Ameren Illinois (AILIN) 10-Q 6 May 24 2024 Q1 Quarterly report Financial data

Cover Page

Cover Page - shares	3 Months Ended
	Mar. 31, 2024	Apr. 30, 2024
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2024
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		266,670,374
Entity Central Index Key	0001002910
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Amendment Flag	false
Union Electric Company
Entity Information [Line Items]
Entity File Number	1-2967
Entity Registrant Name	Union Electric Company
Entity Tax Identification Number	43-0559760
Entity Incorporation, State or Country Code	MO
Entity Address, Address Line One	1901 Chouteau Avenue
Entity Address, City or Town	St. Louis
Entity Address, State or Province	MO
Entity Address, Postal Zip Code	63103
City Area Code	(314)
Local Phone Number	621-3222
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
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	2024
Document Fiscal Period Focus	Q1
Amendment Flag	false
Ameren Illinois Company
Entity Information [Line Items]
Entity File Number	1-3672
Entity Registrant Name	Ameren Illinois Company
Entity Tax Identification Number	37-0211380
Entity Incorporation, State or Country Code	IL
Entity Address, Address Line One	10 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	2024
Document Fiscal Period Focus	Q1
Amendment Flag	false

Consolidated Statement of Incom

Consolidated Statement of Income (Loss) and Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating Revenues:
Total operating revenues	$ 1,816	$ 2,062
Operating Expenses:
Fuel and purchased power	328	608
Natural gas purchased for resale	151	208
Other operations and maintenance	470	448
Depreciation and amortization	361	320
Taxes other than income taxes	135	127
Total operating expenses	1,445	1,711
Operating Income	371	351
Other Income, Net	89	78
Interest Charges	154	127
Income Before Income Taxes	306	302
Income Taxes	44	37
Net Income	262	265
Less: Net Income Attributable to Noncontrolling Interests	1	1
Net Income Attributable to Ameren Common Shareholders	261	264
Pension and other postretirement benefit plan activity, net of income taxes (benefit)	(1)	(1)
Comprehensive Income	261	264
Less: Comprehensive Income Attributable to Noncontrolling Interests	1	1
Comprehensive Income Attributable to Ameren Common Shareholders	$ 260	$ 263
Earnings Per Share, Basic [Abstract]
Earnings per Common Share – Basic	$ 0.98	$ 1.01
Earnings Per Share, Diluted [Abstract]
Earnings per Common Share – Diluted	$ 0.98	$ 1
Weighted-average Common Shares Outstanding – Basic	266.4	262.2
Weighted-average Common Shares Outstanding – Diluted	266.8	263.1
Electric
Operating Revenues:
Total operating revenues	$ 1,364	$ 1,590
Natural gas
Operating Revenues:
Total operating revenues	452	472
Union Electric Company
Operating Revenues:
Total operating revenues	775	923
Operating Expenses:
Fuel and purchased power	166	321
Natural gas purchased for resale	28	47
Other operations and maintenance	254	239
Depreciation and amortization	195	176
Taxes other than income taxes	87	80
Total operating expenses	730	863
Operating Income	45	60
Other Income, Net	44	19
Interest Charges	62	51
Income Before Income Taxes	27	28
Income Taxes	1	(1)
Net Income	26	29
Preferred Stock Dividends	1	1
Net Income Attributable to Parent	25	28
Union Electric Company | Electric
Operating Revenues:
Total operating revenues	714	841
Union Electric Company | Natural gas
Operating Revenues:
Total operating revenues	61	82
Ameren Illinois Company
Operating Revenues:
Total operating revenues	1,000	1,101
Operating Expenses:
Purchased Power	164	287
Natural gas purchased for resale	123	161
Other operations and maintenance	210	202
Depreciation and amortization	153	133
Taxes other than income taxes	44	42
Total operating expenses	694	825
Operating Income	306	276
Other Income, Net	31	37
Interest Charges	55	47
Income Before Income Taxes	282	266
Income Taxes	67	68
Net Income	215	198
Net Income Attributable to Parent	215	198
Ameren Illinois Company | Electric
Operating Revenues:
Total operating revenues	609	710
Ameren Illinois Company | Natural gas
Operating Revenues:
Total operating revenues	$ 391	$ 391

Consolidated Statement of Inc_2

Consolidated Statement of Income (Loss) and Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Income Statement [Abstract]
Pension and other postretirement benefit plan activity, tax	$ 0	$ 0

Consolidated Balance Sheet

Consolidated Balance Sheet - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Current Assets:
Cash and cash equivalents	$ 85	$ 25
Accounts receivable - trade (less allowance for doubtful accounts)	507	494
Unbilled revenue	272	319
Miscellaneous accounts receivable	82	106
Inventories	679	733
Current regulatory assets	356	365
Other current assets	103	139
Total current assets	2,084	2,181
Property, Plant, and Equipment, Net	34,114	33,776
Investments and Other Assets:
Nuclear decommissioning trust fund	1,232	1,150
Goodwill	411	411
Regulatory assets	1,904	1,810
Pension and other postretirement benefits	597	581
Other assets	964	921
Total investments and other assets	5,108	4,873
TOTAL ASSETS	41,306	40,830
Current Liabilities:
Current maturities of long-term debt	1,149	849
Short-term debt	868	536
Accounts and wages payable	647	1,136
Customer deposits	190	176
Other current liabilities	651	648
Total current liabilities	3,505	3,345
Long-term Debt, Net	15,167	15,121
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and tax credits, net	4,251	4,176
Regulatory liabilities	5,593	5,512
Asset retirement obligations	779	772
Other deferred credits and liabilities	439	426
Total deferred credits and other liabilities	11,062	10,886
Commitments and Contingencies
Shareholders’ Equity:
Common Stock	3	3
Other paid-in capital, principally premium on common stock	7,228	7,216
Retained earnings	4,219	4,136
Accumulated other comprehensive loss	(7)	(6)
Total shareholders’ equity	11,443	11,349
Noncontrolling Interests	129	129
Total equity	11,572	11,478
TOTAL LIABILITIES AND EQUITY	41,306	40,830
Union Electric Company
Current Assets:
Cash and cash equivalents	2	0
Unbilled revenue	140	163
Miscellaneous accounts receivable	34	26
Inventories	499	508
Current regulatory assets	124	101
Other current assets	52	68
Total current assets	1,077	1,142
Property, Plant, and Equipment, Net	17,418	17,250
Investments and Other Assets:
Nuclear decommissioning trust fund	1,232	1,150
Regulatory assets	738	755
Pension and other postretirement benefits	161	157
Other assets	157	152
Total investments and other assets	2,288	2,214
TOTAL ASSETS	20,783	20,606
Current Liabilities:
Current maturities of long-term debt	350	350
Short-term debt	444	170
Borrowings from money pool	0	306
Taxes accrued	80	28
Other current liabilities	206	222
Total current liabilities	1,432	1,747
Long-term Debt, Net	6,336	5,991
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and tax credits, net	2,164	2,122
Regulatory liabilities	3,011	2,959
Asset retirement obligations	776	768
Other deferred credits and liabilities	76	56
Total deferred credits and other liabilities	6,027	5,905
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	3,672	3,647
Total shareholders’ equity	6,988	6,963
TOTAL LIABILITIES AND EQUITY	20,783	20,606
Union Electric Company | Nonrelated Party
Current Assets:
Accounts receivable - trade (less allowance for doubtful accounts)	179	204
Current Liabilities:
Accounts and wages payable	311	618
Union Electric Company | Related Party
Current Assets:
Accounts receivable - trade (less allowance for doubtful accounts)	47	72
Current Liabilities:
Accounts and wages payable	41	53
Ameren Illinois Company
Current Assets:
Cash and cash equivalents	0	0
Unbilled revenue	132	156
Miscellaneous accounts receivable	17	44
Inventories	176	225
Current regulatory assets	223	252
Other current assets	42	62
Total current assets	917	1,047
Property, Plant, and Equipment, Net	14,779	14,632
Investments and Other Assets:
Goodwill	411	411
Regulatory assets	1,140	1,035
Pension and other postretirement benefits	400	394
Other assets	632	603
Total investments and other assets	2,583	2,443
TOTAL ASSETS	18,279	18,122
Current Liabilities:
Current maturities of long-term debt	300	0
Short-term debt	424	366
Borrowings from money pool	54	135
Customer deposits	152	141
Regulatory Liability, Current	56	71
Other current liabilities	280	298
Total current liabilities	1,610	1,433
Long-term Debt, Net	4,933	5,232
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and tax credits, net	1,948	1,906
Regulatory liabilities	2,445	2,418
Other deferred credits and liabilities	303	308
Total deferred credits and other liabilities	4,696	4,632
Commitments and Contingencies
Shareholders’ Equity:
Common Stock	0	0
Other paid-in capital, principally premium on common stock	3,020	3,020
Preferred stock	49	49
Retained earnings	3,971	3,756
Total shareholders’ equity	7,040	6,825
TOTAL LIABILITIES AND EQUITY	18,279	18,122
Ameren Illinois Company | Nonrelated Party
Current Assets:
Accounts receivable - trade (less allowance for doubtful accounts)	313	273
Current Liabilities:
Accounts and wages payable	260	370
Ameren Illinois Company | Related Party
Current Assets:
Accounts receivable - trade (less allowance for doubtful accounts)	14	35
Current Liabilities:
Accounts and wages payable	$ 84	$ 52

Consolidated Balance Sheet (Par

Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Accounts Receivable, Allowance for Credit Loss, Current	$ 37	$ 30
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	266,600,000	266,300,000
Union Electric Company
Accounts Receivable, Allowance for Credit Loss, Current	$ 11	$ 12
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	$ 26	$ 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	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash Flows From Operating Activities:
Net income	$ 262	$ 265
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	379	350
Amortization of nuclear fuel	18	19
Amortization of debt issuance costs and premium/discounts	5	3
Deferred income taxes and investment tax credits, net	44	35
Allowance for equity funds used during construction	(9)	(9)
Stock-based compensation costs	8	8
Other	16	(6)
Changes in assets and liabilities:
Receivables	52	112
Inventories	54	37
Accounts and wages payable	(284)	(362)
Taxes accrued	70	50
Regulatory assets and liabilities	(95)	(40)
Assets, other	9	(14)
Liabilities, other	11	(6)
Pension and other postretirement benefits	(56)	(58)
Counterparty collateral, net	8	112
Net cash provided by operating activities	492	496
Cash Flows From Investing Activities:
Capital expenditures	(890)	(931)
Nuclear fuel expenditures	(12)	(20)
Purchases of securities – nuclear decommissioning trust fund	(70)	(29)
Sales and maturities of securities – nuclear decommissioning trust fund	66	17
Other	0	(1)
Net cash used in investing activities	(906)	(964)
Cash Flows From Financing Activities:
Dividends on common stock	(178)	(165)
Dividends paid to noncontrolling interest holders	(1)	(1)
Short-term debt, net	332	179
Issuances of long-term debt	347	499
Issuances of common stock	10	5
Employee payroll taxes related to stock-based compensation	(8)	(20)
Debt issuance costs	(5)	(5)
Other	0	(3)
Net cash provided by financing activities	497	489
Net change in cash, cash equivalents, and restricted cash	83	21
Cash, cash equivalents, and restricted cash at beginning of year	272	216
Cash, cash equivalents, and restricted cash at end of period	355	237
Union Electric Company
Cash Flows From Operating Activities:
Net income	26	29
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	212	205
Amortization of nuclear fuel	18	19
Amortization of debt issuance costs and premium/discounts	2	2
Deferred income taxes and investment tax credits, net	27	15
Allowance for equity funds used during construction	(9)	(4)
Other	17	(3)
Changes in assets and liabilities:
Receivables	43	74
Inventories	9	(41)
Accounts and wages payable	(222)	(238)
Taxes accrued	92	38
Regulatory assets and liabilities	(24)	14
Assets, other	1	2
Liabilities, other	4	(11)
Pension and other postretirement benefits	(20)	(21)
Counterparty collateral, net	1	73
Net cash provided by operating activities	177	153
Cash Flows From Investing Activities:
Capital expenditures	(466)	(481)
Nuclear fuel expenditures	(12)	(20)
Purchases of securities – nuclear decommissioning trust fund	(70)	(29)
Sales and maturities of securities – nuclear decommissioning trust fund	66	17
Net cash used in investing activities	(482)	(513)
Cash Flows From Financing Activities:
Dividends on preferred stock	(1)	(1)
Short-term debt, net	274	(132)
Money pool borrowings, net	(306)	0
Issuances of long-term debt	347	499
Debt issuance costs	(3)	(5)
Other	0	(3)
Net cash provided by financing activities	311	358
Net change in cash, cash equivalents, and restricted cash	6	(2)
Cash, cash equivalents, and restricted cash at beginning of year	10	13
Cash, cash equivalents, and restricted cash at end of period	16	11
Ameren Illinois Company
Cash Flows From Operating Activities:
Net income	215	198
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	153	133
Amortization of debt issuance costs and premium/discounts	1	1
Deferred income taxes and investment tax credits, net	27	37
Allowance for equity funds used during construction	0	(4)
Other	5	6
Changes in assets and liabilities:
Receivables	1	26
Inventories	49	78
Accounts and wages payable	(31)	(112)
Taxes accrued	64	25
Regulatory assets and liabilities	(66)	(52)
Assets, other	6	(8)
Liabilities, other	6	30
Pension and other postretirement benefits	(22)	(24)
Counterparty collateral, net	7	39
Net cash provided by operating activities	415	373
Cash Flows From Investing Activities:
Capital expenditures	(373)	(407)
Other	1	0
Net cash used in investing activities	(372)	(407)
Cash Flows From Financing Activities:
Short-term debt, net	58	60
Money pool borrowings, net	(81)	0
Net cash provided by financing activities	(23)	60
Net change in cash, cash equivalents, and restricted cash	20	26
Cash, cash equivalents, and restricted cash at beginning of year	234	191
Cash, cash equivalents, and restricted cash at end of period	$ 254	$ 217

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 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 year at Dec. 31, 2022			$ 6,860	$ 3,646	$ (1)			$ 129					$ 3,111					$ 3,190
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			12
Stock-based compensation activity			(11)
Net income	$ 265								$ 29				29	$ 198				198
Net income attributable to Ameren common shareholders	264			264
Dividends on common stock				(165)
Preferred stock dividends													(1)
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 year at Dec. 31, 2022	262,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan	100,000
Shares issued for stock-based compensation	500,000
Common stock shares outstanding at end of period at Mar. 31, 2023	262,600,000
End of period at Mar. 31, 2023	$ 10,736	$ 3	6,861	3,745	(2)	$ (2)		129		$ 511	$ 2,725	$ 80	3,139		$ 0	$ 2,929	$ 49	3,388
Shareholders' equity, end of year at Mar. 31, 2023							$ 10,607		6,455					6,366
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 0.63
Beginning of year at Dec. 31, 2023	$ 11,478		7,216	4,136	(6)			129					3,647					3,756
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan			10
Stock-based compensation activity			2
Net income	262								$ 26				26	$ 215				215
Net income attributable to Ameren common shareholders	261			261
Dividends on common stock				(178)
Preferred stock dividends													(1)
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 year at Dec. 31, 2023	266,300,000								102,100,000					25,500,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under the DRPlus and 401(k) plan	100,000
Shares issued for stock-based compensation	200,000
Common stock shares outstanding at end of period at Mar. 31, 2024	266,600,000								102,100,000					25,500,000
End of period at Mar. 31, 2024	$ 11,572	$ 3	$ 7,228	$ 4,219	$ (7)	$ (7)		$ 129		$ 511	$ 2,725	$ 80	$ 3,672		$ 0	$ 3,020	$ 49	$ 3,971
Shareholders' equity, end of year at Mar. 31, 2024	$ 11,443						$ 11,443		$ 6,988					$ 7,040
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per common share	$ 0.67

