AMEREN CORP, 10-Q filed on 5/5/2025
Quarterly Report
v3.25.1
Cover Page - shares
 3 Months Ended
Mar. 31, 2025
Apr. 30, 2025
Entity Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Mar. 31, 2025  
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   270,278,917
Entity Central Index Key 0001002910  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2025  
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 2025  
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 2025  
Document Fiscal Period Focus Q1  
Amendment Flag false  
v3.25.1
Consolidated Statement of Income (Loss) and Comprehensive Income - USD ($)
shares in Millions, $ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Operating Revenues:    
Operating Revenues $ 2,097 $ 1,816
Operating Expenses:    
Fuel and purchased power 502 328
Natural gas purchased for resale 169 151
Other operations and maintenance 485 470
Depreciation and amortization 367 361
Taxes other than income taxes 144 135
Total operating expenses 1,667 1,445
Operating Income 430 371
Other Income, Net 85 89
Interest Charges 175 154
Income Before Income Taxes 340 306
Income Taxes 50 44
Net Income 290 262
Less: Net Income Attributable to Noncontrolling Interests 1 1
Preferred Stock Dividends 1 1
Net income attributable to Ameren common shareholders 289 261
Pension and other postretirement benefit plan activity, net of income taxes (benefit) of $— and $—, respectively 0 (1)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax (4) 0
Comprehensive Income 286 261
Less: Comprehensive Income Attributable to Noncontrolling Interests 1 1
Comprehensive Income Attributable to Ameren Common Shareholders $ 285 $ 260
Earnings Per Share, Basic [Abstract]    
Earnings per Common Share - Basic and Diluted $ 1.07 $ 0.98
Earnings Per Share, Diluted [Abstract]    
Earnings per Common Share - Basic and Diluted $ 1.07 $ 0.98
Weighted-average Common Shares Outstanding – Basic 270.0 266.4
Weighted-average Common Shares Outstanding – Diluted 271.4 266.8
Electric    
Operating Revenues:    
Operating Revenues $ 1,622 $ 1,364
Natural gas    
Operating Revenues:    
Operating Revenues 475 452
Union Electric Company    
Operating Revenues:    
Operating Revenues 957 775
Operating Expenses:    
Fuel and purchased power 330 166
Natural gas purchased for resale 30 28
Other operations and maintenance 250 254
Depreciation and amortization 194 195
Taxes other than income taxes 89 87
Total operating expenses 893 730
Operating Income 64 45
Other Income, Net 43 44
Interest Charges 60 62
Income Before Income Taxes 47 27
Income Taxes 4 1
Net Income 43 26
Net Income 43 26
Preferred Stock Dividends 1 1
Net income attributable to Ameren common shareholders 42 25
Union Electric Company | Electric    
Operating Revenues:    
Operating Revenues 893 714
Union Electric Company | Natural gas    
Operating Revenues:    
Operating Revenues 64 61
Ameren Illinois Company    
Operating Revenues:    
Operating Revenues 1,100 1,000
Operating Expenses:    
Purchased Power 175 164
Natural gas purchased for resale 139 123
Other operations and maintenance 236 210
Depreciation and amortization 159 153
Taxes other than income taxes 51 44
Total operating expenses 760 694
Operating Income 340 306
Other Income, Net 34 31
Interest Charges 62 55
Income Before Income Taxes 312 282
Income Taxes 76 67
Net Income 236 215
Net Income 236 215
Net income attributable to Ameren common shareholders 236 215
Ameren Illinois Company | Electric    
Operating Revenues:    
Operating Revenues 689 609
Ameren Illinois Company | Natural gas    
Operating Revenues:    
Operating Revenues $ 411 $ 391
v3.25.1
Consolidated Statement of Income (Loss) and Comprehensive Income (Parenthetical) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Income Statement [Abstract]    
Pension and other postretirement benefit plan activity, tax $ 0 $ 0
Unrealized net loss on derivative hedging instruments, tax $ 0 $ 0
v3.25.1
Consolidated Balance Sheet - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Current Assets:    
Cash and cash equivalents $ 23 $ 7
Accounts receivable - trade (less allowance for doubtful accounts) 667 525
Unbilled revenue 253 346
Miscellaneous accounts receivable 327 96
Inventories 669 762
Current regulatory assets 340 366
Other current assets 176 162
Total current assets 2,455 2,264
Property, Plant, and Equipment, Net 37,010 36,304
Investments and Other Assets:    
Nuclear decommissioning trust fund 1,312 1,342
Goodwill 411 411
Regulatory Asset 2,569 2,397
Pension and other postretirement benefits 765 757
Other assets 1,143 1,123
Total investments and other assets 6,200 6,030
TOTAL ASSETS 45,665 44,598
Current Liabilities:    
Current maturities of long-term debt 17 317
Short-term debt 1,252 1,143
Accounts and wages payable 702 1,059
Interest accrued 159 196
Customer deposits 223 223
Other current liabilities 510 475
Total current liabilities 2,863 3,413
Long-term debt, net 18,354 17,262
Deferred Credits and Other Liabilities:    
Accumulated deferred income taxes and tax credits, net 4,782 4,474
Regulatory liabilities 5,953 5,897
Asset retirement obligations 830 822
Other deferred credits and liabilities 535 487
Total deferred credits and other liabilities 12,100 11,680
Commitments and Contingencies
Shareholders’ Equity:    
Common Stock 3 3
Other paid-in capital, principally premium on common stock 7,524 7,513
Retained earnings 4,702 4,604
Accumulated other comprehensive loss (10) (6)
Total shareholders’ equity 12,219 12,114
Noncontrolling Interests 129 129
Total equity 12,348 12,243
TOTAL LIABILITIES AND EQUITY 45,665 44,598
Variable Interest Entity, Primary Beneficiary    
Investments and Other Assets:    
Regulatory Asset 459 465
Current Liabilities:    
Current maturities of long-term debt 17 17
Long-term debt, net 449 448
Union Electric Company    
Current Assets:    
Cash and cash equivalents 7 0
Advances to money pool 0 43
Unbilled revenue 128 170
Miscellaneous accounts receivable 272 33
Inventories 472 514
Current regulatory assets 119 66
Other current assets 85 70
Total current assets 1,363 1,145
Property, Plant, and Equipment, Net 19,228 18,788
Investments and Other Assets:    
Nuclear decommissioning trust fund 1,312 1,342
Regulatory Asset 1,401 1,366
Pension and other postretirement benefits 212 211
Other assets 239 254
Total investments and other assets 3,164 3,173
TOTAL ASSETS 23,755 23,106
Current Liabilities:    
Current maturities of long-term debt 17 17
Short-term debt 629 0
Taxes accrued 77 29
Interest accrued 70 88
Other current liabilities 199 206
Total current liabilities 1,369 1,019
Deferred Credits and Other Liabilities:    
Accumulated deferred income taxes and tax credits, net 2,488 2,217
Regulatory liabilities 3,177 3,176
Asset retirement obligations 826 818
Other deferred credits and liabilities 176 150
Total deferred credits and other liabilities 6,667 6,361
Commitments and Contingencies
Shareholders’ Equity:    
Common Stock 511 511
Other paid-in capital, principally premium on common stock 3,201 3,201
Preferred stock 80 80
Retained earnings 4,198 4,206
Total shareholders’ equity 7,990 7,998
TOTAL LIABILITIES AND EQUITY 23,755 23,106
Union Electric Company | Variable Interest Entity, Primary Beneficiary    
Investments and Other Assets:    
Regulatory Asset 459 465
Current Liabilities:    
Current maturities of long-term debt 17 17
Long-term debt, net 449 448
Union Electric Company | Nonrelated Party    
Current Assets:    
Accounts receivable - trade (less allowance for doubtful accounts) 236 209
Current Liabilities:    
Accounts and wages payable 335 629
Long-term debt, net 7,672 7,671
Union Electric Company | Related Party    
Current Assets:    
Accounts receivable - trade (less allowance for doubtful accounts) 44 40
Current Liabilities:    
Accounts and wages payable 42 50
Long-term debt, net 57 57
Ameren Illinois Company    
Current Assets:    
Cash and cash equivalents 4 0
Unbilled revenue 125 175
Miscellaneous accounts receivable 21 28
Inventories 193 244
Prepaid assets 54 59
Current regulatory assets 208 281
Other current assets 16 8
Total current assets 1,058 1,110
Property, Plant, and Equipment, Net 15,772 15,530
Investments and Other Assets:    
Goodwill 411 411
Regulatory Asset 1,143 1,011
Pension and other postretirement benefits 478 471
Other assets 731 697
Total investments and other assets 2,763 2,590
TOTAL ASSETS 19,593 19,230
Current Liabilities:    
Current maturities of long-term debt 0 300
Short-term debt 189 88
Borrowings from money pool 0 37
Interest accrued 57 59
Customer deposits 187 185
Current regulatory liabilities 89 79
Other current liabilities 159 172
Total current liabilities 1,045 1,318
Deferred Credits and Other Liabilities:    
Accumulated deferred income taxes and tax credits, net 2,193 2,143
Regulatory liabilities 2,625 2,573
Other deferred credits and liabilities 298 273
Total deferred credits and other liabilities 5,116 4,989
Commitments and Contingencies
Shareholders’ Equity:    
Common Stock 0 0
Other paid-in capital, principally premium on common stock 3,056 3,056
Preferred stock 49 49
Retained earnings 4,427 4,266
Total shareholders’ equity 7,532 7,371
TOTAL LIABILITIES AND EQUITY 19,593 19,230
Ameren Illinois Company | Nonrelated Party    
Current Assets:    
Accounts receivable - trade (less allowance for doubtful accounts) 415 300
Current Liabilities:    
Accounts and wages payable 293 324
Long-term debt, net 5,897 5,549
Ameren Illinois Company | Related Party    
Current Assets:    
Accounts receivable - trade (less allowance for doubtful accounts) 22 15
Current Liabilities:    
Accounts and wages payable 71 74
Long-term debt, net $ 3 $ 3
v3.25.1
Consolidated Balance Sheet (Parenthetical) - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Accounts Receivable, Allowance for Credit Loss, Current $ 41 $ 30
Regulatory Asset 2,569 2,397
Current maturities of long-term debt 17 317
Long-term debt, net $ 18,354 $ 17,262
Common stock, par value (in dollars per share) $ 0.01 $ 0.01
Common stock, shares authorized (in shares) 400,000,000.0 400,000,000.0
Common Stock, Shares, Outstanding 270,300,000 269,900,000
Variable Interest Entity, Primary Beneficiary    
Regulatory Asset $ 459 $ 465
Current maturities of long-term debt 17 17
Long-term debt, net 449 448
Union Electric Company    
Accounts Receivable, Allowance for Credit Loss, Current 12 12
Regulatory Asset 1,401 1,366
Current maturities of long-term debt $ 17 $ 17
Common stock, par value (in dollars per share) $ 5 $ 5
Common stock, shares authorized (in shares) 150,000,000.0 150,000,000.0
Common Stock, Shares, Outstanding 102,100,000 102,100,000
Union Electric Company | Variable Interest Entity, Primary Beneficiary    
Regulatory Asset $ 459 $ 465
Current maturities of long-term debt 17 17
Long-term debt, net 449 448
Ameren Illinois Company    
Accounts Receivable, Allowance for Credit Loss, Current 29 18
Regulatory Asset 1,143 1,011
Current maturities of long-term debt $ 0 $ 300
Common stock, no par value (in dollars per share) $ 0 $ 0
Common stock, shares authorized (in shares) 45,000,000.0 45,000,000.0
Common Stock, Shares, Outstanding 25,500,000 25,500,000
v3.25.1
Consolidated Statement of Cash Flows - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Cash Flows From Operating Activities:    
Net income $ 290 $ 262
Adjustments to reconcile net income to net cash provided by operating activities:    
Depreciation and amortization 395 379
Amortization of nuclear fuel 20 18
Amortization of debt issuance costs and premium/discounts 5 5
Deferred income taxes and tax credits, net 116 44
Allowance for equity funds used during construction (16) (9)
Stock-based compensation costs 7 8
Other 7 16
Changes in assets and liabilities:    
Receivables (68) 52
Inventories 93 54
Accounts and wages payable (291) (284)
Taxes accrued (8) 70
Regulatory assets and liabilities (70) (95)
Assets, other 0 15
Liabilities, other (10) 13
Pension and other postretirement benefits (39) (56)
Net cash provided by operating activities 431 492
