	Ameren Illinois Company Retained Earnings:
Beginning of period at Dec. 31, 2021			$ 6,502	$ 3,182	$ 13			$ 129					$ 2,595			$ 2,914		$ 2,677
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			37
Capital contributions from parent														$ 0		0
Stock-based compensation activity			9
Net income	$ 915								$ 550				550	376				376
Net income attributable to Ameren common shareholders	911			911
Dividends on common stock				(457)
Preferred stock dividends													(3)					(1)
Change in deferred retirement benefit costs	1				1
Net income attributable to noncontrolling interest holders	$ (4)							4
Dividends paid to noncontrolling interest holders								(4)
Common stock shares outstanding at beginning of period at Dec. 31, 2021	257,700,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan	400,000
Shares issued for stock-based compensation	400,000
Common stock shares outstanding at end of period at Sep. 30, 2022	258,500,000
End of period at Sep. 30, 2022	$ 10,330	$ 3	6,548	3,636	14	$ 14		129		$ 511	$ 2,725	$ 80	3,142		$ 0	2,914	$ 49	3,052
Shareholders' equity, end of year at Sep. 30, 2022							$ 10,201		6,458					6,015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 1.77
Beginning of period at Jun. 30, 2022			6,527	3,336	14			129					2,745			2,914		2,949
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			12
Capital contributions from parent																0
Stock-based compensation activity			9
Net income	$ 453								398				398	103				103
Net income attributable to Ameren common shareholders	452			452
Dividends on common stock				(152)
Preferred stock dividends													(1)					0
Change in deferred retirement benefit costs	0				0
Net income attributable to noncontrolling interest holders	$ (1)							1
Dividends paid to noncontrolling interest holders								(1)
Common stock shares outstanding at beginning of period at Jun. 30, 2022	258,400,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan	100,000
Shares issued for stock-based compensation	0
Common stock shares outstanding at end of period at Sep. 30, 2022	258,500,000
End of period at Sep. 30, 2022	$ 10,330	3	6,548	3,636	14	14		129		511	2,725	80	3,142		0	2,914	49	3,052
Shareholders' equity, end of year at Sep. 30, 2022							10,201		6,458					6,015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 0.59
Beginning of period at Dec. 31, 2022	$ 10,637		6,860	3,646	(1)			129					3,111			2,929		3,190
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			35
Capital contributions from parent														50		50
Stock-based compensation activity			5
Net income	998								$ 544				544	$ 453				453
Net income attributable to Ameren common shareholders	994			994
Dividends on common stock				(496)
Preferred stock dividends													(3)					(1)
Change in deferred retirement benefit costs	(3)				(3)
Net income attributable to noncontrolling interest holders	$ (4)							4
Dividends paid to noncontrolling interest holders								(4)
Common stock shares outstanding at beginning of period at Dec. 31, 2022	262,000,000								102,100,000					25,500,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan	400,000
Shares issued for stock-based compensation	500,000
Common stock shares outstanding at end of period at Sep. 30, 2023	262,900,000								102,100,000					25,500,000
End of period at Sep. 30, 2023	$ 11,172	3	6,900	4,144	(4)	(4)		129		511	2,725	80	3,652		0	2,979	49	3,642
Shareholders' equity, end of year at Sep. 30, 2023	$ 11,043						11,043		$ 6,968					$ 6,670
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 1.89
Beginning of period at Jun. 30, 2023			6,880	3,817	(3)			129					3,241			2,929		3,517
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			12
Capital contributions from parent																50
Stock-based compensation activity			8
Net income	$ 494								$ 412				412	$ 125				125
Net income attributable to Ameren common shareholders	493			493
Dividends on common stock				(166)
Preferred stock dividends													(1)					0
Change in deferred retirement benefit costs	(1)				(1)
Net income attributable to noncontrolling interest holders	$ (1)							1
Dividends paid to noncontrolling interest holders								(1)
Common stock shares outstanding at beginning of period at Jun. 30, 2023	262,700,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan	200,000
Shares issued for stock-based compensation	0
Common stock shares outstanding at end of period at Sep. 30, 2023	262,900,000								102,100,000					25,500,000
End of period at Sep. 30, 2023	$ 11,172	$ 3	$ 6,900	$ 4,144	$ (4)	$ (4)		$ 129		$ 511	$ 2,725	$ 80	$ 3,652		$ 0	$ 2,979	$ 49	$ 3,642
Shareholders' equity, end of year at Sep. 30, 2023	$ 11,043						$ 11,043		$ 6,968					$ 6,670
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 0.63

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES General Ameren, headquartered in St. Louis, Missouri, is a public utility holding company whose primary assets are its equity interests in its subsidiaries. Ameren’s subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. Dividends on Ameren’s common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren’s principal subsidiaries are listed below. Ameren has other subsidiaries that conduct other activities, such as providing shared services. • Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri. • Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois. • ATXI operates a FERC rate-regulated electric transmission business in the MISO. 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 acquisition of renewable generation projects. Ameren Illinois has no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated. Our accounting policies conform to GAAP. Our financial statements reflect all adjustments (which include normal, recurring adjustments) that are necessary, in our opinion, for a fair presentation of our results. The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. Such estimates and assumptions affect reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of financial statements, and reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates. The results of operations for an interim period may not give a true indication of results that may be expected for a full year. These financial statements should be read in conjunction with the financial statements and accompanying notes included in the Form 10-K. Variable Interest Entities As of September 30, 2023, and December 31, 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 September 30, 2023, Ameren’s maximum exposure to loss related to these variable interests is limited to its investment of $73 million plus associated outstanding funding commitments of $14 million. COLI Ameren 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 September 30, 2023, the cash surrender value of COLI at Ameren and Ameren Illinois was $250 million (December 31, 2022 – $246 million) and $122 million (December 31, 2022 – $118 million), respectively, while total borrowings against the policies were $116 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.

Rate And Regulatory Matters

Rate And Regulatory Matters	9 Months Ended
	Sep. 30, 2023
Public Utilities, General Disclosures [Abstract]
RATE AND REGULATORY MATTERS	RATE AND REGULATORY MATTERS Below is a summary of updates to significant regulatory proceedings and related legal proceedings. See Note 2 – Rate and Regulatory Matters under Part II, Item 8, of the Form 10-K for additional information and a summary of our regulatory frameworks. We are unable to predict the ultimate outcome of these matters, the timing of final decisions of the various agencies and courts, or the impact on our results of operations, financial position, or liquidity. Missouri 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 is 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 certain 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. For additional information regarding the property tax tracker and the IRA, see Note 2 – Rate and Regulatory Matters and Note 12 – Income Taxes under Part II, Item 8, in the Form 10-K. 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: Boomtown Solar Project (a)(b) Huck Finn Solar Project (b)(c) Split Rail Solar Project (d) Cass County Solar Project (d) Vandalia Solar Project (d) Bowling Green Solar Project (d) Agreement type Build-transfer Build-transfer Build-transfer (e) Development-transfer (e)(f) Self-build (e)(g) Self-build (e)(g) Facility size 150-MW 200-MW 300-MW 150-MW 50-MW 50-MW Status of MoPSC CCN Approved April 2023 Approved February 2023 Filed June 2023 (h) Filed June 2023 (h) Filed June 2023 (h) Filed June 2023 (h) Status of FERC approval of acquisition Received October 2023 Received March 2023 Expect to request by mid-2024 Not applicable Not applicable Not applicable Earliest completion date (i) Fourth quarter 2024 Fourth quarter 2024 Mid-2026 Fourth quarter 2024 Fourth quarter 2025 First quarter 2026 (a) The Boomtown Solar Project is expected to support Ameren Missouri’s transition to renewable energy generation and serve customers under the Renewable Solutions Program discussed below. (b) These projects collectively represent approximately $0.65 billion of expected capital expenditures. (c) 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. (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 October 2023, the MoPSC staff filed a recommendation that the MoPSC should not approve Ameren Missouri’s requests for CCNs for these solar projects, arguing Ameren Missouri did not adequately demonstrate the facilities are needed to continue providing service to customers. Ameren Missouri expects decisions on the CCNs by the MoPSC in the first quarter of 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. Collection under the tariff will not begin until the assets of the Boomtown Solar Project are placed in service. 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. MoPSC Staff Review of Planned Rush Island Energy Center Retirement In February 2022, the MoPSC issued an order directing the MoPSC staff to review Ameren Missouri’s planned accelerated retirement of the Rush Island Energy Center as a result of the NSR and Clean Air Act Litigation discussed in Note 9 – Commitments and Contingencies. The MoPSC staff’s review 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. In Ameren Missouri’s electric service regulatory rate review discussed above, the MoPSC staff recommended a lower rate base for the Rush Island Energy Center claiming imprudent actions by Ameren Missouri. While the nonunanimous stipulation and agreement approved by the June 2023 MoPSC electric rate order did not specify any rate base disallowance, it did not preclude parties to the agreement from raising issues regarding the prudence of Ameren Missouri’s actions and decisions with regard to the energy center in future proceedings. Ameren Missouri is unable to predict the results of this matter. Results of the review could be used in other MoPSC proceedings, which could have a material adverse effect on the results of operations, financial position, and liquidity of Ameren and Ameren Missouri. 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 the 2024 program year, 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 if Ameren Missouri achieves certain program spending goals. In 2024, Ameren Missouri expects to invest $76 million in energy-efficiency programs. Illinois MYRP In January 2023, Ameren Illinois filed an MYRP with the ICC, which was subsequently revised in September 2023, to be used in setting electric distribution service rates for 2024 through 2027. Under the MYRP, the ICC would approve base rates for electric distribution service to be charged to customers for each calendar year of the four-year period. Related to this MYRP filing, the ICC staff submitted its recommendation and the administrative law judges issued a proposed order in September 2023 and October 2023, respectively. The following table includes the forecasted revenue requirement, the ROE, the capital structure common equity percentage, and the forecasted average annual rate base for 2024 through 2027, as reflected in Ameren Illinois’ revised MYRP filing, the ICC staff’s filing, and the administrative law judges’ proposed order: Ameren Illinois’ ICC Staff’s Administrative Law Judges’ Year 2024 2025 2026 2027 2024 2025 2026 2027 2024 2025 2026 2027 Forecasted Revenue Requirement (in millions) (a) $1,289 $1,385 $1,480 $1,556 $1,211 $1,295 $1,383 $1,435 $1,219 $1,306 $1,389 $1,450 ROE (b)(c) 10.5% 10.5% 10.5% 10.5% 8.9% 8.9% 8.9% 8.9% 9.24% 9.24% 9.24% 9.24% Capital Structure Common Equity Percentage (c)(d) 53.99% 53.97% 54.02% 54.03% 50% 50% 50% 50% 50% 50% 50% 50% Forecasted Average Annual Rate Base (in billions) $4.3 $4.6 $4.9 $5.2 $4.1 $4.4 $4.6 $4.8 $4.1 $4.4 $4.6 $4.8 (a) If an initial rate increase phase-in provision, discussed below, is approved by the ICC, it would not affect the annual revenue requirement, but would affect the timing of associated recovery from customers. (b) The ICC staff filing recommended an ROE based on the annual average of the monthly yields of the 30-year United States Treasury bonds plus 580 basis points, to be updated annually for each applicable calendar year of the MYRP. An estimated ROE of 8.9% was used to calculate the forecasted revenue requirements in the ICC staff filing, which is based on the average monthly yields of the 30-year United States Treasury bonds for 2022. The ICC staff proposed that variances in the revenue requirement resulting from a change in the ROE would be excluded from the reconciliation cap discussed below. (c) In November 2023, Ameren Illinois updated its requested ROE and capital structure common equity percentage to 9.85% and 52% for all years, respectively. (d) A capital structure of up to and including 50% common equity is deemed prudent and reasonable by law. A higher equity ratio requires specific ICC approval. The administrative law judges’ October 2023 proposed order recommends a capital structure that is the lower of 50% or Ameren Illinois’ actual equity ratio, excluding goodwill. Under an MYRP, the IETL permits any initial rate increase to be phased in, with at least 50% of the first annual period’s approved rate increase reflected in rates in the first annual period, with the remaining portion deferred as a regulatory asset that earns a return at the applicable WACC and is collected from customers over a period not to exceed two years beginning within one year after the second annual period’s rates are effective. Ameren Illinois’ revised MYRP filing utilizes this phase-in provision and proposes to defer 50% of the requested 2024 rate increase of $177 million as a regulatory asset to be collected from customers in 2026. Ameren Illinois recognizes revenues that have been authorized for rate recovery when amounts are expected to be collected from customers within two years from the end of an applicable year. The ICC staff’s filing and the administrative law judges’ proposed order do not utilize a phase-in provision. An ICC decision in this proceeding is required by December 2023, with new rates effective starting in January 2024. Ameren Illinois cannot predict the level of any electric distribution service rate change the ICC may approve, or whether any rate change that may eventually be approved will be sufficient for Ameren Illinois to recover its costs to the extent those costs are subject to and exceed the reconciliation cap discussed below and earn a reasonable return on its investments when the rate change goes into effect. The MYRP also allows Ameren Illinois to 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 would be 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 through riders outside of base rates, such as riders for electric energy-efficiency investments, power procurement and transmission services, renewable energy credits, zero emission credits, certain environmental costs, and bad debt write-offs, among others. Ameren Illinois’ existing riders will remain effective and electric distribution service revenues will continue to be decoupled from sales volumes under the MYRP. The actual revenue requirement for a particular year would incorporate Ameren Illinois’ year-end rate base and actual capital structure for such year, provided that the common equity ratio in such capital structure may not exceed that approved by the ICC in the MYRP. Excluding the proposed phase-in of the initial rate increase discussed above, and subject to the reconciliation cap, if a given year’s revenue amount collected from customers varies from the approved revenue requirement, an adjustment would be 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 would then be collected from, or refunded to, customers within two years from the end of the applicable annual period. Under the MYRP, the ROE approved by the ICC will be subject to annual adjustments based on performance metrics. In 2022, the ICC issued an order approving total ROE incentives and penalties of 24 basis points, 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 will 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. 2022 Electric Distribution Revenue Requirement Reconciliation Adjustment Request In April 2023, Ameren Illinois filed for a reconciliation adjustment to its 2022 electric distribution service revenue requirement with the ICC. In November 2023, Ameren Illinois filed a revised reconciliation adjustment, requesting recovery of $117 million. The reconciliation adjustment reflects Ameren Illinois’ actual 2022 recoverable costs, year-end rate base, and capital structure, which was composed of 52% common equity. In August 2023, the ICC staff submitted its calculation of the reconciliation adjustment, recommending recovery of $110 million, which is based on a capital structure composed of 50% common equity. In October 2023, the administrative law judges issued a proposed order consistent with the ICC staff’s recommendation. An ICC decision in this proceeding is required by December 2023, and any approved adjustment would be collected from customers in 2024. Electric Customer Energy-Efficiency Investments In May 2023, Ameren Illinois filed its annual electric energy-efficiency formula rate update to increase its rates by $27 million with the ICC. In August 2023, the ICC staff submitted a calculation of the revenue requirement included in Ameren Illinois’ filing, recommending a $24 million increase in rates. An ICC decision in this proceeding is required by December 2023, with new rates effective January 2024. 2023 Natural Gas Delivery Service Regulatory Rate Review In January 2023, Ameren Illinois filed a request with the ICC seeking approval to increase its annual revenues for natural gas delivery service. In October 2023, Ameren Illinois filed a revised request seeking to increase its annual revenues by $140 million, which includes an estimated $77 million of annual revenues that would otherwise be recovered under riders. The revised request is based on a 10.22% allowed ROE, a capital structure composed of 52% common equity, and a rate base of $2.9 billion. In an attempt to reduce regulatory lag, Ameren Illinois used a 2024 future test year in this proceeding. In October 2023, the ICC staff recommended an increase to annual revenues for natural gas delivery service of $127 million, which includes an estimated $77 million of annual revenues that would otherwise be recovered under riders. The recommendation is based on a 9.89% ROE, a capital structure composed of 50% common equity, and a rate base of $2.9 billion. In July 2023, other intervenors recommended an increase to annual revenues ranging from $98 million to $106 million, which were based on varying rate base amounts, a 9.5% ROE, and a capital structure composed of 52% common equity. In September 2023, the administrative law judge issued a proposed order consistent with the ICC staff’s recommendation. In October 2023, the other intervenors revised their recommendation to include a capital structure composed of 50% common equity, but did not revise their recommended revenue requirement. A decision by the ICC in this proceeding is required by late November 2023, with new rates expected to be effective by early December 2023. Ameren Illinois cannot predict the level of any delivery service rate change the ICC may approve, nor whether any rate change that may eventually be approved will be sufficient to enable Ameren Illinois to recover its costs and to earn a reasonable return on investments when the rate changes go into effect. 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 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 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 is 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. 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. In October 2023, the FERC 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. 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 $19 million and $13 million, respectively, based on each company’s 2023 projected rate base.

Short-Term Debt And Liquidity

Short-Term Debt And Liquidity	9 Months Ended
	Sep. 30, 2023
Debt Disclosure [Abstract]
SHORT-TERM DEBT AND LIQUIDITY	SHORT-TERM DEBT AND LIQUIDITY The liquidity needs of the Ameren Companies are typically supported through the use of available cash, drawings under committed credit agreements, commercial paper issuances, and, in the case of Ameren Missouri and Ameren Illinois, short-term affiliate borrowings. See Note 4 – Short-term Debt and Liquidity under Part II, Item 8, in the Form 10-K for a description of our indebtedness provisions and other covenants as well as a description of money pool arrangements. Short-term Borrowings The Missouri Credit Agreement and the Illinois Credit Agreement are available to support issuances under Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper programs, respectively, subject to borrowing sublimits, and the issuance of letters of credit. As of September 30, 2023, based on commercial paper outstanding and letters of credit issued under the Credit Agreements, along with cash and cash equivalents, the net liquidity available to Ameren (parent), Ameren Missouri, and Ameren Illinois, collectively, was $1.3 billion. The Ameren Companies were in compliance with the covenants in their Credit Agreements as of September 30, 2023. As of September 30, 2023, the ratios of consolidated indebtedness to consolidated total capitalization, calculated in accordance with the provisions of the Credit Agreements, were 59%, 49%, and 45% for Ameren, Ameren Missouri, and Ameren Illinois, respectively. The following table presents commercial paper outstanding, net of issuance discounts, as of September 30, 2023, and December 31, 2022. There were no borrowings outstanding under the Credit Agreements as of September 30, 2023, or December 31, 2022. September 30, 2023 December 31, 2022 Ameren (parent) $ 1,124 $ 477 Ameren Missouri 157 329 Ameren Illinois 59 264 Ameren consolidated $ 1,340 $ 1,070 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 nine months ended September 30, 2023 and 2022: Ameren Ameren Ameren Ameren 2023 Average daily amount outstanding $ 687 $ 306 $ 181 $ 1,174 Weighted-average interest rate 5.29 % 5.15 % 5.15 % 5.24 % Peak amount outstanding during period (a) $ 1,127 $ 592 $ 450 $ 1,381 Peak interest rate 5.60 % 5.60 % 5.60 % 5.60 % 2022 Average daily amount outstanding $ 439 $ 253 $ 99 $ 791 Weighted-average interest rate 1.58 % 1.16 % 1.77 % 1.47 % Peak amount outstanding during period (a) $ 690 $ 539 $ 354 $ 1,222 Peak interest rate 3.55 % 3.55 % 3.60 % 3.60 % (a) The timing of peak outstanding commercial paper issuances and borrowings under the Credit Agreements varies by company. Therefore, the sum of individual company peak amounts may not equal the Ameren consolidated peak for the period. Money Pools Ameren has money pool agreements with and among its subsidiaries to coordinate and provide for certain short-term cash and working capital requirements. The average interest rate for borrowings under the utility money pool for the three and nine months ended September 30, 2023, was 5.50% and 5.20%, respectively (2022 – 2.48% and 1.29%, respectively). See Note 8 – Related-party Transactions for the amount of interest income and expense from the utility money pool arrangements recorded by Ameren Missouri and Ameren Illinois for the three and nine months ended September 30, 2023 and 2022.