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2024
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 also has other subsidiaries that conduct other activities, such as providing shared services. • Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri. • Ameren 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 ownership of renewable generation projects. Ameren Illinois has no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated. Our accounting policies conform to GAAP. Our financial statements reflect all adjustments (which include normal, recurring adjustments) that are necessary, in our opinion, for a fair presentation of our results. The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. Such estimates and assumptions affect reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of financial statements, and the reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates. The results of operations for an interim period may not give a true indication of results that may be expected for a full year. These financial statements should be read in conjunction with the financial statements and accompanying notes included in the Form 10-K. Variable Interest Entities As of March 31, 2024, and December 31, 2023, Ameren had unconsolidated variable interests in various equity method investments, primarily to advance clean and resilient energy technologies, totaling $74 million and $73 million, respectively, included in “Other assets” on Ameren’s consolidated balance sheet. Any earnings or losses related to these investments are included in “Other Income, Net” on Ameren’s consolidated statement of income and comprehensive income. Ameren is not the primary beneficiary of these investments because it does not have the power to direct matters that most significantly affect the activities of these variable interest entities. As of March 31, 2024, Ameren’s maximum exposure to loss related to these variable interests is limited to its investment of $74 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 March 31, 2024, the cash surrender value of COLI at Ameren and Ameren Illinois was $255 million (December 31, 2023 – $248 million) and $112 million (December 31, 2023 – $111 million), respectively, while total borrowings against the policies were $104 million (December 31, 2023 – $104 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	3 Months Ended
	Mar. 31, 2024
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 Solar Generation Facilities During 2022 and 2023, Ameren Missouri, and certain subsidiaries of Ameren Missouri, entered into agreements to acquire and/or construct various solar generation facilities, which, if placed in-service, would be eligible for recovery under the PISA. The following table provides information with respect to each agreement: Huck Finn Solar Project (a)(b) Boomtown Solar Project (b)(c) Split Rail Solar Project (d) Cass County Solar Project (c) Vandalia Solar Project (b)(d) Bowling Green Solar Project (b)(d) Agreement type Build-transfer Build-transfer Build-transfer Development-transfer (e) Self-build (f) Self-build (f) Facility size 200-MW 150-MW 300-MW 150-MW 50-MW 50-MW Status of MoPSC CCN Approved February 2023 Approved April 2023 Approved March 2024 Filed June 2023 (g) Approved March 2024 Approved March 2024 Status of FERC approval of acquisition Received March 2023 Received October 2023 Expect to request by mid-2024 Not applicable Not applicable Not applicable Earliest completion date (h) Fourth quarter 2024 Fourth quarter 2024 Mid-2026 Fourth quarter 2024 Fourth quarter 2025 First quarter 2026 (a) The Huck Finn Solar Project is expected to support Ameren Missouri’s compliance with the state of Missouri’s renewable energy standard. Investments in the project will be eligible for recovery under the RESRAM. (b) These projects collectively represent approximately $0.85 billion of expected capital expenditures. (c) The Boomtown and Cass County solar projects are expected to support Ameren Missouri’s transition to renewable energy generation and serve customers under the Renewable Solutions Program. (d) These solar projects are expected to support Ameren Missouri’s transition to renewable energy generation. (e) 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 take over construction management of the Cass County facility after obtaining a CCN from the MoPSC and acquiring the project. Acquisition of the project is expected by mid-2024. (f) Ameren Missouri entered into engineering, procurement, and construction agreements to construct these solar projects. (g) Approval for the CCN is conditioned upon full subscription of the project capacity under the Renewable Solutions Program, a commercial, industrial, and governmental customer program. Ameren Missouri expects a decision by the MoPSC on the Cass County Solar Project CCN once this project’s capacity under the Renewable Solutions Program is fully subscribed. (h) Expected completion dates are dependent on the timing of regulatory approvals, among other things. Securitization of Rush Island Energy Center Costs In November 2023, Ameren Missouri petitioned the MoPSC for a financing order to authorize the issuance of securitized utility tariff bonds to finance $519 million of costs related to the planned accelerated retirement of the Rush Island Energy Center, which includes the expected remaining unrecovered net plant balance associated with the facility, among other costs. Ameren Missouri requested to collect the amounts necessary to repay the bonds over approximately 15 years from the date of bond issuance. In March 2024, the MoPSC staff filed an updated response to Ameren Missouri’s petition that stated Ameren Missouri’s decision to accelerate the retirement of the Rush Island Energy Center was prudent and recommended that $497 million of costs be financed through securitized utility tariff bonds. However, the MoPSC staff claimed Ameren Missouri’s prior actions that resulted in the adverse ruling in the NSR and Clean Air Act Litigation discussed in Note 9 – Commitments and Contingencies were imprudent and recommended that the impact of those actions on customers be considered in future regulatory proceedings. In February 2024, the MoOPC filed a response to Ameren Missouri’s petition that opposes the issuance of securitized utility tariff bonds. If Ameren Missouri is not allowed to recover Rush Island Energy Center costs through securitization or if future regulatory proceedings result in revenue reductions based on Ameren Missouri’s prior actions that resulted in the adverse ruling in the NSR and Clean Air Act litigation, it could have a material adverse effect on the results of operations, financial position, and liquidity of Ameren and Ameren Missouri. Ameren Missouri expects a decision by the MoPSC by the end of June 2024, but cannot predict the ultimate outcome of this regulatory proceeding. MEEIA In January 2024, Ameren Missouri filed a proposed customer energy-efficiency plan with the MoPSC under the MEEIA. This filing proposed a three-year plan, which includes a portfolio of customer energy-efficiency programs, along with the continued use of the MEEIA rider, which allows Ameren Missouri to collect from, or refund to, customers any difference in actual MEEIA program costs and related lost electric revenues and the amounts collected from customers. If the plan is approved, Ameren Missouri intends to invest $123 million annually in the proposed customer energy-efficiency programs from 2025 to 2027. In addition, Ameren Missouri requested performance incentives applicable to each plan year to earn revenues by achieving certain customer energy-efficiency savings and target spending goals. If 100% of the goals are achieved, Ameren Missouri would earn performance incentive revenues totaling $56 million over the three-year plan. Ameren Missouri also requested additional performance incentives applicable to each plan year totaling up to $14 million over the three-year plan, if Ameren Missouri exceeds 100% of the goals. Ameren Missouri expects a decision by the MoPSC by October 2024, but cannot predict the ultimate outcome of this regulatory proceeding. Illinois MYRP In December 2023, the ICC issued an order in Ameren Illinois' MYRP proceeding approving base rates for electric distribution services for 2024 through 2027 and rejecting Ameren Illinois' Grid Plan, which was addressed as part of the MYRP proceeding. Rate changes consistent with the order became effective in January 2024. The December 2023 order adopted an alternative methodology to establish a rate base and revenue requirements for the years 2024 through 2027 using Ameren Illinois’ previously approved 2022 year-end rate base. The 2022 year-end rate base will remain in effect through 2027 unless subsequently changed by the ICC in the rehearing discussed below or if approval of a revised Grid Plan results in an update of each year’s revenue requirement. Pursuant to the order, in March 2024, Ameren Illinois filed a revised Grid Plan and a revised MYRP to update the requested revenue requirements for 2024 through 2027. An ICC decision on the revised Grid Plan and updated revenue requirements is expected by December 2024 with rates effective in January 2025. In January 2024, the ICC partially denied a rehearing requested by Ameren Illinois to revise the allowed ROE in the December 2023 order and granted Ameren Illinois’ rehearing request to consider whether it is appropriate to use the 2022 year-end rate base for each year of the MYRP and to include a base level of investments to maintain grid reliability in each year of the MYRP. Additionally, the scope of the rehearing includes a review of certain operations and maintenance expenses in each year of the MYRP. In February 2024, Ameren Illinois filed its request in the rehearing proceeding, and subsequently updated the request in April 2024, proposing an updated 2024 revenue requirement of $1,213 million, which is based on a $4.2 billion rate base, a capital structure composed of 50% common equity, and an allowed ROE of 8.72%. In April 2024, the ICC staff filed its recommendation in the rehearing proceeding. The ICC staff recommended a 2024 revenue requirement of $1,195 million, which is based on a $4.0 billion rate base, a capital structure composed of 50% common equity, and an allowed ROE of 8.72%. An ICC decision in the rehearing proceeding is expected by late June 2024, with new rates effective July 2024. Also, in January 2024, Ameren Illinois filed an appeal of the December 2023 ICC order and the partial denial of Ameren Illinois’ request for rehearing, including the 8.72% ROE, to the Illinois Appellate Court for the Fifth Judicial District. The court is under no deadline to address the appeal. Ameren Illinois cannot predict the ultimate outcome of the revised Grid Plan filing, its request to update the associated MYRP revenue requirements for 2024 through 2027, the rehearing proceeding, or the appeal to the Illinois Appellate Court for the Fifth Judicial District. The following table presents the approved revenue requirements, ROE, capital structure common equity percentage, and annual rate base in the ICC’s December 2023 order, as well as the proposed revenue requirements and annual rate base amounts in the March 2024 revised MYRP: Year Revenue Requirement (in millions) ROE Capital Structure Common Equity Percentage Annual Rate Base (in billions) ICC’s December 2023 MYRP Order: 2024 $1,162 8.72% 50% $3.9 2025 $1,210 8.72% 50% $3.9 2026 $1,242 8.72% 50% $3.9 2027 $1,255 8.72% 50% $3.9 Ameren Illinois’ March 2024 Revised MYRP: 2024 $1,207 (a) 50% $4.2 2025 $1,286 (a) 50% $4.4 2026 $1,371 (a) 50% $4.7 2027 $1,433 (a) 50% $4.9 (a) Based on an allowed ROE of 8.72%. Ameren Illinois’ filing requests the ICC to increase the allowed ROE to 9.24%. The approved revenue requirements in the ICC’s December 2023 order represent a cumulative four-year increase of $142 million compared to a cumulative increase of $321 million in Ameren Illinois’ March 2024 revised MYRP. 2023 Electric Distribution Revenue Requirement Reconciliation Adjustment Request In April 2024, Ameren Illinois filed for a reconciliation adjustment to its 2023 electric distribution service revenue requirement with the ICC, requesting recovery of $160 million. The reconciliation adjustment reflects a capital structure composed of 50% common equity and Ameren Illinois’ actual 2023 recoverable costs and year-end rate base. An ICC decision in this proceeding is required by December 2024, and any approved adjustment would be collected from customers in 2025. This is the final revenue requirement reconciliation under the IEIMA formula framework. 2023 Natural Gas Delivery Service Rate Order In November 2023, the ICC issued an order in Ameren Illinois’ January 2023 natural gas delivery service regulatory rate review, which resulted in an increase to its annual revenues for natural gas delivery service of $112 million based on a 9.44% allowed ROE, a capital structure composed of 50% common equity, and a rate base of approximately $2.85 billion. The order reflected a reduction of approximately $93 million of planned distribution and transmission capital investments included in Ameren Illinois’ requested revenue increase, which used a 2024 future test year. The new rates became effective on November 28, 2023. In December 2023, Ameren Illinois filed a request for rehearing of the ICC’s November 2023 order. The filing requested the ICC revise the order to include an allowed ROE of at least 9.89%, a capital structure composed of 52% common equity, and the reversal of the approximately $93 million reduction of planned distribution and transmission capital investments included in the order, among other things. In January 2024, the ICC denied Ameren Illinois’ rehearing request. Subsequently, in January 2024, Ameren Illinois filed an appeal of the November 2023 ICC order and the January 2024 ICC denial of Ameren Illinois’ request for rehearing to the Illinois Appellate Court for the Fifth Judicial District. The court is under no deadline to address the appeal. Ameren Illinois cannot predict the ultimate outcome of this appeal. QIP Reconciliation Hearing In March 2021, Ameren Illinois filed a request with the ICC to initiate a reconciliation proceeding to determine the accuracy and prudence of natural gas capital investments recovered under the QIP rider during 2020. In October 2023, the Illinois Attorney General’s office challenged the recovery of capital investments that were made during 2020, alleging that the ICC should disallow approximately $53 million in natural gas capital investments as improper and imprudent, providing a potential over-recovery of approximately $3 million in 2020. In October 2023, the ICC staff filed testimony that supports the prudence and reasonableness of the capital investments made during 2020. Ameren Illinois’ 2020 QIP rate recovery request under review by the ICC was within the rate increase limitations allowed by law. The ICC is under no deadline to issue an order in this proceeding. Ameren Illinois cannot predict the ultimate outcome of this regulatory proceeding. MISO Long-Range Transmission Projects CCN 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 February 2024, Ameren Illinois and ATXI filed a request for a CCN, among other things, with the ICC related to the portion of the MISO long-range transmission projects that will be constructed within the ICC’s jurisdiction. A decision by the ICC is expected by mid-2025. Federal FERC Complaint Cases Since November 2013, the allowed base ROE for FERC-regulated transmission rate base under the MISO tariff has been subject to customer complaint cases and has been changed by various FERC orders. In May 2020, the FERC issued an order, which set the allowed base ROE to 10.02% and required refunds, with interest, for the periods November 2013 to February 2015 and from late September 2016 forward. Ameren and Ameren Illinois paid these refunds, including interest, by March 31, 2022. In June and July 2020, Ameren Missouri, Ameren Illinois, and ATXI, as well as various customers, petitioned the United States Court of Appeals for the District of Columbia Circuit for review of the May 2020 order, challenging certain aspects of the new ROE methodology established. The petition filed by Ameren Missouri, Ameren Illinois, and ATXI challenged the refunds required for the period from September 2016 to May 2020. In August 2022, the court issued a ruling that granted the customers’ petition for review, vacated the FERC’s previous MISO ROE-determining orders, and remanded the proceedings to the FERC. The court elected not to rule on the issues raised by Ameren Missouri, Ameren Illinois, and ATXI. The currently allowed base ROE of 10.02% will remain effective for customer billings, but the transmission rates charged during previous periods and the currently effective rates may be subject to refund if the base ROE is changed by the FERC in a future order. The FERC is under no deadline to issue an order related to these proceedings. A 50-basis-point change in the FERC-allowed ROE would affect Ameren’s and Ameren Illinois’ annual revenue by an estimated $21 million and $15 million, respectively, based on each company’s 2024 projected rate base.

Short-Term Debt And Liquidity

Short-Term Debt And Liquidity	3 Months Ended
	Mar. 31, 2024
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 agreements. Short-term Borrowings The Missouri Credit Agreement and the Illinois Credit Agreement are available to support issuances under Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper programs, respectively, subject to borrowing sublimits, and the issuance of letters of credit. As of March 31, 2024, 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 $1.8 billion. The Ameren Companies were in compliance with the covenants in their Credit Agreements as of March 31, 2024. As of March 31, 2024, the ratios of consolidated indebtedness to consolidated total capitalization, calculated in accordance with the provisions of the Credit Agreements, were 60%, 51%, and 45% for Ameren, Ameren Missouri, and Ameren Illinois, respectively. The following table presents commercial paper outstanding, net of issuance discounts, as of March 31, 2024, and December 31, 2023. There were no borrowings outstanding under the Credit Agreements as of March 31, 2024, or December 31, 2023. March 31, 2024 December 31, 2023 Ameren (parent) $ — $ — Ameren Missouri 444 170 Ameren Illinois 424 366 Ameren consolidated $ 868 $ 536 The following table summarizes the activity and relevant interest rates for Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper issuances and borrowings under the Credit Agreements in the aggregate for the three months ended March 31, 2024 and 2023: Ameren Ameren Ameren Ameren 2024 Average daily amount outstanding $ — $ 135 $ 336 $ 471 Weighted-average interest rate — % 5.53 % 5.58 % 5.57 % Peak amount outstanding during period (a) $ — $ 444 $ 425 $ 869 Peak interest rate — % 5.68 % 5.68 % 5.68 % 2023 Average daily amount outstanding $ 506 $ 436 $ 233 $ 1,175 Weighted-average interest rate 4.89 % 4.86 % 4.89 % 4.88 % Peak amount outstanding during period (a) $ 728 $ 592 $ 325 $ 1,381 Peak interest rate 5.55 % 5.55 % 5.60 % 5.60 % (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 amount for the period. Money Pools Ameren has money pool agreements with and among its subsidiaries to coordinate and provide for certain short-term cash and working capital requirements. The average interest rate for borrowings under the utility money pool for the three months ended March 31, 2024, was 5.32% (2023 – 4.80%). See Note 8 – Related-party Transactions for the amount of interest income and expense from the utility money pool agreements recorded by Ameren Missouri and Ameren Illinois for the three months ended March 31, 2024 and 2023.

Long-Term Debt And Equity Finan

Long-Term Debt And Equity Financings	3 Months Ended
	Mar. 31, 2024
Long-Term Debt And Equity Financings [Abstract]
LONG-TERM DEBT AND EQUITY FINANCINGS	LONG-TERM DEBT AND EQUITY FINANCINGS Ameren For the three months ended March 31, 2024, Ameren issued a total of 0.1 million shares of common stock, under its DRPlus and 401(k) plan, and received proceeds of $3 million. As of March 31, 2024, Ameren had a receivable of $7 million related to issuances of common stock under its DRPlus. In addition, in the first quarter of 2024, Ameren issued 0.2 million shares of common stock valued at $16 million upon the settlement of stock-based compensation awards. There were no shares issued under the ATM program for the three months ended March 31, 2024. As of March 31, 2024, Ameren had approximately $770 million of common stock available for sale under the ATM program, which takes into account the forward sale agreements in effect as of March 31, 2024, discussed below. The forward sale agreements outstanding as of March 31, 2024, can be settled at Ameren’s discretion on or prior to dates ranging from October 3, 2024 to February 28, 2025. On a settlement date or dates, if Ameren elects to physically settle a forward sale agreement, Ameren will issue shares of common stock to the counterparties at the then-applicable forward sale price. The initial forward sale price for the agreements ranged from $76.69 to $89.31, with an average initial forward sale price of $80.45. Each initial forward sale price is subject to adjustment based on a floating interest rate factor equal to the overnight bank funding rate less a spread of 75 basis points, and will be subject to decrease on certain dates specified in the forward sale agreements by specified amounts related to expected dividends on shares of the common stock during the term of the forward sale agreements. If the overnight bank funding rate is less than the spread on any day, the interest rate factor will result in a reduction of the forward sale price. The forward sale agreements will be physically settled unless Ameren elects to settle in cash or to net share settle. At March 31, 2024, Ameren could have settled the forward sale agreements with physical delivery of 2.9 million shares of common stock to the respective counterparties in exchange for cash of $231 million. Alternatively, the forward sale agreements could have also been settled at March 31, 2024, with the counterparties delivering approximately $20 million of cash or approximately 0.3 million shares of common stock to Ameren. In connection with the forward sale agreements outstanding at March 31, 2024, the various counterparties, or their affiliates, borrowed from third parties and sold 2.9 million shares of common stock. The gross sales price of these shares totaled $232 million. Ameren has not received any proceeds from such sales of borrowed shares. The forward sale agreements have been classified as equity transactions. Ameren Missouri In January 2024, Ameren Missouri issued $350 million of 5.25% first mortgage bonds due January 2054, with interest payable semiannually on January 15 and July 15 of each year, beginning July 15, 2024. Net proceeds from this issuance were used for capital expenditures and to repay short-term debt. In April 2024, Ameren Missouri issued $500 million of 5.20% first mortgage bonds due April 2034, with interest payable semiannually on April 1 and October 1 of each year, beginning October 1, 2024. Net proceeds from this issuance were used for capital expenditures and to repay short-term debt. In April 2024, $350 million principal amount of Ameren Missouri’s 3.50% senior secured notes matured and were repaid with cash on hand. In April 2024, Ameren Missouri received capital contributions totaling $350 million from Ameren (parent). Indenture Provisions and Other Covenants See Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, in the Form 10-K for a description of our indenture provisions and other covenants, as well as restrictions on the payment of dividends. At March 31, 2024, the Ameren Companies were in compliance with the provisions and covenants contained in their indentures and articles of incorporation, as applicable, and ATXI was in compliance with the provisions and covenants contained in its note purchase agreements. Off-balance-sheet Arrangements At March 31, 2024, none of the Ameren Companies had any material off-balance-sheet financing arrangements, other than their 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	3 Months Ended
	Mar. 31, 2024
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 months ended March 31, 2024 and 2023: Three Months 2024 2023 Ameren: Allowance for equity funds used during construction $ 9 $ 9 Other interest income 8 8 Non-service cost components of net periodic benefit income (a) 76 64 Miscellaneous income 2 2 Earnings related to equity method investments — 2 Donations (2) (2) Miscellaneous expense (4) (5) Total Other Income, Net $ 89 $ 78 Ameren Missouri: Allowance for equity funds used during construction $ 9 $ 4 Other interest income 2 4 Non-service cost components of net periodic benefit income (a) 35 14 Miscellaneous income 1 1 Donations (1) (1) Miscellaneous expense (2) (3) Total Other Income, Net $ 44 $ 19 Ameren Illinois: Allowance for equity funds used during construction $ — $ 4 Interest income 6 4 Non-service cost components of net periodic benefit income 27 31 Miscellaneous income 1 1 Donations (1) (1) Miscellaneous expense (2) (2) Total Other Income, Net $ 31 $ 37 (a) For the three months ended March 31, 2024 and 2023, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $(9) million and $17 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. See Note 11 – Retirement Benefits for additional information.