Cash Flows From Investing Activities:    
Capital expenditures (1,064) (890)
Nuclear fuel expenditures (18) (12)
Purchases of securities – nuclear decommissioning trust fund (107) (70)
Sales and maturities of securities – nuclear decommissioning trust fund 93 66
Other 9 0
Net cash used in investing activities (1,087) (906)
Cash Flows From Financing Activities:    
Dividends on common stock (191) (178)
Dividends paid to noncontrolling interest holders (1) (1)
Short-term debt, net 108 332
Maturities of long-term debt (300) 0
Issuances of long-term debt 1,099 347
Issuances of common stock 13 10
Employee payroll taxes related to stock-based compensation (13) (8)
Debt issuance costs (11) (5)
Net cash provided by financing activities 704 497
Net change in cash, cash equivalents, and restricted cash 48 83
Cash, cash equivalents, and restricted cash at beginning of year 328 272
Cash, cash equivalents, and restricted cash at end of period 376 355
Union Electric Company    
Cash Flows From Operating Activities:    
Net income 43 26
Adjustments to reconcile net income to net cash provided by operating activities:    
Depreciation and amortization 222 212
Amortization of nuclear fuel 20 18
Amortization of debt issuance costs and premium/discounts 2 2
Deferred income taxes and tax credits, net 104 27
Allowance for equity funds used during construction (8) (9)
Other 4 17
Changes in assets and liabilities:    
Receivables 0 43
Inventories 42 9
Accounts and wages payable (250) (222)
Taxes accrued (9) 92
Regulatory assets and liabilities (81) (24)
Assets, other 19 2
Liabilities, other 3 4
Pension and other postretirement benefits (14) (20)
Net cash provided by operating activities 97 177
Cash Flows From Investing Activities:    
Capital expenditures (658) (466)
Nuclear fuel expenditures (18) (12)
Purchases of securities – nuclear decommissioning trust fund (107) (70)
Sales and maturities of securities – nuclear decommissioning trust fund 93 66
Money pool advances, net 43 0
Net cash used in investing activities (647) (482)
Cash Flows From Financing Activities:    
Dividends on common stock (50) 0
Dividends on preferred stock (1) (1)
Short-term debt, net 629 274
Money pool borrowings, net 0 (306)
Issuances of long-term debt 0 347
Debt issuance costs 0 (3)
Net cash provided by financing activities 578 311
Net change in cash, cash equivalents, and restricted cash 28 6
Cash, cash equivalents, and restricted cash at beginning of year 17 10
Cash, cash equivalents, and restricted cash at end of period 45 16
Ameren Illinois Company    
Cash Flows From Operating Activities:    
Net income 236 215
Adjustments to reconcile net income to net cash provided by operating activities:    
Depreciation and amortization 159 153
Amortization of debt issuance costs and premium/discounts 2 1
Deferred income taxes and tax credits, net 29 27
Allowance for equity funds used during construction (7) 0
Other 3 5
Changes in assets and liabilities:    
Receivables (78) 1
Inventories 51 49
Accounts and wages payable (34) (31)
Taxes accrued 0 64
Regulatory assets and liabilities 8 (66)
Assets, other (18) 11
Liabilities, other 8 8
Pension and other postretirement benefits (17) (22)
Net cash provided by operating activities 342 415
Cash Flows From Investing Activities:    
Capital expenditures (363) (373)
Other 0 1
Net cash used in investing activities (363) (372)
Cash Flows From Financing Activities:    
Dividends on common stock (75) 0
Short-term debt, net 101 58
Money pool borrowings, net (37) (81)
Maturities of long-term debt (300) 0
Issuances of long-term debt 350 0
Debt issuance costs (4) 0
Net cash provided by financing activities 35 (23)
Net change in cash, cash equivalents, and restricted cash 14 20
Cash, cash equivalents, and restricted cash at beginning of year 302 234
Cash, cash equivalents, and restricted cash at end of period $ 316 $ 254
v3.25.1
Consolidated Statement of Stockholders' Equity - USD ($)
$ in Millions
Total
Common Stock
Other Paid-in Capital:
Retained Earnings:
Derivative Financial Instruments
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, 2023     $ 7,216 $ 4,136 $ 0 $ (6)     $ 129     $ 2,725   $ 3,647     $ 3,020   $ 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         $ 215        
Net income attributable to Ameren common shareholders 261     261           25         215        
Dividends on common stock       (178)                   0         0
Dividends on preferred stock                           (1)          
Change in derivative financial instruments         0                            
Change in deferred retirement benefit costs (1)         (1)                          
Net income attributable to noncontrolling interest holders $ (1)               1                    
Dividends paid to noncontrolling interest holders                 (1)                    
Common stock shares outstanding at beginning of year at Dec. 31, 2023 266,300,000                                    
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                                    
End of period at Mar. 31, 2024 $ 11,572 $ 3 7,228 4,219 0 (7) $ (7)   129   $ 511   $ 80 3,672   $ 0   $ 49 3,971
Shareholders' equity, end of year at Mar. 31, 2024               $ 11,443   6,988         7,040        
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Dividends per common share $ 0.67                                    
Beginning of year at Dec. 31, 2024 $ 12,243   7,513 4,604 3 (9)     129     $ 3,201   4,206     $ 3,056   4,266
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Shares issued under the DRPlus and 401(k) plan     15                                
Stock-based compensation activity     (4)                                
Net income 290                 43         236        
Net income attributable to Ameren common shareholders 289     289           $ 42         $ 236        
Dividends on common stock       (191)                   (50)         (75)
Dividends on preferred stock                           (1)          
Change in derivative financial instruments         (4)                            
Change in deferred retirement benefit costs 0         0                          
Net income attributable to noncontrolling interest holders $ (1)               1                    
Dividends paid to noncontrolling interest holders                 (1)                    
Common stock shares outstanding at beginning of year at Dec. 31, 2024 269,900,000                 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 300,000                                    
Common stock shares outstanding at end of period at Mar. 31, 2025 270,300,000                 102,100,000         25,500,000        
End of period at Mar. 31, 2025 $ 12,348 $ 3 $ 7,524 $ 4,702 $ (1) $ (9) $ (10)   $ 129   $ 511   $ 80 $ 4,198   $ 0   $ 49 $ 4,427
Shareholders' equity, end of year at Mar. 31, 2025 $ 12,219             $ 12,219   $ 7,990         $ 7,532        
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Dividends per common share $ 0.71                                    
v3.25.1
Summary Of Significant Accounting Policies
 3 Months Ended
Mar. 31, 2025
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 within 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 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 statement of our results. The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. Such estimates and assumptions affect reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of financial statements, and the reported amounts of revenues and expenses during the reported periods. Actual results could differ from those estimates. 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 contained in this Form 10-Q should be read in conjunction with the financial statements and accompanying notes included in the Form 10-K.
Variable Interest Entities
Variable Interest Entities that are Consolidated
AMF was formed in 2024, for the purpose of issuing and servicing securitized utility tariff bonds related to costs for the accelerated retirement of the Rush Island Energy Center. Ameren Missouri is the primary beneficiary of this entity because it has the power to direct the activities that most significantly impact the economic performance of the company, as well as the obligation to absorb losses or the right to receive benefits from the company. The entity is considered a variable interest entity primarily because its equity capitalization is insufficient to support its operations. The entity’s primary assets and liabilities are comprised of regulatory assets related to the unrecovered net plant balance associated with the facility, among other costs, and long-term debt. Ameren and Ameren Missouri consolidate AMF, which Ameren Missouri wholly owns, and both manages and controls the entity’s operating activities. For additional information on the securitization of the Rush Island Energy Center costs, see Note 2 – Rate and Regulatory Matters under Part II, Item 8, of the Form 10-K. For additional information on the securitized tariff bond issuance, see Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, of the Form 10‑K.
The following table presents the carrying values of AMF’s assets and liabilities included on Ameren’s and Ameren Missouri’s consolidated balance sheets as of March 31, 2025 and December 31, 2024:
20252024
Unbilled revenue(a)
$2 $— 
Other current assets(a)
15 2 
Noncurrent regulatory assets(a)
459 465 
Current maturities of long-term debt(b)
17 17 
Interest accrued (b)
6 1 
Current regulatory liabilities(c)
5 — 
Long-term debt, net(b)
449 448 
(a)Assets may be used only to meet AMF’s obligations and commitments.
(b)The securitized tariff bondholders have no recourse to Ameren Missouri.
(c)Included in “Other current liabilities” on Ameren Missouri’s balance sheet.
Variable Interest Entities that are Not Consolidated
As of March 31, 2025, and December 31, 2024, Ameren had unconsolidated variable interests in various equity method investments, primarily to advance clean and resilient energy technologies, totaling $71 million and $74 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, 2025, Ameren’s maximum exposure to loss related to these variable interest entities is limited to the investment in these partnerships of $71 million plus associated outstanding funding commitments of $34 million.
COLI
Ameren (parent) and Ameren Illinois have COLI, which is recorded at the net cash surrender value. The net cash surrender value is the amount that can be realized under the insurance policies at the balance sheet date. As of March 31, 2025, the cash surrender value of COLI at Ameren and Ameren Illinois was $259 million (December 31, 2024 – $260 million) and $120 million (December 31, 2024 – $118 million), respectively, while total borrowings against the policies were $110 million (December 31, 2024 – $110 million) at both Ameren and Ameren Illinois. Ameren and Ameren Illinois have the right to offset the borrowings against the cash surrender value of the policies and, consequently, present the net asset in “Other assets” on their respective balance sheets. The net cash surrender value of Ameren’s COLI is affected by the investment performance of a separate account in which Ameren holds a beneficial interest.
v3.25.1
Rate And Regulatory Matters
 3 Months Ended
Mar. 31, 2025
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
Missouri Senate Bill 4
In April 2025, Missouri Senate Bill 4 was enacted and will become effective in August 2025. The law includes certain provisions that affect the regulation of Ameren Missouri’s electric and natural gas businesses. These provisions create modifications to the PISA and integrated resource planning, allow the MoPSC to authorize inclusion of construction work in progress in rate base for new natural gas-fired generation facilities and new generation facilities approved through integrated resource planning, and allow natural gas utilities to file regulatory rate reviews using a future test year, among other things.