Long-Term Debt And Equity Finan

Long-Term Debt And Equity Financings	9 Months Ended
	Sep. 30, 2023
Long-Term Debt And Equity Financings [Abstract]
LONG-TERM DEBT AND EQUITY FINANCINGS	LONG-TERM DEBT AND EQUITY FINANCINGS Ameren For the three and nine months ended September 30, 2023, Ameren issued a total of 0.2 million and 0.4 million shares of common stock, respectively, under its DRPlus and 401(k) plan, and received proceeds of $5 million and $28 million, respectively. As of September 30, 2023, Ameren had a receivable of $7 million related to issuances of common stock under its DRPlus and 401(k) plan. In addition, in the first quarter of 2023, Ameren issued 0.5 million shares of common stock valued at $37 million upon the settlement of stock-based compensation awards. In May 2023, Ameren filed a Form S-3 registration statement with the SEC, registering 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. There were no shares issued under the ATM program for the three and nine months ended September 30, 2023. As of September 30, 2023, Ameren had approximately $910 million of common stock available for sale under the ATM program, which takes into account the forward sale agreements in effect as of September 30, 2023, discussed below. The forward sale agreements outstanding as of September 30, 2023, can be settled at Ameren’s discretion on or prior to dates ranging from January 10, 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 $81.83 to $94.63, with an average initial forward sale price of $91.23. Each initial forward sale price is subject to adjustment based on a floating interest rate factor equal to the overnight bank funding rate less a spread of 75 basis points, and will be subject to decrease on certain dates specified in the forward sale agreements by specified amounts related to expected dividends on shares of the common stock during the term of the forward sale agreements. If the overnight bank funding rate is less than the spread on any day, the interest rate factor will result in a reduction of the forward sale price. The forward sale agreements will be physically settled unless Ameren elects to settle in cash or to net share settle. At September 30, 2023, Ameren could have settled the forward sale agreements with physical delivery of 4.3 million shares of common stock to the respective counterparties in exchange for cash of $390 million. Alternatively, the forward sale agreements could have also been settled at September 30, 2023, with the counterparties delivering approximately $72 million of cash or approximately 1.0 million shares of common stock to Ameren. In connection with the forward sale agreements outstanding at September 30, 2023, the various counterparties, or their affiliates, borrowed from third parties and sold 4.3 million shares of common stock. The gross sales price of these shares totaled $392 million. Ameren has not received any proceeds from such sales of borrowed shares. The forward sale agreements have been classified as equity transactions. Ameren Missouri 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. 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. Ameren Illinois received capital contributions totaling $50 million from Ameren (parent) during the nine months ended September 30, 2023. Indenture Provisions and Other Covenants See Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, in the Form 10-K for a description of our indenture provisions and other covenants, as well as restrictions on the payment of dividends. At September 30, 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. Off-balance-sheet Arrangements At September 30, 2023, none of the Ameren Companies had any material off-balance-sheet financing arrangements, other than Ameren’s investment 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

Other Income, Net	9 Months Ended
	Sep. 30, 2023
Other Nonoperating Income (Expense) [Abstract]
OTHER INCOME, NET	OTHER INCOME, NET The following table presents the components of “Other Income, Net” in the Ameren Companies’ statements of income for the three and nine months ended September 30, 2023 and 2022: Three Months Nine Months 2023 2022 2023 2022 Ameren: Allowance for equity funds used during construction $ 16 $ 12 $ 39 $ 31 Interest income on industrial development revenue bonds — 6 1 18 Other interest income 6 2 23 6 Non-service cost components of net periodic benefit income (a) 84 45 211 138 Miscellaneous income 1 3 4 8 Earnings (losses) related to equity method investments — (3) 2 1 Donations (1) (1) (5) (5) Miscellaneous expense (5) (6) (14) (17) Total Other Income, Net $ 101 $ 58 $ 261 $ 180 Ameren Missouri: Allowance for equity funds used during construction $ 8 $ 7 $ 20 $ 17 Interest income on industrial development revenue bonds — 6 1 18 Other interest income 3 1 8 2 Non-service cost components of net periodic benefit income (a) 34 13 62 41 Miscellaneous income 1 1 3 3 Donations — — (2) (2) Miscellaneous expense (2) (3) (7) (7) Total Other Income, Net $ 44 $ 25 $ 85 $ 72 Ameren Illinois: Allowance for equity funds used during construction $ 5 $ 5 $ 15 $ 14 Interest income 4 1 14 4 Non-service cost components of net periodic benefit income 31 21 93 63 Miscellaneous income — 3 2 5 Donations (1) (1) (3) (3) Miscellaneous expense (2) (3) (6) (8) Total Other Income, Net $ 37 $ 26 $ 115 $ 75 (a) For the three and nine months ended September 30, 2023 the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $(2) million and $32 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 deferral was $5 million and $16 million, respectively, for the three and nine months ended September 30, 2022. See Note 11 – Retirement Benefits for additional information.

Derivative Financial Instrument

Derivative Financial Instruments	9 Months Ended
	Sep. 30, 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. 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 September 30, 2023, and December 31, 2022, all contracts that met the definition of a derivative and were not eligible for the NPNS exception received regulatory deferral. Cash flows for all derivative financial instruments are classified in cash flows from operating activities. The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of September 30, 2023, and December 31, 2022. As of September 30, 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) September 30, 2023 December 31, 2022 Commodity Ameren Missouri Ameren Illinois Ameren Ameren Missouri Ameren Illinois Ameren Fuel oils (in gallons) 19 — 19 18 — 18 Natural gas (in mmbtu) 52 213 265 48 157 205 Power (in MWhs) 1 5 6 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 September 30, 2023, and December 31, 2022: September 30, 2023 December 31, 2022 Balance Sheet Location Ameren Ameren Ameren Ameren Ameren Ameren Fuel oils Other current assets $ 6 $ — $ 6 $ 13 $ — $ 13 Other assets 2 — 2 3 — 3 Natural gas Other current assets 1 6 7 7 23 30 Other assets 5 3 8 9 11 20 Power Other current assets 7 — 7 14 2 16 Other assets — — — — 4 4 Uranium Other current assets 5 — 5 2 — 2 Other assets — — — 1 — 1 Total assets $ 26 $ 9 $ 35 $ 49 $ 40 $ 89 Natural gas Other current liabilities 7 25 32 7 20 27 Other deferred credits and liabilities 6 16 22 2 9 11 Power Other current liabilities 7 8 15 59 2 61 Other deferred credits and liabilities — 56 56 — 37 37 Total liabilities $ 20 $ 105 $ 125 $ 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. Th e following table p rovides the recognized gross derivative balances and the net amounts of those derivatives subject to an enforceable master netting arrangement or similar agreement as of September 30, 2023, and December 31, 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 September 30, 2023 Assets: Ameren Missouri $ 26 $ 6 $ — $ 20 Ameren Illinois 9 5 — 4 Ameren $ 35 $ 11 $ — $ 24 Liabilities: Ameren Missouri $ 20 $ 6 $ 5 $ 9 Ameren Illinois 105 5 — 100 Ameren $ 125 $ 11 $ 5 $ 109 December 31, 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 September 30, 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 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 September 30, 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 Potential Aggregate Amount of Additional Collateral Required (b) Ameren Missouri $ 14 $ — $ 8 Ameren Illinois 41 — 35 Ameren $ 55 $ — $ 43 (a) Before consideration of master netting arrangements or similar agreements.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Fair Value Disclosures	FAIR VALUE MEASUREMENTSFair value is defined as the price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Fair value measurements are classified in three levels based on the fair value hierarchy as defined by GAAP. See Note 8 – Fair Value Measurements under Part II, Item 8, of the Form 10-K for information related to hierarchy levels and valuation techniques. We consider nonperformance risk in our valuation of derivative instruments by analyzing our own credit standing and the credit standing of our counterparties, and by considering any credit enhancements (e.g., collateral). Included in our valuation, and based on current market conditions, is a valuation adjustment for counterparty default derived from market data such as the price of credit default swaps, bond yields, and credit ratings. No material gains or losses related to valuation adjustments for counterparty default risk were recorded at Ameren, Ameren Missouri, or Ameren Illinois in the three and nine months ended September 30, 2023 or 2022. At September 30, 2023, and December 31, 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 September 30, 2023, and December 31, 2022: September 30, 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 $ 8 $ — $ — $ 8 $ 16 $ — $ — $ 16 Natural gas — 6 — 6 1 15 — 16 Power — — 7 7 — — 14 14 Uranium — — 5 5 — — 3 3 Total derivative assets – commodity contracts $ 8 $ 6 $ 12 $ 26 $ 17 $ 15 $ 17 $ 49 Nuclear decommissioning trust fund: Equity securities: U.S. large capitalization $ 703 $ — $ — $ 703 $ 618 $ — $ — $ 618 Debt securities: U.S. Treasury and agency securities — 138 — 138 — 137 — 137 Corporate bonds — 126 — 126 — 122 — 122 Other — 70 — 70 — 70 — 70 Total nuclear decommissioning trust fund $ 703 $ 334 $ — $ 1,037 (a) $ 618 $ 329 $ — $ 947 (a) Total Ameren Missouri $ 711 $ 340 $ 12 $ 1,063 $ 635 $ 344 $ 17 $ 996 Ameren Illinois Derivative assets – commodity contracts: Natural gas $ — $ 6 $ 3 $ 9 $ 1 $ 28 $ 5 $ 34 Power — — — — — — 6 6 Total Ameren Illinois $ — $ 6 $ 3 $ 9 $ 1 $ 28 $ 11 $ 40 Ameren Derivative assets – commodity contracts (b) $ 8 $ 12 $ 15 $ 35 $ 18 $ 43 $ 28 $ 89 Nuclear decommissioning trust fund (c) 703 334 — 1,037 (a) 618 329 — 947 (a) Total Ameren $ 711 $ 346 $ 15 $ 1,072 $ 636 $ 372 $ 28 $ 1,036 Liabilities: Ameren Missouri Derivative liabilities – commodity contracts: Natural gas — 11 2 13 — 6 3 9 Power 6 — 1 7 57 — 2 59 Total Ameren Missouri $ 6 $ 11 $ 3 $ 20 $ 57 $ 6 $ 5 $ 68 Ameren Illinois Derivative liabilities – commodity contracts: Natural gas $ 2 $ 34 $ 5 $ 41 $ — $ 19 $ 10 $ 29 Power — — 64 64 — — 39 39 Total Ameren Illinois $ 2 $ 34 $ 69 $ 105 $ — $ 19 $ 49 $ 68 Ameren Derivative liabilities – commodity contracts (b) $ 8 $ 45 $ 72 $ 125 $ 57 $ 25 $ 54 $ 136 (a) Balance excludes $5 million and $11 million of cash and cash equivalents, receivables, payables, and accrued income, net, for September 30, 2023, and December 31, 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 the fair value of Ameren’s nuclear decommissioning trust fund by investment type. Level 3 fuel oils, natural gas, and uranium derivative contract assets and liabilities measured at fair value on a recurring basis were immaterial for all periods presented. The following table presents the fair value reconciliation of Level 3 power derivative contract assets and liabilities measured at fair value on a recurring basis for the three and nine months ended September 30, 2023 and 2022: 2023 2022 Ameren Missouri Ameren Illinois Ameren Ameren Missouri Ameren Illinois Ameren For the three months ended September 30: Beginning balance at July 1 $ 14 $ (68) $ (54) $ (36) $ (44) $ (80) Realized and unrealized gains/(losses) included in regulatory assets/liabilities (5) 1 (4) (10) 30 20 Settlements (3) 3 — 38 (6) 32 Ending balance at September 30 $ 6 $ (64) $ (58) $ (8) $ (20) $ (28) Change in unrealized gains/(losses) related to assets/liabilities held at September 30 $ (5) $ 1 $ (4) $ (3) $ 28 $ 25 For the nine months ended September 30: Beginning balance at January 1 $ 12 $ (33) $ (21) $ (15) $ (117) $ (132) Realized and unrealized gains/(losses) included in regulatory assets/liabilities 3 (40) (37) (56) 105 49 Settlements (9) 9 — 63 (8) 55 Ending balance at September 30 $ 6 $ (64) $ (58) $ (8) $ (20) $ (28) Change in unrealized gains/(losses) related to assets/liabilities held at September 30 $ 6 $ (31) $ (25) $ (39) $ 100 $ 61 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 September 30, 2023, and December 31, 2022: Fair Value Weighted Average (b) Commodity Assets Liabilities Valuation Technique(s) Unobservable Input (a) Range 2023 Power (c) $ 7 $ (65) Discounted cash flow Average forward peak and off-peak pricing – forwards/swaps ($/MWh) 32 – 63 43 Nodal basis ($/MWh) (10) – (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 the carrying amount and, by level within the fair value hierarchy, the fair value of financial assets and liabilities disclosed, but not recorded, at fair value as of September 30, 2023, and December 31, 2022: Carrying Fair Value Level 1 Level 2 Level 3 Total September 30, 2023 Ameren: Cash, cash equivalents, and restricted cash $ 246 $ 246 $ — $ — $ 246 Short-term debt 1,340 — 1,340 — 1,340 Long-term debt (including current portion) 14,678 (a) — 11,985 432 (b) 12,417 Ameren Missouri: Cash, cash equivalents, and restricted cash $ 13 $ 13 $ — $ — $ 13 Short-term debt 157 — 157 — 157 Long-term debt (including current portion) 6,341 (a) — 5,287 — 5,287 Ameren Illinois: Cash, cash equivalents, and restricted cash $ 225 $ 225 $ — $ — $ 225 Short-term debt 59 — 59 — 59 Long-term debt (including current portion) 5,231 (a) — 4,419 — 4,419 December 31, 2022 Ameren: Cash, cash equivalents, and restricted cash $ 216 $ 216 $ — $ — $ 216 Investment 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 Investment 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 $105 million, $45 million, and $48 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of September 30, 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 an investment in industrial development revenue bonds, classified as held-to-maturity, that were equal to the finance obligation for the Audrain CT energy center. As of December 31, 2022, the carrying amount of the investment in industrial development revenue bonds and the finance obligation approximated fair value.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2023
Related Party Transactions [Abstract]
RELATED PARTY TRANSACTIONS	RELATED-PARTY TRANSACTIONS In the ordinary course of business, Ameren Missouri and Ameren Illinois have engaged in, and may in the future engage in, affiliate transactions. These transactions primarily consist of natural gas and power purchases and sales, services received or rendered, and borrowings and lendings. Transactions between Ameren’s subsidiaries are reported as affiliate transactions on their individual financial statements, but those transactions are eliminated in consolidation for Ameren’s consolidated financial statements. For a discussion of material related-party agreements and money pool arrangements, see Note 13 – Related-party Transactions and Note 4 – Short-term Debt and Liquidity under Part II, Item 8, of the Form 10-K. Support Services Agreements Ameren Missouri and Ameren Illinois had long-term receivables included in “Other assets” from Ameren Services of $28 million and $31 million, respectively, as of September 30, 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. Tax Allocation Agreement See Note 1 – Summary of Significant Accounting Policies under Part II, Item 8, of the Form 10-K for a discussion of the tax allocation agreement. The following table presents the affiliate balances related to income taxes for Ameren Missouri and Ameren Illinois as of September 30, 2023, and December 31, 2022: September 30, 2023 December 31, 2022 Ameren Missouri Ameren Illinois Ameren Missouri Ameren Illinois Income taxes payable to parent (a) $ 29 $ 81 $ — $ 50 Income taxes receivable from parent (b) — — 39 — (a) Included in “Accounts payable – affiliates” on the balance sheet. (b) Included in “Accounts receivable – affiliates” on the balance sheet. Effects of Related-party Transactions on the Statement of Income The following table presents the impact on Ameren Missouri and Ameren Illinois of related-party transactions for the three and nine months ended September 30, 2023 and 2022: Three Months Nine Months Agreement Income Statement Ameren Ameren Ameren Ameren Ameren Missouri power supply Operating Revenues 2023 $ 2 $ (a) $ 2 $ (a) agreements with Ameren Illinois 2022 2 (a) 7 (a) Ameren Missouri and Ameren Illinois Operating Revenues 2023 $ 7 $ (b) $ 25 $ (b) rent and facility services 2022 6 (b) 18 (b) Ameren Missouri and Ameren Illinois miscellaneous Operating Revenues 2023 $ (b) $ 2 $ (b) $ 2 support services 2022 (b) (b) (b) 1 Total Operating Revenues 2023 $ 9 $ 2 $ 27 $ 2 2022 8 (b) 25 1 Ameren Illinois power supply Purchased Power 2023 $ (a) $ 2 $ (a) $ 2 agreements with Ameren Missouri 2022 (a) 2 (a) 7 Ameren Missouri and Ameren Illinois Purchased Power 2023 $ (b) $ 1 $ 1 $ 1 transmission services from ATXI 2022 1 (b) 1 (b) Total Purchased Power 2023 $ (b) $ 3 $ 1 $ 3 2022 1 2 1 7 Ameren Missouri and Ameren Illinois Other Operations and Maintenance 2023 $ (b) $ (b) $ (b) $ 2 rent and facility services 2022 (b) 1 (b) 2 Ameren Services support services Other Operations and Maintenance 2023 $ 36 $ 33 $ 106 $ 101 agreement 2022 38 36 109 103 Total Other Operations and 2023 $ 36 $ 33 $ 106 $ 103 Maintenance 2022 38 37 109 105 Money pool borrowings (advances) (Interest Charges)/Other Income, Net 2023 $ (b) $ (b) $ (b) $ (b) 2022 (b) (b) (b) (b) (a) Not applicable. (b) Amount less than $1 million.

Commitments And Contingencies

Commitments And Contingencies	9 Months Ended
	Sep. 30, 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 in this report and in the Form 10-K, will not have a material adverse effect on our results of operations, financial position, or liquidity. Reference is made to Note 1 – Summary of Significant Accounting Policies, Note 2 – Rate and Regulatory Matters, Note 9 – Callaway Energy Center, Note 13 – Related-party Transactions, and Note 14 – Commitments and Contingencies under Part II, Item 8, of the Form 10-K. See also Note 1 – Summary of Significant Accounting Policies, Note 2 – Rate and Regulatory Matters, Note 8 – Related-party Transactions, and Note 10 – Callaway Energy Center of this report. Environmental Matters Our electric generation, transmission, and distribution and natural gas distribution and storage operations must comply with a variety of statutes and regulations relating to the protection of the environment and human health and safety including permitting programs implemented 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 SO 2 , particulate matter, NO x , mercury, toxic metals and acid gases, and CO 2 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. Seasonal nighttime curtailment began again in April 2023. Ameren Missouri resumed nighttime operations in November 2023, but 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 2023 through 2027 in order to comply with existing environmental regulations. Additional capital expenditures for environmental controls beyond 2027 could be required. This estimate of capital expenditures includes surface impoundment closure and corrective action measures required by the CCR Rule and potential modifications to cooling water intake structures at existing power plants under Clean Water Act rules, all of which are discussed below. In addition to planned retirements of coal-fired energy centers as set forth in the 2023 IRP filed with the MoPSC in September 2023 and as noted in the NSR and Clean Air Act litigation discussed below and Illinois emissions standards discussed in Note 14 – Commitments and Contingencies under Part II, Item 8, of the Form 10-K, 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 laws and rules 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 rules. Clean Air Act Federal and state laws, including the CSAPR, regulate emissions of SO 2 and NO x 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 NO x 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 NO x 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, which is expected in 2024. Ameren Missouri has complied 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 other existing NO x air pollution control equipment. Restrictions on the use of state budget NO x allowances for compliance with NO x 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. CO 2 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 proposed rule that would set CO 2 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 November 2021, the court of appeals issued an order denying requests for re-consideration sought by both Ameren Missouri and the United States Department of Justice. 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 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 for the period between September 2023 and 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 expects to seek approval from the MoPSC in 2023, 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. As of September 30, 2023, the Rush Island Energy Center had a net plant balance of approximately $550 million included in plant to be abandoned, net, within “Property, Plant, and Equipment, Net” and a rate base of approximately $0.5 billion. See Note 1 – Summary of Significant Accounting Policies under Part II, Item 8, of the Form 10-K for additional information regarding plant to be abandoned, net. Ameren Missouri is unable to predict the ultimate resolution of this matter; however, such resolution could have a material adverse effect on the results of operations, financial position, and liquidity of Ameren and Ameren Missouri. Clean Water Act The EPA’s regulations implementing Section 316(b) of the Clean Water Act require power plant operators to evaluate cooling water intake structures and identify measures for reducing the number of aquatic organisms impinged on a power plant’s cooling water intake screens or entrained through the plant’s cooling water system. All of Ameren Missouri’s coal-fired and nuclear energy centers are subject to the cooling water intake structures rule. Requirements of the rule are implemented by state regulators through the permit renewal process of each power plant’s water discharge permit. 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 pending at its Sioux Energy Center and retired Meramec Energy Center. Ameren Missouri plans to substantially complete the closures of surface impoundments as required by the CCR Rule by the end of 2024. 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 September 30, 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 September 30, 2023, Ameren Illinois has remediated the majority of the 44 former MGP sites in Illinois with an estimated remaining obligation related to these former MGP sites at $60 million to $112 million. Ameren and Ameren Illinois recorded a liability of $60 million to represent the estimated minimum obligation for these sites, as no other amount within the range was a better estimate. About half of the remaining liability recorded relates to remediation activities that are expected to be completed after 2023. 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. The scope of the remediation activities at these former MGP sites may increase as remediation efforts continue. Considerable uncertainty remains in these estimates because many site-specific factors can influence the actual costs, including unanticipated underground structures, the degree to which groundwater is encountered, regulatory changes, local ordinances, and site accessibility. The actual costs and timing of completion may vary substantially from these estimates. Our operations or those of our predecessor companies involve the use of, disposal of, and, in appropriate circumstances, the cleanup of substances regulated under environmental laws. We are unable to determine whether such historical practices will result in future environmental commitments, including additional or more stringent cleanup standards, or will affect our results of operations, financial position, or liquidity.