Derivative Financial Instrument

Derivative Financial Instruments	3 Months Ended
	Mar. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DERIVATIVE FINANCIAL INSTRUMENTS	DERIVATIVE FINANCIAL INSTRUMENTS We use derivatives to manage the risk of changes in market prices for natural gas, power, and uranium, as well as the risk of changes in rail transportation surcharges through fuel oil hedges. Such price fluctuations may cause the following: • an unrealized appreciation or depreciation of our contracted commitments to purchase or sell when purchase or sale prices under the commitments are compared with current commodity prices; • market values of natural gas and uranium inventories that differ from the cost of those commodities in inventory; • actual cash outlays for the purchase of these commodities that differ from anticipated cash outlays; and • actual off-system sales revenues that differ from anticipated revenues. The derivatives that we use to hedge these risks are governed by our risk management policies for forward contracts, futures, options, and swaps. Our net positions are continually assessed within our structured hedging programs to determine whether new or offsetting transactions are required. The goal of the hedging program is generally to mitigate financial risks while ensuring that sufficient volumes are available to meet our requirements. Contracts we enter into as part of our risk management program may be settled financially, settled by physical delivery, or net settled with the counterparty. All contracts considered to be derivative instruments are required to be recorded on the balance sheet at their fair values, unless the NPNS exception applies. Many of our physical contracts, such as our purchased power contracts, qualify for the NPNS exception to derivative accounting rules. The revenue or expense on NPNS contracts is recognized at the contract price upon physical delivery. The following disclosures exclude NPNS contracts and other non-derivative commodity contracts that are accounted for under the accrual method of accounting. If we determine that a contract meets the definition of a derivative and is not eligible for the NPNS exception, we review the contract to determine whether the resulting gains or losses qualify for regulatory deferral. Derivative contracts that qualify for regulatory deferral are recorded at fair value, with changes in fair value recorded as regulatory assets or liabilities in the period in which the change occurs. We believe derivative losses and gains deferred as regulatory assets and liabilities are probable of recovery, or refund, through future rates charged to customers. Regulatory assets and liabilities are amortized to operating income as related losses and gains are reflected in rates charged to customers. Therefore, gains and losses on these derivatives have no effect on operating income. As of March 31, 2024, and December 31, 2023, all contracts that met the definition of a derivative and were not eligible for the NPNS exception received regulatory deferral. The cash flows from our derivative financial instruments follow the cash flow classification of the hedged item. The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of March 31, 2024, and December 31, 2023. As of March 31, 2024, these contracts extended through October 2026, October 2029 and May 2032 for fuel oils, natural gas and power, respectively. Quantity (in millions) March 31, 2024 December 31, 2023 Commodity Ameren Missouri Ameren Illinois Ameren Ameren Missouri Ameren Illinois Ameren Fuel oils (in gallons) 17 — 17 17 — 17 Natural gas (in mmbtu) 54 224 278 53 218 271 Power (in MWhs) — 5 5 — 5 5 Uranium (pounds in thousands) — — — 186 — 186 The following table presents the carrying value and balance sheet location of all derivative commodity contracts, none of which were designated as hedging instruments, as of March 31, 2024, and December 31, 2023: March 31, 2024 December 31, 2023 Balance Sheet Location Ameren Ameren Ameren Ameren Ameren Ameren Fuel oils Other current assets $ 2 $ — $ 2 $ 2 $ — $ 2 Natural gas Other current assets — 2 2 — — — Other assets 3 2 5 3 3 6 Power Other current assets 2 — 2 5 — 5 Uranium Other current assets — — — 9 — 9 Total assets $ 7 $ 4 $ 11 $ 19 $ 3 $ 22 Fuel oils Other current liabilities $ 1 $ — $ 1 $ 1 $ — $ 1 Other deferred credits and liabilities — — — 1 — 1 Natural gas Other current liabilities 11 43 54 12 45 57 Other deferred credits and liabilities 8 28 36 10 30 40 Power Other current liabilities — 11 11 1 12 13 Other deferred credits and liabilities — 43 43 — 56 56 Total liabilities $ 20 $ 125 $ 145 $ 25 $ 143 $ 168 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 March 31, 2024, and December 31, 2023: 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 March 31, 2024 Assets: Ameren Missouri $ 7 $ 5 $ — $ 2 Ameren Illinois 4 2 — 2 Ameren $ 11 $ 7 $ — $ 4 Liabilities: Ameren Missouri $ 20 $ 5 $ — $ 15 Ameren Illinois 125 2 1 122 Ameren $ 145 $ 7 $ 1 $ 137 December 31, 2023 Assets: Ameren Missouri $ 19 $ 6 $ — $ 13 Ameren Illinois 3 1 — 2 Ameren $ 22 $ 7 $ — $ 15 Liabilities: Ameren Missouri $ 25 $ 6 $ — $ 19 Ameren Illinois 143 1 6 136 Ameren $ 168 $ 7 $ 6 $ 155 (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 March 31, 2024, 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 March 31, 2024, 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 $ 20 $ — $ 15 Ameren Illinois 71 1 68 Ameren $ 91 $ 1 $ 83 (a) Before consideration of master netting arrangements or similar agreements. (b)

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Fair Value Disclosures	FAIR VALUE MEASUREMENTS Fair value is defined as the price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Fair value measurements are classified in three levels based on the fair value hierarchy as defined by GAAP. See Note 8 – Fair Value Measurements under Part II, Item 8, of the Form 10-K for information related to hierarchy levels and valuation techniques. We consider nonperformance risk in our valuation of derivative instruments by analyzing our own credit standing and the credit standing of our counterparties, and by considering any credit enhancements (e.g., collateral). Included in our valuation, and based on current market conditions, is a valuation adjustment for counterparty default derived from market data such as the price of credit default swaps, bond yields, and credit ratings. No material gains or losses related to valuation adjustments for counterparty default risk were recorded at Ameren, Ameren Missouri, or Ameren Illinois in the three months ended March 31, 2024 or 2023. At March 31, 2024, and December 31, 2023, the counterparty default risk valuation adjustment related to derivative contracts was immaterial for Ameren, Ameren Missouri, and Ameren Illinois. The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of March 31, 2024, and December 31, 2023: March 31, 2024 December 31, 2023 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets: Ameren Missouri Derivative assets – commodity contracts: Fuel oils $ 2 $ — $ — $ 2 $ 2 $ — $ — $ 2 Natural gas — 3 — 3 — 3 — 3 Power — — 2 2 — — 5 5 Uranium — — — — — — 9 9 Total derivative assets – commodity contracts $ 2 $ 3 $ 2 $ 7 $ 2 $ 3 $ 14 $ 19 Nuclear decommissioning trust fund: Equity securities: U.S. large capitalization $ 868 $ — $ — $ 868 $ 787 $ — $ — $ 787 Debt securities: U.S. Treasury and agency securities — 145 — 145 — 150 — 150 Corporate bonds — 139 — 139 — 136 — 136 Other — 72 — 72 — 68 — 68 Total nuclear decommissioning trust fund $ 868 $ 356 $ — $ 1,224 (a) $ 787 $ 354 $ — $ 1,141 (a) Total Ameren Missouri $ 870 $ 359 $ 2 $ 1,231 $ 789 $ 357 $ 14 $ 1,160 Ameren Illinois Derivative assets – commodity contracts: Natural gas $ — $ 1 $ 3 $ 4 $ — $ 1 $ 2 $ 3 Power — — — — — — — — Total Ameren Illinois $ — $ 1 $ 3 $ 4 $ — $ 1 $ 2 $ 3 Ameren Derivative assets – commodity contracts (b) $ 2 $ 4 $ 5 $ 11 $ 2 $ 4 $ 16 $ 22 Nuclear decommissioning trust fund (c) 868 356 — 1,224 (a) 787 354 — 1,141 (a) Total Ameren $ 870 $ 360 $ 5 $ 1,235 $ 789 $ 358 $ 16 $ 1,163 Liabilities: Ameren Missouri Derivative liabilities – commodity contracts: Fuel oils $ 1 $ — $ — $ 1 $ 2 $ — $ — $ 2 Natural gas — 18 1 19 — 19 3 22 Power — — — — — — 1 1 Total Ameren Missouri $ 1 $ 18 $ 1 $ 20 $ 2 $ 19 $ 4 $ 25 Ameren Illinois Derivative liabilities – commodity contracts: Natural gas $ 2 $ 61 $ 8 $ 71 $ 4 $ 60 $ 11 $ 75 Power — — 54 54 — — 68 68 Total Ameren Illinois $ 2 $ 61 $ 62 $ 125 $ 4 $ 60 $ 79 $ 143 Ameren Derivative liabilities – commodity contracts (b) $ 3 $ 79 $ 63 $ 145 $ 6 $ 79 $ 83 $ 168 (a) Balance excludes $8 million and $9 million of cash and cash equivalents, receivables, payables, and accrued income, net, for March 31, 2024, and December 31, 2023, 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 months ended March 31, 2024 and 2023: 2024 2023 Ameren Missouri Ameren Illinois Ameren Ameren Missouri Ameren Illinois Ameren For the three months ended March 31: Beginning balance at January 1 $ 4 $ (68) $ (64) $ 12 $ (33) $ (21) Realized and unrealized gains/(losses) included in regulatory assets/liabilities (1) 10 9 (6) (20) (26) Settlements (1) 4 3 (1) 1 — Ending balance at March 31 $ 2 $ (54) $ (52) $ 5 $ (52) $ (47) Change in unrealized gains/(losses) related to assets/liabilities held at March 31 $ — $ 11 $ 11 $ (2) $ (18) $ (20) All gains or losses related to our Level 3 derivative commodity contracts are expected to be recovered or returned through customer rates; therefore, there is no impact to either net income or other comprehensive income resulting from changes in the fair value of these instruments. The following table describes the valuation techniques and significant unobservable inputs utilized for the fair value of our Level 3 power derivative contract assets and liabilities as of March 31, 2024, and December 31, 2023: Fair Value Weighted Average (b) Commodity Assets Liabilities Valuation Technique(s) Unobservable Input (a) Range 2024 Power (c) $ 2 $ (54) Discounted cash flow Average forward peak and off-peak pricing – forwards/swaps ($/MWh) 22 – 68 45 Nodal basis ($/MWh) (8) – (2) (5) 2023 Power (c) $ 5 $ (69) Discounted cash flow Average forward peak and off-peak pricing – forwards/swaps ($/MWh) 31 – 65 43 Nodal basis ($/MWh) (8) – (1) (5) (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. The following table sets forth the carrying amount and, by level within the fair value hierarchy, the fair value of long-term debt (including current portion) disclosed, but not recorded, at fair value as of March 31, 2024, and December 31, 2023: Long-Term Debt (Including Current Portion): Carrying Amount (a) Fair Value Level 2 Level 3 Total March 31, 2024 Ameren 16,316 14,258 453 (b) 14,711 Ameren Missouri 6,686 5,923 — 5,923 Ameren Illinois 5,233 4,668 — 4,668 December 31, 2023 Ameren 15,970 14,366 467 (b) 14,833 Ameren Missouri 6,341 5,800 — 5,800 Ameren Illinois 5,232 4,867 — 4,867 (a) Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $114 million, $48 million, and $46 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of March 31, 2024. Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $111 million, $45 million, and $47 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2023. (b) The Level 3 fair value amount consists of ATXI’s senior unsecured notes. The Ameren Companies’ carrying amounts of cash, cash equivalents, and restricted cash approximate fair value and are considered Level 1 in the fair value hierarchy. The Ameren Companies’ short-term borrowings approximate fair value because of the short-term nature of these instruments and are considered Level 2 in the fair value hierarchy.

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2024
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 agreements, 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 March 31, 2024, and $31 million and $34 million, respectively, as of December 31, 2023, related to Ameren Services’ allocated portion of Ameren’s pension and postretirement benefit plans. In December 2023, ATXI placed in service a transmission operations control center. Rental revenues received by ATXI from Ameren Services associated with this facility are affiliate transactions and are eliminated in consolidation for Ameren’s consolidated financial statements. Ameren Services’ rental expenses incurred are subsequently allocated to Ameren Missouri and Ameren Illinois as part of the Ameren Services support agreement. Tax Allocation Agreement See Note 1 – Summary of Significant Accounting Policies under Part II, Item 8, of the Form 10-K for a discussion of the tax allocation agreement. The following table presents the affiliate balances related to income taxes for Ameren Missouri and Ameren Illinois as of March 31, 2024, and December 31, 2023: March 31, 2024 December 31, 2023 Ameren Missouri Ameren Illinois Ameren Missouri Ameren Illinois Income taxes payable to parent (a) $ — $ 43 $ — $ 2 Income taxes receivable from parent (b) 32 — 56 22 (a) Included in “Accounts payable – affiliates” on the balance sheet. (b) Included in “Accounts receivable – affiliates” on the balance sheet. Effects of Related-party Transactions on the Statement of Income The following table presents the impact on Ameren Missouri and Ameren Illinois of related-party transactions for the three months ended March 31, 2024 and 2023: Three Months Agreement Income Statement Ameren Ameren Ameren Missouri power supply Operating Revenues 2024 $ (b) $ (a) agreements with Ameren Illinois 2023 (b) (a) Ameren Missouri and Ameren Illinois Operating Revenues 2024 $ 7 $ (b) rent and facility services 2023 10 (b) Ameren Missouri and Ameren Illinois miscellaneous Operating Revenues 2024 $ (b) $ 1 support services 2023 (b) (b) Total Operating Revenues 2024 $ 7 $ 1 2023 10 (b) Ameren Illinois power supply Purchased Power 2024 $ (a) $ (b) agreements with Ameren Missouri 2023 (a) (b) Ameren Missouri and Ameren Illinois Purchased Power 2024 $ 2 $ (b) transmission services from ATXI 2023 (b) (b) Total Purchased Power 2024 $ 2 $ (b) 2023 (b) (b) Ameren Missouri and Ameren Illinois Other Operations and Maintenance 2024 $ (b) $ (b) rent and facility services 2023 (b) 2 Ameren Services support services Other Operations and Maintenance 2024 $ 38 $ 37 agreement 2023 35 35 Total Other Operations and 2024 $ 38 $ 37 Maintenance 2023 35 37 Money pool interest (Interest Charges)/Other Income, Net 2024 $ (3) $ (2) 2023 (b) (b) (a) Not applicable. (b) Amount less than $1 million.