Pursuant to the law, the PISA has been modified to include new natural gas generating units placed in service after the effective date of the law as qualifying property, plant, and equipment eligible for deferral and recovery of 85% of the related depreciation expense. These new natural gas generating units will also be included in the 85% of rate base allowed to earn a return at the applicable WACC under the PISA. The law also reduced the annual limit on increases to the electric service revenue requirement used to set customer rates, compared to the revenue requirement established in the immediately preceding rate order, due to the inclusion of incremental PISA deferrals in the revenue requirement. The annual limit currently in effect is 2.5% and will change to 2.25%, prorated monthly, for revenue requirements approved by
the MoPSC after August 2025. Furthermore, the PISA's effective date has been extended through 2035, unless Ameren Missouri requests and receives MoPSC approval of an extension through 2040.
In addition, the law also made modifications to integrated resource planning, which requires Missouri electric utilities to file plans for meeting their customers' long-term energy needs. By August 2027, the MoPSC will publish a schedule for Missouri electric utilities to file integrated resource plans every four years. The MoPSC will be required to issue an order on the plans and shall determine whether the electric utility has submitted sufficient documentation and selected preferred resource plans representing a reasonable and prudent means of the utility's load serving obligations at just and reasonable rates. In making this determination, the MoPSC shall consider whether the plans appropriately balance specific factors described in the law. If the MoPSC approves the plans, requests for CCNs for new generation facilities to be constructed or acquired as a part of the approved plans shall be deemed necessary and convenient and the scope of the CCN proceedings to review projects will be limited. The approved generation facilities will also be eligible to include construction work in progress in rate base, subject to MoPSC approval, which would improve the timeliness of cash recovery. Utilities are not allowed to capitalize allowance for funds used during construction on amounts included in rate base under this provision. The amount of construction work in progress to be included in rate base is limited to prudently incurred expenditures made within the construction period for the facility.
Further, outside of the integrated resource planning process discussed above, the law allows a Missouri electric utility to request that the MoPSC authorize the inclusion of construction work in progress for new natural gas-fired generation facilities in rate base. Under this provision, utilities are not allowed to capitalize allowance for funds used during construction on projects approved to include construction work in progress in rate base. The amount of construction work in progress to be included in rate base is limited to prudently incurred expenditures made within the construction period for the facility. The provisions allowing for the inclusion of construction work in progress on natural gas-fired generation in rate base expire in December 2035, unless Ameren Missouri requests and receives MoPSC approval of an extension through 2045.
Also, beginning in July 2026 the law allows natural gas utilities to file regulatory rate reviews using a future test year, subject to MoPSC approval. If a natural gas utility is allowed to use a future test year, a reconciliation of the actual rate base and certain forecasted costs will be performed 45 days after the end of the test year. If a given year’s actual revenue requirement is less than the revenue requirement approved by the MoPSC due to changes in rate base or certain other costs, an adjustment is made to reduce natural gas operating revenues with an offset to a regulatory liability to reflect that test year’s amounts. The regulatory liability will then be refunded to customers in the next regulatory rate review and will accrue carrying costs at the applicable WACC.
April 2025 MoPSC Electric Rate Order
In April 2025, the MoPSC issued an order in Ameren Missouri’s 2024 electric service regulatory rate review, approving nonunanimous stipulations and agreements. The order authorizes an increase of $355 million to Ameren Missouri’s annual revenue requirement for electric retail service, effective June 1, 2025. The approved revenue requirement was based on infrastructure investments as of December 31, 2024. The order did not explicitly specify an ROE, capital structure, rate base, or any rate base disallowances. The order provides for the continued use of all existing riders and trackers. The order also changed annualized depreciation, regulatory asset and liability amortization amounts, and the base level of expenses for trackers. On an annualized basis, these changes reflect an increase in “Depreciation and amortization” of approximately $70 million, among other expense changes, on Ameren’s and Ameren Missouri’s consolidated statements of income.
2024 Natural Gas Delivery Service Regulatory Rate Review
In September 2024, Ameren Missouri filed a request with the MoPSC seeking approval to increase its annual revenues for natural gas delivery service. In May 2025, Ameren Missouri filed an updated request seeking approval to increase its annual revenues for natural gas delivery service by $38 million. The natural gas rate increase request is based on a 10.25% ROE, a capital structure composed of 52% common equity, a rate base of $525 million, and a test year ended March 31, 2024, with certain pro-forma adjustments allowed through the true-up date of December 31, 2024. The request includes the continued use of all of Ameren Missouri’s existing riders and trackers. The natural gas rate increase request reflects investments in infrastructure to ensure the safe delivery of natural gas.
In May 2025, the MoPSC staff recommended an increase to Ameren Missouri’s annual revenues for natural gas delivery service of $32 million based on a 9.64% ROE, a capital structure composed of 52% common equity as of the true-up date of December 31, 2024, and a rate base of $482 million. The MoPSC staff supported the continued use of all of Ameren Missouri’s existing riders and trackers.
The MoPSC proceeding relating to the proposed natural gas delivery service rate changes will take place over 11 months, with a decision by the MoPSC expected by August 2025 and new rates effective by September 2025. Ameren Missouri cannot predict the level of any natural gas delivery service rate change the MoPSC may approve, whether the requested regulatory recovery mechanisms will be continued, or whether any rate change that may eventually be approved will be sufficient for Ameren Missouri to recover its costs and earn a reasonable return on its investments when the rate change goes into effect.
Generation Facilities
Ameren Missouri, and certain subsidiaries of Ameren Missouri, are parties to agreements to acquire and/or construct various generation facilities. The solar generation facilities are eligible for recovery under the PISA. The Castle Bluff Natural Gas Project is also eligible for recovery under the PISA pursuant to Missouri Senate Bill 4 discussed above. The following table provides information with respect to each agreement:
Agreement typeFacility sizeStatus of MoPSC CCNStatus of FERC approval of acquisition
In-service date(a)
Vandalia Solar Project(b)(c)
Self-build
50-MW
Approved March 2024Not applicableFourth quarter 2025
Bowling Green Solar Project(b)(c)
Self-build
50-MW
Approved March 2024Not applicableFirst quarter 2026
Split Rail Solar Project(b)(c)
Build-transfer
300-MW
Approved March 2024Received November 2024Mid-2026
Castle Bluff Natural Gas Project(b)
Self-build
800-MW
Approved October 2024Not applicableFourth quarter 2027
(a)In-service dates are dependent on the timing of construction completion, among other things.
(b)These projects collectively represent approximately $1.7 billion of capital expenditures.
(c)These solar projects are expected to support Ameren Missouri’s transition to renewable energy generation.
MISO Long-Range Transmission Projects CCN
In 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 or awarded via a competitive bid process to various utilities, including Ameren. In 2024, ATXI filed requests for CCNs, among other things, with the MoPSC related to the MISO long-range transmission projects that it expects to construct within the MoPSC’s jurisdiction. Decisions by the MoPSC are expected in 2025.
Illinois
MYRP
In December 2024, the ICC issued an order in connection with a revised Grid Plan and a revised MYRP filed by Ameren Illinois in March 2024, approving revenue requirements for electric distribution services for 2024 through 2027 of $1,206 million, $1,287 million, $1,367 million, and $1,421 million, respectively. Using the 2023 revenue requirement as a starting point, the approved revenue requirements in the ICC’s December 2024 order represent a cumulative four-year increase of $308 million. Rate changes consistent with the December 2024 order became effective in December 2024. In January 2025, Ameren Illinois filed a request for rehearing of the ICC’s December 2024 order to revise the allowed ROE and to include an asset associated with other postretirement benefits in the rate base, among other things. Subsequently, in February 2025, the ICC denied the rehearing request. In March 2025, Ameren Illinois filed an appeal of the ICC’s December 2024 order to the Illinois Appellate Court for the Fifth Judicial District. In addition, Ameren Illinois filed an appeal related to orders issued by the ICC in December 2023 and June 2024 related to the MYRP proceeding. The appellate court is under no deadline to address the appeals, and Ameren Illinois cannot predict the ultimate outcome of the appeals.
2024 Electric Distribution Service Revenue Requirement Reconciliation Adjustment
In April 2025, Ameren Illinois filed a reconciliation adjustment to its 2024 electric distribution service revenue requirement with the ICC, requesting recovery of $61 million. The adjustment reflects Ameren Illinois’ actual 2024 recoverable costs, 2024 year-end rate base, and a capital structure composed of 50% common equity. An ICC decision in this proceeding is required by December 2025, and any approved adjustment would be collected from customers in 2026.
Electric Energy Efficiency Plan
In February 2025, Ameren Illinois filed an energy-efficiency plan with the ICC, which includes annual investments in electric energy-efficiency programs up to $126 million per year from 2026 through 2029. The ICC has the ability to reduce the amount of electric energy-efficiency savings goals in future program years if there are insufficient cost-effective programs available, which could reduce the investments in electric energy-efficiency programs. A decision by the ICC in this proceeding is expected by September 2025.
2025 Natural Gas Delivery Service Rate Review
In January 2025, Ameren Illinois filed a request with the ICC seeking approval to increase its annual revenues for natural gas delivery service by $140 million. The request is based on a 10.7% ROE, a capital structure composed of 52% common equity, and a rate base of $3.3 billion. Ameren Illinois used a 2026 future test year in this proceeding. A decision by the ICC in this proceeding is required by early
December 2025, with new rates expected to be effective in December 2025. Ameren Illinois cannot predict the level of any delivery service rate change the ICC may approve, nor whether any rate change that may eventually be approved will be sufficient to enable Ameren Illinois to recover its costs and to earn a reasonable return on investments when the rate changes go into effect.
MISO Long-Range Transmission Projects CCN
In 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 or awarded via a competitive bidding process to various utilities, including Ameren. In 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 they will construct within the ICC’s jurisdiction. A decision by the ICC is expected by mid-2025.
Federal
MISO Transmission Rate Incentives
In 2024, the MISO approved a first set of second tranche projects related to its preliminary long-range transmission planning roadmap of projects through 2039. A portion of these projects were assigned to Ameren and are estimated to cost approximately $1.3 billion, based on the MISO’s cost estimate. In May 2025, the MISO and Ameren Services, on behalf of Ameren Missouri, Ameren Illinois, and ATXI, filed a request with the FERC to allow transmission rate incentives relating to the second tranche projects assigned to Ameren. If approved by the FERC, the incentives would allow construction work in progress to be included in rate base for projects constructed by ATXI, thereby improving the timeliness of cash recovery, and would allow recovery of prudently incurred costs, subject to FERC approval, for any portion of the projects if they are abandoned for reasons beyond the control of Ameren. If approved, ATXI would not capitalize allowance for funds used during construction on the related projects. A decision by the FERC is expected by the end of 2025.