Callaway Energy Center

Callaway Energy Center	9 Months Ended
	Sep. 30, 2023
Nuclear Waste Matters [Abstract]
CALLAWAY ENERGY CENTER	CALLAWAY ENERGY CENTER See Note 9 – Callaway Energy Center under Part II, Item 8, of the Form 10-K for information regarding spent nuclear fuel recovery, recovery of decommissioning costs, and the nuclear decommissioning trust fund. The fair value of the trust fund for Ameren Missouri’s Callaway Energy Center is reported as “Nuclear decommissioning trust fund” in Ameren’s and Ameren Missouri’s balance sheets. This amount is legally restricted and may be used only to fund the costs of nuclear decommissioning. Changes in the fair value of the trust fund are recorded as an increase or decrease to the nuclear decommissioning trust fund, with an offsetting adjustment to the related regulatory liability. Ameren and Ameren Missouri have recorded an ARO for the Callaway Energy Center decommissioning costs at fair value, which represents the present value of estimated future cash outflows. Annual decommissioning costs of $7 million are included in the costs used to establish electric rates for Ameren Missouri’s customers. Every three years, the MoPSC requires Ameren Missouri to file an updated cost study and funding analysis for decommissioning its Callaway Energy Center. An updated cost study and funding analysis was last filed with the MoPSC in November 2020. Ameren Missouri expects to file an updated cost study with the MoPSC by December 2023 and has reflected the 2023 updated cost study results in the related ARO at September 30, 2023. In February 2021, the MoPSC approved no change in electric rates for decommissioning costs based on Ameren Missouri’s updated cost study funding analysis. See Note 13 – Supplemental Information for more information on Ameren Missouri’s AROs. Insurance The following table presents insurance coverage at Ameren Missouri’s Callaway Energy Center at October 31, 2023: Type and Source of Coverage Most Recent Maximum Coverages Maximum Assessments Public liability and nuclear worker liability: American Nuclear Insurers January 1, 2023 $ 450 $ — Pool participation (a) 16,095 (a) 166 (b) $ 16,545 (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 $450 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 insurance limits, 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

Retirement Benefits	9 Months Ended
	Sep. 30, 2023
Retirement Benefits [Abstract]
RETIREMENT BENEFITS	RETIREMENT BENEFITS The following table presents the components of the net periodic benefit cost (income) incurred for Ameren’s pension and postretirement benefit plans for the three and nine months ended September 30, 2023 and 2022: Pension Benefits Postretirement Benefits Three Months Nine Months Three Months Nine Months 2023 2022 2023 2022 2023 2022 2023 2022 Service cost (a) $ 10 $ 31 $ 56 $ 95 $ 3 $ 5 $ 9 $ 15 Non-service cost components: Interest cost 55 42 166 123 11 8 34 25 Expected return on plan assets (b) (84) (80) (251) (240) (22) (21) (68) (64) Amortization of (b) : Prior service benefit — — — — (1) (1) (3) (3) Actuarial (gain) loss (29) 7 (86) 19 (12) (5) (35) (14) Total non-service cost components (c) $ (58) $ (31) $ (171) $ (98) $ (24) $ (19) $ (72) $ (56) Net periodic benefit income (d) $ (48) $ — $ (115) $ (3) $ (21) $ (14) $ (63) $ (41) (a) Service cost, net of capitalization, is reflected in “Operating Expenses – Other operations and maintenance” on Ameren’s statement of income. (b) Prior service benefit is amortized on a straight-line basis over the average future service of active participants benefiting under a 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 5 – 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. Ameren Missouri and Ameren Illinois are responsible for their respective share of Ameren’s pension and other postretirement costs. The following table presents the respective share of net periodic pension and other postretirement benefit costs (income) incurred for the three and nine months ended September 30, 2023 and 2022: Pension Benefits Postretirement Benefits Three Months Nine Months Three Months Nine Months 2023 2022 2023 2022 2023 2022 2023 2022 Ameren Missouri (a) $ (24) $ — $ (59) $ (2) $ (8) $ (3) $ (23) $ (10) Ameren Illinois (21) 1 (48) 2 (13) (11) (40) (31) Other (3) (1) (8) (3) — — — — Ameren (a) $ (48) $ — $ (115) $ (3) $ (21) $ (14) $ (63) $ (41) (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 rates.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES The following table presents a reconciliation of the federal statutory corporate income tax rate to the effective income tax rate for the three and nine months ended September 30, 2023 and 2022: Ameren Ameren Missouri Ameren Illinois 2023 2022 2023 2022 2023 2022 Three Months Federal statutory corporate income tax rate 21 % 21 % 21 % 21 % 21 % 21 % Increases (decreases) from: Amortization of deferred investment tax credit — — (1) (1) — — Amortization of excess deferred taxes (a) (7) (8) (15) (15) (2) (2) Depreciation differences (1) — — — — — Renewable and other tax credits (b) (5) (4) (11) (10) (1) — State tax 4 4 3 3 7 7 Stock-based compensation — 1 — — — — Cash surrender value of COLI — 1 — — — — Effective income tax rate 12 % 15 % (3) % (2) % 25 % 26 % Nine Months Federal statutory corporate income tax rate 21 % 21 % 21 % 21 % 21 % 21 % Increases (decreases) from: Amortization of deferred investment tax credit — — (1) (1) — — Amortization of excess deferred taxes (a) (8) (8) (15) (15) (2) (2) Depreciation differences — — — — (1) — Renewable and other tax credits (b) (5) (4) (11) (10) — — State tax 5 5 3 3 7 7 Effective income tax rate 13 % 14 % (3) % (2) % 25 % 26 % (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.

Supplemental Information

Supplemental Information	9 Months Ended
	Sep. 30, 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 at September 30, 2023, and December 31, 2022: September 30, 2023 December 31, 2022 Ameren Ameren Ameren Ameren Ameren Ameren “Cash and cash equivalents” $ 8 $ 3 $ — $ 10 $ — $ — Restricted cash included in “Other current assets” 13 5 5 13 5 6 Restricted cash included in “Other assets” 220 — 220 185 — 185 Restricted cash included in “Nuclear decommissioning trust fund” 5 5 — 8 8 — Total cash, cash equivalents, and restricted cash $ 246 $ 13 $ 225 $ 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 September 30, 2023, and December 31, 2022, “Other current liabilities” on Ameren’s and Ameren Illinois’ balance sheets included payables for purchased receivables of $50 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 three and nine months ended September 30, 2023 and 2022: Three Months Nine Months 2023 2022 2023 2022 Ameren: Beginning of period $ 39 $ 30 $ 31 $ 29 Bad debt expense 18 14 41 23 Charged to other accounts (a) 2 1 3 3 Net write-offs (26) (14) (42) (24) End of period $ 33 $ 31 $ 33 $ 31 Ameren Missouri: Beginning of period $ 12 $ 12 $ 13 $ 13 Bad debt expense 5 3 9 6 Net write-offs (5) (3) (10) (7) End of period $ 12 $ 12 $ 12 $ 12 Ameren Illinois: (b) Beginning of period $ 27 $ 18 $ 18 $ 16 Bad debt expense 13 11 32 17 Charged to other accounts (a) 2 1 3 3 Net write-offs (21) (11) (32) (17) End of period $ 21 $ 19 $ 21 $ 19 (a) 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. (b) Ameren Illinois has riders 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. The table above does not include the impact related to the riders. As of September 30, 2023, accounts receivable balances that were 30 days or greater past due or that were a part of a deferred payment arrangement represented 17%, 8%, and 26%, or $106 million, $25 million, and $81 million, of Ameren’s, Ameren Missouri’s, and Ameren Illinois’ customer trade receivables before allowance for doubtful accounts, respectively. In comparison, as of September 30, 2022, these percentages were 17%, 12%, and 21%, or $117 million, $39 million, and $78 million, for Ameren, Ameren Missouri, and Ameren Illinois, respectively. Supplemental Cash Flow Information The following table provides noncash financing and investing activity excluded from the statements of cash flows for the nine months ended September 30, 2023 and 2022: September 30, 2023 September 30, 2022 Ameren Ameren Ameren Ameren Ameren Ameren Investing: Accrued capital expenditures, including nuclear fuel expenditures $ 518 $ 246 $ 237 $ 367 $ 187 $ 180 Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund 66 66 — (262) (262) — Return of investment in industrial development revenue bonds (a) 240 240 — — — — Financing: Issuance of common stock for stock-based compensation $ 37 $ — $ — $ 31 $ — $ — Issuance of common stock under the DRPlus 7 — — 8 — — Termination of a financing obligation (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. Asset Retirement Obligations The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the nine months ended September 30, 2023: Ameren Ameren Ameren Balance at December 31, 2022 $ 782 (a) $ 4 (b) $ 786 (a) Liabilities settled (9) — (9) Accretion 25 (c) — 25 (c) Change in estimates (18) — (18) Balance at September 30, 2023 $ 780 (a) $ 4 (b) $ 784 (a) (a) Balance included $23 million in “Other current liabilities” on the balance sheet as of both September 30, 2023, and December 31, 2022. (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. Stock-based Compensation In the first quarter of 2023, Ameren granted 265,422 performance share units with a grant date fair value of $24 million and 116,701 restricted share units with a grant date fair value of $10 million. Awards vest approximately 3 years after the grant date or on a pro-rata basis upon death or eligible retirement. The performance share units vest based on the achievement of certain specified market performance measures (227,494 performance share units) or clean energy transition targets (37,928 performance share units). The exact number of shares issued pursuant to a performance share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the performance goals. For the nine months ended September 30, 2023 and 2022, excess tax benefits associated with the settlement of stock-based compensation awards reduced income tax expense by $6 million and $5 million, respectively. Deferred Compensation At September 30, 2023, and December 31, 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. Operating Revenues As of September 30, 2023 and 2022, our remaining performance obligations for contracts with a term greater than one year were immaterial. The Ameren Companies elected not to disclose the aggregate amount of the transaction price allocated to the performance obligations that are unsatisfied as of the end of the reporting period for contracts with an initial expected term of one year or less. See Note 14 – Segment Information for disaggregated revenue information. Excise Taxes Ameren Missouri and Ameren Illinois collect from their customers excise taxes, including municipal and state excise taxes and gross receipts taxes that are levied on the sale or distribution of natural gas and electricity. The following table presents the excise taxes recorded on a gross basis in “Operating Revenues – Electric,” “Operating Revenues – Natural gas” and “Operating Expenses – Taxes other than income taxes” on the statements of income for the three and nine months ended September 30, 2023 and 2022: Three Months Nine Months 2023 2022 2023 2022 Ameren Missouri $ 60 $ 55 $ 133 $ 128 Ameren Illinois 27 28 90 101 Ameren $ 87 $ 83 $ 223 $ 229 Earnings per Share The following table reconciles the basic weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the three and nine months ended September 30, 2023 and 2022: Three Months Nine Months 2023 2022 2023 2022 Weighted-average Common Shares Outstanding – Basic 262.8 258.4 262.5 258.2 Assumed settlement of performance share units and restricted stock units 0.6 0.9 0.7 1.0 Dilutive effect of forward sale agreements — 0.2 — 0.1 Weighted-average Common Shares Outstanding – Diluted (a) 263.4 259.5 263.2 259.3 (a) There was an immaterial number of anti-dilutive performance share units excluded from the earnings per diluted share calculations for the three and nine months ended September 30, 2023 and 2022. The outstanding forward sale agreements as of September 30, 2023, were anti-dilutive for the three and nine months ended September 30, 2023, and excluded from the earnings per diluted share calculation as calculated using the treasury stock method.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2023
Segment Reporting [Abstract]
SEGMENT INFORMATION	SEGMENT INFORMATION The following tables present revenues, net income attributable to common shareholders, and capital expenditures by segment at Ameren and Ameren Illinois for the three and nine months ended September 30, 2023 and 2022. Ameren, Ameren Missouri, and Ameren Illinois management review segment capital expenditure information rather than any individual or total asset amount. For additional information about our segments, see Note 16 – Segment Information under Part II, Item 8, of the Form 10-K. Ameren Ameren Missouri Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Transmission Other Intersegment Eliminations Ameren Three Months 2023: External revenues $ 1,228 $ 557 $ 121 $ 154 $ — $ — $ 2,060 Intersegment revenues 9 1 1 34 — (45) — Net income (loss) attributable to Ameren common shareholders 411 66 (5) 86 (a) (65) — 493 Capital expenditures 341 177 80 160 2 (11) 749 Three Months 2022: External revenues $ 1,351 $ 672 $ 146 $ 137 $ — $ — $ 2,306 Intersegment revenues 8 — — 32 — (40) — Net income (loss) attributable to Ameren common shareholders 397 51 (4) 78 (a) (70) — 452 Capital expenditures 431 163 114 187 1 3 899 Nine Months 2023: External revenues $ 3,074 $ 1,721 $ 664 $ 423 $ — $ — $ 5,882 Intersegment revenues 27 1 1 89 — (118) — Net income (loss) attributable to Ameren common shareholders 541 193 93 229 (a) (62) — 994 Capital expenditures 1,255 527 221 570 7 (9) 2,571 Nine Months 2022: External revenues $ 3,071 $ 1,640 $ 811 $ 389 $ — $ — $ 5,911 Intersegment revenues 25 1 — 76 — (102) — Net income (loss) attributable to Ameren common shareholders 547 151 82 199 (a) (68) — 911 Capital expenditures 1,237 444 232 519 4 1 2,437 (a) Ameren Transmission earnings reflect 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 Three Months 2023: External revenues $ 558 $ 122 $ 103 $ — $ 783 Intersegment revenues — — 33 (33) — Net income (loss) available to common shareholder 66 (5) 64 — 125 Capital expenditures 177 80 125 — 382 Three Months 2022: External revenues $ 672 $ 146 $ 86 $ — $ 904 Intersegment revenues — — 31 (31) — Net income (loss) available to common shareholder 51 (4) 56 — 103 Capital expenditures 163 114 169 — 446 Nine Months 2023: External revenues $ 1,722 $ 665 $ 276 $ — $ 2,663 Intersegment revenues — — 87 (87) — Net income available to common shareholder 193 93 166 — 452 Capital expenditures 527 221 478 — 1,226 Nine Months 2022: External revenues $ 1,641 $ 811 $ 245 $ — $ 2,697 Intersegment revenues — — 75 (75) — Net income available to common shareholder 151 82 142 — 375 Capital expenditures 444 232 469 — 1,145 The following tables present disaggregated revenues by segment at Ameren and Ameren Illinois for the three and nine months ended September 30, 2023 and 2022. 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, off-system sales, and capacity revenues. Ameren Ameren Missouri Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Transmission Intersegment Eliminations Ameren Three Months 2023: Residential $ 590 $ 330 $ — $ — $ — $ 920 Commercial 468 189 — — — 657 Industrial 107 40 — — — 147 Other 54 (1) (a) — 188 (44) 197 Total electric revenues $ 1,219 $ 558 $ — $ 188 $ (44) $ 1,921 Residential $ 9 $ — $ 75 $ — $ — $ 84 Commercial 5 — 19 — — 24 Industrial 1 — 1 — — 2 Other 3 — 27 — (1) 29 Total natural gas revenues $ 18 $ — $ 122 $ — $ (1) $ 139 Total revenues (b) $ 1,237 $ 558 $ 122 $ 188 $ (45) $ 2,060 Ameren Missouri Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Transmission Intersegment Eliminations Ameren Three Months 2022: Residential $ 564 $ 407 $ — $ — $ — $ 971 Commercial 430 233 — — — 663 Industrial 99 47 — — — 146 Other 245 (15) (a) — 169 (39) 360 Total electric revenues $ 1,338 $ 672 $ — $ 169 $ (39) $ 2,140 Residential $ 11 $ — $ 89 $ — $ — $ 100 Commercial 6 — 25 — — 31 Industrial 1 — 5 — — 6 Other 3 — 27 — (1) 29 Total natural gas revenues $ 21 $ — $ 146 $ — $ (1) $ 166 Total revenues (b) $ 1,359 $ 672 $ 146 $ 169 $ (40) $ 2,306 Nine Months 2023: Residential $ 1,274 $ 1,049 $ — $ — $ — $ 2,323 Commercial 1,026 582 — — — 1,608 Industrial 243 136 — — — 379 Other 435 (45) (a) — 512 (116) 786 Total electric revenues $ 2,978 $ 1,722 $ — $ 512 $ (116) $ 5,096 Residential $ 74 $ — $ 469 $ — $ — $ 543 Commercial 34 — 121 — — 155 Industrial 4 — 10 — — 14 Other 11 — 65 — (2) 74 Total natural gas revenues $ 123 $ — $ 665 $ — $ (2) $ 786 Total revenues (b) $ 3,101 $ 1,722 $ 665 $ 512 $ (118) $ 5,882 Nine Months 2022: Residential $ 1,267 $ 954 $ — $ — $ — $ 2,221 Commercial 968 571 — — — 1,539 Industrial 229 145 — — — 374 Other 502 (29) (a) — 465 (101) 837 Total electric revenues $ 2,966 $ 1,641 $ — $ 465 $ (101) $ 4,971 Residential $ 78 $ — $ 575 $ — $ — $ 653 Commercial 36 — 152 — — 188 Industrial 4 — 33 — — 37 Other 12 — 51 — (1) 62 Total natural gas revenues $ 130 $ — $ 811 $ — $ (1) $ 940 Total revenues (b) $ 3,096 $ 1,641 $ 811 $ 465 $ (102) $ 5,911 (a) Includes over-recoveries of various riders. (b) The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the three and nine months ended September 30, 2023 and 2022: Ameren Missouri Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Transmission Ameren Three Months 2023: Revenues from alternative revenue programs $ (9) $ (94) $ (1) $ (5) $ (109) Other revenues not from contracts with customers (1) (a) 2 — — 1 (a) Three Months 2022: Revenues from alternative revenue programs $ 14 $ (83) $ (3) $ (11) $ (83) Other revenues not from contracts with customers (45) (a) 2 — — (43) (a) Nine Months 2023: Revenues from alternative revenue programs $ (11) $ 30 $ 36 $ 8 $ 63 Other revenues not from contracts with customers (9) (a) 6 2 — (1) (a) Nine Months 2022: Revenues from alternative revenue programs $ 8 $ 13 $ (5) $ (14) $ 2 Other revenues not from contracts with customers (81) (a), (b) 5 2 — (74) (a), (b) (a) Includes net realized losses on derivative power contracts. (b) Includes insurance recoveries related to lost sales associated with the December 2020 Callaway Energy Center maintenance outage. See Note 9 – Callaway Energy Center under Part II, Item 8, of the Form 10-K for additional information. Ameren Illinois Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Illinois Transmission Intersegment Eliminations Ameren Illinois Three Months 2023: Residential $ 330 $ 75 $ — $ — $ 405 Commercial 189 19 — — 208 Industrial 40 1 — — 41 Other (1) (a) 27 136 (33) 129 Total revenues (b) $ 558 $ 122 $ 136 $ (33) $ 783 Three Months 2022: Residential $ 407 $ 89 $ — $ — $ 496 Commercial 233 25 — — 258 Industrial 47 5 — — 52 Other (15) (a) 27 117 (31) 98 Total revenues (b) $ 672 $ 146 $ 117 $ (31) $ 904 Nine Months 2023: Residential $ 1,049 $ 469 $ — $ — $ 1,518 Commercial 582 121 — — 703 Industrial 136 10 — — 146 Other (45) (a) 65 363 (87) 296 Total revenues (b) $ 1,722 $ 665 $ 363 $ (87) $ 2,663 Nine Months 2022: Residential $ 954 $ 575 $ — $ — $ 1,529 Commercial 571 152 — — 723 Industrial 145 33 — — 178 Other (29) (a) 51 320 (75) 267 Total revenues (b) $ 1,641 $ 811 $ 320 $ (75) $ 2,697 (a) Includes over-recoveries of various riders. (b) The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the Ameren Illinois segments for the three and nine months ended September 30, 2023 and 2022: Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Illinois Transmission Ameren Illinois Three Months 2023: Revenues from alternative revenue programs $ (94) $ (1) $ (6) $ (101) Other revenues not from contracts with customers 2 — — 2 Three Months 2022: Revenues from alternative revenue programs $ (83) $ (3) $ (10) $ (96) Other revenues not from contracts with customers 2 — — 2 Nine Months 2023: Revenues from alternative revenue programs $ 30 $ 36 $ 4 $ 70 Other revenues not from contracts with customers 6 2 — 8 Nine Months 2022: Revenues from alternative revenue programs $ 13 $ (5) $ (12) $ (4) Other revenues not from contracts with customers 5 2 — 7