Commitments And Contingencies

Commitments And Contingencies	3 Months Ended
	Mar. 31, 2024
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 2024, but the extent and duration of the curtailment is currently unknown as assessment of mitigation technologies is ongoing. Ameren Missouri does not anticipate these operating curtailments will have a material impact on its results of operations, financial position, or liquidity. Ameren and Ameren Missouri estimate that they will need to make capital expenditures of $90 million to $120 million from 2024 through 2028 in order to comply with environmental regulations in place prior to the EPA’s final rules on CO 2 emissions, MATS, effluent limitations guidelines, and CCR management issued in April 2024 and discussed below. Additional capital expenditures for environmental controls beyond 2028 could be required. This estimate of capital expenditures includes surface impoundment closure and corrective action measures required by the CCR Rule and modifications to cooling water intake structures at existing power plants under Clean Water Act rules, all of which are discussed below. In addition to planned retirements of coal-fired energy centers as set forth in the 2023 IRP filed with the MoPSC in September 2023 and as noted below with respect to the NSR and Clean Air Act litigation and Illinois emissions standards 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 statutes and regulations and environmental enforcement and remediation matters that affect or could affect our operations. The EPA periodically amends and revises its regulations and proposes amendments to regulations and guidelines, which could ultimately result in the revision of all or part of such regulations. Clean Air Act Federal and state laws, including the CSAPR, regulate emissions of 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. In December 2023, the United States Supreme Court agreed to hear challenges to the Good Neighbor Plan and heard oral argument in February 2024, with a decision expected by June 2024. Ameren Missouri complies with the current CSAPR requirements by minimizing emissions through the use of low-sulfur coal, operation of two scrubbers at its Sioux Energy Center, and optimization of existing NO x air pollution control equipment. Reducing the amount 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 April 2024, the EPA issued a final rule that sets CO 2 emission standards for existing coal-fired and new natural gas-fired power plants. The rule requires the adoption of carbon capture technology and/or natural gas co-firing for coal-fired power plants and carbon capture technology for new natural gas-fired power plants as a means to reduce CO 2 emissions. Certain affected power plants are required to comply with the rule through a phased-in approach or retire. Legal challenges to the final rule are expected. Ameren and Ameren Missouri are assessing the impacts of the final rule and, at this time, cannot predict the impacts on their results of operations, financial position, and liquidity. MATS In April 2024, the EPA revised the MATS by establishing a more stringent standard for emissions of particulate matter, requiring the use of continuous emissions monitoring systems. Ameren and Ameren Missouri are assessing the impacts of the revised rule and, at this time, cannot predict the impacts on their results of operations, financial position, and liquidity. NSR and Clean Air Act Litigation In January 2011, the United States Department of Justice, on behalf of the EPA, filed a complaint against Ameren Missouri in the United States District Court for the Eastern District of Missouri alleging that projects performed in 2007 and 2010 at the coal-fired Rush Island Energy Center violated provisions of the Clean Air Act and Missouri law. In January 2017, the district court issued a liability ruling against Ameren Missouri and, in September 2019, entered a remedy order that required Ameren Missouri to install a flue gas desulfurization system at the Rush Island Energy Center and a dry sorbent injection system at the Labadie Energy Center. Following an appeal from Ameren Missouri, in August 2021, the United States Court of Appeals for the Eighth Circuit affirmed the liability ruling and the district court’s remedy order as it related to the installation of a flue gas desulfurization system at the Rush Island Energy Center, but reversed the order as it related to the installation of a dry sorbent injection system at the Labadie Energy Center. In September 2023, the district court granted Ameren Missouri’s request to modify the remedy order to allow the retirement of the Rush Island Energy Center in advance of its previously expected retirement date of 2039 in lieu of installing a flue gas desulfurization system. In its amended remedy order, the district court established an October 15, 2024 retirement date to allow for the completion of various transmission reliability projects and, in the interim, authorized Ameren Missouri to operate the energy center only as needed and as directed by the MISO. The United States Department of Justice is seeking an order from the district court providing for additional mitigation relief related to prior emissions. Ameren Missouri contends that the retirement of the Rush Island Energy Center, which eliminates all future emissions from the energy center, mitigates claims relating to prior emissions. In March 2024, the district court ordered Ameren Missouri and the United States Department of Justice to file proposed draft orders outlining additional mitigation relief. In May 2024, Ameren Missouri filed a proposed draft order that includes retiring the Rush Island Energy Center, a program to provide electric buses and charging stations to schools in the metro St. Louis area, a program to provide air filters to eligible Ameren Missouri electric residential customers, and the retirement of SO 2 allowances. Excluding the accelerated retirement of the Rush Island Energy Center, these programs are estimated to cost approximately $20 million. Also in May 2024, the United States Department of Justice filed a proposed draft order that includes a program to provide electric buses and charging stations to schools in the metro St. Louis area and a program to provide air filters to eligible Ameren Missouri electric residential customers. These programs include a significantly greater number of buses, charging stations, and air filters than Ameren Missouri’s proposal and the United States Department of Justice estimates these programs would cost approximately $120 million. As of March 31, 2024, Ameren and Ameren Missouri recorded a $20 million liability in “Other current liabilities” on its consolidated balance sheet related to the cost of potential additional mitigation, which represents the estimated minimum liability, as no other amount within the range was a better estimate. The district court is expected to hold a hearing in mid-2024 and an order is expected in the second half of 2024. Depending on the scope and basis of the order, Ameren Missouri or the United States Department of Justice could appeal any additional mitigation relief ordered. The MISO designated the Rush Island 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, 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 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 Part II, Item 8, of the Form 10-K for additional information. In connection with the accelerated retirement of the Rush Island Energy Center, Ameren Missouri is seeking approval from the MoPSC to finance the costs associated with the retirement, including the remaining unrecovered net plant balance associated with the facility, through the issuance of securitized utility tariff bonds pursuant to Missouri’s securitization statute. Costs associated with the retirement would exclude any additional mitigation relief ordered in the NSR and Clean Air Act litigation discussed above. See Note 2 – Rate and Regulatory Matters for additional information. As of March 31, 2024, the Rush Island Energy Center had a net plant balance of $520 million included in plant to be abandoned, net, within “Property, Plant, and Equipment, Net”. 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 Among other items, the Clean Water Act requires power plant operators to evaluate cooling water intake structures and identify measures for reducing the number of aquatic organisms impinged on a power plant’s cooling water intake screens or entrained through the plant’s cooling water system. All of Ameren Missouri’s coal-fired and nuclear energy centers are subject to this cooling water intake structures rule. Requirements of the rule are implemented by state regulators through the permit renewal process of each power plant’s water discharge permit. Permits for Ameren Missouri’s coal-fired and nuclear energy centers have been issued or are in the process of renewal. In 2015, the EPA issued a rule to revise the effluent limitation guidelines applicable to steam electric generating units. These guidelines established national standards for water discharges, prohibit effluent discharges of certain waste streams, and impose more stringent limitations on certain water discharges from power plants by 2025. To comply with these guidelines, Ameren Missouri installed dry ash handling systems and wastewater treatment facilities at its coal-fired energy centers. In April 2024, the EPA issued new effluent limitation guidelines that established a zero discharge limit for flue gas desulfurization wastewater, bottom ash transport water, and combustion residual leachate. Ameren and Ameren Missouri are assessing the impacts of these new guidelines and, at this time, cannot predict the impacts on their results of operations, financial position, and liquidity. CCR Management The EPA’s CCR Rule establishes requirements for the management and disposal of CCR from coal-fired power plants and has resulted in the closure of surface impoundments at Ameren Missouri’s energy centers, with closures of surface impoundments in process at its Sioux Energy Center and retired Meramec Energy Center. Ameren Missouri plans to substantially complete the closures of remaining surface impoundments by the end of 2026. Ameren Missouri’s CCR management compliance plan includes installation of groundwater monitoring equipment and groundwater treatment facilities. Ameren and Ameren Missouri have AROs of $40 million recorded on their respective balance sheets as of March 31, 2024, associated with CCR storage facilities. In April 2024, the EPA revised the CCR Rule to impose groundwater monitoring, and corrective action, closure, and post-closure requirements on certain active and inactive CCR surface impoundments. Ameren and Ameren Missouri are assessing the impacts of this rule revision and, at this time, cannot predict the impacts on their results of operations, financial position, and liquidity. Remediation The Ameren Companies are involved in a number of remediation actions to clean up sites impacted by the use or disposal of materials containing hazardous substances. Federal and state laws can require responsible parties to fund remediation regardless of their degree of fault, the legality of original disposal, or the ownership of a disposal site. As of March 31, 2024, Ameren Illinois has remediated the majority of the 44 former MGP sites in Illinois with an estimated remaining obligation primarily related to three of these former MGP sites at $46 million to $96 million. Ameren and Ameren Illinois recorded a liability of $46 million to represent the estimated minimum obligation for these sites, as no other amount within the range was a better estimate. Ameren cannot estimate the completion date of the estimated remaining obligation due to site accessibility, among other things. The scope of the remediation activities at these former MGP sites may increase as remediation efforts continue. Considerable uncertainty remains in these estimates because many site-specific factors can influence the actual costs, including unanticipated underground structures, the degree to which groundwater is impacted, regulatory changes, local ordinances, and site accessibility. The actual costs and timing of completion may vary substantially from these estimates. The ICC allows Ameren Illinois to recover MGP remediation and related litigation costs from its electric and natural gas utility customers through environmental cost riders that are subject to annual prudence reviews by the ICC. Our operations or those of our predecessor companies involve the use of, disposal of, and, in appropriate circumstances, the cleanup of substances regulated under environmental laws. We are unable to determine whether such historical practices will result in future environmental commitments, including additional or more stringent cleanup standards, or will affect our results of operations, financial position, or liquidity.

Callaway Energy Center

Callaway Energy Center	3 Months Ended
	Mar. 31, 2024
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 filed with the MoPSC in December 2023 and is reflected within the ARO. Ameren Missouri’s filing supported no change in electric service rates for decommissioning costs. There is no deadline by which the MoPSC must issue an order regarding the filing. 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 April 1, 2024: Type and Source of Coverage Most Recent Maximum Coverages Maximum Assessments Public liability and nuclear worker liability: American Nuclear Insurers January 1, 2024 $ 500 $ — Pool participation (a) 15,763 (a) 166 (b) $ 16,263 (c) $ 166 Property damage: NEIL and EMANI April 1, 2024 $ 3,200 (d) $ 28 (e) Accidental outage: NEIL April 1, 2024 $ 490 (f) $ 11 (e) (a) Provided through mandatory participation in an industrywide retrospective premium assessment program. The maximum coverage available is dependent on the number of United States commercial reactors participating in the program. (b) Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $500 million in the event of an incident at any licensed United States commercial reactor, payable at $24.7 million per year. (c) Limit of liability for each incident under the Price-Anderson liability provisions of the Atomic Energy Act of 1954, as amended. This limit is subject to change to account for the effects of inflation and changes in the number of licensed power reactors. (d) NEIL provides $2.7 billion in property damage, stabilization, decontamination, and premature decommissioning insurance for radiation events and $0.7 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 $291 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	3 Months Ended
	Mar. 31, 2024
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 months ended March 31, 2024 and 2023: Pension Benefits Postretirement Benefits Three Months Three Months 2024 2023 2024 2023 Service cost (a) $ 21 $ 23 $ 3 $ 3 Non-service cost components: Interest cost 55 55 11 11 Expected return on plan assets (b) (82) (83) (23) (23) Amortization of (b) : Prior service benefit — — (1) (1) Actuarial (gain) (17) (29) (10) (11) Total non-service cost components (c) $ (44) $ (57) $ (23) $ (24) Net periodic benefit income (d) $ (23) $ (34) $ (20) $ (21) (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 months ended March 31, 2024 and 2023: Pension Benefits Postretirement Benefits Three Months Three Months 2024 2023 2024 2023 Ameren Missouri (a) $ (12) $ (18) $ (7) $ (8) Ameren Illinois (9) (14) (13) (13) Other (2) (2) — — Ameren (a) $ (23) $ (34) $ (20) $ (21) (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	3 Months Ended
	Mar. 31, 2024
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES The following table presents a reconciliation of the federal statutory corporate income tax rate to the effective income tax rate for the three months ended March 31, 2024 and 2023: Ameren Ameren Missouri Ameren Illinois 2024 2023 2024 2023 2024 2023 Three Months Federal statutory corporate income tax rate 21 % 21 % 21 % 21 % 21 % 21 % Increases (decreases) from: Amortization of excess deferred taxes (a) (8) (8) (12) (16) (4) (2) Renewable and other tax credits (b) (4) (5) (8) (10) — — State tax 6 6 4 4 7 7 Stock-based compensation 1 (1) — — — — Other depreciation differences (1) — (1) — — — Other permanent items (1) (1) — (3) — (1) Effective income tax rate 14 % 12 % 4 % (4) % 24 % 25 % (a) Reflects the amortization of amounts resulting from the revaluation of deferred income taxes subject to regulatory ratemaking, which are being refunded to customers. Deferred income taxes are revalued when federal or state income tax rates change, and the offset to the revaluation of deferred income taxes subject to regulatory ratemaking is recorded to a regulatory asset or liability. (b) The benefit of the credits associated with Missouri renewable energy standard compliance is refunded to customers through the RESRAM.

Supplemental Information

Supplemental Information	3 Months Ended
	Mar. 31, 2024
Supplemental Information [Abstract]
Supplemental Information	SUPPLEMENTAL INFORMATION Cash, Cash Equivalents, and Restricted Cash The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows at March 31, 2024, and December 31, 2023: March 31, 2024 December 31, 2023 Ameren Ameren Ameren Ameren Ameren Ameren “Cash and cash equivalents” $ 85 $ 2 $ — $ 25 $ — $ — Restricted cash included in “Other current assets” 13 5 6 13 5 5 Restricted cash included in “Other assets” 248 — 248 229 — 229 Restricted cash included in “Nuclear decommissioning trust fund” 9 9 — 5 5 — Total cash, cash equivalents, and restricted cash $ 355 $ 16 $ 254 $ 272 $ 10 $ 234 Restricted cash included in “Other current assets” primarily represents funds held by an irrevocable Voluntary Employee Beneficiary Association (VEBA) trust, which provides health care benefits for active employees. Restricted cash included in “Other assets” on Ameren’s and Ameren Illinois’ balance sheets primarily represents amounts collected under a cost recovery rider restricted for use in the procurement of renewable energy credits and amounts in a trust fund restricted for the use of funding certain asbestos-related claims. Accounts Receivable “Accounts receivable – trade” on Ameren’s and Ameren Illinois’ balance sheets include certain receivables purchased at a discount from alternative retail electric suppliers that elect to participate in the utility consolidated billing program. At March 31, 2024, and December 31, 2023, “Other current liabilities” on Ameren’s and Ameren Illinois’ balance sheets included payables for purchased receivables of $43 million and $42 million, respectively. The following table provides a reconciliation of the beginning and ending amount of the allowance for doubtful accounts for the three months ended March 31, 2024 and 2023: Three Months 2024 2023 Ameren: Beginning of period $ 30 $ 31 Bad debt expense 10 10 Charged to other accounts (a) 3 — Net write-offs (6) (7) End of period $ 37 $ 34 Ameren Missouri: Beginning of period $ 12 $ 13 Bad debt expense 1 2 Net write-offs (2) (3) End of period $ 11 $ 12 Ameren Illinois: (b) Beginning of period $ 18 $ 18 Bad debt expense 9 8 Charged to other accounts (a) 3 — Net write-offs (4) (4) End of period $ 26 $ 22 (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 rate-adjustment mechanisms that allow it to recover the difference between its actual net bad debt write-offs under GAAP, including those associated with receivables purchased from alternative retail electric suppliers, and the amount of net bad debt write-offs included in its base rates. The table above does not include the impact related to the riders. Supplemental Cash Flow Information The following table provides noncash financing and investing activity excluded from the statements of cash flows for the three months ended March 31, 2024 and 2023: March 31, 2024 March 31, 2023 Ameren Ameren Ameren Ameren Ameren Ameren Investing: Accrued capital expenditures, including nuclear fuel expenditures $ 310 $ 169 $ 122 $ 298 $ 153 $ 138 Net realized and unrealized gain – nuclear decommissioning trust fund 74 74 — 54 54 — Return of investment in industrial development revenue bonds (a) — — — 240 240 — Financing: Issuance of common stock for stock-based compensation $ 16 $ — $ — $ 37 $ — $ — Issuance of common stock under the DRPlus 7 — — 7 — — 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 three months ended March 31, 2024: Ameren Ameren Ameren Balance at December 31, 2023 $ 787 (a) $ 4 (b) $ 791 (a) Liabilities settled — (1) (1) Accretion 8 (c) — 8 (c) Balance at March 31, 2024 $ 795 (a) $ 3 (b) $ 798 (a) (a) Balance included $19 million in “Other current liabilities” on the balance sheet as of both March 31, 2024, and December 31, 2023. (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 2024, Ameren granted 359,133 performance share units with a grant date fair value of $21 million and 153,887 restricted share units with a grant date fair value of $11 million. Awards vest approximately 3 years after the grant date based on continued employment 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 (307,816 performance share units) or clean energy transition targets (51,317 performance share units). The exact number of shares issued pursuant to a performance share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the performance goals. For the three months ended March 31, 2024 and 2023, excess tax benefits (deficiencies) associated with the settlement of stock-based compensation awards increased income tax expense by $1 million and reduced income tax expense by $6 million, respectively. Deferred Compensation At March 31, 2024, and December 31, 2023, the present value of benefits to be paid for deferred compensation obligations was $87 million and $85 million, respectively, which was primarily reflected in “Other deferred credits and liabilities” on Ameren’s consolidated balance sheet. Operating Revenues As of March 31, 2024 and 2023, our remaining performance obligations for contracts with a term greater than one year were immaterial. The Ameren Companies elected not to disclose the aggregate amount of the transaction price allocated to the performance obligations that are unsatisfied as of the end of the reporting period for contracts with an initial expected term of one year or less. See Note 14 – Segment Information for disaggregated revenue information. Excise Taxes Ameren Missouri and Ameren Illinois collect from their customers excise taxes, including municipal and state excise taxes and gross receipts taxes that are levied on the sale or distribution of natural gas and electricity. The following table presents the excise taxes recorded on a gross basis in “Operating Revenues – Electric,” “Operating Revenues – Natural gas” and “Operating Expenses – Taxes other than income taxes” on the statements of income for the three months ended March 31, 2024 and 2023: Three Months 2024 2023 Ameren Missouri $ 35 $ 34 Ameren Illinois 37 37 Ameren $ 72 $ 71 Earnings per Share The following table reconciles the basic weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the three months ended March 31, 2024 and 2023: Three Months 2024 2023 Weighted-average Common Shares Outstanding – Basic 266.4 262.2 Assumed settlement of performance share units and restricted stock units 0.4 0.9 Weighted-average Common Shares Outstanding – Diluted (a) 266.8 263.1 (a) There was an immaterial number of anti-dilutive performance share units excluded from the earnings per diluted share calculations for the three months ended March 31, 2024 and 2023. The outstanding forward sale agreements as of March 31, 2024 and 2023, were anti-dilutive for the three months ended March 31, 2024 and 2023, and were excluded from the earnings per diluted share calculation as calculated using the treasury stock method. For additional information about our outstanding forward sale agreements, see Note 4 – Long-term Debt and Equity Financings.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2024
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 months ended March 31, 2024 and 2023. 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 2024: External revenues $ 768 $ 506 $ 391 $ 151 $ — $ — $ 1,816 Intersegment revenues 7 — — 34 — (41) — Net income attributable to Ameren common shareholders 25 56 106 72 (a) 2 — 261 Capital expenditures 466 184 60 166 2 12 890 Three Months 2023: External revenues $ 913 $ 624 $ 391 $ 134 $ — $ — $ 2,062 Intersegment revenues 10 — — 29 — (39) — Net income attributable to Ameren common shareholders 28 61 87 71 (a) 17 — 264 Capital expenditures 481 170 51 213 3 13 931 (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 2024: External revenues $ 506 $ 391 $ 103 $ — $ 1,000 Intersegment revenues — — 28 (28) — Net income available to common shareholder 56 106 53 — 215 Capital expenditures 184 60 129 — 373 Three Months 2023: External revenues $ 624 $ 391 $ 86 $ — $ 1,101 Intersegment revenues — — 28 (28) — Net income available to common shareholder 61 87 50 — 198 Capital expenditures 170 51 186 — 407 The following tables present disaggregated revenues by segment at Ameren and Ameren Illinois for the three months ended March 31, 2024 and 2023. 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 2024: Residential $ 341 $ 297 $ — $ — $ — $ 638 Commercial 259 165 — — — 424 Industrial 61 45 — — — 106 Other 53 (1) (a) — 185 (41) 196 Total electric revenues $ 714 $ 506 $ — $ 185 $ (41) $ 1,364 Residential $ 40 $ — $ 287 $ — $ — $ 327 Commercial 16 — 68 — — 84 Industrial 2 — 4 — — 6 Other 3 — 32 — — 35 Total natural gas revenues $ 61 $ — $ 391 $ — $ — $ 452 Total revenues (b) $ 775 $ 506 $ 391 $ 185 $ (41) $ 1,816 Three Months 2023: Residential $ 324 $ 382 $ — $ — $ — $ 706 Commercial 247 200 — — — 447 Industrial 61 48 — — — 109 Other 209 (6) (a) — 163 (38) 328 Total electric revenues $ 841 $ 624 $ — $ 163 $ (38) $ 1,590 Residential $ 52 $ — $ 296 $ — $ — $ 348 Commercial 23 — 77 — — 100 Industrial 2 — 7 — — 9 Other 5 — 11 — (1) 15 Total natural gas revenues $ 82 $ — $ 391 $ — $ (1) $ 472 Total revenues (b) $ 923 $ 624 $ 391 $ 163 $ (39) $ 2,062 (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 months ended March 31, 2024 and 2023: Ameren Missouri Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Transmission Ameren Three Months 2024: Revenues from alternative revenue programs $ (6) $ 39 $ 19 $ 9 $ 61 Other revenues not from contracts with customers 1 2 1 — 4 Three Months 2023: Revenues from alternative revenue programs $ (2) $ 64 $ 28 $ 8 $ 98 Other revenues not from contracts with customers (6) (a) 2 1 — (3) (a) (a) Includes net realized losses on derivative power contracts. Ameren Illinois Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Illinois Transmission Intersegment Eliminations Ameren Illinois Three Months 2024: Residential $ 297 $ 287 $ — $ — $ 584 Commercial 165 68 — — 233 Industrial 45 4 — — 49 Other (1) (a) 32 131 (28) 134 Total revenues (b) $ 506 $ 391 $ 131 $ (28) $ 1,000 Three Months 2023: Residential $ 382 $ 296 $ — $ — $ 678 Commercial 200 77 — — 277 Industrial 48 7 — — 55 Other (6) (a) 11 114 (28) 91 Total revenues (b) $ 624 $ 391 $ 114 $ (28) $ 1,101 (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 months ended March 31, 2024 and 2023: Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Illinois Transmission Ameren Illinois Three Months 2024: Revenues from alternative revenue programs $ 39 $ 19 $ 8 $ 66 Other revenues not from contracts with customers 2 1 — 3 Three Months 2023: Revenues from alternative revenue programs $ 64 $ 28 $ 7 $ 99 Other revenues not from contracts with customers 2 1 — 3