FERC ROE 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 October 2024, the FERC issued an order, which decreased the allowed base ROE from 10.02% to 9.98% and required refunds, with interest, for the periods from November 2013 to February 2015 and from late September 2016 forward. In November 2024, the MISO transmission owners, including Ameren Missouri, Ameren Illinois, and ATXI, filed a request for rehearing with the FERC, arguing, among other things, the FERC should not have ordered refunds back to September 2016 or imposed interest on those refunds. Also in November 2024, another intervenor filed a request for rehearing with the FERC, requesting the FERC correct aspects of the ROE methodology used in the October 2024 order and reconsider its decision in a February 2015 complaint case to deny refunds for the period from February 2015 to May 2016. In January 2025, the MISO transmission owners, including Ameren Missouri, Ameren Illinois, and ATXI, filed an appeal of the October 2024 order to the United States Court of Appeals for the District of Columbia Circuit. In March 2025, the FERC issued an order rejecting all rehearing requests. In April 2025, the MISO transmission owners, including Ameren Missouri, Ameren Illinois, and ATXI, filed an appeal of the March 2025 order to the United States Court of Appeals for the District of Columbia Circuit.
As of March 31, 2025, Ameren and Ameren Illinois had recorded liabilities in "Current regulatory liabilities" on their balance sheets of $11 million and $7 million, respectively, to reflect the expected refunds, including interest, associated with the allowed base ROE set by the October 2024 order.
v3.25.1
Short-Term Debt And Liquidity
 3 Months Ended
Mar. 31, 2025
Debt Disclosure [Abstract]  
SHORT-TERM DEBT AND LIQUIDITY SHORT-TERM DEBT AND LIQUIDITY
The liquidity needs of the Ameren Companies are 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, of 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 to support the issuance of letters of credit. As of March 31, 2025, based on commercial paper outstanding and letters of credit issued under the Credit Agreements, along with cash and cash equivalents, the net liquidity available to Ameren (parent), Ameren Missouri, and Ameren Illinois, collectively, was $1.3 billion. The Ameren Companies were in compliance with the covenants in their Credit Agreements as of March 31, 2025. As of March 31, 2025, the ratios of consolidated indebtedness to consolidated total capitalization, calculated in accordance with the provisions of the Credit Agreements, were 61%, 50%, 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, 2025, and December 31, 2024. There were no borrowings outstanding under the Credit Agreements as of March 31, 2025, or December 31, 2024.
March 31, 2025December 31, 2024
Ameren (parent)$434 $1,055 
Ameren Missouri629 — 
Ameren Illinois189 88 
Ameren consolidated$1,252 $1,143 
The following table summarizes the activity and relevant interest rates for Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper issuances under the Credit Agreements for the three months ended March 31, 2025 and 2024:
Ameren
(parent)		Ameren
Missouri		Ameren
Illinois		Ameren
Consolidated
2025
Average daily amount outstanding$898 $313 $82 $1,293 
Weighted-average interest rate4.61 %4.59 %4.56 %4.60 %
Peak amount outstanding during period(a)
$1,139 $630 $189 $1,603 
Peak interest rate4.75 %4.70 %4.69 %4.75 %
2024
Average daily amount outstanding$— $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 %
(a)The timing of peak outstanding commercial paper issuances 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, 2025, was 4.52% (2024 – 5.32%). 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, 2025 and 2024.
v3.25.1
Long-Term Debt And Equity Financings
 3 Months Ended
Mar. 31, 2025
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, 2025, Ameren issued a total of 0.1 million shares of common stock, under its DRPlus and 401(k) plan, and received proceeds of $6 million. As of March 31, 2025, Ameren had a receivable of $9 million related to issuances of common stock under its DRPlus and 401(k) plan. In addition, in the first quarter of 2025, Ameren issued 0.3 million shares of common stock valued at $25 million upon the settlement of stock-based compensation awards.
There were no shares issued under the ATM program during the three months ended March 31, 2025. As of March 31, 2025, Ameren had approximately $230 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, 2025, discussed below.
The forward sale agreements outstanding as of March 31, 2025, can be settled at Ameren’s discretion on or prior to dates ranging from January 23, 2026 to March 6, 2026. On a settlement date or dates, if Ameren elects to physically settle a forward sale agreement, Ameren will issue shares of common stock to the counterparties at the then-applicable forward sale price. The initial forward sale price for the agreements ranged from $81.00 to $98.66, with an average initial forward sale price of $91.02. 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 or more than the spread on any day, the interest rate factor will result in a reduction or an increase, respectively, 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, 2025, Ameren could have settled the forward sale agreements with physical delivery of 5.8 million shares of common stock to the respective counterparties in exchange for cash of $530 million. Alternatively, the forward sale agreements could have also been settled at March 31, 2025, with delivery of approximately $55 million of cash or approximately 0.6 million shares of common stock to the counterparties. In connection with the forward sale agreements outstanding at March 31, 2025, the various counterparties, or their affiliates, borrowed from third parties and sold 5.8 million shares of common stock. The gross sales price of these shares totaled $535 million. Ameren does not receive any proceeds from such sales of borrowed shares. The forward sale agreements have been classified as equity transactions.
In March 2025, Ameren (parent) issued $750 million of 5.375% senior unsecured notes due March 2035, with interest payable semiannually on March 15 and September 15 of each year, beginning September 15, 2025. Net proceeds from this issuance were used for general corporate purposes, including the repayment of short-term debt.
Ameren Missouri
In April 2025, Ameren Missouri issued $500 million of 5.25% first mortgage bonds due April 2035, with interest payable semiannually on April 15 and October 15 of each year, beginning October 15, 2025. Net proceeds from this issuance were used to repay short-term debt.
Ameren Illinois
In March 2025, Ameren Illinois issued $350 million of 5.625% first mortgage bonds due March 2055, with interest payable semiannually on March 1 and September 1 of each year, beginning September 1, 2025. Net proceeds from this issuance were used to repay $300 million principal amount of its 3.25% senior secured notes that matured in March 2025 and short-term debt.
Indenture Provisions and Other Covenants
See Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, of 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, 2025, 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, 2025, none of the Ameren Companies had any material off-balance-sheet financing arrangements, other than their investment in unconsolidated variable interest entities, letters of credit, 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.
v3.25.1
Other Income, Net
 3 Months Ended
Mar. 31, 2025
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, 2025 and 2024:
Three Months
20252024
Ameren:
Allowance for equity funds used during construction
$16 $9 
Other interest income
11 8 
Non-service cost components of net periodic benefit income(a)
66 76 
Miscellaneous income
3 2 
Earnings (losses) related to equity method investments(4)— 
Donations
(2)(2)
Miscellaneous expense
(5)(4)
Total Other Income, Net$85 $89 
Ameren Missouri:
Allowance for equity funds used during construction
$8 $9 
Other interest income
2 2 
Non-service cost components of net periodic benefit income(a)
35 35 
Miscellaneous income
1 1 
Donations
(1)(1)
Miscellaneous expense
(2)(2)
Total Other Income, Net$43 $44 
Ameren Illinois:
Allowance for equity funds used during construction
$7 $— 
Other interest income9 6 
Non-service cost components of net periodic benefit income
20 27 
Miscellaneous income
2 1 
Donations
(1)(1)
Miscellaneous expense(3)(2)
Total Other Income, Net$34 $31 
(a)For the three months ended March 31, 2025 and 2024, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $(16) million and $(9) 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.
v3.25.1
Derivative Financial Instruments
 3 Months Ended
Mar. 31, 2025
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 interest rates, 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 inventories that differ from the cost of this commodity in inventory;
•actual cash outlays for interest expense and the purchase of 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, 2025, and December 31, 2024, all commodity contracts that met the definition of a derivative and were not eligible for the NPNS exception received regulatory deferral. Interest rate hedges discussed below do not receive regulatory deferral and were included in accumulated OCI. The cash flows from our derivative financial instruments follow the cash flow classification of the hedged item.
Starting in 2024, Ameren (parent) entered into interest rate swaps to hedge a portion of its interest rate risk on cash flows related to forecasted debt issuances through 2026. The interest rate swaps are designated as cash flow hedges and the corresponding changes in fair value each period are initially recorded on the balance sheet in “Accumulated other comprehensive loss” and reclassified into earnings when the debt is issued and the corresponding interest payments affect earnings during the debt term. As of March 31, 2025, and December 31, 2024, Ameren had interest rate swaps with notional amounts of $280 million and $140 million respectively. Ameren recorded an unrealized net loss on the change in fair value of interest rate swaps of $4 million to "Accumulated other comprehensive loss" for the period ending March 31, 2025.
The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of March 31, 2025, and December 31, 2024. As of March 31, 2025, these contracts extended through October 2028, October 2030 and May 2032 for fuel oils, natural gas, and power, respectively.
Quantity (in millions, except as indicated)
March 31, 2025December 31, 2024
CommodityAmeren MissouriAmeren IllinoisAmerenAmeren MissouriAmeren IllinoisAmeren
Fuel oils (in gallons)24 — 24 23 — 23 
Natural gas (in mmbtu)47 221 268 45 213 258 
Power (in MWhs)— 4 4 — 4 4 
The following table presents the carrying value and balance sheet location of all derivative commodity contracts, none of which were designated as hedging instruments because all qualify for regulatory deferral, as of March 31, 2025, and December 31, 2024:
March 31, 2025December 31, 2024
Balance Sheet LocationAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois		Ameren
Natural gasOther current assets4 11 15 2 2 4 
Other assets2 5 7 2 4 6 
PowerOther current assets5 — 5 6 — 6 
Total assets$11 $16 $27 $10 $6 $16 
Fuel oilsOther current liabilities$2 $— $2 $2 $— $2 
Other deferred credits and liabilities1 — 1 2 — 2 
Natural gasOther current liabilities2 6 8 5 22 27 
Other deferred credits and liabilities7 14 21 6 13 19 
PowerOther current liabilities— 7 7 — 10 10 
Other deferred credits and liabilities— 60 60 — 43 43 
Total liabilities$12 $87 $99 $15 $88 $103 
The Ameren Companies elect to present the fair value amounts of derivative assets and derivative liabilities subject to an enforceable master netting arrangement or similar agreement at the gross amounts on the balance sheet. However, if the gross amounts recognized on the balance sheet were netted with derivative instruments and cash collateral received or posted, the net amounts would not be materially different from the gross amounts at March 31, 2025, and December 31, 2024.