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended	9 Months Ended
	Sep. 30, 2023 shares	Sep. 30, 2023 shares
Trading Arrangements, by Individual
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false
Martin J. Lyons, Jr. [Member]
Trading Arrangements, by Individual
Material Terms of Trading Arrangement		On August 23, 2023, Martin J. Lyons, Jr., then President and Chief Executive Officer of Ameren, adopted a Rule 10b5-1 trading arrangement. Mr. Lyons' Rule 10b5-1 trading arrangement provides for the sale of 50% of any net shares of Ameren common stock received, after tax withholding, in connection with certain previously awarded restricted stock units and performance share units that will vest upon payment in March 2024 and March 2025. The estimated maximum number of shares to be sold pursuant to the Rule 10b5-1 trading arrangement is 40,775 shares. The actual number of shares sold pursuant to the Rule 10b5-1 trading arrangement will depend on the actual number of shares earned pursuant to the awards, which is generally dependent on the Company's achievement of certain performance measures, the actual dividends paid by the Company during the applicable vesting periods, and Mr. Lyons' continued employment and individual performance during the applicable vesting periods. Mr. Lyons' Rule 10b5-1 trading arrangement will terminate on the earlier of: (i) March 31, 2025; (ii) execution of all trades or expiration of all orders relating to such trades under the Rule 10b5-1 trading arrangement; or (iii) such date as the Rule 10b5-1 trading arrangement is otherwise terminated according to its terms.
Name	Martin J. Lyons, Jr.
Title	President and Chief Executive Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	August 23, 2023
Arrangement Duration	586 days
Aggregate Available	40,775	40,775

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Nature of Operations	Ameren, headquartered in St. Louis, Missouri, is a public utility holding company whose primary assets are its equity interests in its subsidiaries. Ameren’s subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. Dividends on Ameren’s common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren’s principal subsidiaries are listed below. Ameren has other subsidiaries that conduct other activities, such as providing shared services. • Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri. • Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois. • ATXI operates a FERC rate-regulated electric transmission business in the MISO.
Consolidation	Ameren’s and Ameren Missouri’s financial statements are prepared on a consolidated basis and therefore include the accounts of their majority-owned subsidiaries. All intercompany transactions have been eliminated. Ameren Missouri’s subsidiaries were created for the acquisition of renewable generation projects. Ameren Illinois has no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated. Our accounting policies conform to GAAP. Our financial statements reflect all adjustments (which include normal, recurring adjustments) that are necessary, in our opinion, for a fair presentation of our results. The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. Such estimates and assumptions affect reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of financial statements, and reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates. The results of operations for an interim period may not give a true indication of results that may be expected for a full year. These financial statements should be read in conjunction with the financial statements and accompanying notes included in the Form 10-K.
Consolidation, Variable Interest Entity, Policy	Variable Interest Entities As of September 30, 2023, and December 31, 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 September 30, 2023, Ameren’s maximum exposure to loss related to these variable interests is limited to its investment of $73 million plus associated outstanding funding commitments of $14 million.
Life Insurance, Corporate Or Bank Owned	COLIAmeren 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.
Derivatives, Policy	We use derivatives to manage the risk of changes in market prices for natural gas, power, and uranium, as well as the risk of changes in rail transportation surcharges through fuel oil hedges. Such price fluctuations may cause the following: • an unrealized appreciation or depreciation of our contracted commitments to purchase or sell when purchase or sale prices under the commitments are compared with current commodity prices; • market values of natural gas and uranium inventories that differ from the cost of those commodities in inventory; • actual cash outlays for the purchase of these commodities that differ from anticipated cash outlays; and • actual off-system sales revenues that differ from anticipated revenues. The derivatives that we use to hedge these risks are governed by our risk management policies for forward contracts, futures, options, and swaps. Our net positions are continually assessed within our structured hedging programs to determine whether new or offsetting transactions are required. The goal of the hedging program is generally to mitigate financial risks while ensuring that sufficient volumes are available to meet our requirements. Contracts we enter into as part of our risk management program may be settled financially, settled by physical delivery, or net settled with the counterparty. All contracts considered to be derivative instruments are required to be recorded on the balance sheet at their fair values, unless the NPNS exception applies. Many of our physical contracts, such as our purchased power contracts, qualify for the NPNS exception to derivative accounting rules. The revenue or expense on NPNS contracts is recognized at the contract price upon physical delivery. The
Deferred Compensation	Deferred Compensation At September 30, 2023, and December 31, 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.
Revenue from Contract with Customer	Operating Revenues As of September 30, 2023 and 2022, our remaining performance obligations for contracts with a term greater than one year were immaterial. The Ameren Companies elected not to disclose the aggregate amount of the transaction price allocated to the performance obligations that are unsatisfied as of the end of the reporting period for contracts with an initial expected term of one year or less. See Note 14 – Segment Information for disaggregated revenue information.
Excise Taxes	Excise TaxesAmeren Missouri and Ameren Illinois collect from their customers excise taxes, including municipal and state excise taxes and gross receipts taxes that are levied on the sale or distribution of natural gas and electricity.

Rate and Regulatory Matters (Ta

Rate and Regulatory Matters (Tables)	9 Months Ended
	Sep. 30, 2023
Regulated Operations [Abstract]
Schedule of Solar Projects	The following table provides information with respect to each agreement: Boomtown Solar Project (a)(b) Huck Finn Solar Project (b)(c) Split Rail Solar Project (d) Cass County Solar Project (d) Vandalia Solar Project (d) Bowling Green Solar Project (d) Agreement type Build-transfer Build-transfer Build-transfer (e) Development-transfer (e)(f) Self-build (e)(g) Self-build (e)(g) Facility size 150-MW 200-MW 300-MW 150-MW 50-MW 50-MW Status of MoPSC CCN Approved April 2023 Approved February 2023 Filed June 2023 (h) Filed June 2023 (h) Filed June 2023 (h) Filed June 2023 (h) Status of FERC approval of acquisition Received October 2023 Received March 2023 Expect to request by mid-2024 Not applicable Not applicable Not applicable Earliest completion date (i) Fourth quarter 2024 Fourth quarter 2024 Mid-2026 Fourth quarter 2024 Fourth quarter 2025 First quarter 2026 (a) The Boomtown Solar Project is expected to support Ameren Missouri’s transition to renewable energy generation and serve customers under the Renewable Solutions Program discussed below. (b) These projects collectively represent approximately $0.65 billion of expected capital expenditures. (c) 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. (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 October 2023, the MoPSC staff filed a recommendation that the MoPSC should not approve Ameren Missouri’s requests for CCNs for these solar projects, arguing Ameren Missouri did not adequately demonstrate the facilities are needed to continue providing service to customers. Ameren Missouri expects decisions on the CCNs by the MoPSC in the first quarter of 2024. (i) Expected completion dates are dependent on the timing of regulatory approvals, among other things.
Schedule of MYRP details	The following table includes the forecasted revenue requirement, the ROE, the capital structure common equity percentage, and the forecasted average annual rate base for 2024 through 2027, as reflected in Ameren Illinois’ revised MYRP filing, the ICC staff’s filing, and the administrative law judges’ proposed order: Ameren Illinois’ ICC Staff’s Administrative Law Judges’ Year 2024 2025 2026 2027 2024 2025 2026 2027 2024 2025 2026 2027 Forecasted Revenue Requirement (in millions) (a) $1,289 $1,385 $1,480 $1,556 $1,211 $1,295 $1,383 $1,435 $1,219 $1,306 $1,389 $1,450 ROE (b)(c) 10.5% 10.5% 10.5% 10.5% 8.9% 8.9% 8.9% 8.9% 9.24% 9.24% 9.24% 9.24% Capital Structure Common Equity Percentage (c)(d) 53.99% 53.97% 54.02% 54.03% 50% 50% 50% 50% 50% 50% 50% 50% Forecasted Average Annual Rate Base (in billions) $4.3 $4.6 $4.9 $5.2 $4.1 $4.4 $4.6 $4.8 $4.1 $4.4 $4.6 $4.8 (a) If an initial rate increase phase-in provision, discussed below, is approved by the ICC, it would not affect the annual revenue requirement, but would affect the timing of associated recovery from customers. (b) The ICC staff filing recommended an ROE based on the annual average of the monthly yields of the 30-year United States Treasury bonds plus 580 basis points, to be updated annually for each applicable calendar year of the MYRP. An estimated ROE of 8.9% was used to calculate the forecasted revenue requirements in the ICC staff filing, which is based on the average monthly yields of the 30-year United States Treasury bonds for 2022. The ICC staff proposed that variances in the revenue requirement resulting from a change in the ROE would be excluded from the reconciliation cap discussed below. (c) In November 2023, Ameren Illinois updated its requested ROE and capital structure common equity percentage to 9.85% and 52% for all years, respectively. (d) A capital structure of up to and including 50% common equity is deemed prudent and reasonable by law. A higher equity ratio requires specific ICC approval. The administrative law judges’ October 2023 proposed order recommends a capital structure that is the lower of 50% or Ameren Illinois’ actual equity ratio, excluding goodwill.

Short-Term Debt and Liquidity (

Short-Term Debt and Liquidity (Tables)	9 Months Ended
	Sep. 30, 2023
Debt Disclosure [Abstract]
Schedule of Short-term Debt	The following table presents commercial paper outstanding, net of issuance discounts, as of September 30, 2023, and December 31, 2022. There were no borrowings outstanding under the Credit Agreements as of September 30, 2023, or December 31, 2022. September 30, 2023 December 31, 2022 Ameren (parent) $ 1,124 $ 477 Ameren Missouri 157 329 Ameren Illinois 59 264 Ameren consolidated $ 1,340 $ 1,070 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 nine months ended September 30, 2023 and 2022: Ameren Ameren Ameren Ameren 2023 Average daily amount outstanding $ 687 $ 306 $ 181 $ 1,174 Weighted-average interest rate 5.29 % 5.15 % 5.15 % 5.24 % Peak amount outstanding during period (a) $ 1,127 $ 592 $ 450 $ 1,381 Peak interest rate 5.60 % 5.60 % 5.60 % 5.60 % 2022 Average daily amount outstanding $ 439 $ 253 $ 99 $ 791 Weighted-average interest rate 1.58 % 1.16 % 1.77 % 1.47 % Peak amount outstanding during period (a) $ 690 $ 539 $ 354 $ 1,222 Peak interest rate 3.55 % 3.55 % 3.60 % 3.60 % (a) The timing of peak outstanding commercial paper issuances and borrowings under the Credit Agreements varies by company. Therefore, the sum of individual company peak amounts may not equal the Ameren consolidated peak for the period.

Other Income, Net (Tables)

Other Income, Net (Tables)	9 Months Ended
	Sep. 30, 2023
Other Nonoperating Income (Expense) [Abstract]
Other Income And Expenses	The following table presents the components of “Other Income, Net” in the Ameren Companies’ statements of income for the three and nine months ended September 30, 2023 and 2022: Three Months Nine Months 2023 2022 2023 2022 Ameren: Allowance for equity funds used during construction $ 16 $ 12 $ 39 $ 31 Interest income on industrial development revenue bonds — 6 1 18 Other interest income 6 2 23 6 Non-service cost components of net periodic benefit income (a) 84 45 211 138 Miscellaneous income 1 3 4 8 Earnings (losses) related to equity method investments — (3) 2 1 Donations (1) (1) (5) (5) Miscellaneous expense (5) (6) (14) (17) Total Other Income, Net $ 101 $ 58 $ 261 $ 180 Ameren Missouri: Allowance for equity funds used during construction $ 8 $ 7 $ 20 $ 17 Interest income on industrial development revenue bonds — 6 1 18 Other interest income 3 1 8 2 Non-service cost components of net periodic benefit income (a) 34 13 62 41 Miscellaneous income 1 1 3 3 Donations — — (2) (2) Miscellaneous expense (2) (3) (7) (7) Total Other Income, Net $ 44 $ 25 $ 85 $ 72 Ameren Illinois: Allowance for equity funds used during construction $ 5 $ 5 $ 15 $ 14 Interest income 4 1 14 4 Non-service cost components of net periodic benefit income 31 21 93 63 Miscellaneous income — 3 2 5 Donations (1) (1) (3) (3) Miscellaneous expense (2) (3) (6) (8) Total Other Income, Net $ 37 $ 26 $ 115 $ 75 (a) For the three and nine months ended September 30, 2023 the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $(2) million and $32 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 deferral was $5 million and $16 million, respectively, for the three and nine months ended September 30, 2022. See Note 11 – Retirement Benefits for additional information.

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2023
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Open Gross Derivative Volumes By Commodity Type	The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of September 30, 2023, and December 31, 2022. As of September 30, 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) September 30, 2023 December 31, 2022 Commodity Ameren Missouri Ameren Illinois Ameren Ameren Missouri Ameren Illinois Ameren Fuel oils (in gallons) 19 — 19 18 — 18 Natural gas (in mmbtu) 52 213 265 48 157 205 Power (in MWhs) 1 5 6 1 6 7 Uranium (pounds in thousands) 186 — 186 514 — 514
Derivative Instruments Carrying Value	The following table presents the carrying value and balance sheet location of all derivative commodity contracts, none of which were designated as hedging instruments, as of September 30, 2023, and December 31, 2022: September 30, 2023 December 31, 2022 Balance Sheet Location Ameren Ameren Ameren Ameren Ameren Ameren Fuel oils Other current assets $ 6 $ — $ 6 $ 13 $ — $ 13 Other assets 2 — 2 3 — 3 Natural gas Other current assets 1 6 7 7 23 30 Other assets 5 3 8 9 11 20 Power Other current assets 7 — 7 14 2 16 Other assets — — — — 4 4 Uranium Other current assets 5 — 5 2 — 2 Other assets — — — 1 — 1 Total assets $ 26 $ 9 $ 35 $ 49 $ 40 $ 89 Natural gas Other current liabilities 7 25 32 7 20 27 Other deferred credits and liabilities 6 16 22 2 9 11 Power Other current liabilities 7 8 15 59 2 61 Other deferred credits and liabilities — 56 56 — 37 37 Total liabilities $ 20 $ 105 $ 125 $ 68 $ 68 $ 136
Offsetting Assets and Liabilities	Th e following table p rovides the recognized gross derivative balances and the net amounts of those derivatives subject to an enforceable master netting arrangement or similar agreement as of September 30, 2023, and December 31, 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 September 30, 2023 Assets: Ameren Missouri $ 26 $ 6 $ — $ 20 Ameren Illinois 9 5 — 4 Ameren $ 35 $ 11 $ — $ 24 Liabilities: Ameren Missouri $ 20 $ 6 $ 5 $ 9 Ameren Illinois 105 5 — 100 Ameren $ 125 $ 11 $ 5 $ 109 December 31, 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.
Derivative Instruments With Credit Risk-Related Contingent Features	The following table presents, as of September 30, 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 Potential Aggregate Amount of Additional Collateral Required (b) Ameren Missouri $ 14 $ — $ 8 Ameren Illinois 41 — 35 Ameren $ 55 $ — $ 43 (a) Before consideration of master netting arrangements or similar agreements. (b) As collateral requirements with certain counterparties are based on master netting arrangements or similar agreements, the aggregate amount of additional collateral required to be posted is determined after consideration of the effects of such arrangements.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis	The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of September 30, 2023, and December 31, 2022: September 30, 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 $ 8 $ — $ — $ 8 $ 16 $ — $ — $ 16 Natural gas — 6 — 6 1 15 — 16 Power — — 7 7 — — 14 14 Uranium — — 5 5 — — 3 3 Total derivative assets – commodity contracts $ 8 $ 6 $ 12 $ 26 $ 17 $ 15 $ 17 $ 49 Nuclear decommissioning trust fund: Equity securities: U.S. large capitalization $ 703 $ — $ — $ 703 $ 618 $ — $ — $ 618 Debt securities: U.S. Treasury and agency securities — 138 — 138 — 137 — 137 Corporate bonds — 126 — 126 — 122 — 122 Other — 70 — 70 — 70 — 70 Total nuclear decommissioning trust fund $ 703 $ 334 $ — $ 1,037 (a) $ 618 $ 329 $ — $ 947 (a) Total Ameren Missouri $ 711 $ 340 $ 12 $ 1,063 $ 635 $ 344 $ 17 $ 996 Ameren Illinois Derivative assets – commodity contracts: Natural gas $ — $ 6 $ 3 $ 9 $ 1 $ 28 $ 5 $ 34 Power — — — — — — 6 6 Total Ameren Illinois $ — $ 6 $ 3 $ 9 $ 1 $ 28 $ 11 $ 40 Ameren Derivative assets – commodity contracts (b) $ 8 $ 12 $ 15 $ 35 $ 18 $ 43 $ 28 $ 89 Nuclear decommissioning trust fund (c) 703 334 — 1,037 (a) 618 329 — 947 (a) Total Ameren $ 711 $ 346 $ 15 $ 1,072 $ 636 $ 372 $ 28 $ 1,036 Liabilities: Ameren Missouri Derivative liabilities – commodity contracts: Natural gas — 11 2 13 — 6 3 9 Power 6 — 1 7 57 — 2 59 Total Ameren Missouri $ 6 $ 11 $ 3 $ 20 $ 57 $ 6 $ 5 $ 68 Ameren Illinois Derivative liabilities – commodity contracts: Natural gas $ 2 $ 34 $ 5 $ 41 $ — $ 19 $ 10 $ 29 Power — — 64 64 — — 39 39 Total Ameren Illinois $ 2 $ 34 $ 69 $ 105 $ — $ 19 $ 49 $ 68 Ameren Derivative liabilities – commodity contracts (b) $ 8 $ 45 $ 72 $ 125 $ 57 $ 25 $ 54 $ 136 (a) Balance excludes $5 million and $11 million of cash and cash equivalents, receivables, payables, and accrued income, net, for September 30, 2023, and December 31, 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 the fair value of Ameren’s nuclear decommissioning trust fund by investment type.
Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level Three In The Fair Value Hierarchy	The following table presents the fair value reconciliation of Level 3 power derivative contract assets and liabilities measured at fair value on a recurring basis for the three and nine months ended September 30, 2023 and 2022: 2023 2022 Ameren Missouri Ameren Illinois Ameren Ameren Missouri Ameren Illinois Ameren For the three months ended September 30: Beginning balance at July 1 $ 14 $ (68) $ (54) $ (36) $ (44) $ (80) Realized and unrealized gains/(losses) included in regulatory assets/liabilities (5) 1 (4) (10) 30 20 Settlements (3) 3 — 38 (6) 32 Ending balance at September 30 $ 6 $ (64) $ (58) $ (8) $ (20) $ (28) Change in unrealized gains/(losses) related to assets/liabilities held at September 30 $ (5) $ 1 $ (4) $ (3) $ 28 $ 25 For the nine months ended September 30: Beginning balance at January 1 $ 12 $ (33) $ (21) $ (15) $ (117) $ (132) Realized and unrealized gains/(losses) included in regulatory assets/liabilities 3 (40) (37) (56) 105 49 Settlements (9) 9 — 63 (8) 55 Ending balance at September 30 $ 6 $ (64) $ (58) $ (8) $ (20) $ (28) Change in unrealized gains/(losses) related to assets/liabilities held at September 30 $ 6 $ (31) $ (25) $ (39) $ 100 $ 61
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis, Valuation Techniques	The following table describes the valuation techniques and significant unobservable inputs utilized for the fair value of our Level 3 power derivative contract assets and liabilities as of September 30, 2023, and December 31, 2022: Fair Value Weighted Average (b) Commodity Assets Liabilities Valuation Technique(s) Unobservable Input (a) Range 2023 Power (c) $ 7 $ (65) Discounted cash flow Average forward peak and off-peak pricing – forwards/swaps ($/MWh) 32 – 63 43 Nodal basis ($/MWh) (10) – (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.
Schedule of Financial Assets and Liabilities	The following table sets forth the carrying amount and, by level within the fair value hierarchy, the fair value of financial assets and liabilities disclosed, but not recorded, at fair value as of September 30, 2023, and December 31, 2022: Carrying Fair Value Level 1 Level 2 Level 3 Total September 30, 2023 Ameren: Cash, cash equivalents, and restricted cash $ 246 $ 246 $ — $ — $ 246 Short-term debt 1,340 — 1,340 — 1,340 Long-term debt (including current portion) 14,678 (a) — 11,985 432 (b) 12,417 Ameren Missouri: Cash, cash equivalents, and restricted cash $ 13 $ 13 $ — $ — $ 13 Short-term debt 157 — 157 — 157 Long-term debt (including current portion) 6,341 (a) — 5,287 — 5,287 Ameren Illinois: Cash, cash equivalents, and restricted cash $ 225 $ 225 $ — $ — $ 225 Short-term debt 59 — 59 — 59 Long-term debt (including current portion) 5,231 (a) — 4,419 — 4,419 December 31, 2022 Ameren: Cash, cash equivalents, and restricted cash $ 216 $ 216 $ — $ — $ 216 Investment 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 Investment 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 $105 million, $45 million, and $48 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of September 30, 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 an investment in industrial development revenue bonds, classified as held-to-maturity, that were equal to the finance obligation for the Audrain CT energy center. As of December 31, 2022, the carrying amount of the investment in industrial development revenue bonds and the finance obligation approximated fair value.