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Mar. 31, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2024
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 also has other subsidiaries that conduct other activities, such as providing shared services. • Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri. • Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois. • ATXI operates a FERC rate-regulated electric transmission business in the MISO.
Consolidation	Ameren’s and Ameren Missouri’s financial statements are prepared on a consolidated basis and therefore include the accounts of their majority-owned subsidiaries. All intercompany transactions have been eliminated. Ameren Missouri’s subsidiaries were created for the ownership of renewable generation projects. Ameren Illinois has no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated. Our accounting policies conform to GAAP. Our financial statements reflect all adjustments (which include normal, recurring adjustments) that are necessary, in our opinion, for a fair presentation of our results. The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. Such estimates and assumptions affect reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of financial statements, and the reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates. The results of operations for an interim period may not give a true indication of results that may be expected for a full year. These financial statements should be read in conjunction with the financial statements and accompanying notes included in the Form 10-K.
Consolidation, Variable Interest Entity, Policy	Variable Interest Entities As of March 31, 2024, and December 31, 2023, Ameren had unconsolidated variable interests in various equity method investments, primarily to advance clean and resilient energy technologies, totaling $74 million and $73 million, respectively, included in “Other assets” on Ameren’s consolidated balance sheet. Any earnings or losses related to these investments are included in “Other Income, Net” on Ameren’s consolidated statement of income and comprehensive income. Ameren is not the primary beneficiary of these investments because it does not have the power to direct matters that most significantly affect the activities of these variable interest entities. As of March 31, 2024, Ameren’s maximum exposure to loss related to these variable interests is limited to its investment of $74 million plus associated outstanding funding commitments of $14 million.
Life Insurance, Corporate Or Bank Owned	COLI
Derivatives, Policy	We use derivatives to manage the risk of changes in market prices for natural gas, power, and uranium, as well as the risk of changes in rail transportation surcharges through fuel oil hedges. Such price fluctuations may cause the following: • an unrealized appreciation or depreciation of our contracted commitments to purchase or sell when purchase or sale prices under the commitments are compared with current commodity prices; • market values of natural gas and uranium inventories that differ from the cost of those commodities in inventory; • actual cash outlays for the purchase of these commodities that differ from anticipated cash outlays; and • actual off-system sales revenues that differ from anticipated revenues. The derivatives that we use to hedge these risks are governed by our risk management policies for forward contracts, futures, options, and swaps. Our net positions are continually assessed within our structured hedging programs to determine whether new or offsetting transactions are required. The goal of the hedging program is generally to mitigate financial risks while ensuring that sufficient volumes are available to meet our requirements. Contracts we enter into as part of our risk management program may be settled financially, settled by physical delivery, or net settled with the counterparty. All contracts considered to be derivative instruments are required to be recorded on the balance sheet at their fair values, unless the NPNS exception applies. Many of our physical contracts, such as our purchased power contracts, qualify for the NPNS exception to derivative accounting rules. The revenue or expense on NPNS contracts is recognized at the contract price upon physical delivery. The following disclosures exclude NPNS contracts and other non-derivative commodity contracts that are accounted for under the accrual method of accounting. 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.
Deferred Compensation	Deferred Compensation At March 31, 2024, and December 31, 2023, the present value of benefits to be paid for deferred compensation obligations was $87 million and $85 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 March 31, 2024 and 2023, 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 Taxes

Rate and Regulatory Matters (Ta

Rate and Regulatory Matters (Tables)	3 Months Ended
	Mar. 31, 2024
Regulated Operations [Abstract]
Schedule of Solar Projects	The following table provides information with respect to each agreement: Huck Finn Solar Project (a)(b) Boomtown Solar Project (b)(c) Split Rail Solar Project (d) Cass County Solar Project (c) Vandalia Solar Project (b)(d) Bowling Green Solar Project (b)(d) Agreement type Build-transfer Build-transfer Build-transfer Development-transfer (e) Self-build (f) Self-build (f) Facility size 200-MW 150-MW 300-MW 150-MW 50-MW 50-MW Status of MoPSC CCN Approved February 2023 Approved April 2023 Approved March 2024 Filed June 2023 (g) Approved March 2024 Approved March 2024 Status of FERC approval of acquisition Received March 2023 Received October 2023 Expect to request by mid-2024 Not applicable Not applicable Not applicable Earliest completion date (h) Fourth quarter 2024 Fourth quarter 2024 Mid-2026 Fourth quarter 2024 Fourth quarter 2025 First quarter 2026 (a) The Huck Finn Solar Project is expected to support Ameren Missouri’s compliance with the state of Missouri’s renewable energy standard. Investments in the project will be eligible for recovery under the RESRAM. (b) These projects collectively represent approximately $0.85 billion of expected capital expenditures. (c) The Boomtown and Cass County solar projects are expected to support Ameren Missouri’s transition to renewable energy generation and serve customers under the Renewable Solutions Program. (d) These solar projects are expected to support Ameren Missouri’s transition to renewable energy generation. (e) 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 take over construction management of the Cass County facility after obtaining a CCN from the MoPSC and acquiring the project. Acquisition of the project is expected by mid-2024. (f) Ameren Missouri entered into engineering, procurement, and construction agreements to construct these solar projects. (g) Approval for the CCN is conditioned upon full subscription of the project capacity under the Renewable Solutions Program, a commercial, industrial, and governmental customer program. Ameren Missouri expects a decision by the MoPSC on the Cass County Solar Project CCN once this project’s capacity under the Renewable Solutions Program is fully subscribed. (h) Expected completion dates are dependent on the timing of regulatory approvals, among other things.
Schedule of MYRP details	The following table presents the approved revenue requirements, ROE, capital structure common equity percentage, and annual rate base in the ICC’s December 2023 order, as well as the proposed revenue requirements and annual rate base amounts in the March 2024 revised MYRP: Year Revenue Requirement (in millions) ROE Capital Structure Common Equity Percentage Annual Rate Base (in billions) ICC’s December 2023 MYRP Order: 2024 $1,162 8.72% 50% $3.9 2025 $1,210 8.72% 50% $3.9 2026 $1,242 8.72% 50% $3.9 2027 $1,255 8.72% 50% $3.9 Ameren Illinois’ March 2024 Revised MYRP: 2024 $1,207 (a) 50% $4.2 2025 $1,286 (a) 50% $4.4 2026 $1,371 (a) 50% $4.7 2027 $1,433 (a) 50% $4.9 (a) Based on an allowed ROE of 8.72%. Ameren Illinois’ filing requests the ICC to increase the allowed ROE to 9.24%.

Short-Term Debt and Liquidity (

Short-Term Debt and Liquidity (Tables)	3 Months Ended
	Mar. 31, 2024
Debt Disclosure [Abstract]
Schedule of Short-term Debt	The following table presents commercial paper outstanding, net of issuance discounts, as of March 31, 2024, and December 31, 2023. There were no borrowings outstanding under the Credit Agreements as of March 31, 2024, or December 31, 2023. March 31, 2024 December 31, 2023 Ameren (parent) $ — $ — Ameren Missouri 444 170 Ameren Illinois 424 366 Ameren consolidated $ 868 $ 536 The following table summarizes the activity and relevant interest rates for Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper issuances and borrowings under the Credit Agreements in the aggregate for the three months ended March 31, 2024 and 2023: Ameren Ameren Ameren Ameren 2024 Average daily amount outstanding $ — $ 135 $ 336 $ 471 Weighted-average interest rate — % 5.53 % 5.58 % 5.57 % Peak amount outstanding during period (a) $ — $ 444 $ 425 $ 869 Peak interest rate — % 5.68 % 5.68 % 5.68 % 2023 Average daily amount outstanding $ 506 $ 436 $ 233 $ 1,175 Weighted-average interest rate 4.89 % 4.86 % 4.89 % 4.88 % Peak amount outstanding during period (a) $ 728 $ 592 $ 325 $ 1,381 Peak interest rate 5.55 % 5.55 % 5.60 % 5.60 % (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 amount for the period.

Other Income, Net (Tables)

Other Income, Net (Tables)	3 Months Ended
	Mar. 31, 2024
Other Nonoperating Income (Expense) [Abstract]
Other Income And Expenses	The following table presents the components of “Other Income, Net” in the Ameren Companies’ statements of income for the three months ended March 31, 2024 and 2023: Three Months 2024 2023 Ameren: Allowance for equity funds used during construction $ 9 $ 9 Other interest income 8 8 Non-service cost components of net periodic benefit income (a) 76 64 Miscellaneous income 2 2 Earnings related to equity method investments — 2 Donations (2) (2) Miscellaneous expense (4) (5) Total Other Income, Net $ 89 $ 78 Ameren Missouri: Allowance for equity funds used during construction $ 9 $ 4 Other interest income 2 4 Non-service cost components of net periodic benefit income (a) 35 14 Miscellaneous income 1 1 Donations (1) (1) Miscellaneous expense (2) (3) Total Other Income, Net $ 44 $ 19 Ameren Illinois: Allowance for equity funds used during construction $ — $ 4 Interest income 6 4 Non-service cost components of net periodic benefit income 27 31 Miscellaneous income 1 1 Donations (1) (1) Miscellaneous expense (2) (2) Total Other Income, Net $ 31 $ 37 (a) For the three months ended March 31, 2024 and 2023, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $(9) million and $17 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. See Note 11 – Retirement Benefits for additional information.

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Open Gross Derivative Volumes By Commodity Type	The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of March 31, 2024, and December 31, 2023. As of March 31, 2024, these contracts extended through October 2026, October 2029 and May 2032 for fuel oils, natural gas and power, respectively. Quantity (in millions) March 31, 2024 December 31, 2023 Commodity Ameren Missouri Ameren Illinois Ameren Ameren Missouri Ameren Illinois Ameren Fuel oils (in gallons) 17 — 17 17 — 17 Natural gas (in mmbtu) 54 224 278 53 218 271 Power (in MWhs) — 5 5 — 5 5 Uranium (pounds in thousands) — — — 186 — 186
Derivative Instruments Carrying Value	The following table presents the carrying value and balance sheet location of all derivative commodity contracts, none of which were designated as hedging instruments, as of March 31, 2024, and December 31, 2023: March 31, 2024 December 31, 2023 Balance Sheet Location Ameren Ameren Ameren Ameren Ameren Ameren Fuel oils Other current assets $ 2 $ — $ 2 $ 2 $ — $ 2 Natural gas Other current assets — 2 2 — — — Other assets 3 2 5 3 3 6 Power Other current assets 2 — 2 5 — 5 Uranium Other current assets — — — 9 — 9 Total assets $ 7 $ 4 $ 11 $ 19 $ 3 $ 22 Fuel oils Other current liabilities $ 1 $ — $ 1 $ 1 $ — $ 1 Other deferred credits and liabilities — — — 1 — 1 Natural gas Other current liabilities 11 43 54 12 45 57 Other deferred credits and liabilities 8 28 36 10 30 40 Power Other current liabilities — 11 11 1 12 13 Other deferred credits and liabilities — 43 43 — 56 56 Total liabilities $ 20 $ 125 $ 145 $ 25 $ 143 $ 168
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 March 31, 2024, and December 31, 2023: 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 March 31, 2024 Assets: Ameren Missouri $ 7 $ 5 $ — $ 2 Ameren Illinois 4 2 — 2 Ameren $ 11 $ 7 $ — $ 4 Liabilities: Ameren Missouri $ 20 $ 5 $ — $ 15 Ameren Illinois 125 2 1 122 Ameren $ 145 $ 7 $ 1 $ 137 December 31, 2023 Assets: Ameren Missouri $ 19 $ 6 $ — $ 13 Ameren Illinois 3 1 — 2 Ameren $ 22 $ 7 $ — $ 15 Liabilities: Ameren Missouri $ 25 $ 6 $ — $ 19 Ameren Illinois 143 1 6 136 Ameren $ 168 $ 7 $ 6 $ 155 (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 March 31, 2024, 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 $ 20 $ — $ 15 Ameren Illinois 71 1 68 Ameren $ 91 $ 1 $ 83 (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)	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis	The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of March 31, 2024, and December 31, 2023: March 31, 2024 December 31, 2023 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets: Ameren Missouri Derivative assets – commodity contracts: Fuel oils $ 2 $ — $ — $ 2 $ 2 $ — $ — $ 2 Natural gas — 3 — 3 — 3 — 3 Power — — 2 2 — — 5 5 Uranium — — — — — — 9 9 Total derivative assets – commodity contracts $ 2 $ 3 $ 2 $ 7 $ 2 $ 3 $ 14 $ 19 Nuclear decommissioning trust fund: Equity securities: U.S. large capitalization $ 868 $ — $ — $ 868 $ 787 $ — $ — $ 787 Debt securities: U.S. Treasury and agency securities — 145 — 145 — 150 — 150 Corporate bonds — 139 — 139 — 136 — 136 Other — 72 — 72 — 68 — 68 Total nuclear decommissioning trust fund $ 868 $ 356 $ — $ 1,224 (a) $ 787 $ 354 $ — $ 1,141 (a) Total Ameren Missouri $ 870 $ 359 $ 2 $ 1,231 $ 789 $ 357 $ 14 $ 1,160 Ameren Illinois Derivative assets – commodity contracts: Natural gas $ — $ 1 $ 3 $ 4 $ — $ 1 $ 2 $ 3 Power — — — — — — — — Total Ameren Illinois $ — $ 1 $ 3 $ 4 $ — $ 1 $ 2 $ 3 Ameren Derivative assets – commodity contracts (b) $ 2 $ 4 $ 5 $ 11 $ 2 $ 4 $ 16 $ 22 Nuclear decommissioning trust fund (c) 868 356 — 1,224 (a) 787 354 — 1,141 (a) Total Ameren $ 870 $ 360 $ 5 $ 1,235 $ 789 $ 358 $ 16 $ 1,163 Liabilities: Ameren Missouri Derivative liabilities – commodity contracts: Fuel oils $ 1 $ — $ — $ 1 $ 2 $ — $ — $ 2 Natural gas — 18 1 19 — 19 3 22 Power — — — — — — 1 1 Total Ameren Missouri $ 1 $ 18 $ 1 $ 20 $ 2 $ 19 $ 4 $ 25 Ameren Illinois Derivative liabilities – commodity contracts: Natural gas $ 2 $ 61 $ 8 $ 71 $ 4 $ 60 $ 11 $ 75 Power — — 54 54 — — 68 68 Total Ameren Illinois $ 2 $ 61 $ 62 $ 125 $ 4 $ 60 $ 79 $ 143 Ameren Derivative liabilities – commodity contracts (b) $ 3 $ 79 $ 63 $ 145 $ 6 $ 79 $ 83 $ 168 (a) Balance excludes $8 million and $9 million of cash and cash equivalents, receivables, payables, and accrued income, net, for March 31, 2024, and December 31, 2023, 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 months ended March 31, 2024 and 2023: 2024 2023 Ameren Missouri Ameren Illinois Ameren Ameren Missouri Ameren Illinois Ameren For the three months ended March 31: Beginning balance at January 1 $ 4 $ (68) $ (64) $ 12 $ (33) $ (21) Realized and unrealized gains/(losses) included in regulatory assets/liabilities (1) 10 9 (6) (20) (26) Settlements (1) 4 3 (1) 1 — Ending balance at March 31 $ 2 $ (54) $ (52) $ 5 $ (52) $ (47) Change in unrealized gains/(losses) related to assets/liabilities held at March 31 $ — $ 11 $ 11 $ (2) $ (18) $ (20)
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis, Valuation Techniques	The following table describes the valuation techniques and significant unobservable inputs utilized for the fair value of our Level 3 power derivative contract assets and liabilities as of March 31, 2024, and December 31, 2023: Fair Value Weighted Average (b) Commodity Assets Liabilities Valuation Technique(s) Unobservable Input (a) Range 2024 Power (c) $ 2 $ (54) Discounted cash flow Average forward peak and off-peak pricing – forwards/swaps ($/MWh) 22 – 68 45 Nodal basis ($/MWh) (8) – (2) (5) 2023 Power (c) $ 5 $ (69) Discounted cash flow Average forward peak and off-peak pricing – forwards/swaps ($/MWh) 31 – 65 43 Nodal basis ($/MWh) (8) – (1) (5) (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.
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 long-term debt (including current portion) disclosed, but not recorded, at fair value as of March 31, 2024, and December 31, 2023: Long-Term Debt (Including Current Portion): Carrying Amount (a) Fair Value Level 2 Level 3 Total March 31, 2024 Ameren 16,316 14,258 453 (b) 14,711 Ameren Missouri 6,686 5,923 — 5,923 Ameren Illinois 5,233 4,668 — 4,668 December 31, 2023 Ameren 15,970 14,366 467 (b) 14,833 Ameren Missouri 6,341 5,800 — 5,800 Ameren Illinois 5,232 4,867 — 4,867 (a) Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $114 million, $48 million, and $46 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of March 31, 2024. Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $111 million, $45 million, and $47 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2023. (b) The Level 3 fair value amount consists of ATXI’s senior unsecured notes.