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, 2025, 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. As of March 31, 2025, the aggregate fair value of 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 were each immaterial to Ameren, Ameren Missouri, and Ameren Illinois.
v3.25.1
Fair Value Measurements
 3 Months Ended
Mar. 31, 2025
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, 2025 or 2024. At March 31, 2025, and December 31, 2024, 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, 2025, and December 31, 2024:
March 31, 2025December 31, 2024
Level 1Level 2Level 3TotalLevel 1Level 2Level 3Total
Assets:
Ameren Missouri
Derivative assets – commodity contracts:
Natural gas— 5 1 6 — 4 — 4 
Power— — 5 5 — — 6 6 
Total derivative assets – commodity contracts$— $5 $6 $11 $— $4 $6 $10 
Nuclear decommissioning trust fund:
Equity securities:
U.S. large capitalization$868 $— $— $868 $911 $— $— $911 
Debt securities:
U.S. Treasury and agency securities— 188 — 188 — 191 — 191 
Corporate bonds— 156 — 156 — 145 — 145 
Other— 92 — 92 — 86 — 86 
Total nuclear decommissioning trust fund$868 $436 $— $1,304 
(a) 
$911 $422 $— $1,333 
(a) 
Total Ameren Missouri$868 $441 $6 $1,315 $911 $426 $6 $1,343 
Ameren Illinois
Derivative assets – commodity contracts:
Natural gas$2 $9 $5 $16 $— $3 $3 $6 
Total Ameren Illinois$2 $9 $5 $16 $— $3 $3 $6 
Ameren
Derivative assets – commodity contracts(b)
$2 $14 $11 $27 $— $7 $9 $16 
Nuclear decommissioning trust fund(c)
868 436 — 1,304 
(a) 
911 422 — 1,333 
(a) 
Total Ameren$870 $450 $11 $1,331 $911 $429 $9 $1,349 
Liabilities:
Ameren Missouri
Derivative liabilities – commodity contracts:
Fuel oils$3 $— $— $3 $4 $— $— $4 
Natural gas— 8 1 9 — 11 — 11 
Total Ameren Missouri$3 $8 $1 $12 $4 $11 $— $15 
March 31, 2025December 31, 2024
Level 1Level 2Level 3TotalLevel 1Level 2Level 3Total
Ameren Illinois
Derivative liabilities – commodity contracts:
Natural gas$— $17 $3 $20 $1 $28 $6 $35 
Power— — 67 67 — — 53 53 
Total Ameren Illinois$— $17 $70 $87 $1 $28 $59 $88 
Ameren
Derivative liabilities – commodity contracts(b)
$3 $25 $71 $99 $5 $39 $59 $103 
(a)Balance excludes $8 million and $9 million of cash and cash equivalents, receivables, payables, and accrued income, net, for March 31, 2025, and December 31, 2024, 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 and natural gas 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, 2025 and 2024:
20252024
Ameren MissouriAmeren IllinoisAmerenAmeren MissouriAmeren IllinoisAmeren
For the three months ended March 31:
Beginning balance at January 1$6 $(53)$(47)$4 $(68)$(64)
Realized and unrealized gains/(losses) included in regulatory assets/liabilities2 (16)(14)(1)10 9 
Settlements(3)2 (1)(1)4 3 
Ending balance at March 31
$5 $(67)$(62)$2 $(54)$(52)
Change in unrealized gains/(losses) related to assets/liabilities held at March 31
$2 $(16)$(14)$— $11 $11 
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, 2025, and December 31, 2024:
Fair Value
Weighted Average(b)
CommodityAssetsLiabilitiesValuation Technique(s)
Unobservable Input(a)
Range
2025
Power(c)
$5$(67)Discounted cash flow
Average forward peak and off-peak pricing – forwards/swaps ($/MWh)
32 – 65
41
Nodal basis ($/MWh)
(8) – (2)
(5)
2024
Power(c)
$6$(53)Discounted cash flowAverage forward peak and off-peak pricing – forwards/swaps ($/MWh)
32 – 69
45
Nodal basis ($/MWh)
(8) – (2)
(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, 2025, and December 31, 2024:
Long-Term Debt (Including Current Portion):
Carrying
Amount(a)
Fair Value
Level 2Level 3Total
March 31, 2025
Ameren(b)
$18,371 $16,277 $547 
(c) 
$16,824 
Ameren Missouri(d)
7,746 6,963 — 6,963 
Ameren Illinois(d)
5,900 5,310 — 5,310 
December 31, 2024
Ameren(b)
$17,579 $15,395 $538 
(c) 
$15,933 
Ameren Missouri(d)
7,745 6,926 — 6,926 
Ameren Illinois(d)
5,852 5,243 — 5,243 
(a)Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $133 million, $61 million, and $54 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of March 31, 2025. Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $129 million, $62 million, and $51 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2024.
(b)Amount excludes Ameren (parent)’s repurchase of Ameren Missouri’s senior secured notes and first mortgage bonds and Ameren Illinois’ first mortgage bonds in 2024.
(c)The Level 3 fair value amount consists of ATXI’s senior unsecured notes.
(d)Amount includes Ameren Missouri’s senior secured notes and first mortgage bonds and Ameren Illinois’ first mortgage bonds that were repurchased by Ameren (parent) in 2024.
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.
v3.25.1
Related Party Transactions
 3 Months Ended
Mar. 31, 2025
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 $27 million and $30 million, respectively, as of March 31, 2025, and $29 million and $32 million, respectively, as of December 31, 2024, related to Ameren Services’ allocated portion of Ameren’s pension and postretirement benefit plans.
Tax Allocation Agreement
See Note 1 – Summary of Significant Accounting Policies under Part II, Item 8, of the Form 10-K for a discussion of the tax allocation agreement. The following table presents the affiliate balances related to income taxes for Ameren Missouri and Ameren Illinois as of March 31, 2025, and December 31, 2024:
March 31, 2025December 31, 2024
Ameren MissouriAmeren IllinoisAmeren MissouriAmeren Illinois
Income taxes payable to parent(a)
$—$32$—$32
Income taxes receivable from parent(b)
29—28—
(a)Included in “Accounts payable – affiliates” on the balance sheet.
(b)Included in “Accounts receivable – affiliates” on the balance sheet.
Effects of Related-party Transactions on the Statement of Income
The following table presents the impact on Ameren Missouri and Ameren Illinois of related-party transactions for the three months ended March 31, 2025 and 2024:
Three Months
AgreementIncome Statement
Line Item		Ameren
Missouri		Ameren
Illinois
Ameren Missouri power supplyOperating Revenues2025$(a)$(a)
agreements with Ameren Illinois
2024(b)(a)
Ameren Missouri and Ameren IllinoisOperating Revenues2025$7 $(b)
rent and facility services
20247 (b)
Ameren Missouri and Ameren Illinois miscellaneousOperating Revenues2025$(b)$2 
support services2024(b)1 
Total Operating Revenues2025$7 $2 
20247 1 
Ameren Illinois power supplyPurchased Power2025$(a)$(a)
agreements with Ameren Missouri
2024(a)(b)
Ameren Missouri and Ameren IllinoisPurchased Power2025$3 $(b)
transmission services from ATXI20242 (b)
Total Purchased Power2025$3 $(b)
20242 (b)
Ameren Missouri and Ameren IllinoisOther Operations and Maintenance2025$(b)$1 
rent and facility services
2024(b)(b)
Ameren Services support servicesOther Operations and Maintenance2025$44 $40 
agreement
202438 37 
Total Other Operations and2025$44 $41 
Maintenance202438 37 
Money pool interest(Interest Charges)/Other Income, Net2025$(b)$(b)
2024(3)(2)
Long-term debt, net - related parties(Interest Charges)2025(b)(b)
2024— — 
(a)Not applicable.
(b)Amount less than $1 million.
v3.25.1
Commitments And Contingencies
 3 Months Ended
Mar. 31, 2025
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 regulate air emissions; protect water bodies; manage the 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.
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 and natural gas-fired energy centers. Compliance obligations under the Clean Air Act include
the NSPS, the MATS, emission allowance programs and the CSAPR, and the National Ambient Air Quality Standards, which are subject to periodic review for certain pollutants. Collectively, these regulations cover a variety of pollutants, such as SO2, particulate matter, NOx, mercury, toxic metals and acid gases, and CO2 emissions. Regulations implementing the Clean Water Act govern potential impacts from our operations on water bodies including wetlands subject to the Act, as well as evaluation of the ecological and biological impact of those operations. Implementation of the Clean Air Act and the Clean Water Act requirements typically occurs through the issuance of permits by state regulators or resource agencies, and capital expenditures associated with compliance could be significant. Coal-fired energy centers must comply with management and disposal requirements for coal ash under the Resource Conservation and Recovery Act and federal regulations known as the CCR Rule. Surface impoundments at Ameren Missouri’s coal-fired energy centers are subject to closure and groundwater monitoring requirements and the implementations of corrective measures if necessary. 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 Energy Center curtailed nighttime operations from April through October to limit impacts on protected species during the critical biological season. The extent and duration of future curtailments are 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 may need to make capital expenditures of $900 million to $1 billion from 2025 through 2029 to comply with environmental regulations and additional capital expenditures beyond 2029 could be required. These estimates include capital expenditures that may be necessary to comply with regulations issued by the EPA in 2024 relating to CO2 emissions and MATS discussed below, assuming these regulations are not revised. This estimate of capital expenditures also includes surface impoundment closure and corrective action measures required by the 2015 CCR Rule and modifications to cooling water intake structures at existing power plants under Clean Water Act rules in place prior to 2024, all of which are discussed below. Congress and the EPA could review and revise compliance requirements. In addition to planned retirements of coal-fired energy centers that were included in Ameren Missouri’s 2025 Change to the 2023 PRP and with respect to the 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. Accordingly, 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 their timing, and varying cost of potential compliance strategies, among other things.
The following sections describe the significant environmental statutes and regulations and environmental enforcement and remediation matters that affect or could affect our operations. The EPA could ultimately revise all or part of such regulations.
Clean Air Act
Federal and state laws, including the CSAPR, regulate emissions of SO2 and NOx through the reduction of emissions at their source and the use and retirement of emission allowances available for state budgets. In April 2022, the EPA proposed the Good Neighbor Rule, which includes additional NOx emission reductions from power plants through revisions to the CSAPR and in January 2023, the EPA rejected Missouri’s proposed state implementation plan for addressing the transport of ozone under that rule. The EPA’s disapproval of states’ implementation plans and adoption of a federal implementation plan resulted in litigation in multiple appellate courts including the United States Court of Appeals for the Eighth Circuit and the United States Supreme Court. In February 2025, the EPA requested that the appellate courts suspend the Good Neighbor Rule cases indefinitely and indicated it was reviewing the basis for the disapproval of the state implementation plans, including Missouri’s. In February and April 2025, the appellate courts granted the EPA’s requests to suspend the Good Neighbor Rule cases. Ameren Missouri complies with the current CSAPR requirements by minimizing emissions with low-sulfur coal, operation of two scrubbers at its Sioux Energy Center, and optimization of existing NOx air pollution control equipment. Reducing the amount of state budget NOx allowances for compliance with NOx emission limits could result in the need for additional controls on Ameren Missouri’s generating units and/or the reduction of operations. Any costs for compliance are expected to be recovered from customers, subject to MoPSC prudence review, through the FAC or higher base rates.