Related Party Transactions (Tab

Related Party Transactions (Tables)	9 Months Ended
	Sep. 30, 2023
Related Party Transactions [Abstract]
Schedule of Affiliate Receivables and Payables	The following table presents the affiliate balances related to income taxes for Ameren Missouri and Ameren Illinois as of September 30, 2023, and December 31, 2022: September 30, 2023 December 31, 2022 Ameren Missouri Ameren Illinois Ameren Missouri Ameren Illinois Income taxes payable to parent (a) $ 29 $ 81 $ — $ 50 Income taxes receivable from parent (b) — — 39 — (a) Included in “Accounts payable – affiliates” on the balance sheet. (b) Included in “Accounts receivable – affiliates” on the balance sheet.
Schedule of Related Party Transactions	The following table presents the impact on Ameren Missouri and Ameren Illinois of related-party transactions for the three and nine months ended September 30, 2023 and 2022: Three Months Nine Months Agreement Income Statement Ameren Ameren Ameren Ameren Ameren Missouri power supply Operating Revenues 2023 $ 2 $ (a) $ 2 $ (a) agreements with Ameren Illinois 2022 2 (a) 7 (a) Ameren Missouri and Ameren Illinois Operating Revenues 2023 $ 7 $ (b) $ 25 $ (b) rent and facility services 2022 6 (b) 18 (b) Ameren Missouri and Ameren Illinois miscellaneous Operating Revenues 2023 $ (b) $ 2 $ (b) $ 2 support services 2022 (b) (b) (b) 1 Total Operating Revenues 2023 $ 9 $ 2 $ 27 $ 2 2022 8 (b) 25 1 Ameren Illinois power supply Purchased Power 2023 $ (a) $ 2 $ (a) $ 2 agreements with Ameren Missouri 2022 (a) 2 (a) 7 Ameren Missouri and Ameren Illinois Purchased Power 2023 $ (b) $ 1 $ 1 $ 1 transmission services from ATXI 2022 1 (b) 1 (b) Total Purchased Power 2023 $ (b) $ 3 $ 1 $ 3 2022 1 2 1 7 Ameren Missouri and Ameren Illinois Other Operations and Maintenance 2023 $ (b) $ (b) $ (b) $ 2 rent and facility services 2022 (b) 1 (b) 2 Ameren Services support services Other Operations and Maintenance 2023 $ 36 $ 33 $ 106 $ 101 agreement 2022 38 36 109 103 Total Other Operations and 2023 $ 36 $ 33 $ 106 $ 103 Maintenance 2022 38 37 109 105 Money pool borrowings (advances) (Interest Charges)/Other Income, Net 2023 $ (b) $ (b) $ (b) $ (b) 2022 (b) (b) (b) (b) (a) Not applicable. (b) Amount less than $1 million.

Callaway Energy Center (Tables)

Callaway Energy Center (Tables)	9 Months Ended
	Sep. 30, 2023
Nuclear Waste Matters [Abstract]
Schedule of Insurance Coverage at Callaway Energy Center	The following table presents insurance coverage at Ameren Missouri’s Callaway Energy Center at October 31, 2023: Type and Source of Coverage Most Recent Maximum Coverages Maximum Assessments Public liability and nuclear worker liability: American Nuclear Insurers January 1, 2023 $ 450 $ — Pool participation (a) 16,095 (a) 166 (b) $ 16,545 (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 $450 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.

Retirement Benefits (Tables)

Retirement Benefits (Tables)	9 Months Ended
	Sep. 30, 2023
Retirement Benefits [Abstract]
Components Of Net Periodic Benefit Cost	The following table presents the components of the net periodic benefit cost (income) incurred for Ameren’s pension and postretirement benefit plans for the three and nine months ended September 30, 2023 and 2022: Pension Benefits Postretirement Benefits Three Months Nine Months Three Months Nine Months 2023 2022 2023 2022 2023 2022 2023 2022 Service cost (a) $ 10 $ 31 $ 56 $ 95 $ 3 $ 5 $ 9 $ 15 Non-service cost components: Interest cost 55 42 166 123 11 8 34 25 Expected return on plan assets (b) (84) (80) (251) (240) (22) (21) (68) (64) Amortization of (b) : Prior service benefit — — — — (1) (1) (3) (3) Actuarial (gain) loss (29) 7 (86) 19 (12) (5) (35) (14) Total non-service cost components (c) $ (58) $ (31) $ (171) $ (98) $ (24) $ (19) $ (72) $ (56) Net periodic benefit income (d) $ (48) $ — $ (115) $ (3) $ (21) $ (14) $ (63) $ (41) (a) Service cost, net of capitalization, is reflected in “Operating Expenses – Other operations and maintenance” on Ameren’s statement of income. (b) Prior service benefit is amortized on a straight-line basis over the average future service of active participants benefiting under a 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 5 – 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.
Summary Of Benefit Plan Costs Incurred	Ameren Missouri and Ameren Illinois are responsible for their respective share of Ameren’s pension and other postretirement costs. The following table presents the respective share of net periodic pension and other postretirement benefit costs (income) incurred for the three and nine months ended September 30, 2023 and 2022: Pension Benefits Postretirement Benefits Three Months Nine Months Three Months Nine Months 2023 2022 2023 2022 2023 2022 2023 2022 Ameren Missouri (a) $ (24) $ — $ (59) $ (2) $ (8) $ (3) $ (23) $ (10) Ameren Illinois (21) 1 (48) 2 (13) (11) (40) (31) Other (3) (1) (8) (3) — — — — Ameren (a) $ (48) $ — $ (115) $ (3) $ (21) $ (14) $ (63) $ (41) (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 rates.

Income Taxes Income Taxes (Tabl

Income Taxes Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation	The following table presents a reconciliation of the federal statutory corporate income tax rate to the effective income tax rate for the three and nine months ended September 30, 2023 and 2022: Ameren Ameren Missouri Ameren Illinois 2023 2022 2023 2022 2023 2022 Three Months Federal statutory corporate income tax rate 21 % 21 % 21 % 21 % 21 % 21 % Increases (decreases) from: Amortization of deferred investment tax credit — — (1) (1) — — Amortization of excess deferred taxes (a) (7) (8) (15) (15) (2) (2) Depreciation differences (1) — — — — — Renewable and other tax credits (b) (5) (4) (11) (10) (1) — State tax 4 4 3 3 7 7 Stock-based compensation — 1 — — — — Cash surrender value of COLI — 1 — — — — Effective income tax rate 12 % 15 % (3) % (2) % 25 % 26 % Nine Months Federal statutory corporate income tax rate 21 % 21 % 21 % 21 % 21 % 21 % Increases (decreases) from: Amortization of deferred investment tax credit — — (1) (1) — — Amortization of excess deferred taxes (a) (8) (8) (15) (15) (2) (2) Depreciation differences — — — — (1) — Renewable and other tax credits (b) (5) (4) (11) (10) — — State tax 5 5 3 3 7 7 Effective income tax rate 13 % 14 % (3) % (2) % 25 % 26 % (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.

Supplemental Information (Table

Supplemental Information (Tables)	9 Months Ended
	Sep. 30, 2023
Supplemental Information [Abstract]
Schedule of Cash and Cash Equivalents Including Restricted Cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows at September 30, 2023, and December 31, 2022: September 30, 2023 December 31, 2022 Ameren Ameren Ameren Ameren Ameren Ameren “Cash and cash equivalents” $ 8 $ 3 $ — $ 10 $ — $ — Restricted cash included in “Other current assets” 13 5 5 13 5 6 Restricted cash included in “Other assets” 220 — 220 185 — 185 Restricted cash included in “Nuclear decommissioning trust fund” 5 5 — 8 8 — Total cash, cash equivalents, and restricted cash $ 246 $ 13 $ 225 $ 216 $ 13 $ 191
Schedule of Accounts, Notes, Loans and Financing Receivable	The following table provides a reconciliation of the beginning and ending amount of the allowance for doubtful accounts for the three and nine months ended September 30, 2023 and 2022: Three Months Nine Months 2023 2022 2023 2022 Ameren: Beginning of period $ 39 $ 30 $ 31 $ 29 Bad debt expense 18 14 41 23 Charged to other accounts (a) 2 1 3 3 Net write-offs (26) (14) (42) (24) End of period $ 33 $ 31 $ 33 $ 31 Ameren Missouri: Beginning of period $ 12 $ 12 $ 13 $ 13 Bad debt expense 5 3 9 6 Net write-offs (5) (3) (10) (7) End of period $ 12 $ 12 $ 12 $ 12 Ameren Illinois: (b) Beginning of period $ 27 $ 18 $ 18 $ 16 Bad debt expense 13 11 32 17 Charged to other accounts (a) 2 1 3 3 Net write-offs (21) (11) (32) (17) End of period $ 21 $ 19 $ 21 $ 19 (a) 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. (b) Ameren Illinois has riders 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. The table above does not include the impact related to the riders.
Schedule of Cash Flow, Supplemental Disclosures	The following table provides noncash financing and investing activity excluded from the statements of cash flows for the nine months ended September 30, 2023 and 2022: September 30, 2023 September 30, 2022 Ameren Ameren Ameren Ameren Ameren Ameren Investing: Accrued capital expenditures, including nuclear fuel expenditures $ 518 $ 246 $ 237 $ 367 $ 187 $ 180 Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund 66 66 — (262) (262) — Return of investment in industrial development revenue bonds (a) 240 240 — — — — Financing: Issuance of common stock for stock-based compensation $ 37 $ — $ — $ 31 $ — $ — Issuance of common stock under the DRPlus 7 — — 8 — — Termination of a financing obligation (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.
Asset Retirement Obligation Disclosure	The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the nine months ended September 30, 2023: Ameren Ameren Ameren Balance at December 31, 2022 $ 782 (a) $ 4 (b) $ 786 (a) Liabilities settled (9) — (9) Accretion 25 (c) — 25 (c) Change in estimates (18) — (18) Balance at September 30, 2023 $ 780 (a) $ 4 (b) $ 784 (a) (a) Balance included $23 million in “Other current liabilities” on the balance sheet as of both September 30, 2023, and December 31, 2022. (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.
Schedule of excise taxes	The following table presents the excise taxes recorded on a gross basis in “Operating Revenues – Electric,” “Operating Revenues – Natural gas” and “Operating Expenses – Taxes other than income taxes” on the statements of income for the three and nine months ended September 30, 2023 and 2022: Three Months Nine Months 2023 2022 2023 2022 Ameren Missouri $ 60 $ 55 $ 133 $ 128 Ameren Illinois 27 28 90 101 Ameren $ 87 $ 83 $ 223 $ 229
Schedule of Earnings Per Share, Basic and Diluted	The following table reconciles the basic weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the three and nine months ended September 30, 2023 and 2022: Three Months Nine Months 2023 2022 2023 2022 Weighted-average Common Shares Outstanding – Basic 262.8 258.4 262.5 258.2 Assumed settlement of performance share units and restricted stock units 0.6 0.9 0.7 1.0 Dilutive effect of forward sale agreements — 0.2 — 0.1 Weighted-average Common Shares Outstanding – Diluted (a) 263.4 259.5 263.2 259.3 (a) There was an immaterial number of anti-dilutive performance share units excluded from the earnings per diluted share calculations for the three and nine months ended September 30, 2023 and 2022. The outstanding forward sale agreements as of September 30, 2023, were anti-dilutive for the three and nine months ended September 30, 2023, and excluded from the earnings per diluted share calculation as calculated using the treasury stock method.