Related Party Transactions (Tab

Related Party Transactions (Tables)	3 Months Ended
	Mar. 31, 2024
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 March 31, 2024, and December 31, 2023: March 31, 2024 December 31, 2023 Ameren Missouri Ameren Illinois Ameren Missouri Ameren Illinois Income taxes payable to parent (a) $ — $ 43 $ — $ 2 Income taxes receivable from parent (b) 32 — 56 22 (a) Included in “Accounts payable – affiliates” on the balance sheet. (b) Included in “Accounts receivable – affiliates” on the balance sheet.
Schedule of Related Party Transactions	The following table presents the impact on Ameren Missouri and Ameren Illinois of related-party transactions for the three months ended March 31, 2024 and 2023: Three Months Agreement Income Statement Ameren Ameren Ameren Missouri power supply Operating Revenues 2024 $ (b) $ (a) agreements with Ameren Illinois 2023 (b) (a) Ameren Missouri and Ameren Illinois Operating Revenues 2024 $ 7 $ (b) rent and facility services 2023 10 (b) Ameren Missouri and Ameren Illinois miscellaneous Operating Revenues 2024 $ (b) $ 1 support services 2023 (b) (b) Total Operating Revenues 2024 $ 7 $ 1 2023 10 (b) Ameren Illinois power supply Purchased Power 2024 $ (a) $ (b) agreements with Ameren Missouri 2023 (a) (b) Ameren Missouri and Ameren Illinois Purchased Power 2024 $ 2 $ (b) transmission services from ATXI 2023 (b) (b) Total Purchased Power 2024 $ 2 $ (b) 2023 (b) (b) Ameren Missouri and Ameren Illinois Other Operations and Maintenance 2024 $ (b) $ (b) rent and facility services 2023 (b) 2 Ameren Services support services Other Operations and Maintenance 2024 $ 38 $ 37 agreement 2023 35 35 Total Other Operations and 2024 $ 38 $ 37 Maintenance 2023 35 37 Money pool interest (Interest Charges)/Other Income, Net 2024 $ (3) $ (2) 2023 (b) (b) (a) Not applicable. (b) Amount less than $1 million.

Callaway Energy Center (Tables)

Callaway Energy Center (Tables)	3 Months Ended
	Mar. 31, 2024
Nuclear Waste Matters [Abstract]
Schedule of Insurance Coverage at Callaway Energy Center	The following table presents insurance coverage at Ameren Missouri’s Callaway Energy Center at April 1, 2024: Type and Source of Coverage Most Recent Maximum Coverages Maximum Assessments Public liability and nuclear worker liability: American Nuclear Insurers January 1, 2024 $ 500 $ — Pool participation (a) 15,763 (a) 166 (b) $ 16,263 (c) $ 166 Property damage: NEIL and EMANI April 1, 2024 $ 3,200 (d) $ 28 (e) Accidental outage: NEIL April 1, 2024 $ 490 (f) $ 11 (e) (a) Provided through mandatory participation in an industrywide retrospective premium assessment program. The maximum coverage available is dependent on the number of United States commercial reactors participating in the program. (b) Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $500 million in the event of an incident at any licensed United States commercial reactor, payable at $24.7 million per year. (c) Limit of liability for each incident under the Price-Anderson liability provisions of the Atomic Energy Act of 1954, as amended. This limit is subject to change to account for the effects of inflation and changes in the number of licensed power reactors. (d) NEIL provides $2.7 billion in property damage, stabilization, decontamination, and premature decommissioning insurance for radiation events and $0.7 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 $291 million.

Retirement Benefits (Tables)

Retirement Benefits (Tables)	3 Months Ended
	Mar. 31, 2024
Retirement Benefits [Abstract]
Components Of Net Periodic Benefit Cost	The following table presents the components of the net periodic benefit cost (income) incurred for Ameren’s pension and postretirement benefit plans for the three months ended March 31, 2024 and 2023: Pension Benefits Postretirement Benefits Three Months Three Months 2024 2023 2024 2023 Service cost (a) $ 21 $ 23 $ 3 $ 3 Non-service cost components: Interest cost 55 55 11 11 Expected return on plan assets (b) (82) (83) (23) (23) Amortization of (b) : Prior service benefit — — (1) (1) Actuarial (gain) (17) (29) (10) (11) Total non-service cost components (c) $ (44) $ (57) $ (23) $ (24) Net periodic benefit income (d) $ (23) $ (34) $ (20) $ (21) (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 months ended March 31, 2024 and 2023: Pension Benefits Postretirement Benefits Three Months Three Months 2024 2023 2024 2023 Ameren Missouri (a) $ (12) $ (18) $ (7) $ (8) Ameren Illinois (9) (14) (13) (13) Other (2) (2) — — Ameren (a) $ (23) $ (34) $ (20) $ (21) (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 (Tables)

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 2024
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation	The following table presents a reconciliation of the federal statutory corporate income tax rate to the effective income tax rate for the three months ended March 31, 2024 and 2023: Ameren Ameren Missouri Ameren Illinois 2024 2023 2024 2023 2024 2023 Three Months Federal statutory corporate income tax rate 21 % 21 % 21 % 21 % 21 % 21 % Increases (decreases) from: Amortization of excess deferred taxes (a) (8) (8) (12) (16) (4) (2) Renewable and other tax credits (b) (4) (5) (8) (10) — — State tax 6 6 4 4 7 7 Stock-based compensation 1 (1) — — — — Other depreciation differences (1) — (1) — — — Other permanent items (1) (1) — (3) — (1) Effective income tax rate 14 % 12 % 4 % (4) % 24 % 25 % (a) Reflects the amortization of amounts resulting from the revaluation of deferred income taxes subject to regulatory ratemaking, which are being refunded to customers. Deferred income taxes are revalued when federal or state income tax rates change, and the offset to the revaluation of deferred income taxes subject to regulatory ratemaking is recorded to a regulatory asset or liability. (b) 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)	3 Months Ended
	Mar. 31, 2024
Supplemental Information [Abstract]
Schedule of Cash and Cash Equivalents Including Restricted Cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows at March 31, 2024, and December 31, 2023: March 31, 2024 December 31, 2023 Ameren Ameren Ameren Ameren Ameren Ameren “Cash and cash equivalents” $ 85 $ 2 $ — $ 25 $ — $ — Restricted cash included in “Other current assets” 13 5 6 13 5 5 Restricted cash included in “Other assets” 248 — 248 229 — 229 Restricted cash included in “Nuclear decommissioning trust fund” 9 9 — 5 5 — Total cash, cash equivalents, and restricted cash $ 355 $ 16 $ 254 $ 272 $ 10 $ 234
Schedule of Accounts, Notes, Loans and Financing Receivable	The following table provides a reconciliation of the beginning and ending amount of the allowance for doubtful accounts for the three months ended March 31, 2024 and 2023: Three Months 2024 2023 Ameren: Beginning of period $ 30 $ 31 Bad debt expense 10 10 Charged to other accounts (a) 3 — Net write-offs (6) (7) End of period $ 37 $ 34 Ameren Missouri: Beginning of period $ 12 $ 13 Bad debt expense 1 2 Net write-offs (2) (3) End of period $ 11 $ 12 Ameren Illinois: (b) Beginning of period $ 18 $ 18 Bad debt expense 9 8 Charged to other accounts (a) 3 — Net write-offs (4) (4) End of period $ 26 $ 22 (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 rate-adjustment mechanisms that allow it to recover the difference between its actual net bad debt write-offs under GAAP, including those associated with receivables purchased from alternative retail electric suppliers, and the amount of net bad debt write-offs included in its base rates. 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 three months ended March 31, 2024 and 2023: March 31, 2024 March 31, 2023 Ameren Ameren Ameren Ameren Ameren Ameren Investing: Accrued capital expenditures, including nuclear fuel expenditures $ 310 $ 169 $ 122 $ 298 $ 153 $ 138 Net realized and unrealized gain – nuclear decommissioning trust fund 74 74 — 54 54 — Return of investment in industrial development revenue bonds (a) — — — 240 240 — Financing: Issuance of common stock for stock-based compensation $ 16 $ — $ — $ 37 $ — $ — Issuance of common stock under the DRPlus 7 — — 7 — — 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 three months ended March 31, 2024: Ameren Ameren Ameren Balance at December 31, 2023 $ 787 (a) $ 4 (b) $ 791 (a) Liabilities settled — (1) (1) Accretion 8 (c) — 8 (c) Balance at March 31, 2024 $ 795 (a) $ 3 (b) $ 798 (a) (a) Balance included $19 million in “Other current liabilities” on the balance sheet as of both March 31, 2024, and December 31, 2023. (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 months ended March 31, 2024 and 2023: Three Months 2024 2023 Ameren Missouri $ 35 $ 34 Ameren Illinois 37 37 Ameren $ 72 $ 71
Schedule of Earnings Per Share, Basic and Diluted	The following table reconciles the basic weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the three months ended March 31, 2024 and 2023: Three Months 2024 2023 Weighted-average Common Shares Outstanding – Basic 266.4 262.2 Assumed settlement of performance share units and restricted stock units 0.4 0.9 Weighted-average Common Shares Outstanding – Diluted (a) 266.8 263.1 (a) There was an immaterial number of anti-dilutive performance share units excluded from the earnings per diluted share calculations for the three months ended March 31, 2024 and 2023. The outstanding forward sale agreements as of March 31, 2024 and 2023, were anti-dilutive for the three months ended March 31, 2024 and 2023, and were excluded from the earnings per diluted share calculation as calculated using the treasury stock method. For additional information about our outstanding forward sale agreements, see Note 4 – Long-term Debt and Equity Financings.

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2024
Segment Reporting [Abstract]
Schedule Of Segment Reporting Information By Segment	The following tables present revenues, net income attributable to common shareholders, and capital expenditures by segment at Ameren and Ameren Illinois for the three months ended March 31, 2024 and 2023. 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 2024: External revenues $ 768 $ 506 $ 391 $ 151 $ — $ — $ 1,816 Intersegment revenues 7 — — 34 — (41) — Net income attributable to Ameren common shareholders 25 56 106 72 (a) 2 — 261 Capital expenditures 466 184 60 166 2 12 890 Three Months 2023: External revenues $ 913 $ 624 $ 391 $ 134 $ — $ — $ 2,062 Intersegment revenues 10 — — 29 — (39) — Net income attributable to Ameren common shareholders 28 61 87 71 (a) 17 — 264 Capital expenditures 481 170 51 213 3 13 931 (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 2024: External revenues $ 506 $ 391 $ 103 $ — $ 1,000 Intersegment revenues — — 28 (28) — Net income available to common shareholder 56 106 53 — 215 Capital expenditures 184 60 129 — 373 Three Months 2023: External revenues $ 624 $ 391 $ 86 $ — $ 1,101 Intersegment revenues — — 28 (28) — Net income available to common shareholder 61 87 50 — 198 Capital expenditures 170 51 186 — 407
Disaggregation of Revenue	The following tables present disaggregated revenues by segment at Ameren and Ameren Illinois for the three months ended March 31, 2024 and 2023. 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 2024: Residential $ 341 $ 297 $ — $ — $ — $ 638 Commercial 259 165 — — — 424 Industrial 61 45 — — — 106 Other 53 (1) (a) — 185 (41) 196 Total electric revenues $ 714 $ 506 $ — $ 185 $ (41) $ 1,364 Residential $ 40 $ — $ 287 $ — $ — $ 327 Commercial 16 — 68 — — 84 Industrial 2 — 4 — — 6 Other 3 — 32 — — 35 Total natural gas revenues $ 61 $ — $ 391 $ — $ — $ 452 Total revenues (b) $ 775 $ 506 $ 391 $ 185 $ (41) $ 1,816 Three Months 2023: Residential $ 324 $ 382 $ — $ — $ — $ 706 Commercial 247 200 — — — 447 Industrial 61 48 — — — 109 Other 209 (6) (a) — 163 (38) 328 Total electric revenues $ 841 $ 624 $ — $ 163 $ (38) $ 1,590 Residential $ 52 $ — $ 296 $ — $ — $ 348 Commercial 23 — 77 — — 100 Industrial 2 — 7 — — 9 Other 5 — 11 — (1) 15 Total natural gas revenues $ 82 $ — $ 391 $ — $ (1) $ 472 Total revenues (b) $ 923 $ 624 $ 391 $ 163 $ (39) $ 2,062 (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 months ended March 31, 2024 and 2023: Ameren Missouri Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Transmission Ameren Three Months 2024: Revenues from alternative revenue programs $ (6) $ 39 $ 19 $ 9 $ 61 Other revenues not from contracts with customers 1 2 1 — 4 Three Months 2023: Revenues from alternative revenue programs $ (2) $ 64 $ 28 $ 8 $ 98 Other revenues not from contracts with customers (6) (a) 2 1 — (3) (a) (a) Includes net realized losses on derivative power contracts. Ameren Illinois Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Illinois Transmission Intersegment Eliminations Ameren Illinois Three Months 2024: Residential $ 297 $ 287 $ — $ — $ 584 Commercial 165 68 — — 233 Industrial 45 4 — — 49 Other (1) (a) 32 131 (28) 134 Total revenues (b) $ 506 $ 391 $ 131 $ (28) $ 1,000 Three Months 2023: Residential $ 382 $ 296 $ — $ — $ 678 Commercial 200 77 — — 277 Industrial 48 7 — — 55 Other (6) (a) 11 114 (28) 91 Total revenues (b) $ 624 $ 391 $ 114 $ (28) $ 1,101 (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 months ended March 31, 2024 and 2023: Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Illinois Transmission Ameren Illinois Three Months 2024: Revenues from alternative revenue programs $ 39 $ 19 $ 8 $ 66 Other revenues not from contracts with customers 2 1 — 3 Three Months 2023: Revenues from alternative revenue programs $ 64 $ 28 $ 7 $ 99 Other revenues not from contracts with customers 2 1 — 3

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Basis Of Presentation And Significant Accounting Policies [Line Items]
Unconsolidated variable interest	$ 74	$ 73
Cash Surrender Value of Life Insurance	255	248
Corporate owned life insurance, borrowings	104	104
Ameren Illinois Company
Basis Of Presentation And Significant Accounting Policies [Line Items]
Cash Surrender Value of Life Insurance	112	111
Corporate owned life insurance, borrowings	104	$ 104
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)	1 Months Ended		3 Months Ended						12 Months Ended
	Mar. 31, 2024 USD ($)	Nov. 30, 2023 USD ($)	Mar. 31, 2024 USD ($)	Jun. 30, 2023 MWh	Mar. 31, 2023 USD ($)	Sep. 30, 2022 MWh	Jun. 30, 2022 MWh	Mar. 31, 2022 MWh	Dec. 31, 2025 USD ($)
Rate And Regulatory Matters [Line Items]
Capital expenditures			$ 890,000,000		$ 931,000,000
Union Electric Company
Rate And Regulatory Matters [Line Items]
Capital expenditures			466,000,000		$ 481,000,000
Union Electric Company | Rush Island Energy Center
Rate And Regulatory Matters [Line Items]
Costs to be Securitized		$ 519,000,000
Amortization of Regulatory Asset		$ 15
MoPSC Staff Recommended Costs to be Securitized	$ 497,000,000
Union Electric Company | Solar generation facility
Rate And Regulatory Matters [Line Items]
Capital expenditures			$ 850,000,000
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 | Electric | MEEIA 2024 | Forecast
Rate And Regulatory Matters [Line Items]
Energy efficiency investments in MEEIA 2019 programs									$ 123,000,000
Percentage of MEEIA Energy Efficiency Goals Achieved									100%
Incentive award if energy efficiency goals are achieved									$ 56,000,000
Incentive award if energy efficiency goals are exceeded									$ 14,000,000