CO2 Emissions Standards
In April 2024, the EPA issued a final rule that sets CO2 emission standards for existing coal-fired and new natural gas-fired power plants based on the emissions expected from 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. Affected power plants are required to comply with the rule through a phased-in approach or retire. Compliance with the new rule could be required as early as 2030 for certain existing coal-fired power plants and
2032 for certain new natural gas-fired power plants. Litigation regarding the rule has been stayed, and the EPA has indicated it intends to reconsider the rule and issue a proposed rule by mid-2025, followed by a final rule by the end of 2025. Ameren and Ameren Missouri estimate capital expenditures of approximately $580 million may be necessary to comply with the final rule assuming it is not revised or overturned. Ameren and Ameren Missouri are monitoring the ongoing legal challenges and regulatory developments but, at this time, cannot predict the final impacts of the final rule 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, as well as requiring the use of continuous emissions monitoring systems. In April 2025, the EPA granted Ameren Missouri a two-year extension of the compliance deadline for the Labadie and Sioux energy centers, which is now set for July 2029. Litigation regarding the revised rule has been stayed, and the EPA has indicated it intends to reconsider the revised rule. Ameren and Ameren Missouri estimate capital expenditures of approximately $320 million may be necessary to comply with the April 2024 rule assuming it is not revised. Ameren and Ameren Missouri are monitoring the ongoing legal challenges and regulatory developments but, at this time, cannot predict the final impacts of the final rule on their results of operations, financial position, and liquidity.
NSPS
In November 2024, the EPA issued a proposed rule revising the NSPS to limit emissions of NOx from natural gas-fired stationary CTs. If adopted as proposed, the rule would require such natural gas facilities which began construction after December 13, 2024, to install certain pollution control equipment to limit emissions of NOx. In addition, the EPA proposed to maintain the current limits for SO2 at such natural gas facilities. Ameren and Ameren Missouri cannot predict the potential impacts of any such rule on their results of operations, financial position, and liquidity until a final rule is adopted.
Clean Water Act
All of Ameren Missouri’s coal-fired and nuclear energy centers are subject to Clean Water Act requirements to 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. Cooling water intake requirements 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.
CCR Management
The EPA’s 2015 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. 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 and disposal units not previously included in the 2015 CCR Rule. Ameren and Ameren Missouri have AROs of $46 million associated with CCR storage facilities recorded on their respective balance sheets as of March 31, 2025. This amount includes an immaterial incremental ARO related to the 2024 CCR Rule, which may be revised as additional site studies are performed. The EPA could reconsider aspects of the 2015 and 2024 CCR rules. Ameren and Ameren Missouri are monitoring the ongoing legal challenges and regulatory developments but, at this time, cannot predict the final impacts of the 2024 CCR Rule 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, 2025, 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 $47 million to $91 million. Ameren and Ameren Illinois recorded a liability of $47 million to represent the estimated minimum obligation for these sites, as no other amount within the range was a better estimate. Ameren and Ameren Illinois cannot estimate the completion dates 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. Such historical practices may result in future environmental commitments, including additional or more stringent cleanup standards. We are unable to determine whether such historical practices will affect our results of operations, financial position, or liquidity.
v3.25.1
Callaway Energy Center
 3 Months Ended
Mar. 31, 2025
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. In February 2025, Ameren Missouri and the MoPSC Staff entered into a non-unanimous stipulation and agreement to reduce annual customer contributions for funding the Callaway Energy Center decommissioning costs from $7 million to zero, as the trust fund level exceeded the estimated future decommissioning costs at the time of the agreement. The remaining intervenors did not object to reducing the customer contributions to zero. A decision by the MoPSC on the stipulation and agreement is expected in May 2025. 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, 2025:
Type and Source of CoverageMost Recent
Renewal Date		Maximum CoveragesMaximum Assessments
for Single Incidents
Public liability and nuclear worker liability:
American Nuclear InsurersJanuary 1, 2025$500 $— 
Pool participation(a)15,763 
(a) 
166 
(b) 
$16,263 
(c) 
$166 
Property damage:
NEIL and EMANIApril 1, 2025$3,200 
(d)
$22 
(e) 
Accidental outage:
NEILApril 1, 2025$490 
(f) 
$9 
(e) 
(a)Provided through mandatory participation in an industrywide retrospective premium assessment program. The maximum coverage available is dependent on the number of United States commercial reactors participating in the program.
(b)Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $500 million in the event of an incident at any licensed United States commercial reactor, payable at $25 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 retrospective 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.
v3.25.1
Retirement Benefits
 3 Months Ended
Mar. 31, 2025
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, 2025 and 2024:
Pension BenefitsPostretirement Benefits
Three MonthsThree Months
2025202420252024
Service cost(a)
$21 $21 $2 $3 
Non-service cost components:
Interest cost58 55 11 11 
Expected return on plan assets(b)
(76)(82)(23)(23)
Amortization of(b):
Prior service cost (credit)— — (1)(1)
Actuarial (gain)(10)(17)(9)(10)
Total non-service cost components(c)
$(28)$(44)$(22)$(23)
Net periodic benefit income(d)
$(7)$(23)$(20)$(20)
(a)Service cost, net of capitalization, is reflected in “Operating Expenses – Other operations and maintenance” on Ameren’s statement of income.
(b)Prior service cost (credit) 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 customer 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, 2025 and 2024:
Pension BenefitsPostretirement Benefits
Three MonthsThree Months
2025202420252024
Ameren Missouri(a)
$(4)$(12)$(7)$(7)
Ameren Illinois(2)(9)(13)(13)
Other(1)(2)— — 
Ameren(a)
$(7)$(23)$(20)$(20)
(a)Does not include the impact of the tracker for the difference between the level of pension and postretirement benefit costs (income) incurred by Ameren Missouri under GAAP and the level of such costs included in customer rates.
v3.25.1
Income Taxes
 3 Months Ended
Mar. 31, 2025
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, 2025 and 2024:
AmerenAmeren MissouriAmeren Illinois
202520242025202420252024
Three Months
Federal statutory corporate income tax rate21 %21 %21 %21 %21 %21 %
Increases (decreases) from:
Amortization of excess deferred taxes(a)
(7)(8)

(8)(12)

(3)(4)
Amortization of deferred investment tax credit(1)— (1)— — — 
Renewable and other tax credits(b)
(4)(4)(7)(8)— — 
State tax6 6 4 4 7 7 
Depreciation differences(1)(1)(1)(1)(1)— 
Stock-based compensation— 1 — — — — 
Other permanent items— (1)— — — — 
Effective income tax rate14 %14 %8 %4 %24 %24 %
(a)Reflects the amortization of amounts resulting from the revaluation of deferred income taxes subject to regulatory ratemaking, which are being refunded to customers.
(b)The benefit of the credits associated with Missouri renewable energy standard compliance is refunded to customers through the RESRAM. The benefit of the credits associated with the production and investment tax credit tracker will be refunded to customers based on MoPSC approval in a regulatory rate review.
v3.25.1
Supplemental Information
 3 Months Ended
Mar. 31, 2025
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, 2025, and December 31, 2024:
March 31, 2025December 31, 2024
AmerenAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois
“Cash and cash equivalents”$23 $7 $4 $7 $— $— 
Restricted cash included in “Other current assets”40 32 5 15 7 6 
Restricted cash included in “Other assets”307 — 307 296 — 296 
Restricted cash included in “Nuclear decommissioning trust fund”6 6 — 10 10 — 
Total cash, cash equivalents, and restricted cash$376 $45 $316 $328 $17 $302 
Restricted cash included in “Other current assets” represents funds held by an irrevocable Voluntary Employee Beneficiary Association (VEBA) trust, which provides health care benefits for active employees on Ameren’s, Ameren Missouri’s, and Ameren Illinois’ balance sheets, funds held in an escrow account for programs established as a result of a 2024 court order resolving outstanding claims in the NSR and Clean Air Act litigation on Ameren’s and Ameren Missouri’s balance sheets, and AMF’s restricted cash for payments for securitized utility tariff bonds on Ameren’s and Ameren Missouri’s balance sheets. 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, 2025, and December 31, 2024, “Other current liabilities” on Ameren’s and Ameren Illinois’ balance sheets included payables for purchased receivables of $47 million and $43 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, 2025 and 2024:
Three Months
20252024
Ameren:
Beginning of period$30 $30 
Bad debt expense16 10 
Charged to other accounts(a)
1 3 
Net write-offs(6)(6)
End of period$41 $37 
Ameren Missouri:
Beginning of period$12 $12 
Bad debt expense2 1 
Net write-offs(2)(2)
End of period$12 $11 
Ameren Illinois:(b)
Beginning of period$18 $18 
Bad debt expense14 9 
Charged to other accounts(a)
1 3 
Net write-offs(4)(4)
End of period$29 $26 
(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, 2025 and 2024:
March 31, 2025March 31, 2024
AmerenAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois
Investing:
Accrued capital expenditures, including nuclear fuel expenditures$381 $214 $159 $310 $169 $122 
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund(40)(40)— 74 74 — 
Financing:
Issuance of common stock for stock-based compensation$25 $— $— $16 $— $— 
Issuance of common stock under the DRPlus9 — — 7 — — 
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, 2025:
Ameren
Missouri		Ameren
Illinois		Ameren
Balance at December 31, 2024
$823 
(a) 
$4 
(b) 
$827 
(a) 
Liabilities settled(1)— (1)
Accretion9 
(c) 
— 

9 
(c) 
Balance at March 31, 2025
$831 
(a) 
$4 
(b) 
$835 
(a) 
(a)Balance included $5 million in “Other current liabilities” on the balance sheet as of both March 31, 2025, and December 31, 2024.
(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 2025, Ameren granted 275,869 performance share units with a grant date fair value of $33 million and 118,213 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 (236,448 performance share units) or clean energy transition targets (39,421 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, 2025 and 2024, excess tax benefits (deficiencies) associated with the settlement of stock-based compensation awards decreased income tax expense by $1 million and increased income tax expense by $1 million, respectively.
Deferred Compensation
At March 31, 2025, and December 31, 2024, the present value of benefits to be paid for deferred compensation obligations was $79 million and $79 million, respectively, which was primarily reflected in “Other deferred credits and liabilities” on Ameren’s consolidated balance sheet.