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2023
Segment Reporting [Abstract]
Schedule Of Segment Reporting Information By Segment	The following tables present revenues, net income attributable to common shareholders, and capital expenditures by segment at Ameren and Ameren Illinois for the three and nine months ended September 30, 2023 and 2022. Ameren, Ameren Missouri, and Ameren Illinois management review segment capital expenditure information rather than any individual or total asset amount. For additional information about our segments, see Note 16 – Segment Information under Part II, Item 8, of the Form 10-K. Ameren Ameren Missouri Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Transmission Other Intersegment Eliminations Ameren Three Months 2023: External revenues $ 1,228 $ 557 $ 121 $ 154 $ — $ — $ 2,060 Intersegment revenues 9 1 1 34 — (45) — Net income (loss) attributable to Ameren common shareholders 411 66 (5) 86 (a) (65) — 493 Capital expenditures 341 177 80 160 2 (11) 749 Three Months 2022: External revenues $ 1,351 $ 672 $ 146 $ 137 $ — $ — $ 2,306 Intersegment revenues 8 — — 32 — (40) — Net income (loss) attributable to Ameren common shareholders 397 51 (4) 78 (a) (70) — 452 Capital expenditures 431 163 114 187 1 3 899 Nine Months 2023: External revenues $ 3,074 $ 1,721 $ 664 $ 423 $ — $ — $ 5,882 Intersegment revenues 27 1 1 89 — (118) — Net income (loss) attributable to Ameren common shareholders 541 193 93 229 (a) (62) — 994 Capital expenditures 1,255 527 221 570 7 (9) 2,571 Nine Months 2022: External revenues $ 3,071 $ 1,640 $ 811 $ 389 $ — $ — $ 5,911 Intersegment revenues 25 1 — 76 — (102) — Net income (loss) attributable to Ameren common shareholders 547 151 82 199 (a) (68) — 911 Capital expenditures 1,237 444 232 519 4 1 2,437 (a) Ameren Transmission earnings reflect 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 Three Months 2023: External revenues $ 558 $ 122 $ 103 $ — $ 783 Intersegment revenues — — 33 (33) — Net income (loss) available to common shareholder 66 (5) 64 — 125 Capital expenditures 177 80 125 — 382 Three Months 2022: External revenues $ 672 $ 146 $ 86 $ — $ 904 Intersegment revenues — — 31 (31) — Net income (loss) available to common shareholder 51 (4) 56 — 103 Capital expenditures 163 114 169 — 446 Nine Months 2023: External revenues $ 1,722 $ 665 $ 276 $ — $ 2,663 Intersegment revenues — — 87 (87) — Net income available to common shareholder 193 93 166 — 452 Capital expenditures 527 221 478 — 1,226 Nine Months 2022: External revenues $ 1,641 $ 811 $ 245 $ — $ 2,697 Intersegment revenues — — 75 (75) — Net income available to common shareholder 151 82 142 — 375 Capital expenditures 444 232 469 — 1,145
Disaggregation of Revenue	The following tables present disaggregated revenues by segment at Ameren and Ameren Illinois for the three and nine months ended September 30, 2023 and 2022. 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, off-system sales, and capacity revenues. Ameren Ameren Missouri Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Transmission Intersegment Eliminations Ameren Three Months 2023: Residential $ 590 $ 330 $ — $ — $ — $ 920 Commercial 468 189 — — — 657 Industrial 107 40 — — — 147 Other 54 (1) (a) — 188 (44) 197 Total electric revenues $ 1,219 $ 558 $ — $ 188 $ (44) $ 1,921 Residential $ 9 $ — $ 75 $ — $ — $ 84 Commercial 5 — 19 — — 24 Industrial 1 — 1 — — 2 Other 3 — 27 — (1) 29 Total natural gas revenues $ 18 $ — $ 122 $ — $ (1) $ 139 Total revenues (b) $ 1,237 $ 558 $ 122 $ 188 $ (45) $ 2,060 Ameren Missouri Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Transmission Intersegment Eliminations Ameren Three Months 2022: Residential $ 564 $ 407 $ — $ — $ — $ 971 Commercial 430 233 — — — 663 Industrial 99 47 — — — 146 Other 245 (15) (a) — 169 (39) 360 Total electric revenues $ 1,338 $ 672 $ — $ 169 $ (39) $ 2,140 Residential $ 11 $ — $ 89 $ — $ — $ 100 Commercial 6 — 25 — — 31 Industrial 1 — 5 — — 6 Other 3 — 27 — (1) 29 Total natural gas revenues $ 21 $ — $ 146 $ — $ (1) $ 166 Total revenues (b) $ 1,359 $ 672 $ 146 $ 169 $ (40) $ 2,306 Nine Months 2023: Residential $ 1,274 $ 1,049 $ — $ — $ — $ 2,323 Commercial 1,026 582 — — — 1,608 Industrial 243 136 — — — 379 Other 435 (45) (a) — 512 (116) 786 Total electric revenues $ 2,978 $ 1,722 $ — $ 512 $ (116) $ 5,096 Residential $ 74 $ — $ 469 $ — $ — $ 543 Commercial 34 — 121 — — 155 Industrial 4 — 10 — — 14 Other 11 — 65 — (2) 74 Total natural gas revenues $ 123 $ — $ 665 $ — $ (2) $ 786 Total revenues (b) $ 3,101 $ 1,722 $ 665 $ 512 $ (118) $ 5,882 Nine Months 2022: Residential $ 1,267 $ 954 $ — $ — $ — $ 2,221 Commercial 968 571 — — — 1,539 Industrial 229 145 — — — 374 Other 502 (29) (a) — 465 (101) 837 Total electric revenues $ 2,966 $ 1,641 $ — $ 465 $ (101) $ 4,971 Residential $ 78 $ — $ 575 $ — $ — $ 653 Commercial 36 — 152 — — 188 Industrial 4 — 33 — — 37 Other 12 — 51 — (1) 62 Total natural gas revenues $ 130 $ — $ 811 $ — $ (1) $ 940 Total revenues (b) $ 3,096 $ 1,641 $ 811 $ 465 $ (102) $ 5,911 (a) Includes over-recoveries of various riders. (b) The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the three and nine months ended September 30, 2023 and 2022: Ameren Missouri Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Transmission Ameren Three Months 2023: Revenues from alternative revenue programs $ (9) $ (94) $ (1) $ (5) $ (109) Other revenues not from contracts with customers (1) (a) 2 — — 1 (a) Three Months 2022: Revenues from alternative revenue programs $ 14 $ (83) $ (3) $ (11) $ (83) Other revenues not from contracts with customers (45) (a) 2 — — (43) (a) Nine Months 2023: Revenues from alternative revenue programs $ (11) $ 30 $ 36 $ 8 $ 63 Other revenues not from contracts with customers (9) (a) 6 2 — (1) (a) Nine Months 2022: Revenues from alternative revenue programs $ 8 $ 13 $ (5) $ (14) $ 2 Other revenues not from contracts with customers (81) (a), (b) 5 2 — (74) (a), (b) (a) Includes net realized losses on derivative power contracts. (b) Includes insurance recoveries related to lost sales associated with the December 2020 Callaway Energy Center maintenance outage. See Note 9 – Callaway Energy Center under Part II, Item 8, of the Form 10-K for additional information. Ameren Illinois Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Illinois Transmission Intersegment Eliminations Ameren Illinois Three Months 2023: Residential $ 330 $ 75 $ — $ — $ 405 Commercial 189 19 — — 208 Industrial 40 1 — — 41 Other (1) (a) 27 136 (33) 129 Total revenues (b) $ 558 $ 122 $ 136 $ (33) $ 783 Three Months 2022: Residential $ 407 $ 89 $ — $ — $ 496 Commercial 233 25 — — 258 Industrial 47 5 — — 52 Other (15) (a) 27 117 (31) 98 Total revenues (b) $ 672 $ 146 $ 117 $ (31) $ 904 Nine Months 2023: Residential $ 1,049 $ 469 $ — $ — $ 1,518 Commercial 582 121 — — 703 Industrial 136 10 — — 146 Other (45) (a) 65 363 (87) 296 Total revenues (b) $ 1,722 $ 665 $ 363 $ (87) $ 2,663 Nine Months 2022: Residential $ 954 $ 575 $ — $ — $ 1,529 Commercial 571 152 — — 723 Industrial 145 33 — — 178 Other (29) (a) 51 320 (75) 267 Total revenues (b) $ 1,641 $ 811 $ 320 $ (75) $ 2,697 (a) Includes over-recoveries of various riders. (b) The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the Ameren Illinois segments for the three and nine months ended September 30, 2023 and 2022: Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Illinois Transmission Ameren Illinois Three Months 2023: Revenues from alternative revenue programs $ (94) $ (1) $ (6) $ (101) Other revenues not from contracts with customers 2 — — 2 Three Months 2022: Revenues from alternative revenue programs $ (83) $ (3) $ (10) $ (96) Other revenues not from contracts with customers 2 — — 2 Nine Months 2023: Revenues from alternative revenue programs $ 30 $ 36 $ 4 $ 70 Other revenues not from contracts with customers 6 2 — 8 Nine Months 2022: Revenues from alternative revenue programs $ 13 $ (5) $ (12) $ (4) Other revenues not from contracts with customers 5 2 — 7

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Basis Of Presentation And Significant Accounting Policies [Line Items]
Unconsolidated variable interest	$ 73	$ 68
Cash Surrender Value of Life Insurance	250	246
Corporate owned life insurance, borrowings	116	110
Ameren Illinois Company
Basis Of Presentation And Significant Accounting Policies [Line Items]
Cash Surrender Value of Life Insurance	122	118
Corporate owned life insurance, borrowings	116	$ 110
Partnership Funding Commitment
Basis Of Presentation And Significant Accounting Policies [Line Items]
Outstanding funding commitments	$ 14

Rate And Regulatory Matters (Na

Rate And Regulatory Matters (Narrative-Missouri) (Details) $ in Millions	3 Months Ended					9 Months Ended
	Sep. 30, 2023 USD ($)	Jun. 30, 2023 MWh	Sep. 30, 2022 USD ($) MWh	Jun. 30, 2022 MWh	Mar. 31, 2022 MWh	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)
Rate And Regulatory Matters [Line Items]
Depreciation and amortization	$ 369		$ 350			$ 1,024	$ 965
Other Income, Net	101		58			261	180
Capital expenditures						2,571	2,437
Revenues	2,060		2,306			5,882	5,911
Union Electric Company
Rate And Regulatory Matters [Line Items]
Depreciation and amortization	217		208			579	550
Other Income, Net	$ 44		$ 25			85	72
Capital expenditures						1,255	$ 1,237
Union Electric Company | Solar generation facility
Rate And Regulatory Matters [Line Items]
Capital expenditures						650
Union Electric Company | Electric | Final Rate Order
Rate And Regulatory Matters [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount						140
Reduction to annualized base level of net energy costs						40
Depreciation and amortization						90
Other Income, Net						100
Union Electric Company | Electric | MEEIA 2019 [Domain]
Rate And Regulatory Matters [Line Items]
Revenues						12
Energy efficiency investments in MEEIA 2019 programs						$ 76
Union Electric Company | Build-transfer | Solar generation facility
Rate And Regulatory Matters [Line Items]
Amount of Megawatts | MWh		300		200	150
Union Electric Company | Development-transfer | Solar generation facility
Rate And Regulatory Matters [Line Items]
Amount of Megawatts | MWh		150
Union Electric Company | Self-build | Solar generation facility
Rate And Regulatory Matters [Line Items]
Amount of Megawatts | MWh		50	50
Union Electric Company | Maximum
Rate And Regulatory Matters [Line Items]
Percentage of energy sourced from renewable resources		100%

Rate And Regulatory Matters (_2

Rate And Regulatory Matters (Narrative-Illinois) (Details) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Dec. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) numberOfProposedPerformanceMetrics	Sep. 30, 2022 USD ($)	Dec. 31, 2027 USD ($)	Dec. 31, 2026 USD ($)	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Rate And Regulatory Matters [Line Items]
Revenues		$ 2,060	$ 2,306	$ 5,882	$ 5,911
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Revenues		$ 783	$ 904	$ 2,663	$ 2,697
Ameren Illinois Company | Maximum
Rate And Regulatory Matters [Line Items]
ICC required RTO cost benefit study duration				10 years
Ameren Illinois Company | Minimum
Rate And Regulatory Matters [Line Items]
ICC required RTO cost benefit study duration				5 years
Ameren Illinois Company | Electric Distribution
Rate And Regulatory Matters [Line Items]
Requested Return on Equity Adjustment				0.24%
Number of Performance Metrics | numberOfProposedPerformanceMetrics				7
IETL | Ameren Illinois Company | Electric Distribution
Rate And Regulatory Matters [Line Items]
ICC recommended return on equity percentage				5.80%	8.90%
Public Utilities, Approved Equity Capital Structure, Percentage				50%
Amortization Period				2 years
Amortization Start Date				1 year
Multi-Year Rate Plan Reconciliation Cap				105%
IETL | Ameren Illinois Company | Electric Distribution | Forecast
Rate And Regulatory Matters [Line Items]
Multi-year rate plan requested revenue requirement						$ 1,556	$ 1,480	$ 1,385	$ 1,289
Public Utilities, Requested Return on Equity, Percentage	9.85%					10.50%	10.50%	10.50%	10.50%
Public Utilities, Requested Equity Capital Structure, Percentage	52%					54.03%	54.02%	53.97%	53.99%
Rate Base						$ 5,200	$ 4,900	$ 4,600	$ 4,300
Multi-year rate plan ICC staff recommended revenue requirement						$ 1,435	$ 1,383	$ 1,295	$ 1,211
ICC recommended return on equity percentage						8.90%	8.90%	8.90%	8.90%
ICC staff recommended equity capital structure						50%	50%	50%	50%
ICC staff recommended rate base						$ 4,800	$ 4,600	$ 4,400	$ 4,100
Multi-year rate plan ALJ proposed revenue requirement						$ 1,450	$ 1,389	$ 1,306	$ 1,219
ALJ proposed return on equity percentage						9.24%	9.24%	9.24%	9.24%
ALJ proposed equity capital structure						50%	50%	50%	50%
ALJ proposed rate base						$ 4,800	$ 4,600	$ 4,400	$ 4,100
Public Utilities, Requested Rate Increase (Decrease), Percentage							50%
Public Utilities, Requested Rate Increase (Decrease), Amount									$ 177
IETL | Ameren Illinois Company | Electric Distribution | Maximum | Forecast
Rate And Regulatory Matters [Line Items]
ALJ proposed equity capital structure	50%
IETL | Ameren Illinois Company | Electric Distribution | Minimum
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Percentage				50%
Pending Rate Case | Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Electric energy-efficiency rate increase				$ 27
ICC staff recommended electric energy-efficiency rate increase				$ 24
Pending Rate Case | Ameren Illinois Company | Electric Distribution
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Equity Capital Structure, Percentage				52%
ICC staff recommended equity capital structure				50%
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 117
ICC staff recommended rate increase				$ 110
Pending Rate Case | Ameren Illinois Company | Natural gas
Rate And Regulatory Matters [Line Items]
Intervenor recommended return on equity				9.50%
Intervenor recommended equity capital structure				52%
Pending Rate Case | Ameren Illinois Company | Natural gas | Subsequent Event
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Return on Equity, Percentage	10.22%
Public Utilities, Requested Equity Capital Structure, Percentage	52%
Rate Base	$ 2,900
ICC recommended return on equity percentage	9.89%
ICC staff recommended equity capital structure	50%
ICC staff recommended rate base	$ 2,900
Public Utilities, Requested Rate Increase (Decrease), Amount	140
ICC staff recommended rate increase	127
Revenues	$ 77
Intervenor recommended equity capital structure	50%
Natural Gas Capital Investments Challenged as Imprudent	$ 53
Challenged Recoveries Under the QIP	$ 3
Pending Rate Case | Ameren Illinois Company | Natural gas | Maximum
Rate And Regulatory Matters [Line Items]
Intervenor recommended rate increase				$ 106
Pending Rate Case | Ameren Illinois Company | Natural gas | Minimum
Rate And Regulatory Matters [Line Items]
Intervenor recommended rate increase				$ 98

Rate And Regulatory Matters (_3

Rate And Regulatory Matters (Narrative-Federal) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2020	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Rate And Regulatory Matters [Line Items]
ROE Change				0.50%
Revenues		$ 2,060	$ 2,306	$ 5,882	$ 5,911
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Revenues		$ 783	$ 904	2,663	$ 2,697
Midwest Independent Transmission System Operator, Inc
Rate And Regulatory Matters [Line Items]
Revenues				19
Midwest Independent Transmission System Operator, Inc | Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Revenues				$ 13
Midwest Independent Transmission System Operator, Inc | Final Rate Order
Rate And Regulatory Matters [Line Items]
Approved return on equity percentage	10.02%

Short-Term Debt And Liquidity_2

Short-Term Debt And Liquidity (Narrative) (Details) $ in Billions	3 Months Ended		9 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2022	Sep. 30, 2023 USD ($)	Sep. 30, 2022
Credit Agreements
Short-term Debt [Line Items]
Net Liquidity Available	$ 1.3		$ 1.3
Actual debt-to-capital ratio	0.59		0.59
Utilities
Short-term Debt [Line Items]
Short-term Debt, Weighted Average Interest Rate, over Time	5.50%	2.48%	5.20%	1.29%
Union Electric Company | Missouri Credit Agreement
Short-term Debt [Line Items]
Actual debt-to-capital ratio	0.49		0.49
Ameren Illinois Company | Illinois Credit Agreement
Short-term Debt [Line Items]
Actual debt-to-capital ratio	0.45		0.45

Short-Term Debt and Liquidity_3

Short-Term Debt and Liquidity (Short-Term Debt outstanding) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Short-term Debt [Line Items]
Short-term debt	$ 1,340	$ 1,070
Union Electric Company
Short-term Debt [Line Items]
Short-term debt	157	329
Ameren Illinois Company
Short-term Debt [Line Items]
Short-term debt	59	264
Commercial Paper
Short-term Debt [Line Items]
Short-term debt	1,340	1,070
Commercial Paper | Parent Company
Short-term Debt [Line Items]
Short-term debt	1,124	477
Commercial Paper | Union Electric Company
Short-term Debt [Line Items]
Short-term debt	157	329
Commercial Paper | Ameren Illinois Company
Short-term Debt [Line Items]
Short-term debt	$ 59	$ 264

Short-Term Debt and Liquidity_4

Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Short-term Debt [Line Items]
Average daily amount outstanding	$ 1,174	$ 791
Weighted-average interest rate	5.24%	1.47%
Short-term Debt, Maximum Amount Outstanding During Period	$ 1,381	$ 1,222
Peak interest rate	5.60%	3.60%
Parent Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 687	$ 439
Weighted-average interest rate	5.29%	1.58%
Short-term Debt, Maximum Amount Outstanding During Period	$ 1,127	$ 690
Peak interest rate	5.60%	3.55%
Union Electric Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 306	$ 253
Weighted-average interest rate	5.15%	1.16%
Short-term Debt, Maximum Amount Outstanding During Period	$ 592	$ 539
Peak interest rate	5.60%	3.55%
Ameren Illinois Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 181	$ 99
Weighted-average interest rate	5.15%	1.77%
Short-term Debt, Maximum Amount Outstanding During Period	$ 450	$ 354
Peak interest rate	5.60%	3.60%

Long-Term debt and Equity Fin_2

Long-Term debt and Equity Financings (Details) $ / shares in Units, shares in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2023 USD ($) shares	Mar. 31, 2023 USD ($) shares	Sep. 30, 2022 USD ($) shares	Sep. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2022 USD ($) shares
Long-Term Debt And Equity Financings [Line Items]
Shares issued under the DRPlus and 401(k) plan | shares	0.2		0.1	0.4	0.4
Issuances of common stock				$ 28,000,000	$ 29,000,000
Stock Issued During Period, Shares, Other | shares	0	0.5	0	0.5	0.4
Stock Issued During Period, Value, Other		$ 37,000,000
Common Stock, Shares Authorized Under DRPlus Plan | shares	3			3
Maximum Value Of Shares To Be Issued Under ATM Program	$ 910,000,000			$ 910,000,000
Forward Contract Indexed to Issuer's Equity, Basis Spread	75			75
Termination of a financing obligation				$ 240,000,000	$ 0
Minimum
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares				$ 81.83
Maximum
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares				94.63
Weighted Average
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares				$ 91.23
Dividend reinvestment and 401 (k) plans
Long-Term Debt And Equity Financings [Line Items]
Issuances of common stock	$ 5,000,000			$ 28,000,000
Accrued Proceeds from Issuance of Common Stock				$ 7,000,000
Forward Sale Agreements Outstanding
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Shares, at Fair Value | shares	4.3			4.3
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value	$ 390,000,000			$ 390,000,000
Period End Net Cash Settlement Price	72,000,000			72,000,000
Period End Net Share Settlement Price	1,000,000			1,000,000
Forward Sale Agreement Equity Offering Shares	4,300,000			4,300,000
Forward Sale Agreement Gross Sales Price	392,000,000			392,000,000
Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Termination of a financing obligation				240,000,000	0
Union Electric Company | Secured Debt | Senior Secured Notes 5.45% Due 2053
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount	$ 500,000,000			$ 500,000,000
Debt Instrument, Interest Rate, Stated Percentage	5.45%			5.45%
Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Capital contributions from parent				$ 50,000,000	0
Termination of a financing obligation				0	0
Ameren Illinois Company | Other Paid-in Capital:
Long-Term Debt And Equity Financings [Line Items]
Capital contributions from parent	$ 50,000,000		$ 0	50,000,000	$ 0
Ameren Illinois Company | Secured Debt | First Mortgage Bonds 0.375% Due 2023
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount	$ 100,000,000			$ 100,000,000
Debt Instrument, Interest Rate, Stated Percentage	0.375%			0.375%
Ameren Illinois Company | Secured Debt | First Mortgage Bonds 4.95% Due 2033
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount	$ 500,000,000			$ 500,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.95%			4.95%

Other Income, Net (Details)

Other Income, Net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	$ 16	$ 12	$ 39	$ 31
Interest income on industrial development revenue bonds	0	6	1	18
Other interest income	6	2	23	6
Non-service cost components of net periodic benefit income	84	45	211	138
Miscellaneous income	1	3	4	8
Income (Loss) from Equity Method Investments	0	(3)	2	1
Donations	(1)	(1)	(5)	(5)
Miscellaneous expense	(5)	(6)	(14)	(17)
Total Other Income, Net	101	58	261	180
Union Electric Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	8	7	20	17
Interest income on industrial development revenue bonds	0	6	1	18
Other interest income	3	1	8	2
Non-service cost components of net periodic benefit income	34	13	62	41
Miscellaneous income	1	1	3	3
Donations	0	0	(2)	(2)
Miscellaneous expense	(2)	(3)	(7)	(7)
Total Other Income, Net	44	25	85	72
Defined Benefit Plan, Non-service Cost or Income Components - Tracker	(2)	5	32	16
Ameren Illinois Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	5	5	15	14
Other interest income	4	1	14	4
Non-service cost components of net periodic benefit income	31	21	93	63
Miscellaneous income	0	3	2	5
Donations	(1)	(1)	(3)	(3)
Miscellaneous expense	(2)	(3)	(6)	(8)
Total Other Income, Net	$ 37	$ 26	$ 115	$ 75

Derivative Financial Instrume_3

Derivative Financial Instruments (Open Gross Derivative Volumes By Commodity Type) (Detail) lb in Thousands, gal in Millions, MWh in Millions, MMBTU in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2023 MWh MMBTU lb gal	Dec. 31, 2022 MMBTU MWh lb gal
Fuel oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	19	18
Natural gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	265	205
Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh	6	7
Uranium
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Mass | lb	186	514
Union Electric Company | Fuel oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	19	18
Union Electric Company | Natural gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	52	48
Union Electric Company | Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh	1	1
Union Electric Company | Uranium
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Mass | lb	186	514
Ameren Illinois Company | Fuel oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	0	0
Ameren Illinois Company | Natural gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	213	157
Ameren Illinois Company | Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh	5	6
Ameren Illinois Company | Uranium
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Mass | lb	0	0