Rate And Regulatory Matters (_2

Rate And Regulatory Matters (Narrative-Illinois) (Details) - USD ($) $ in Millions	1 Months Ended			3 Months Ended			12 Months Ended
	Dec. 31, 2023	Nov. 30, 2023	Oct. 31, 2023	Jun. 30, 2024	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2027	Dec. 31, 2026	Dec. 31, 2025	Dec. 31, 2024
Rate And Regulatory Matters [Line Items]
Capital expenditures					$ 890	$ 931
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Capital expenditures					$ 373	$ 407
Ameren Illinois Company | Natural gas
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Return on Equity, Percentage	9.89%
Public Utilities, Requested Equity Capital Structure, Percentage	52%
IETL | Ameren Illinois Company | Electric Distribution | Forecast
Rate And Regulatory Matters [Line Items]
Multi-year rate plan rehearing requested revenue requirement										$ 1,213
Multi-year rate plan rehearing requested rate base										$ 4,200
Public Utilities, Approved Equity Capital Structure, Percentage							50%	50%	50%	50%
Approved return on equity percentage							8.72%	8.72%	8.72%	8.72%
ICC staff multi-year rate plan rehearing recommended revenue requirement										$ 1,195
ICC staff multi-year rate plan rehearing recommended rate base										4,000
Multi-year rate plan approved revenue requirement							$ 1,255	$ 1,242	$ 1,210	1,162
Approved rate base							3,900	3,900	3,900	3,900
Multi-year rate plan requested revenue requirement							1,433	1,371	1,286	1,207
Multi-year rate plan requested rate base							$ 4,900	$ 4,700	$ 4,400	$ 4,200
Public Utilities, Requested Return on Equity, Percentage							9.24%	9.24%	9.24%	9.24%
Public Utilities, Approved Rate Increase (Decrease), Amount										$ 142
Public Utilities, Requested Rate Increase (Decrease), Amount										$ 321
Pending Rate Case | Ameren Illinois Company | Electric Distribution | Subsequent Event
Rate And Regulatory Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 160
Public Utilities, Requested Equity Capital Structure, Percentage				50%
Pending Rate Case | Ameren Illinois Company | Natural gas
Rate And Regulatory Matters [Line Items]
Capital expenditures			$ 53
Over-Recovery Challenged by the Attorney General			$ 3
Final Rate Order | Ameren Illinois Company | Natural gas
Rate And Regulatory Matters [Line Items]
Public Utilities, Approved Equity Capital Structure, Percentage		50%
Approved return on equity percentage		9.44%
Approved rate base		$ 2,850
Public Utilities, Requested Rate Increase (Decrease), Amount		112
Capital expenditures	$ 93	$ 93

Rate And Regulatory Matters (_3

Rate And Regulatory Matters (Narrative-Federal) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	May 31, 2020	Mar. 31, 2024	Mar. 31, 2023
Rate And Regulatory Matters [Line Items]
ROE Change		0.50%
Revenues		$ 1,816	$ 2,062
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Revenues		1,000	$ 1,101
Midwest Independent Transmission System Operator, Inc
Rate And Regulatory Matters [Line Items]
Revenues		21
Midwest Independent Transmission System Operator, Inc | Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Revenues		$ 15
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
	Mar. 31, 2024 USD ($)	Mar. 31, 2023
Credit Agreements
Short-term Debt [Line Items]
Net Liquidity Available	$ 1.8
Actual debt-to-capital ratio	0.60
Utilities
Short-term Debt [Line Items]
Short-term Debt, Weighted Average Interest Rate, over Time	5.32%	4.80%
Union Electric Company | Missouri Credit Agreement
Short-term Debt [Line Items]
Actual debt-to-capital ratio	0.51
Ameren Illinois Company | Illinois Credit Agreement
Short-term Debt [Line Items]
Actual debt-to-capital ratio	0.45

Short-Term Debt and Liquidity_3

Short-Term Debt and Liquidity (Short-Term Debt outstanding) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Short-term Debt [Line Items]
Short-term debt	$ 868	$ 536
Union Electric Company
Short-term Debt [Line Items]
Short-term debt	444	170
Ameren Illinois Company
Short-term Debt [Line Items]
Short-term debt	424	366
Commercial Paper
Short-term Debt [Line Items]
Short-term debt	868	536
Commercial Paper | Parent Company
Short-term Debt [Line Items]
Short-term debt	0	0
Commercial Paper | Union Electric Company
Short-term Debt [Line Items]
Short-term debt	444	170
Commercial Paper | Ameren Illinois Company
Short-term Debt [Line Items]
Short-term debt	$ 424	$ 366

Short-Term Debt and Liquidity_4

Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Short-term Debt [Line Items]
Average daily amount outstanding	$ 471	$ 1,175
Weighted-average interest rate	5.57%	4.88%
Short-term Debt, Maximum Amount Outstanding During Period	$ 869	$ 1,381
Peak interest rate	5.68%	5.60%
Parent Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 0	$ 506
Weighted-average interest rate	0%	4.89%
Short-term Debt, Maximum Amount Outstanding During Period	$ 0	$ 728
Peak interest rate	0%	5.55%
Union Electric Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 135	$ 436
Weighted-average interest rate	5.53%	4.86%
Short-term Debt, Maximum Amount Outstanding During Period	$ 444	$ 592
Peak interest rate	5.68%	5.55%
Ameren Illinois Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 336	$ 233
Weighted-average interest rate	5.58%	4.89%
Short-term Debt, Maximum Amount Outstanding During Period	$ 425	$ 325
Peak interest rate	5.68%	5.60%

Long-Term debt and Equity Fin_2

Long-Term debt and Equity Financings (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		4 Months Ended
	Mar. 31, 2024 USD ($) $ / shares shares	Mar. 31, 2023 USD ($) shares	Apr. 30, 2024 USD ($)	Jan. 31, 2024 USD ($)
Long-Term Debt And Equity Financings [Line Items]
Shares issued under the DRPlus and 401(k) plan | shares	0.1	0.1
Issuances of common stock	$ 10	$ 5
Stock Issued During Period, Shares, Other | shares	0.2	0.5
Stock Issued During Period, Value, Other	$ 16
Maximum Value Of Shares To Be Issued Under ATM Program	$ 770
Forward Contract Indexed to Issuer's Equity, Basis Spread	75
Minimum
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares	$ 76.69
Maximum
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares	89.31
Weighted Average
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares	$ 80.45
Dividend reinvestment and 401 (k) plans
Long-Term Debt And Equity Financings [Line Items]
Issuances of common stock	$ 3
Accrued Proceeds from Issuance of Common Stock	$ 7
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	2.9
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value	$ 231
Period End Net Cash Settlement Price	20
Period End Net Share Settlement Price	$ 0.3
Forward Sale Agreement Equity Offering Shares | shares	2.9
Forward Sale Agreement Gross Sales Price	$ 232
Union Electric Company | Subsequent Event | Other Paid-in Capital:
Long-Term Debt And Equity Financings [Line Items]
Capital contributions from parent			$ 350
Union Electric Company | Secured Debt | First Mortgage Bonds, 5.25%, Due 2054 - $350 Issuance
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount				$ 350
Debt Instrument, Interest Rate, Stated Percentage				5.25%
Union Electric Company | Secured Debt | Senior Secured Notes 5.20% Due 2034 | Subsequent Event
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount			$ 500
Debt Instrument, Interest Rate, Stated Percentage			5.20%
Union Electric Company | Secured Debt | Senior Secured Notes350 Due2024 | Subsequent Event
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount			$ 350
Debt Instrument, Interest Rate, Stated Percentage			3.50%

Other Income, Net (Details)

Other Income, Net (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	$ 9	$ 9
Other interest income	8	8
Non-service cost components of net periodic benefit income	76	64
Miscellaneous income	2	2
Income (Loss) from Equity Method Investments	0	2
Donations	(2)	(2)
Miscellaneous expense	(4)	(5)
Total Other Income, Net	89	78
Union Electric Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	9	4
Other interest income	2	4
Non-service cost components of net periodic benefit income	35	14
Miscellaneous income	1	1
Donations	(1)	(1)
Miscellaneous expense	(2)	(3)
Total Other Income, Net	44	19
Defined Benefit Plan, Non-service Cost or Income Components - Tracker	(9)	17
Ameren Illinois Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	0	4
Other interest income	6	4
Non-service cost components of net periodic benefit income	27	31
Miscellaneous income	1	1
Donations	(1)	(1)
Miscellaneous expense	(2)	(2)
Total Other Income, Net	$ 31	$ 37

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	3 Months Ended		6 Months Ended
	Mar. 31, 2024 MMBTU MWh lb gal	Mar. 31, 2023 lb	Jun. 30, 2023 MWh MMBTU gal
Fuel oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	17		17
Natural gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	278		271
Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh	5		5
Uranium
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Mass | lb	0	186
Union Electric Company | Fuel oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	17		17
Union Electric Company | Natural gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	54		53
Union Electric Company | Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh	0		0
Union Electric Company | Uranium
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Mass | lb	0	186
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	224		218
Ameren Illinois Company | Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh	5		5
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	Mar. 31, 2024	Dec. 31, 2023
Derivative [Line Items]
Derivative Assets	$ 11	$ 22
Derivative Liability	145	168
Fuel oils | Other current assets
Derivative [Line Items]
Derivative Assets	2	2
Fuel oils | Other current liabilities
Derivative [Line Items]
Derivative Liability	1	1
Fuel oils | Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	0	1
Natural gas | Other current assets
Derivative [Line Items]
Derivative Assets	2	0
Natural gas | Other assets
Derivative [Line Items]
Derivative Assets	5	6
Natural gas | Other current liabilities
Derivative [Line Items]
Derivative Liability	54	57
Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	36	40
Power | Other current assets
Derivative [Line Items]
Derivative Assets	2	5
Power | Other current liabilities
Derivative [Line Items]
Derivative Liability	11	13
Power | Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	43	56
Uranium | Other current assets
Derivative [Line Items]
Derivative Assets	0	9
Union Electric Company
Derivative [Line Items]
Derivative Assets	7	19
Derivative Liability	20	25
Union Electric Company | Fuel oils | Other current assets
Derivative [Line Items]
Derivative Assets	2	2
Union Electric Company | Fuel oils | Other current liabilities
Derivative [Line Items]
Derivative Liability	1	1
Union Electric Company | Fuel oils | Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	0	1
Union Electric Company | Natural gas | Other current assets
Derivative [Line Items]
Derivative Assets	0	0
Union Electric Company | Natural gas | Other assets
Derivative [Line Items]
Derivative Assets	3	3
Union Electric Company | Natural gas | Other current liabilities
Derivative [Line Items]
Derivative Liability	11	12
Union Electric Company | Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	8	10
Union Electric Company | Power | Other current assets
Derivative [Line Items]
Derivative Assets	2	5
Union Electric Company | Power | Other current liabilities
Derivative [Line Items]
Derivative Liability	0	1
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	0	9
Ameren Illinois Company
Derivative [Line Items]
Derivative Assets	4	3
Derivative Liability	125	143
Ameren Illinois Company | Fuel oils | Other current assets
Derivative [Line Items]
Derivative Assets	0	0
Ameren Illinois Company | Fuel oils | Other current liabilities
Derivative [Line Items]
Derivative Liability	0	0
Ameren Illinois Company | Fuel oils | Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	0	0
Ameren Illinois Company | Natural gas | Other current assets
Derivative [Line Items]
Derivative Assets	2	0
Ameren Illinois Company | Natural gas | Other assets
Derivative [Line Items]
Derivative Assets	2	3
Ameren Illinois Company | Natural gas | Other current liabilities
Derivative [Line Items]
Derivative Liability	43	45
Ameren Illinois Company | Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	28	30
Ameren Illinois Company | Power | Other current assets
Derivative [Line Items]
Derivative Assets	0	0
Ameren Illinois Company | Power | Other current liabilities
Derivative [Line Items]
Derivative Liability	11	12
Ameren Illinois Company | Power | Other deferred credits and liabilities
Derivative [Line Items]
Derivative Liability	43	56
Ameren Illinois Company | Uranium | Other current 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	Mar. 31, 2024	Dec. 31, 2023
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	$ 11	$ 22
Gross derivative instruments not offset in the balance sheet	7	7
Gross cash collateral received not offset in the balance sheet	0	0
Net derivative asset	4	15
Gross derivative liability amount recognized on the balance sheet	145	168
Gross derivative instruments not offset in the balance sheet	7	7
Gross cash collateral posted not offset in the balance sheet	1	6
Net derivative liability	137	155
Union Electric Company
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	7	19
Gross derivative instruments not offset in the balance sheet	5	6
Gross cash collateral received not offset in the balance sheet	0	0
Net derivative asset	2	13
Gross derivative liability amount recognized on the balance sheet	20	25
Gross derivative instruments not offset in the balance sheet	5	6
Gross cash collateral posted not offset in the balance sheet	0	0
Net derivative liability	15	19
Ameren Illinois Company
Derivative [Line Items]
Gross derivative asset amount recognized on the balance sheet	4	3
Gross derivative instruments not offset in the balance sheet	2	1
Gross cash collateral received not offset in the balance sheet	0	0
Net derivative asset	2	2
Gross derivative liability amount recognized on the balance sheet	125	143
Gross derivative instruments not offset in the balance sheet	2	1
Gross cash collateral posted not offset in the balance sheet	1	6
Net derivative liability	$ 122	$ 136

Derivative Financial Instrume_6

Derivative Financial Instruments (Derivative Instruments with Credit Risk-Related Contingent Features) (Details) $ in Millions	Mar. 31, 2024 USD ($)
Derivative [Line Items]
Aggregate Fair Value of Derivative Liabilities	$ 91
Cash Collateral Posted	1
Potential Aggregate Amount of Additional Collateral Required	83
Union Electric Company
Derivative [Line Items]
Aggregate Fair Value of Derivative Liabilities	20
Cash Collateral Posted	0
Potential Aggregate Amount of Additional Collateral Required	15
Ameren Illinois Company
Derivative [Line Items]
Aggregate Fair Value of Derivative Liabilities	71
Cash Collateral Posted	1
Potential Aggregate Amount of Additional Collateral Required	$ 68

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	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	$ 1,224	$ 1,141
Assets fair value	1,235	1,163
Excluded receivables, payables, and accrued income, net	8	9
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	868	787
Assets fair value	870	789
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	356	354
Assets fair value	360	358
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Assets fair value	5	16
Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	11	22
Derivative Liability	145	168
Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	2	2
Derivative Liability	3	6
Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	4	4
Derivative Liability	79	79
Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	5	16
Derivative Liability	63	83
Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	1,224	1,141
Assets fair value	1,231	1,160
Union Electric Company | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	868	787
Assets fair value	870	789
Union Electric Company | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	356	354
Assets fair value	359	357
Union Electric Company | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	0	0
Assets fair value	2	14
Union Electric Company | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	7	19
Derivative Liability	20	25
Union Electric Company | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	2	2
Derivative Liability	1	2
Union Electric Company | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	3	3
Derivative Liability	18	19
Union Electric Company | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	2	14
Derivative Liability	1	4
Union Electric Company | Fuel oils | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	2	2
Derivative Liability	1	2
Union Electric Company | Fuel oils | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	2	2
Derivative Liability	1	2
Union Electric Company | Fuel oils | 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 | Fuel oils | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Derivative Liability	0	0
Union Electric Company | Natural gas | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	3	3
Derivative Liability	19	22
Union Electric Company | Natural gas | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Derivative Liability	0	0
Union Electric Company | Natural gas | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	3	3
Derivative Liability	18	19
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	1	3
Union Electric Company | Power | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	2	5
Derivative Liability	0	1
Union Electric Company | Power | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Derivative Liability	0	0
Union Electric Company | 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	2	5
Derivative Liability	0	1
Union Electric Company | Uranium | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	9
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	0	9
Union Electric Company | Equity securities: | U.S. large capitalization
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear decommissioning trust fund:	868	787
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:	868	787
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:	145	150
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:	145	150
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:	139	136
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:	139	136
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:	72	68
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:	72	68
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	4	3
Ameren Illinois Company | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	0	0
Ameren Illinois Company | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	1	1
Ameren Illinois Company | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	3	2
Ameren Illinois Company | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	125	143
Ameren Illinois Company | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	2	4
Ameren Illinois Company | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	61	60
Ameren Illinois Company | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	62	79
Ameren Illinois Company | Natural gas | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	4	3
Derivative Liability	71	75
Ameren Illinois Company | Natural gas | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Derivative Liability	2	4
Ameren Illinois Company | Natural gas | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	1	1
Derivative Liability	61	60
Ameren Illinois Company | Natural gas | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	3	2
Derivative Liability	8	11
Ameren Illinois Company | Power | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Assets	0	0
Derivative Liability	54	68
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	0
Derivative Liability	$ 54	$ 68

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
	Mar. 31, 2024	Mar. 31, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (64)	$ (21)
Included in regulatory assets/liabilities	9	(26)
Settlements, assets	3	0
Change in unrealized gains (losses) related to assets/liabilities held at period end	11	(20)
Ending balance	(52)	(47)
Union Electric Company
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	4	12
Included in regulatory assets/liabilities	(1)	(6)
Settlement, liabilities	(1)	(1)
Change in unrealized gains (losses) related to assets/liabilities held at period end	0	(2)
Ending balance	2	5
Ameren Illinois Company
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(68)	(33)
Included in regulatory assets/liabilities	10	(20)
Settlements, assets	4	1
Change in unrealized gains (losses) related to assets/liabilities held at period end	11	(18)
Ending balance	$ (54)	$ (52)

Fair Value Measurements (Sche_3

Fair Value Measurements (Schedule Of Valuation Process And Unobservable Inputs) (Details) - Power $ in Millions	Mar. 31, 2024 USD ($) $ / MWh	Dec. 31, 2023 USD ($) $ / MWh
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Derivative Assets | $	$ 2	$ 5
Derivative liabilities | $	$ (54)	$ (69)
Commodity Forward Price | Discounted cash flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	22	31
Commodity Forward Price | Discounted cash flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	68	65
Commodity Forward Price | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	45	43
Nodal Basis | Discounted cash flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	(8)	(8)
Nodal Basis | Discounted cash flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	(2)	(1)
Nodal Basis | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Measurement input	(5)	(5)

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	Mar. 31, 2024	Dec. 31, 2023
Carrying Amount(a)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-Term Debt, Carrying Amount	$ 16,316	$ 15,970
Debt Issuance Costs, Net	114	111
Carrying Amount(a) | Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-Term Debt, Carrying Amount	6,686	6,341
Debt Issuance Costs, Net	48	45
Carrying Amount(a) | Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-Term Debt, Carrying Amount	5,233	5,232
Debt Issuance Costs, Net	46	47
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	14,711	14,833
Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	14,258	14,366
Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	453	467
Fair Value | Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	5,923	5,800
Fair Value | Union Electric Company | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	5,923	5,800
Fair Value | Union Electric Company | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	0	0
Fair Value | Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	4,668	4,867
Fair Value | Ameren Illinois Company | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	4,668	4,867
Fair Value | Ameren Illinois Company | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 0	$ 0

Related Party Transactions (Nar

Related Party Transactions (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Related Party Transaction [Line Items]
Other assets	$ 964	$ 921
Union Electric Company
Related Party Transaction [Line Items]
Other assets	157	152
Ameren Illinois Company
Related Party Transaction [Line Items]
Other assets	632	603
Ameren Services Support Services Agreement | Union Electric Company | Related Party
Related Party Transaction [Line Items]
Other assets	28	31
Ameren Services Support Services Agreement | Ameren Illinois Company | Related Party
Related Party Transaction [Line Items]
Other assets	$ 31	$ 34