Operating Revenues
As of March 31, 2025 and 2024, 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, 2025 and 2024:
Three Months
20252024
Ameren Missouri$38 $35 
Ameren Illinois43 37 
Ameren$81 $72 
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, 2025 and 2024:
Three Months
20252024
Weighted-average Common Shares Outstanding – Basic270.0 266.4 
Assumed settlement of performance share units and restricted stock units1.0 0.4 
Dilutive effect of forward sale agreements0.4 — 
Weighted-average Common Shares Outstanding – Diluted(a)
271.4 266.8 
(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, 2025 and 2024. There were no anti-dilutive shares related to the outstanding forward sale agreements as of March 31, 2025 excluded from earnings per diluted share calculations for three months ended March 31, 2025. The outstanding forward sale agreements as of March 31, 2024 were anti-dilutive for the three months ended March 31, 2024, and were excluded from the earnings per diluted share calculation as calculated using the treasury stock method. For additional information about the outstanding forward sale agreements, see Note 4 – Long-term Debt and Equity Financings.
v3.25.1
Segment Information
 3 Months Ended
Mar. 31, 2025
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, 2025 and 2024. 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 MissouriAmeren Illinois Electric DistributionAmeren Illinois Natural GasAmeren TransmissionOtherIntersegment EliminationsAmeren
Three Months 2025:
External revenues$950 $570 $411 $166 $— $— $2,097 
Intersegment revenues7 2 — 44 — (53)— 
Revenue957 572 411 210 — (53)2,097 
Fuel and purchased power(a)
(330)(212)— — — 40 (502)
Natural gas purchased for resale(a)
(30)— (139)— — — (169)
Other operations and maintenance expenses(a)
(250)(166)(55)(19)(8)13 (485)
Other segment items
Depreciation and amortization(194)(91)(32)(48)(2)— (367)
Taxes other than income taxes(89)(21)(29)(1)(4)— (144)
Other income, net43 23 5 7 8 (1)85 
Interest charges(60)(26)(15)(29)(46)1 (175)
Income (taxes) benefit(4)(16)(38)(31)39 — (50)
Noncontrolling interests – preferred stock dividends(1)— — — — — (1)
Net income (loss) attributable to Ameren common shareholders42 63 108 89 
(b)
(13)— 289 
Interest income2 8 — 1 1 (1)11 
Capital expenditures658 167 59 173 2 5 1,064 
Three Months 2024:
External revenues$768 $506 $391 $151 $— $— $1,816 
Intersegment revenues7 — — 34 — (41)— 
Revenue775 506 391 185 — (41)1,816 
Fuel and purchased power(a)
(166)(192)— — — 30 (328)
Natural gas purchased for resale(a)
(28)— (123)— — — (151)
Other operations and maintenance expenses(a)
(254)(136)(58)(19)(14)11 (470)
Other segment items
Depreciation and amortization(195)(93)(33)(39)(1)— (361)
Taxes other than income taxes(87)(17)(26)(2)(3)— (135)
Other income, net44 22 7 2 20 (6)89 
Interest charges(62)(22)(15)(29)(32)6 (154)
Income (taxes) benefit(1)(12)(37)(26)32 — (44)
Noncontrolling interests – preferred stock dividends(1)— — — — — (1)
Net income attributable to Ameren common shareholders25 56 106 72 
(b)
2 — 261 
Interest income2 6 — — 6 (6)8 
Capital expenditures466 184 60 166 2 12 890 
(a)Significant segment expense that is regularly provided to the CODMs. Intersegment expenses are included within the amounts shown.
(b)Ameren Transmission earnings reflect an allocation of financing costs from Ameren (parent).
Ameren Illinois
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionIntersegment EliminationsAmeren Illinois
Three Months 2025:
External revenues$572 $411 $117 $— $1,100 
Intersegment revenues— — 37 (37)— 
Revenue572 411 154 (37)1,100 
Purchased power(a)
(212)— — 37 (175)
Natural gas purchased for resale(a)
— (139)— — (139)
Other operations and maintenance expenses(a)
(166)(55)(15)— (236)
Other segment items
Depreciation and amortization(91)(32)(36)— (159)
Taxes other than income taxes(21)(29)(1)— (51)
Other income, net23 5 6 — 34 
Interest charges(26)(15)(21)— (62)
Income taxes(16)(38)(22)— (76)
Net income available to common shareholder63 108 65 — 236 
Interest income8 — 1 — 9 
Capital expenditures167 59 137 — 363 
Three Months 2024:
External revenues$506 $391 $103 $— $1,000 
Intersegment revenues— — 28 (28)— 
Revenue506 391 131 (28)1,000 
Purchased power(a)
(192)— — 28 (164)
Natural gas purchased for resale(a)
— (123)— — (123)
Other operations and maintenance expenses(a)
(136)(58)(16)— (210)
Other segment items
Depreciation and amortization(93)(33)(27)— (153)
Taxes other than income taxes(17)(26)(1)— (44)
Other income, net22 7 2 — 31 
Interest charges(22)(15)(18)— (55)
Income taxes(12)(37)(18)— (67)
Net income available to common shareholder56 106 53 — 215 
Interest income6 — — — 6 
Capital expenditures184 60 129 — 373 
(a)Significant segment expense that is regularly provided to the CODMs. Intersegment expenses are included within the amounts shown.
The following tables present disaggregated revenues by segment at Ameren and Ameren Illinois for the three months ended March 31, 2025 and 2024. 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 MissouriAmeren Illinois Electric DistributionAmeren Illinois Natural GasAmeren TransmissionIntersegment EliminationsAmeren
Three Months 2025:
Residential$376 $342 $— $— $— $718 
Commercial273 180 — — — 453 
Industrial66 50 — — — 116 
Other178 — — 210 (53)335 
Total electric revenues$893 $572 $— $210 $(53)$1,622 
Residential$43 $— $309 $— $— $352 
Commercial19 — 77 — — 96 
Industrial2 — 4 — — 6 
Other— — 21 — — 21 
Total natural gas revenues$64 $— $411 $— $— $475 
Total revenues(a)
$957 $572 $411 $210 $(53)$2,097 
Three Months 2024:
Residential$341 $297 $— $— $— $638 
Commercial259 165 — — — 424 
Industrial61 45 — — — 106 
Other53 (1)
(b)
— 185 (41)196 
Total electric revenues$714 $506 $— $185 $(41)$1,364 
Residential$40 $— $287 $— $— $327 
Commercial16 — 68 — — 84 
Industrial2 — 4 — — 6 
Other3 — 32 — — 35 
Total natural gas revenues$61 $— $391 $— $— $452 
Total revenues(a)
$775 $506 $391 $185 $(41)$1,816 
(a)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the three months ended March 31, 2025 and 2024:
Ameren MissouriAmeren Illinois Electric DistributionAmeren Illinois Natural GasAmeren TransmissionAmeren
Three Months 2025:
Revenues from alternative revenue programs$(5)$21 $3 $(1)$18 
Other revenues not from contracts with customers1 3 1 — 5 
Three Months 2024:
Revenues from alternative revenue programs$(6)$39 $19 $9 $61 
Other revenues not from contracts with customers1 2 1 — 4 
(b)Includes over-recoveries of various riders.
Ameren Illinois
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionIntersegment EliminationsAmeren Illinois
Three Months 2025:
Residential$342 $309 $— $— $651 
Commercial180 77 — — 257 
Industrial50 4 — — 54 
Other— 21 154 (37)138 
Total revenues(a)
$572 $411 $154 $(37)$1,100 
Three Months 2024:
Residential$297 $287 $— $— $584 
Commercial165 68 — — 233 
Industrial45 4 — — 49 
Other(1)
(b)
32 131 (28)134 
Total revenues(a)
$506 $391 $131 $(28)$1,000 
(a)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the Ameren Illinois segments for the three months ended March 31, 2025 and 2024:
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionAmeren Illinois
Three Months 2025:
Revenues from alternative revenue programs$21 $3 $(1)$23 
Other revenues not from contracts with customers3 1 — 4 
Three Months 2024:
Revenues from alternative revenue programs$39 $19 $8 $66 
Other revenues not from contracts with customers2 1 — 3 
(b)Includes over-recoveries of various riders.
v3.25.1
Insider Trading Arrangements
 3 Months Ended
Mar. 31, 2025
shares
Trading Arrangements, by Individual  
Non-Rule 10b5-1 Arrangement Adopted false
Rule 10b5-1 Arrangement Terminated false
Non-Rule 10b5-1 Arrangement Terminated false
Martin J. Lyons, Jr. [Member]  
Trading Arrangements, by Individual  
Material Terms of Trading Arrangement
On March 11, 2025, Martin J. Lyons, Jr., Chairman, President, and Chief Executive Officer of Ameren, adopted a Rule 10b5-1 trading arrangement. Mr. Lyons’ Rule 10b5-1 trading arrangement provides for the sale of 75% of any net shares of Ameren common stock received, after tax withholding, in connection with certain previously awarded restricted stock units and performance share units that will vest upon payment in March 2026 and March 2027. The estimated maximum number of shares to be sold pursuant to the Rule 10b5-1 trading arrangement is 62,686 shares. The actual number of shares sold pursuant to the Rule 10b5-1 trading arrangement will depend on the actual number of shares earned pursuant to the awards, which is generally dependent on the Company's achievement of certain performance measures, the actual dividends paid by the Company during the applicable vesting periods, and Mr. Lyons’ continued employment and individual performance during the applicable vesting periods. Mr. Lyons’ Rule 10b5-1 trading arrangement will terminate on the earlier of: (i) March 31, 2027; (ii) execution of all trades or expiration of all orders relating to such trades under the Rule 10b5-1 trading arrangement; or (iii) such date as the Rule 10b5-1 trading arrangement is otherwise terminated according to its terms.
Name Martin J. Lyons, Jr.
Title Chairman, President, and Chief Executive Officer of Ameren
Rule 10b5-1 Arrangement Adopted true
Adoption Date March 11, 2025
Expiration Date March 31, 2027
Arrangement Duration 750 days
Aggregate Available 62,686
Michael L. Moehn [Member]  
Trading Arrangements, by Individual  
Material Terms of Trading Arrangement
On March 14, 2025, Michael L. Moehn, Senior Executive Vice President and Chief Financial Officer of Ameren, adopted a Rule 10b5-1 trading arrangement. Mr. Moehn's Rule 10b5-1 trading arrangement provides for the sale of an aggregate 26,000 shares to be sold in four equal quarterly installments between August 2025 and July 2026. Mr. Moehn’s Rule 10b5-1 trading arrangement will terminate on the earlier of: (i) July 31, 2026; (ii) execution of all trades or expiration of all orders relating to such trades under the Rule 10b5-1 trading arrangement; or (iii) such date as the Rule 10b5-1 trading arrangement is otherwise terminated according to its terms.
Name Michael L. Moehn
Title Senior Executive Vice President and Chief Financial Officer of Ameren
Rule 10b5-1 Arrangement Adopted true
Adoption Date March 14, 2025
Expiration Date July 31, 2026
Arrangement Duration 504 days
Aggregate Available 26,000
v3.25.1
Summary Of Significant Accounting Policies (Policies)
 3 Months Ended
Mar. 31, 2025
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 within 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 Illinois has no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated.
Consolidation, Variable Interest Entity, Policy
Variable Interest Entities
Variable Interest Entities that are Consolidated
AMF was formed in 2024, for the purpose of issuing and servicing securitized utility tariff bonds related to costs for the accelerated retirement of the Rush Island Energy Center. Ameren Missouri is the primary beneficiary of this entity because it has the power to direct the activities that most significantly impact the economic performance of the company, as well as the obligation to absorb losses or the right to receive benefits from the company. The entity is considered a variable interest entity primarily because its equity capitalization is insufficient to support its operations. The entity’s primary assets and liabilities are comprised of regulatory assets related to the unrecovered net plant balance associated with the facility, among other costs, and long-term debt. Ameren and Ameren Missouri consolidate AMF, which Ameren Missouri wholly owns, and both manages and controls the entity’s operating activities. For additional information on the securitization of the Rush Island Energy Center costs, see Note 2 – Rate and Regulatory Matters under Part II, Item 8, of the Form 10-K. For additional information on the securitized tariff bond issuance, see Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, of the Form 10‑K.