Derivative Financial Instrume_4

Derivative Financial Instruments (Derivative Instruments Carrying Value) (Detail) - Not Designated As Hedging Instrument - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Derivative [Line Items]
Derivative Assets	$ 35	$ 89
Derivative Liability	125	136
Fuel oils | Other current assets
Derivative [Line Items]
Derivative Assets	6	13
Fuel oils | Other assets
Derivative [Line Items]
Derivative Assets	2	3
Natural gas | Other current assets
Derivative [Line Items]
Derivative Assets	7	30
Natural gas | Other assets
Derivative [Line Items]
Derivative Assets	8	20
Natural gas | Other current liabilities
Derivative [Line Items]
Derivative Liability	32	27
Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	22	11
Power | Other current assets
Derivative [Line Items]
Derivative Assets	7	16
Power | Other assets
Derivative [Line Items]
Derivative Assets	0	4
Power | Other current liabilities
Derivative [Line Items]
Derivative Liability	15	61
Power | Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	56	37
Uranium | Other current assets
Derivative [Line Items]
Derivative Assets	5	2
Uranium | Other assets
Derivative [Line Items]
Derivative Assets	0	1
Union Electric Company
Derivative [Line Items]
Derivative Assets	26	49
Derivative Liability	20	68
Union Electric Company | Fuel oils | Other current assets
Derivative [Line Items]
Derivative Assets	6	13
Union Electric Company | Fuel oils | Other assets
Derivative [Line Items]
Derivative Assets	2	3
Union Electric Company | Natural gas | Other current assets
Derivative [Line Items]
Derivative Assets	1	7
Union Electric Company | Natural gas | Other assets
Derivative [Line Items]
Derivative Assets	5	9
Union Electric Company | Natural gas | Other current liabilities
Derivative [Line Items]
Derivative Liability	7	7
Union Electric Company | Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	6	2
Union Electric Company | Power | Other current assets
Derivative [Line Items]
Derivative Assets	7	14
Union Electric Company | Power | Other assets
Derivative [Line Items]
Derivative Assets	0	0
Union Electric Company | Power | Other current liabilities
Derivative [Line Items]
Derivative Liability	7	59
Union Electric Company | Power | Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	0	0
Union Electric Company | Uranium | Other current assets
Derivative [Line Items]
Derivative Assets	5	2
Union Electric Company | Uranium | Other assets
Derivative [Line Items]
Derivative Assets	0	1
Ameren Illinois Company
Derivative [Line Items]
Derivative Assets	9	40
Derivative Liability	105	68
Ameren Illinois Company | Fuel oils | Other current assets
Derivative [Line Items]
Derivative Assets	0	0
Ameren Illinois Company | Fuel oils | Other assets
Derivative [Line Items]
Derivative Assets	0	0
Ameren Illinois Company | Natural gas | Other current assets
Derivative [Line Items]
Derivative Assets	6	23
Ameren Illinois Company | Natural gas | Other assets
Derivative [Line Items]
Derivative Assets	3	11
Ameren Illinois Company | Natural gas | Other current liabilities
Derivative [Line Items]
Derivative Liability	25	20
Ameren Illinois Company | Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	16	9
Ameren Illinois Company | Power | Other current assets
Derivative [Line Items]
Derivative Assets	0	2
Ameren Illinois Company | Power | Other assets
Derivative [Line Items]
Derivative Assets	0	4
Ameren Illinois Company | Power | Other current liabilities
Derivative [Line Items]
Derivative Liability	8	2
Ameren Illinois Company | Power | Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	56	37
Ameren Illinois Company | Uranium | Other current assets
Derivative [Line Items]
Derivative Assets	0	0
Ameren Illinois Company | Uranium | Other assets
Derivative [Line Items]
Derivative Assets	$ 0	$ 0

Derivative Financial Instrume_5

Derivative Financial Instruments (Offsetting Assets and Liabilities) (Details) - Not Designated As Hedging Instrument - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	$ 35	$ 89
Gross derivative instruments not offset in the balance sheet	11	29
Gross cash collateral received not offset in the balance sheet	0	0
Net derivative asset	24	60
Gross derivative liability amount recognized on the balance sheet	125	136
Gross derivative instruments not offset in the balance sheet	11	29
Gross cash collateral posted not offset in the balance sheet	5	56
Net derivative liability	109	51
Union Electric Company
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	26	49
Gross derivative instruments not offset in the balance sheet	6	9
Gross cash collateral received not offset in the balance sheet	0	0
Net derivative asset	20	40
Gross derivative liability amount recognized on the balance sheet	20	68
Gross derivative instruments not offset in the balance sheet	6	9
Gross cash collateral posted not offset in the balance sheet	5	56
Net derivative liability	9	3
Ameren Illinois Company
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	9	40
Gross derivative instruments not offset in the balance sheet	5	20
Gross cash collateral received not offset in the balance sheet	0	0
Net derivative asset	4	20
Gross derivative liability amount recognized on the balance sheet	105	68
Gross derivative instruments not offset in the balance sheet	5	20
Gross cash collateral posted not offset in the balance sheet	0	0
Net derivative liability	$ 100	$ 48

Derivative Financial Instrume_6

Derivative Financial Instruments (Derivative Instruments with Credit Risk-Related Contingent Features) (Details) $ in Millions	Sep. 30, 2023 USD ($)
Derivative [Line Items]
Aggregate Fair Value of Derivative Liabilities	$ 55
Cash Collateral Posted	0
Potential Aggregate Amount of Additional Collateral Required	43
Union Electric Company
Derivative [Line Items]
Aggregate Fair Value of Derivative Liabilities	14
Cash Collateral Posted	0
Potential Aggregate Amount of Additional Collateral Required	8
Ameren Illinois Company
Derivative [Line Items]
Aggregate Fair Value of Derivative Liabilities	41
Cash Collateral Posted	0
Potential Aggregate Amount of Additional Collateral Required	$ 35

Fair Value Measurements (Schedu

Fair Value Measurements (Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	$ 1,037	$ 947
Assets fair value	1,072	1,036
Excluded receivables, payables, and accrued income, net	5	11
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	703	618
Assets fair value	711	636
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	334	329
Assets fair value	346	372
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Assets fair value	15	28
Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	35	89
Derivative Liability	125	136
Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	8	18
Derivative Liability	8	57
Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	12	43
Derivative Liability	45	25
Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	15	28
Derivative Liability	72	54
Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	1,037	947
Assets fair value	1,063	996
Union Electric Company | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	703	618
Assets fair value	711	635
Union Electric Company | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	334	329
Assets fair value	340	344
Union Electric Company | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Assets fair value	12	17
Union Electric Company | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	26	49
Derivative Liability	20	68
Union Electric Company | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	8	17
Derivative Liability	6	57
Union Electric Company | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	6	15
Derivative Liability	11	6
Union Electric Company | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	12	17
Derivative Liability	3	5
Union Electric Company | Fuel oils | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	8	16
Union Electric Company | Fuel oils | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	8	16
Union Electric Company | Fuel oils | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Union Electric Company | Fuel oils | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Union Electric Company | Natural gas | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	6	16
Derivative Liability	13	9
Union Electric Company | Natural gas | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	1
Derivative Liability	0	0
Union Electric Company | Natural gas | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	6	15
Derivative Liability	11	6
Union Electric Company | Natural gas | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Derivative Liability	2	3
Union Electric Company | Power | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	7	14
Derivative Liability	7	59
Union Electric Company | Power | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Derivative Liability	6	57
Union Electric Company | Power | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Derivative Liability	0	0
Union Electric Company | Power | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	7	14
Derivative Liability	1	2
Union Electric Company | Uranium | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	5	3
Union Electric Company | Uranium | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Union Electric Company | Uranium | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Union Electric Company | Uranium | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	5	3
Union Electric Company | Equity securities: | U.S. large capitalization
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	703	618
Union Electric Company | Equity securities: | U.S. large capitalization | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	703	618
Union Electric Company | Equity securities: | U.S. large capitalization | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company | Equity securities: | U.S. large capitalization | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company | Debt securities: | U.S. Treasury and agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	138	137
Union Electric Company | Debt securities: | U.S. Treasury and agency securities | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company | Debt securities: | U.S. Treasury and agency securities | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	138	137
Union Electric Company | Debt securities: | U.S. Treasury and agency securities | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company | Debt securities: | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	126	122
Union Electric Company | Debt securities: | Corporate bonds | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company | Debt securities: | Corporate bonds | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	126	122
Union Electric Company | Debt securities: | Corporate bonds | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company | Debt securities: | Other Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	70	70
Union Electric Company | Debt securities: | Other Debt Securities | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Union Electric Company | Debt securities: | Other Debt Securities | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	70	70
Union Electric Company | Debt securities: | Other Debt Securities | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	9	40
Ameren Illinois Company | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	0	1
Ameren Illinois Company | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	6	28
Ameren Illinois Company | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	3	11
Ameren Illinois Company | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	105	68
Ameren Illinois Company | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	2	0
Ameren Illinois Company | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	34	19
Ameren Illinois Company | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	69	49
Ameren Illinois Company | Natural gas | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	9	34
Derivative Liability	41	29
Ameren Illinois Company | Natural gas | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	1
Derivative Liability	2	0
Ameren Illinois Company | Natural gas | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	6	28
Derivative Liability	34	19
Ameren Illinois Company | Natural gas | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	3	5
Derivative Liability	5	10
Ameren Illinois Company | Power | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	6
Derivative Liability	64	39
Ameren Illinois Company | Power | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Derivative Liability	0	0
Ameren Illinois Company | Power | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Derivative Liability	0	0
Ameren Illinois Company | Power | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	6
Derivative Liability	$ 64	$ 39

Fair Value Measurements (Sche_2

Fair Value Measurements (Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level Three In The Fair Value Hierarchy) (Details) - Power - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (54)	$ (80)	$ (21)	$ (132)
Included in regulatory assets/liabilities	(4)	20	(37)	49
Settlements, assets		32		55
Settlement, liabilities	0		0
Change in unrealized gains (losses) related to assets/liabilities held at period end	(4)	25	(25)	61
Ending balance	(58)	(28)	(58)	(28)
Union Electric Company
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	14	(36)	12	(15)
Included in regulatory assets/liabilities	(5)	(10)	3	(56)
Settlements, assets		38		63
Settlement, liabilities	(3)		(9)
Change in unrealized gains (losses) related to assets/liabilities held at period end	(5)	(3)	6	(39)
Ending balance	6	(8)	6	(8)
Ameren Illinois Company
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(68)	(44)	(33)	(117)
Included in regulatory assets/liabilities	1	30	(40)	105
Settlements, assets	3		9
Settlement, liabilities		(6)		(8)
Change in unrealized gains (losses) related to assets/liabilities held at period end	1	28	(31)	100
Ending balance	$ (64)	$ (20)	$ (64)	$ (20)

Fair Value Measurements (Sche_3

Fair Value Measurements (Schedule Of Valuation Process And Unobservable Inputs) (Details) - Power $ in Millions	Sep. 30, 2023 USD ($) $ / MWh	Dec. 31, 2022 USD ($) $ / MWh $ / MMBTU
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Derivative Assets | $	$ 7	$ 20
Derivative liabilities | $	$ (65)	$ (41)
Commodity Forward Price | Discounted cash flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	32	38
Commodity Forward Price | Discounted cash flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	63	89
Commodity Forward Price | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	43	51
Nodal Basis | Discounted cash flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	(10)	(10)
Nodal Basis | Discounted cash flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	(1)	(1)
Nodal Basis | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	(5)	(4)
Commodity Future Price | Discounted cash flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Derivative Asset (Liability) Net, Measurement Input [Extensible Enumeration]		Commodity Future Price
Commodity Future Price | Discounted cash flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Derivative Asset (Liability) Net, Measurement Input [Extensible Enumeration]		Commodity Future Price
Commodity Future Price | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input | $ / MMBTU		0

Fair Value Measurements (Sche_4

Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Financial Assets and Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	$ 246	$ 216	$ 180	$ 155
Short-term debt	1,340	1,070
Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	13	13	7	8
Short-term debt	157	329
Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	225	191	$ 166	$ 133
Short-term debt	59	264
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	246	216
Short-term debt	1,340	1,070
Long-term debt (including current portion)	14,678	14,025
Investments in industrial development revenue bonds		240
Debt Issuance Costs, Net	105	99
Carrying Amount | Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	13	13
Short-term debt	157	329
Long-term debt (including current portion)	6,341	6,086
Investments in industrial development revenue bonds		240
Debt Issuance Costs, Net	45	41
Carrying Amount | Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	225	191
Short-term debt	59	264
Long-term debt (including current portion)	5,231	4,835
Debt Issuance Costs, Net	48	44
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	246	216
Short-term Debt, Fair Value	1,340	1,070
Long-term Debt, Fair Value	12,417	12,453
Investments, Fair Value Disclosure		240
Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	246	216
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Investments, Fair Value Disclosure		0
Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	0	0
Short-term Debt, Fair Value	1,340	1,070
Long-term Debt, Fair Value	11,985	11,989
Investments, Fair Value Disclosure		240
Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	432	464
Investments, Fair Value Disclosure		0
Fair Value | Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	13	13
Short-term Debt, Fair Value	157	329
Long-term Debt, Fair Value	5,287	5,365
Investments, Fair Value Disclosure		240
Fair Value | Union Electric Company | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	13	13
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Investments, Fair Value Disclosure		0
Fair Value | Union Electric Company | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	0	0
Short-term Debt, Fair Value	157	329
Long-term Debt, Fair Value	5,287	5,365
Investments, Fair Value Disclosure		240
Fair Value | Union Electric Company | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Investments, Fair Value Disclosure		0
Fair Value | Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	225	191
Short-term Debt, Fair Value	59	264
Long-term Debt, Fair Value	4,419	4,320
Fair Value | Ameren Illinois Company | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	225	191
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Fair Value | Ameren Illinois Company | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	0	0
Short-term Debt, Fair Value	59	264
Long-term Debt, Fair Value	4,419	4,320
Fair Value | Ameren Illinois Company | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, cash equivalents, and restricted cash	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	$ 0	$ 0

Related Party Transactions (Nar

Related Party Transactions (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Related Party Transaction [Line Items]
Other assets	$ 882	$ 768
Union Electric Company
Related Party Transaction [Line Items]
Other assets	137	140
Ameren Illinois Company
Related Party Transaction [Line Items]
Other assets	565	482
Ameren Services Support Services Agreement | Union Electric Company | Related Party
Related Party Transaction [Line Items]
Other assets	28	41
Ameren Services Support Services Agreement | Ameren Illinois Company | Related Party
Related Party Transaction [Line Items]
Other assets	$ 31	$ 43

Related Party Transactions (Sch

Related Party Transactions (Schedule of Affiliate Receivables and Payables) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	$ 955	$ 1,159
Accounts Receivable, Related Parties, Current	597	600
Union Electric Company | Related Party
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	85	43
Accounts Receivable, Related Parties, Current	16	51
Union Electric Company | Income taxes payable to parent | Related Party
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	29	0
Union Electric Company | Income taxes receivable from parent | Related Party
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	0	39
Ameren Illinois Company | Related Party
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	136	93
Accounts Receivable, Related Parties, Current	11	12
Ameren Illinois Company | Income taxes payable to parent | Related Party
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	81	50
Ameren Illinois Company | Income taxes receivable from parent | Related Party
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	$ 0	$ 0

Related Party Transactions (Eff

Related Party Transactions (Effects of Related-party Transactions on the Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Related Party Transaction [Line Items]
Operating Revenues	$ 2,060	$ 2,306	$ 5,882	$ 5,911
Purchased Power	272	563	1,095	1,058
Other operations and maintenance	470	475	1,368	1,427
(Interest Charges)/Other Income, Net	152	126	413	356
Union Electric Company
Related Party Transaction [Line Items]
Operating Revenues	1,237	1,359	3,101	3,096
Purchased Power	75	247	420	458
Other operations and maintenance	256	252	732	744
(Interest Charges)/Other Income, Net	63	58	166	157
Union Electric Company | Ameren Missouri Power Supply Agreements with Ameren Illinois | Related Party
Related Party Transaction [Line Items]
Operating Revenues	2	2	2	7
Union Electric Company | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party
Related Party Transaction [Line Items]
Operating Revenues	7	6	25	18
Other operations and maintenance	1	1	1	1
Union Electric Company | Ameren Missouri and Ameren Illinois Miscellaneous Support Services | Related Party
Related Party Transaction [Line Items]
Operating Revenues	1	1	1	1
Union Electric Company | Total Related Party Operating Revenues | Related Party
Related Party Transaction [Line Items]
Operating Revenues	9	8	27	25
Union Electric Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI | Related Party
Related Party Transaction [Line Items]
Purchased Power	1	1	1	1
Union Electric Company | Purchased Power | Related Party
Related Party Transaction [Line Items]
Purchased Power	1	1	1	1
Union Electric Company | Ameren Services Support Services Agreement | Related Party
Related Party Transaction [Line Items]
Other operations and maintenance	36	38	106	109
Union Electric Company | Total Related Party Other Operations and Maintenance | Related Party
Related Party Transaction [Line Items]
Other operations and maintenance	36	38	106	109
Union Electric Company | Money pool borrowings (advances) | Related Party
Related Party Transaction [Line Items]
(Interest Charges)/Other Income, Net	1	1		1
Ameren Illinois Company
Related Party Transaction [Line Items]
Operating Revenues	783	904	2,663	2,697
Purchased Power	200	319	679	608
Other operations and maintenance	200	215	603	663
(Interest Charges)/Other Income, Net	54	42	151	125
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party
Related Party Transaction [Line Items]
Operating Revenues	1	1	1	1
Other operations and maintenance	1	1	2	2
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Miscellaneous Support Services | Related Party
Related Party Transaction [Line Items]
Operating Revenues	2	1	2	1
Ameren Illinois Company | Total Related Party Operating Revenues | Related Party
Related Party Transaction [Line Items]
Operating Revenues	2	1	2	1
Ameren Illinois Company | Ameren Illinois Power Supply Agreements with Ameren Missouri | Related Party
Related Party Transaction [Line Items]
Purchased Power	2	2	2	7
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI | Related Party
Related Party Transaction [Line Items]
Purchased Power	1	1	1	1
Ameren Illinois Company | Purchased Power | Related Party
Related Party Transaction [Line Items]
Purchased Power	3	2	3	7
Ameren Illinois Company | Ameren Services Support Services Agreement | Related Party
Related Party Transaction [Line Items]
Other operations and maintenance	33	36	101	103
Ameren Illinois Company | Total Related Party Other Operations and Maintenance | Related Party
Related Party Transaction [Line Items]
Other operations and maintenance	33	37	103	105
Ameren Illinois Company | Money pool borrowings (advances) | Related Party
Related Party Transaction [Line Items]
(Interest Charges)/Other Income, Net	$ 1	$ 1	$ 1	$ 1

Commitments And Contingencies (

Commitments And Contingencies (Environmental Matters) (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2023 USD ($) scrubber site	Dec. 31, 2022 USD ($)
Loss Contingencies [Line Items]
Asset Retirement Obligation	$ 784	$ 786
Minimum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	90
Maximum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	$ 120
Union Electric Company
Loss Contingencies [Line Items]
Number of Energy Center Scrubbers | scrubber	2
Asset Retirement Obligation	$ 780	782
Union Electric Company | Coal Fired Electric Generation Equipment
Loss Contingencies [Line Items]
Plant To Be Abandoned, Net	550
Union Electric Company | Minimum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	90
Union Electric Company | Maximum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	120
Ameren Illinois Company
Loss Contingencies [Line Items]
Asset Retirement Obligation	4	$ 4
Manufactured Gas Plant
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 60
Manufactured Gas Plant | Ameren Illinois Company
Loss Contingencies [Line Items]
Number of remediation sites | site	44
Accrual for environmental loss contingencies	$ 60
Manufactured Gas Plant | Ameren Illinois Company | Minimum
Loss Contingencies [Line Items]
Estimate of possible loss	60
Manufactured Gas Plant | Ameren Illinois Company | Maximum
Loss Contingencies [Line Items]
Estimate of possible loss	112
Rush Island Energy Center | Union Electric Company
Loss Contingencies [Line Items]
Rate Base	500
New CCR Rules Estimate
Loss Contingencies [Line Items]
Asset Retirement Obligation	40
New CCR Rules Estimate | Union Electric Company
Loss Contingencies [Line Items]
Asset Retirement Obligation	$ 40