Related Party Transactions (Sch

Related Party Transactions (Schedule of Affiliate Receivables and Payables) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	$ 647	$ 1,136
Accounts Receivable, Related Parties, Current	507	494
Union Electric Company | Related Party
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	41	53
Accounts Receivable, Related Parties, Current	47	72
Union Electric Company | Income taxes payable to parent | Related Party
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	0	0
Union Electric Company | Income taxes receivable from parent | Related Party
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	32	56
Ameren Illinois Company | Related Party
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	84	52
Accounts Receivable, Related Parties, Current	14	35
Ameren Illinois Company | Income taxes payable to parent | Related Party
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	43	2
Ameren Illinois Company | Income taxes receivable from parent | Related Party
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	$ 0	$ 22

Related Party Transactions (Eff

Related Party Transactions (Effects of Related-party Transactions on the Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Related Party Transaction [Line Items]
Operating Revenues	$ 1,816	$ 2,062
Other operations and maintenance	470	448
(Interest Charges)/Other Income, Net	154	127
Union Electric Company
Related Party Transaction [Line Items]
Operating Revenues	775	923
Other operations and maintenance	254	239
(Interest Charges)/Other Income, Net	62	51
Union Electric Company | Ameren Missouri Power Supply Agreements with Ameren Illinois | Related Party
Related Party Transaction [Line Items]
Operating Revenues	1	1
Union Electric Company | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party
Related Party Transaction [Line Items]
Operating Revenues	7	10
Other operations and maintenance	1	1
Union Electric Company | Ameren Missouri and Ameren Illinois Miscellaneous Support Services | Related Party
Related Party Transaction [Line Items]
Operating Revenues	1	1
Union Electric Company | Total Related Party Operating Revenues | Related Party
Related Party Transaction [Line Items]
Operating Revenues	7	10
Union Electric Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI | Related Party
Related Party Transaction [Line Items]
Purchased Power	2	1
Union Electric Company | Purchased Power | Related Party
Related Party Transaction [Line Items]
Purchased Power	2	1
Union Electric Company | Ameren Services Support Services Agreement | Related Party
Related Party Transaction [Line Items]
Other operations and maintenance	38	35
Union Electric Company | Total Related Party Other Operations and Maintenance | Related Party
Related Party Transaction [Line Items]
Other operations and maintenance	38	35
Union Electric Company | Money pool interest | Related Party
Related Party Transaction [Line Items]
(Interest Charges)/Other Income, Net	(3)	1
Ameren Illinois Company
Related Party Transaction [Line Items]
Operating Revenues	1,000	1,101
Purchased Power	164	287
Other operations and maintenance	210	202
(Interest Charges)/Other Income, Net	55	47
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party
Related Party Transaction [Line Items]
Operating Revenues	1	1
Other operations and maintenance	1	2
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Miscellaneous Support Services | Related Party
Related Party Transaction [Line Items]
Operating Revenues	1	1
Ameren Illinois Company | Total Related Party Operating Revenues | Related Party
Related Party Transaction [Line Items]
Operating Revenues	1	1
Ameren Illinois Company | Ameren Illinois Power Supply Agreements with Ameren Missouri | Related Party
Related Party Transaction [Line Items]
Purchased Power	1	1
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI | Related Party
Related Party Transaction [Line Items]
Purchased Power	1	1
Ameren Illinois Company | Purchased Power | Related Party
Related Party Transaction [Line Items]
Purchased Power	1	1
Ameren Illinois Company | Ameren Services Support Services Agreement | Related Party
Related Party Transaction [Line Items]
Other operations and maintenance	37	35
Ameren Illinois Company | Total Related Party Other Operations and Maintenance | Related Party
Related Party Transaction [Line Items]
Other operations and maintenance	37	37
Ameren Illinois Company | Money pool interest | Related Party
Related Party Transaction [Line Items]
(Interest Charges)/Other Income, Net	$ (2)	$ 1

Commitments And Contingencies (

Commitments And Contingencies (Environmental Matters) (Detail) $ in Millions	May 30, 2024 USD ($)	Mar. 31, 2024 USD ($) scrubber site	Dec. 31, 2023 USD ($)
Loss Contingencies [Line Items]
Asset Retirement Obligation		$ 798	$ 791
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		$ 795	787
Union Electric Company | Coal Fired Electric Generation Equipment
Loss Contingencies [Line Items]
Plant To Be Abandoned, Net		520
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		3	$ 4
Rush Island Energy Center Additional Mitigation Relief Proposed by Ameren Missouri | Union Electric Company
Loss Contingencies [Line Items]
Estimate of possible loss		20
Accrual for environmental loss contingencies		20
Rush Island Energy Center Additional Mitigation Relief Proposed by Department of Justice | Union Electric Company | Subsequent Event
Loss Contingencies [Line Items]
Estimate of possible loss	$ 120
Manufactured Gas Plant
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies		46
Manufactured Gas Plant | Ameren Illinois Company
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies		$ 46
Number of remediation sites | site		44
Manufactured Gas Plant | Ameren Illinois Company | Minimum
Loss Contingencies [Line Items]
Estimate of possible loss		$ 46
Manufactured Gas Plant | Ameren Illinois Company | Maximum
Loss Contingencies [Line Items]
Estimate of possible loss		96
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	3 Months Ended
	Mar. 31, 2024 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	$ 500
Insurance Maximum Coverage per Incident	0
Public Liability And Nuclear Worker Liability - Pool Participation
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	15,763
Insurance Maximum Coverage per Incident	166
Threshold Amount For Retrospective Insurance Assessment For Covered Loss Under Public Liability And Nuclear Worker Liability Insurance Policy	500
Maximum Annual Payment Per Incident At Licensed Commercial Nuclear Reactor	24.7
Public Liability
Nuclear Waste Matters [Line Items]
Insurance Aggregate Maximum Coverage	16,263
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	11
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	291
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	700
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
	Mar. 31, 2024	Mar. 31, 2023
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total non-service cost components	$ (76)	$ (64)
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	21	23
Interest cost	55	55
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	(82)	(83)
Prior service benefit	0	0
Actuarial (gain)	(17)	(29)
Total non-service cost components	(44)	(57)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	$ (23)	(34)
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	3
Interest cost	11	11
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	(23)	(23)
Prior service benefit	(1)	(1)
Actuarial (gain)	(10)	(11)
Total non-service cost components	(23)	(24)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total	$ (20)	$ (21)
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
	Mar. 31, 2024	Mar. 31, 2023
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	$ (23)	$ (34)
Pension Plan | Union Electric Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(12)	(18)
Pension Plan | Ameren Illinois Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(9)	(14)
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	(2)	(2)
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	(20)	(21)
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	(7)	(8)
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)	(13)
Other Postretirement Benefit Plan, Defined Benefit | Other Affiliated Entities And Intercompany Eliminations
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	$ 0	$ 0

Income Taxes (Schedule of Effec

Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21%	21%
Increases (decreases) from:
Amortization of excess deferred taxes	(8.00%)	(8.00%)
Renewable and other tax credits	(4.00%)	(5.00%)
State tax	6%	6%
Stock-based compensation	1%	(1.00%)
Depreciation differences	(1.00%)	0%
Other permanent items	(1.00%)	(1.00%)
Effective income tax rate	14%	12%
Union Electric Company
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21%	21%
Increases (decreases) from:
Amortization of excess deferred taxes	(12.00%)	(16.00%)
Renewable and other tax credits	(8.00%)	(10.00%)
State tax	4%	4%
Stock-based compensation	0%	0%
Depreciation differences	(1.00%)	0%
Other permanent items	0%	(3.00%)
Effective income tax rate	4%	(4.00%)
Ameren Illinois Company
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21%	21%
Increases (decreases) from:
Amortization of excess deferred taxes	(4.00%)	(2.00%)
Renewable and other tax credits	0%	0%
State tax	7%	7%
Stock-based compensation	0%	0%
Depreciation differences	0%	0%
Other permanent items	0%	(1.00%)
Effective income tax rate	24%	25%

Supplemental Information (Cash

Supplemental Information (Cash and Cash Equivalents) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	$ 85	$ 25
Restricted cash included in “Other current assets”	13	13
Restricted cash included in “Other assets”	248	229
Restricted cash included in “Nuclear decommissioning trust fund”	9	5
Total cash, cash equivalents, and restricted cash	355	272	$ 237	$ 216
Union Electric Company
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	2	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”	9	5
Total cash, cash equivalents, and restricted cash	16	10	11	13
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”	6	5
Restricted cash included in “Other assets”	248	229
Restricted cash included in “Nuclear decommissioning trust fund”	0	0
Total cash, cash equivalents, and restricted cash	$ 254	$ 234	$ 217	$ 191

Supplemental Information (Allow

Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	$ 30	$ 31
Bad debt expense	10	10
Charged to other accounts	3	0
Net write-offs	(6)	(7)
End of period	37	34
Payables for purchased receivables	43		$ 42
Union Electric Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	12	13
Bad debt expense	1	2
Net write-offs	(2)	(3)
End of period	11	12
Ameren Illinois Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	18	18
Bad debt expense	9	8
Charged to other accounts	3	0
Net write-offs	(4)	(4)
End of period	26	$ 22
Payables for purchased receivables	$ 43		$ 42

Supplemental Information (Suppl

Supplemental Information (Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including nuclear fuel expenditures	$ 310	$ 298
Net realized and unrealized gain – nuclear decommissioning trust fund	74	54
Return on investment in industrial development revenue bonds	0	240
Termination of a financing obligation	0	240
Issuance of common stock for stock-based compensation
Supplemental Cash Flow Information [Line Items]
Stock Issued	16	37
Issuance of common stock under the DRPlus
Supplemental Cash Flow Information [Line Items]
Stock Issued	7	7
Union Electric Company
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including nuclear fuel expenditures	169	153
Net realized and unrealized gain – nuclear decommissioning trust fund	74	54
Return on investment in industrial development revenue bonds	0	240
Termination of a financing obligation	0	240
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	122	138
Net realized and unrealized gain – 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	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	$ 791
Liabilities settled	(1)
Accretion	8
Asset Retirement Obligation, Ending Balance	798
Other current liabilities	651	$ 648
Union Electric Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	787
Liabilities settled	0
Accretion	8
Asset Retirement Obligation, Ending Balance	795
Other current liabilities	206	222
Ameren Illinois Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	4
Liabilities settled	(1)
Accretion	0
Asset Retirement Obligation, Ending Balance	3
Other current liabilities	280	298
Asset Retirement Obligation Balance
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Other current liabilities	19	19
Asset Retirement Obligation Balance | Union Electric Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Other current liabilities	$ 19	$ 19

Supplemental Information (Narra

Supplemental Information (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount	$ 1	$ (6)
Deferred Compensation Liability, Classified, Noncurrent	$ 87		$ 85
Q1 2024 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 2024 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	359,133
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Fair Value	$ 21
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 2024 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	307,816
Performance Shares | Renewable generation and energy storage installation targets | Q1 2024 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	51,317
Restricted Stock Units (RSUs) | Q1 2024 Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	153,887
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Fair Value	$ 11

Supplemental Information (Sch_2

Supplemental Information (Schedule Of Excise Taxes) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Accounting Policies [Line Items]
Excise tax expense	$ 72	$ 71
Union Electric Company
Accounting Policies [Line Items]
Excise tax expense	35	34
Ameren Illinois Company
Accounting Policies [Line Items]
Excise tax expense	$ 37	$ 37

Supplemental Information (Earni

Supplemental Information (Earnings Per Share) (Details) - shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Earnings Per Share Reconciliation [Abstract]
Weighted-average Common Shares Outstanding – Basic	266,400,000	262,200,000
Assumed settlement of performance share units and restricted stock units	400,000	900,000
Weighted-average Common Shares Outstanding – Diluted	266,800,000	263,100,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)	0	0

Segment Information (Schedule O

Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Operating Revenues	$ 1,816	$ 2,062
Net income (loss) attributable to common shareholders	261	264
Capital expenditures	890	931
Union Electric Company
Segment Reporting Information [Line Items]
Operating Revenues	775	923
Net Income (Loss)	25	28
Ameren Illinois Company
Segment Reporting Information [Line Items]
Operating Revenues	1,000	1,101
Net Income (Loss)	215	198
Capital expenditures	373	407
Operating Segments | Union Electric Company
Segment Reporting Information [Line Items]
Operating Revenues	768	913
Net Income (Loss)	25	28
Capital expenditures	466	481
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues	506	624
Net Income (Loss)	56	61
Capital expenditures	184	170
Operating Segments | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Operating Revenues	391	391
Net Income (Loss)	106	87
Capital expenditures	60	51
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
Operating Revenues	151	134
Net Income (Loss)	72	71
Capital expenditures	166	213
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues	506	624
Net Income (Loss)	56	61
Capital expenditures	184	170
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Operating Revenues	391	391
Net Income (Loss)	106	87
Capital expenditures	60	51
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Operating Revenues	103	86
Net Income (Loss)	53	50
Capital expenditures	129	186
Other
Segment Reporting Information [Line Items]
Net Income (Loss)	2	17
Capital expenditures	2	3
Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment revenues	(41)	(39)
Capital expenditures	12	13
Intersegment Eliminations | Union Electric Company
Segment Reporting Information [Line Items]
Intersegment revenues	(7)	(10)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	0	0
Intersegment Eliminations | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Intersegment revenues	0	0
Intersegment Eliminations | Ameren Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	(34)	(29)
Intersegment Eliminations | Ameren Illinois Company
Segment Reporting Information [Line Items]
Intersegment revenues	(28)	(28)
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Natural Gas
Segment Reporting Information [Line Items]
Intersegment revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	$ (28)	$ (28)

Segment Information (Disaggrega

Segment Information (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Operating Revenues	$ 1,816	$ 2,062
Revenues	1,816	2,062
Revenues from alternative revenue programs	61	98
Other revenues not from contracts with customers	4	(3)
Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(6)	(2)
Other revenues not from contracts with customers	1	(6)
Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	39	64
Other revenues not from contracts with customers	2	2
Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	19	28
Other revenues not from contracts with customers	1	1
Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	9	8
Other revenues not from contracts with customers	0	0
Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	1,364	1,590
Revenues	1,364	1,590
Electric | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	638	706
Electric | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	424	447
Electric | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	106	109
Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	196	328
Natural gas
Disaggregation of Revenue [Line Items]
Operating Revenues	452	472
Revenues	452	472
Natural gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	327	348
Natural gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	84	100
Natural gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	6	9
Natural gas | Other
Disaggregation of Revenue [Line Items]
Revenues	35	15
Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Operating Revenues	1,000	1,101
Revenues	1,000	1,101
Revenues from alternative revenue programs	66	99
Other revenues not from contracts with customers	3	3
Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	584	678
Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	233	277
Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	49	55
Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenues	134	91
Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	39	64
Other revenues not from contracts with customers	2	2
Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	19	28
Other revenues not from contracts with customers	1	1
Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	8	7
Other revenues not from contracts with customers	0	0
Ameren Illinois Company | Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	609	710
Ameren Illinois Company | Natural gas
Disaggregation of Revenue [Line Items]
Operating Revenues	391	391
Operating Segments | Union Electric Company
Disaggregation of Revenue [Line Items]
Operating Revenues	768	913
Revenues	775	923
Operating Segments | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Operating Revenues	506	624
Revenues	506	624
Operating Segments | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Operating Revenues	391	391
Revenues	391	391
Operating Segments | Ameren Transmission
Disaggregation of Revenue [Line Items]
Operating Revenues	151	134
Revenues	185	163
Operating Segments | Electric | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	714	841
Operating Segments | Electric | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	341	324
Operating Segments | Electric | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	259	247
Operating Segments | Electric | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	61	61
Operating Segments | Electric | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenues	53	209
Operating Segments | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	506	624
Operating Segments | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	297	382
Operating Segments | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	165	200
Operating Segments | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	45	48
Operating Segments | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	(1)	(6)
Operating Segments | Electric | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments | Electric | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Electric | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	185	163
Operating Segments | Electric | Ameren Transmission | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments | Electric | Ameren Transmission | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments | Electric | Ameren Transmission | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments | Electric | Ameren Transmission | Other
Disaggregation of Revenue [Line Items]
Revenues	185	163
Operating Segments | Natural gas | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	61	82
Operating Segments | Natural gas | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	40	52
Operating Segments | Natural gas | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	16	23
Operating Segments | Natural gas | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	2	2
Operating Segments | Natural gas | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenues	3	5
Operating Segments | Natural gas | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural gas | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	391	391
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	287	296
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	68	77
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	4	7
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	32	11
Operating Segments | Natural gas | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Natural gas | Ameren Transmission | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments | Natural gas | Ameren Transmission | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments | Natural gas | Ameren Transmission | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments | Natural gas | Ameren Transmission | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Operating Revenues	506	624
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Operating Revenues	391	391
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Operating Revenues	103	86
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	506	624
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	297	382
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	165	200
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	45	48
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	(1)	(6)
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	131	114
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Other
Disaggregation of Revenue [Line Items]
Revenues	131	114
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	391	391
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	287	296
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	68	77
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	4	7
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	32	11
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(41)	(39)
Revenues	(41)	(39)
Intersegment Eliminations | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	(7)	(10)
Intersegment Eliminations | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	(34)	(29)
Intersegment Eliminations | Electric
Disaggregation of Revenue [Line Items]
Revenues	(41)	(38)
Intersegment Eliminations | Electric | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations | Electric | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations | Electric | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations | Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	(41)	(38)
Intersegment Eliminations | Natural gas
Disaggregation of Revenue [Line Items]
Revenues	0	(1)
Intersegment Eliminations | Natural gas | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations | Natural gas | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations | Natural gas | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations | Natural gas | Other
Disaggregation of Revenue [Line Items]
Revenues	0	(1)
Intersegment Eliminations | Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Revenues	(28)	(28)
Revenues	(28)	(28)
Intersegment Eliminations | Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
Operating Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenues	(28)	(28)
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Natural Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	$ (28)	$ (28)