Callaway Energy Center (Insuran

Callaway Energy Center (Insurance Disclosure) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2023 USD ($) yr
Nuclear Waste Matters [Line Items]
Decommissioning Cost	$ 7
Frequency of Decommissioning Cost Study	3 years
Number Of Years The Limit Of Liability And The Maximum Potential Annual Payments Are Adjusted	5 years
Number Of Weeks Of Coverage After The First Twelve Weeks Of An Outage | yr	1
Number Of Additional Weeks After Initial Indemnity Coverage For Power Outage | yr	1.365
Public Liability And Nuclear Worker Liability - American Nuclear Insurers
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	$ 450
Insurance Maximum Coverage per Incident	0
Public Liability And Nuclear Worker Liability - Pool Participation
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	16,095
Insurance Maximum Coverage per Incident	166
Threshold Amount For Retrospective Insurance Assessment For Covered Loss Under Public Liability And Nuclear Worker Liability Insurance Policy	450
Maximum Annual Payment Per Incident At Licensed Commercial Nuclear Reactor	24.7
Public Liability
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	16,545
Insurance Maximum Coverage per Incident	166
Property Damage - Nuclear Electric Insurance Ltd
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	3,200
Insurance Maximum Coverage per Incident	28
Accidental Outage - Nuclear Electric Insurance Ltd
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	490
Insurance Maximum Coverage per Incident	9
Amount Of Weekly Indemnity Coverage Commencing Twelve Weeks After Power Outage	4.5
Amount Of Additional Weekly Indemnity Coverage Commencing After Initial Indemnity Coverage	3.6
Amount Of Weekly Indemnity Coverage Thereafter Not Exceeding Policy Limit	490
Sub-Limit Of Amount Of Weekly Indemnity Coverage Thereafter Not Exceeding Policy Limit For Non-Nuclear Events	328
Radiation Event
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	2,700
Aggregate Nuclear Power Industry Insurance Policy Limit For Losses From Terrorist Attacks Within Twelve Month Period	3,200
Non-Radiation Event
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	2,300
Aggregate Nuclear Power Industry Insurance Policy Limit For Losses From Terrorist Attacks Within Twelve Month Period	1,800
Property Damage European Mutual Association for Nuclear Insurance
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	$ 490

Retirement Benefits (Components

Retirement Benefits (Components Of Net Periodic Benefit Cost) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total non-service cost components	$ (84)	$ (45)	$ (211)	$ (138)
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	10	31	56	95
Interest cost	55	42	166	123
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	(84)	(80)	(251)	(240)
Prior service benefit	0	0	0	0
Actuarial (gain) loss	(29)	7	(86)	19
Total non-service cost components	(58)	(31)	(171)	(98)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	(48)	0	$ (115)	(3)
Defined Benefit Plan, Amortization Period of Actuarial Gain (Loss)			10 years
Defined Benefit Plan, Difference Between Actual and Expected Return (Loss) on Plan Assets Amortization Period			4 years
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	3	5	$ 9	15
Interest cost	11	8	34	25
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	(22)	(21)	(68)	(64)
Prior service benefit	(1)	(1)	(3)	(3)
Actuarial (gain) loss	(12)	(5)	(35)	(14)
Total non-service cost components	(24)	(19)	(72)	(56)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	$ (21)	$ (14)	$ (63)	$ (41)
Defined Benefit Plan, Amortization Period of Actuarial Gain (Loss)			10 years
Defined Benefit Plan, Difference Between Actual and Expected Return (Loss) on Plan Assets Amortization Period			4 years

Retirement Benefits (Summary of

Retirement Benefits (Summary of Benefit Plan Costs Incurred) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	$ (48)	$ 0	$ (115)	$ (3)
Pension Plan | Union Electric Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(24)	0	(59)	(2)
Pension Plan | Ameren Illinois Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(21)	1	(48)	2
Pension Plan | Other Affiliated Entities And Intercompany Eliminations
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(3)	(1)	(8)	(3)
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(21)	(14)	(63)	(41)
Other Postretirement Benefit Plan, Defined Benefit | Union Electric Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(8)	(3)	(23)	(10)
Other Postretirement Benefit Plan, Defined Benefit | Ameren Illinois Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(13)	(11)	(40)	(31)
Other Postretirement Benefit Plan, Defined Benefit | Other Affiliated Entities And Intercompany Eliminations
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	$ 0	$ 0	$ 0	$ 0

Income Taxes (Schedule of Effec

Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21%	21%	21%	21%
Increases (decreases) from:
Amortization of deferred investment tax credit	0%	0%	0%	0%
Amortization of excess deferred taxes	(7.00%)	(8.00%)	(8.00%)	(8.00%)
Depreciation differences	(1.00%)	0%	0%	0%
Renewable and other tax credits	(5.00%)	(4.00%)	(5.00%)	(4.00%)
State tax	4%	4%	5%	5%
Stock-based compensation	0%	1%
Cash surrender value of COLI	0%	1%
Effective income tax rate	12%	15%	13%	14%
Union Electric Company
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21%	21%	21%	21%
Increases (decreases) from:
Amortization of deferred investment tax credit	(1.00%)	(1.00%)	(1.00%)	(1.00%)
Amortization of excess deferred taxes	(15.00%)	(15.00%)	(15.00%)	(15.00%)
Depreciation differences	0%	0%	0%	0%
Renewable and other tax credits	(11.00%)	(10.00%)	(11.00%)	(10.00%)
State tax	3%	3%	3%	3%
Stock-based compensation	0%	0%
Cash surrender value of COLI	0%	0%
Effective income tax rate	(3.00%)	(2.00%)	(3.00%)	(2.00%)
Ameren Illinois Company
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21%	21%	21%	21%
Increases (decreases) from:
Amortization of deferred investment tax credit	0%	0%	0%	0%
Amortization of excess deferred taxes	(2.00%)	(2.00%)	(2.00%)	(2.00%)
Depreciation differences	0%	0%	(1.00%)	0%
Renewable and other tax credits	(1.00%)	0%	0%	0%
State tax	7%	7%	7%	7%
Stock-based compensation	0%	0%
Cash surrender value of COLI	0%	0%
Effective income tax rate	25%	26%	25%	26%

Supplemental Information (Cash

Supplemental Information (Cash and Cash Equivalents) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	$ 8	$ 10
Restricted cash included in “Other current assets”	13	13
Restricted cash included in “Other assets”	220	185
Restricted cash included in “Nuclear decommissioning trust fund”	5	8
Total cash, cash equivalents, and restricted cash	246	216	$ 180	$ 155
Union Electric Company
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	3	0
Restricted cash included in “Other current assets”	5	5
Restricted cash included in “Other assets”	0	0
Restricted cash included in “Nuclear decommissioning trust fund”	5	8
Total cash, cash equivalents, and restricted cash	13	13	7	8
Ameren Illinois Company
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	0	0
Restricted cash included in “Other current assets”	5	6
Restricted cash included in “Other assets”	220	185
Restricted cash included in “Nuclear decommissioning trust fund”	0	0
Total cash, cash equivalents, and restricted cash	$ 225	$ 191	$ 166	$ 133

Supplemental Information (Allow

Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	$ 39	$ 30	$ 31	$ 29
Bad debt expense	18	14	41	23
Charged to other accounts	2	1	3	3
Net write-offs	(26)	(14)	(42)	(24)
End of period	33	$ 31	33	$ 31
Payables for purchased receivables	$ 50		$ 50		$ 31
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement	17%	17%	17%	17%
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement	$ 106	$ 117	$ 106	$ 117
Union Electric Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	12	12	13	13
Bad debt expense	5	3	9	6
Net write-offs	(5)	(3)	(10)	(7)
End of period	$ 12	$ 12	$ 12	$ 12
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement	8%	12%	8%	12%
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement	$ 25	$ 39	$ 25	$ 39
Ameren Illinois Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	27	18	18	16
Bad debt expense	13	11	32	17
Charged to other accounts	2	1	3	3
Net write-offs	(21)	(11)	(32)	(17)
End of period	21	$ 19	21	$ 19
Payables for purchased receivables	$ 50		$ 50		$ 31
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement	26%	21%	26%	21%
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement	$ 81	$ 78	$ 81	$ 78

Supplemental Information (Suppl

Supplemental Information (Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including nuclear fuel expenditures	$ 518	$ 367
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund	66	(262)
Return on investment in industrial development revenue bonds	240	0
Termination of a financing obligation	240	0
Issuance of common stock for stock-based compensation
Supplemental Cash Flow Information [Line Items]
Stock Issued	37	31
Issuance of common stock under the DRPlus
Supplemental Cash Flow Information [Line Items]
Stock Issued	7	8
Union Electric Company
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including nuclear fuel expenditures	246	187
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund	66	(262)
Return on investment in industrial development revenue bonds	240	0
Termination of a financing obligation	240	0
Union Electric Company | Issuance of common stock for stock-based compensation
Supplemental Cash Flow Information [Line Items]
Stock Issued	0	0
Union Electric Company | Issuance of common stock under the DRPlus
Supplemental Cash Flow Information [Line Items]
Stock Issued	0	0
Ameren Illinois Company
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including nuclear fuel expenditures	237	180
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund	0	0
Return on investment in industrial development revenue bonds	0	0
Termination of a financing obligation	0	0
Ameren Illinois Company | Issuance of common stock for stock-based compensation
Supplemental Cash Flow Information [Line Items]
Stock Issued	0	0
Ameren Illinois Company | Issuance of common stock under the DRPlus
Supplemental Cash Flow Information [Line Items]
Stock Issued	$ 0	$ 0

Supplemental Information (Sched

Supplemental Information (Schedule of Asset Retirement Obligations) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	$ 786
Liabilities settled	(9)
Accretion	25
Change in estimates	(18)
Asset Retirement Obligation, Ending Balance	784
Other current liabilities	664	$ 738
Union Electric Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	782
Liabilities settled	(9)
Accretion	25
Change in estimates	(18)
Asset Retirement Obligation, Ending Balance	780
Other current liabilities	213	323
Ameren Illinois Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	4
Liabilities settled	0
Accretion	0
Change in estimates	0
Asset Retirement Obligation, Ending Balance	4
Other current liabilities	242	232
Asset Retirement Obligation Balance
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Other current liabilities	23	23
Asset Retirement Obligation Balance | Union Electric Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Other current liabilities	$ 23	$ 23

Supplemental Information (Narra

Supplemental Information (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount	$ 6	$ 5
Deferred Compensation Liability, Classified, Noncurrent	$ 85		$ 87
Q1 2023 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Performance Shares | Q1 2023 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	265,422
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Fair Value	$ 24
Stock Issued During Period Percentage Conversion Of Units, Low End	0%
Stock Issued During Period Percentage Conversion Of Units, High End	200%
Performance Shares | Market performance measures achievement | Q1 2023 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	227,494
Performance Shares | Renewable generation and energy storage installation targets | Q1 2023 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	37,928
Restricted Stock Units (RSUs) | Q1 2023 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	116,701
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Fair Value	$ 10

Supplemental Information (Sch_2

Supplemental Information (Schedule Of Excise Taxes) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Accounting Policies [Line Items]
Excise tax expense	$ 87	$ 83	$ 223	$ 229
Union Electric Company
Accounting Policies [Line Items]
Excise tax expense	60	55	133	128
Ameren Illinois Company
Accounting Policies [Line Items]
Excise tax expense	$ 27	$ 28	$ 90	$ 101

Supplemental Information (Earni

Supplemental Information (Earnings Per Share) (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Earnings Per Share Reconciliation [Abstract]
Weighted-average Common Shares Outstanding – Basic	262,800,000	258,400,000	262,500,000	258,200,000
Assumed settlement of performance share units and restricted stock units	600,000	900,000	700,000	1,000,000
Dilutive effect of forward sale agreements	0	200,000	0	100,000
Weighted-average Common Shares Outstanding – Diluted	263,400,000	259,500,000	263,200,000	259,300,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)	0	0	0	0

Segment Information (Schedule O

Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Segment Reporting Information [Line Items]
Operating Revenues	$ 2,060	$ 2,306	$ 5,882	$ 5,911
Net income (loss) attributable to common shareholders	493	452	994	911
Capital expenditures	749	899	2,571	2,437
Union Electric Company
Segment Reporting Information [Line Items]
Operating Revenues	1,237	1,359	3,101	3,096
Net Income (Loss)	411	397	541	547
Ameren Illinois Company
Segment Reporting Information [Line Items]
Operating Revenues	783	904	2,663	2,697
Net Income (Loss)	125	103	452	375
Capital expenditures	382	446	1,226	1,145
Operating Segments | Union Electric Company
Segment Reporting Information [Line Items]
Operating Revenues	1,228	1,351	3,074	3,071
Net Income (Loss)	411	397	541	547
Capital expenditures	341	431	1,255	1,237
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues	557	672	1,721	1,640
Net Income (Loss)	66	51	193	151
Capital expenditures	177	163	527	444
Operating Segments | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Operating Revenues	121	146	664	811
Net Income (Loss)	(5)	(4)	93	82
Capital expenditures	80	114	221	232
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
Operating Revenues	154	137	423	389
Net Income (Loss)	86	78	229	199
Capital expenditures	160	187	570	519
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues	558	672	1,722	1,641
Net Income (Loss)	66	51	193	151
Capital expenditures	177	163	527	444
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Operating Revenues	122	146	665	811
Net Income (Loss)	(5)	(4)	93	82
Capital expenditures	80	114	221	232
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Operating Revenues	103	86	276	245
Net Income (Loss)	64	56	166	142
Capital expenditures	125	169	478	469
Other
Segment Reporting Information [Line Items]
Net Income (Loss)	(65)	(70)	(62)	(68)
Capital expenditures	2	1	7	4
Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment revenues	(45)	(40)	(118)	(102)
Capital expenditures	(11)	3	(9)	1
Intersegment Eliminations | Union Electric Company
Segment Reporting Information [Line Items]
Intersegment revenues	(9)	(8)	(27)	(25)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	(1)	0	(1)	(1)
Intersegment Eliminations | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Intersegment revenues	(1)	0	(1)	0
Intersegment Eliminations | Ameren Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	(34)	(32)	(89)	(76)
Intersegment Eliminations | Ameren Illinois Company
Segment Reporting Information [Line Items]
Intersegment revenues	(33)	(31)	(87)	(75)
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	$ (33)	$ (31)	$ (87)	$ (75)

Segment Information (Disaggrega

Segment Information (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Operating Revenues	$ 2,060	$ 2,306	$ 5,882	$ 5,911
Revenues	2,060	2,306	5,882	5,911
Revenues from alternative revenue programs	(109)	(83)	63	2
Other revenues not from contracts with customers	1	(43)	(1)	(74)
Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(9)	14	(11)	8
Other revenues not from contracts with customers	(1)	(45)	(9)	(81)
Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(94)	(83)	30	13
Other revenues not from contracts with customers	2	2	6	5
Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(1)	(3)	36	(5)
Other revenues not from contracts with customers	0	0	2	2
Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(5)	(11)	8	(14)
Other revenues not from contracts with customers	0	0	0	0
Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	1,921	2,140	5,096	4,971
Revenues	1,921	2,140	5,096	4,971
Electric | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	920	971	2,323	2,221
Electric | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	657	663	1,608	1,539
Electric | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	147	146	379	374
Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	197	360	786	837
Natural gas
Disaggregation of Revenue [Line Items]
Operating Revenues	139	166	786	940
Revenues	139	166	786	940
Natural gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	84	100	543	653
Natural gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	24	31	155	188
Natural gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	2	6	14	37
Natural gas | Other
Disaggregation of Revenue [Line Items]
Revenues	29	29	74	62
Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Operating Revenues	783	904	2,663	2,697
Revenues	783	904	2,663	2,697
Revenues from alternative revenue programs	(101)	(96)	70	(4)
Other revenues not from contracts with customers	2	2	8	7
Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	405	496	1,518	1,529
Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	208	258	703	723
Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	41	52	146	178
Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenues	129	98	296	267
Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(94)	(83)	30	13
Other revenues not from contracts with customers	2	2	6	5
Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(1)	(3)	36	(5)
Other revenues not from contracts with customers	0	0	2	2
Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(6)	(10)	4	(12)
Other revenues not from contracts with customers	0	0	0	0
Ameren Illinois Company | Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	661	758	1,998	1,886
Ameren Illinois Company | Natural gas
Disaggregation of Revenue [Line Items]
Operating Revenues	122	146	665	811
Operating Segments | Union Electric Company
Disaggregation of Revenue [Line Items]
Operating Revenues	1,228	1,351	3,074	3,071
Revenues	1,237	1,359	3,101	3,096
Operating Segments | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Operating Revenues	557	672	1,721	1,640
Revenues	558	672	1,722	1,641
Operating Segments | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Operating Revenues	121	146	664	811
Revenues	122	146	665	811
Operating Segments | Ameren Transmission
Disaggregation of Revenue [Line Items]
Operating Revenues	154	137	423	389
Revenues	188	169	512	465
Operating Segments | Electric | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	1,219	1,338	2,978	2,966
Operating Segments | Electric | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	590	564	1,274	1,267
Operating Segments | Electric | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	468	430	1,026	968
Operating Segments | Electric | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	107	99	243	229
Operating Segments | Electric | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenues	54	245	435	502
Operating Segments | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	558	672	1,722	1,641
Operating Segments | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	330	407	1,049	954
Operating Segments | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	189	233	582	571
Operating Segments | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	40	47	136	145
Operating Segments | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	(1)	(15)	(45)	(29)
Operating Segments | Electric | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Electric | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	188	169	512	465
Operating Segments | Electric | Ameren Transmission | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Electric | Ameren Transmission | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Electric | Ameren Transmission | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Electric | Ameren Transmission | Other
Disaggregation of Revenue [Line Items]
Revenues	188	169	512	465
Operating Segments | Natural gas | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	18	21	123	130
Operating Segments | Natural gas | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	9	11	74	78
Operating Segments | Natural gas | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	5	6	34	36
Operating Segments | Natural gas | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	1	1	4	4
Operating Segments | Natural gas | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenues	3	3	11	12
Operating Segments | Natural gas | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	122	146	665	811
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	75	89	469	575
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	19	25	121	152
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	1	5	10	33
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	27	27	65	51
Operating Segments | Natural gas | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Operating Revenues	558	672	1,722	1,641
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Operating Revenues	122	146	665	811
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Operating Revenues	103	86	276	245
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	558	672	1,722	1,641
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	330	407	1,049	954
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	189	233	582	571
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	40	47	136	145
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	(1)	(15)	(45)	(29)
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	136	117	363	320
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Other
Disaggregation of Revenue [Line Items]
Revenues	136	117	363	320
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	122	146	665	811
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	75	89	469	575
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	19	25	121	152
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	1	5	10	33
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	27	27	65	51
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(45)	(40)	(118)	(102)
Revenues	(45)	(40)	(118)	(102)
Intersegment Eliminations | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	(9)	(8)	(27)	(25)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	(1)	0	(1)	(1)
Intersegment Eliminations | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	(1)	0	(1)	0
Intersegment Eliminations | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	(34)	(32)	(89)	(76)
Intersegment Eliminations | Electric
Disaggregation of Revenue [Line Items]
Revenues	(44)	(39)	(116)	(101)
Intersegment Eliminations | Electric | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Electric | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Electric | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	(44)	(39)	(116)	(101)
Intersegment Eliminations | Natural gas
Disaggregation of Revenue [Line Items]
Revenues	(1)	(1)	(2)	(1)
Intersegment Eliminations | Natural gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Natural gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Natural gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Natural gas | Other
Disaggregation of Revenue [Line Items]
Revenues	(1)	(1)	(2)	(1)
Intersegment Eliminations | Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Revenues	(33)	(31)	(87)	(75)
Revenues	(33)	(31)	(87)	(75)
Intersegment Eliminations | Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenues	(33)	(31)	(87)	(75)
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	$ (33)	$ (31)	$ (87)	$ (75)