The following table presents the carrying values of AMF’s assets and liabilities included on Ameren’s and Ameren Missouri’s consolidated balance sheets as of March 31, 2025 and December 31, 2024:
20252024
Unbilled revenue(a)
$2 $— 
Other current assets(a)
15 2 
Noncurrent regulatory assets(a)
459 465 
Current maturities of long-term debt(b)
17 17 
Interest accrued (b)
6 1 
Current regulatory liabilities(c)
5 — 
Long-term debt, net(b)
449 448 
(a)Assets may be used only to meet AMF’s obligations and commitments.
(b)The securitized tariff bondholders have no recourse to Ameren Missouri.
(c)Included in “Other current liabilities” on Ameren Missouri’s balance sheet.
Variable Interest Entities that are Not Consolidated
As of March 31, 2025, and December 31, 2024, Ameren had unconsolidated variable interests in various equity method investments, primarily to advance clean and resilient energy technologies, totaling $71 million and $74 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, 2025, Ameren’s maximum exposure to loss related to these variable interest entities is limited to the investment in these partnerships of $71 million plus associated outstanding funding commitments of $34 million.
Life Insurance, Corporate Or Bank Owned
COLI
Ameren (parent) and Ameren Illinois have COLI, which is recorded at the net cash surrender value. The net cash surrender value is the amount that can be realized under the insurance policies at the balance sheet date.
Derivatives, Policy 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.
Deferred Compensation
Deferred Compensation
At March 31, 2025, and December 31, 2024, the present value of benefits to be paid for deferred compensation obligations was $79 million and $79 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, 2025 and 2024, 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
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.
v3.25.1
Accounting Policies (Tables)
 3 Months Ended
Mar. 31, 2025
Accounting Policies [Abstract]  
Schedule of Other Assets and Other Liabilities
The following table presents the carrying values of AMF’s assets and liabilities included on Ameren’s and Ameren Missouri’s consolidated balance sheets as of March 31, 2025 and December 31, 2024:
20252024
Unbilled revenue(a)
$2 $— 
Other current assets(a)
15 2 
Noncurrent regulatory assets(a)
459 465 
Current maturities of long-term debt(b)
17 17 
Interest accrued (b)
6 1 
Current regulatory liabilities(c)
5 — 
Long-term debt, net(b)
449 448 
(a)Assets may be used only to meet AMF’s obligations and commitments.
(b)The securitized tariff bondholders have no recourse to Ameren Missouri.
(c)Included in “Other current liabilities” on Ameren Missouri’s balance sheet.
v3.25.1
Rate and Regulatory Matters (Tables)
 3 Months Ended
Mar. 31, 2025
Regulated Operations [Abstract]  
Schedule of Generation Facilities The following table provides information with respect to each agreement:
Agreement typeFacility sizeStatus of MoPSC CCNStatus of FERC approval of acquisition
In-service date(a)
Vandalia Solar Project(b)(c)
Self-build
50-MW
Approved March 2024Not applicableFourth quarter 2025
Bowling Green Solar Project(b)(c)
Self-build
50-MW
Approved March 2024Not applicableFirst quarter 2026
Split Rail Solar Project(b)(c)
Build-transfer
300-MW
Approved March 2024Received November 2024Mid-2026
Castle Bluff Natural Gas Project(b)
Self-build
800-MW
Approved October 2024Not applicableFourth quarter 2027
(a)In-service dates are dependent on the timing of construction completion, among other things.
(b)These projects collectively represent approximately $1.7 billion of capital expenditures.
(c)These solar projects are expected to support Ameren Missouri’s transition to renewable energy generation.
v3.25.1
Short-Term Debt and Liquidity (Tables)
 3 Months Ended
Mar. 31, 2025
Debt Disclosure [Abstract]  
Schedule of Short-term Debt
The following table presents commercial paper outstanding, net of issuance discounts, as of March 31, 2025, and December 31, 2024. There were no borrowings outstanding under the Credit Agreements as of March 31, 2025, or December 31, 2024.
March 31, 2025December 31, 2024
Ameren (parent)$434 $1,055 
Ameren Missouri629 — 
Ameren Illinois189 88 
Ameren consolidated$1,252 $1,143 
The following table summarizes the activity and relevant interest rates for Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper issuances under the Credit Agreements for the three months ended March 31, 2025 and 2024:
Ameren
(parent)		Ameren
Missouri		Ameren
Illinois		Ameren
Consolidated
2025
Average daily amount outstanding$898 $313 $82 $1,293 
Weighted-average interest rate4.61 %4.59 %4.56 %4.60 %
Peak amount outstanding during period(a)
$1,139 $630 $189 $1,603 
Peak interest rate4.75 %4.70 %4.69 %4.75 %
2024
Average daily amount outstanding$— $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 %
(a)The timing of peak outstanding commercial paper issuances 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.
v3.25.1
Other Income, Net (Tables)
 3 Months Ended
Mar. 31, 2025
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, 2025 and 2024:
Three Months
20252024
Ameren:
Allowance for equity funds used during construction
$16 $9 
Other interest income
11 8 
Non-service cost components of net periodic benefit income(a)
66 76 
Miscellaneous income
3 2 
Earnings (losses) related to equity method investments(4)— 
Donations
(2)(2)
Miscellaneous expense
(5)(4)
Total Other Income, Net$85 $89 
Ameren Missouri:
Allowance for equity funds used during construction
$8 $9 
Other interest income
2 2 
Non-service cost components of net periodic benefit income(a)
35 35 
Miscellaneous income
1 1 
Donations
(1)(1)
Miscellaneous expense
(2)(2)
Total Other Income, Net$43 $44 
Ameren Illinois:
Allowance for equity funds used during construction
$7 $— 
Other interest income9 6 
Non-service cost components of net periodic benefit income
20 27 
Miscellaneous income
2 1 
Donations
(1)(1)
Miscellaneous expense(3)(2)
Total Other Income, Net$34 $31 
(a)For the three months ended March 31, 2025 and 2024, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $(16) million and $(9) 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.
v3.25.1
Derivative Financial Instruments (Tables)
 3 Months Ended
Mar. 31, 2025
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, 2025, and December 31, 2024. As of March 31, 2025, these contracts extended through October 2028, October 2030 and May 2032 for fuel oils, natural gas, and power, respectively.
Quantity (in millions, except as indicated)
March 31, 2025December 31, 2024
CommodityAmeren MissouriAmeren IllinoisAmerenAmeren MissouriAmeren IllinoisAmeren
Fuel oils (in gallons)24 — 24 23 — 23 
Natural gas (in mmbtu)47 221 268 45 213 258 
Power (in MWhs)— 4 4 — 4 4 
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 because all qualify for regulatory deferral, as of March 31, 2025, and December 31, 2024:
March 31, 2025December 31, 2024
Balance Sheet LocationAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois		Ameren
Natural gasOther current assets4 11 15 2 2 4 
Other assets2 5 7 2 4 6 
PowerOther current assets5 — 5 6 — 6 
Total assets$11 $16 $27 $10 $6 $16 
Fuel oilsOther current liabilities$2 $— $2 $2 $— $2 
Other deferred credits and liabilities1 — 1 2 — 2 
Natural gasOther current liabilities2 6 8 5 22 27 
Other deferred credits and liabilities7 14 21 6 13 19 
PowerOther current liabilities— 7 7 — 10 10 
Other deferred credits and liabilities— 60 60 — 43 43 
Total liabilities$12 $87 $99 $15 $88 $103 
v3.25.1
Fair Value Measurements (Tables)
 3 Months Ended
Mar. 31, 2025
Fair Value Disclosures [Abstract]  
Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis
The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of March 31, 2025, and December 31, 2024:
March 31, 2025December 31, 2024
Level 1Level 2Level 3TotalLevel 1Level 2Level 3Total
Assets:
Ameren Missouri
Derivative assets – commodity contracts:
Natural gas— 5 1 6 — 4 — 4 
Power— — 5 5 — — 6 6 
Total derivative assets – commodity contracts$— $5 $6 $11 $— $4 $6 $10 
Nuclear decommissioning trust fund:
Equity securities:
U.S. large capitalization$868 $— $— $868 $911 $— $— $911 
Debt securities:
U.S. Treasury and agency securities— 188 — 188 — 191 — 191 
Corporate bonds— 156 — 156 — 145 — 145 
Other— 92 — 92 — 86 — 86 
Total nuclear decommissioning trust fund$868 $436 $— $1,304 
(a) 
$911 $422 $— $1,333 
(a) 
Total Ameren Missouri$868 $441 $6 $1,315 $911 $426 $6 $1,343 
Ameren Illinois
Derivative assets – commodity contracts:
Natural gas$2 $9 $5 $16 $— $3 $3 $6 
Total Ameren Illinois$2 $9 $5 $16 $— $3 $3 $6 
Ameren
Derivative assets – commodity contracts(b)
$2 $14 $11 $27 $— $7 $9 $16 
Nuclear decommissioning trust fund(c)
868 436 — 1,304 
(a) 
911 422 — 1,333 
(a) 
Total Ameren$870 $450 $11 $1,331 $911 $429 $9 $1,349 
Liabilities:
Ameren Missouri
Derivative liabilities – commodity contracts:
Fuel oils$3 $— $— $3 $4 $— $— $4 
Natural gas— 8 1 9 — 11 — 11 
Total Ameren Missouri$3 $8 $1 $12 $4 $11 $— $15 
March 31, 2025December 31, 2024
Level 1Level 2Level 3TotalLevel 1Level 2Level 3Total
Ameren Illinois
Derivative liabilities – commodity contracts:
Natural gas$— $17 $3 $20 $1 $28 $6 $35 
Power— — 67 67 — — 53 53 
Total Ameren Illinois$— $17 $70 $87 $1 $28 $59 $88 
Ameren
Derivative liabilities – commodity contracts(b)
$3 $25 $71 $99 $5 $39 $59 $103 
(a)Balance excludes $8 million and $9 million of cash and cash equivalents, receivables, payables, and accrued income, net, for March 31, 2025, and December 31, 2024, 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, 2025 and 2024:
20252024
Ameren MissouriAmeren IllinoisAmerenAmeren MissouriAmeren IllinoisAmeren
For the three months ended March 31:
Beginning balance at January 1$6 $(53)$(47)$4 $(68)$(64)
Realized and unrealized gains/(losses) included in regulatory assets/liabilities2 (16)(14)(1)10 9 
Settlements(3)2 (1)(1)4 3 
Ending balance at March 31
$5 $(67)$(62)$2 $(54)$(52)
Change in unrealized gains/(losses) related to assets/liabilities held at March 31
$2 $(16)$(14)$— $11 $11 
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, 2025, and December 31, 2024:
Fair Value
Weighted Average(b)
CommodityAssetsLiabilitiesValuation Technique(s)
Unobservable Input(a)
Range
2025
Power(c)
$5$(67)Discounted cash flow
Average forward peak and off-peak pricing – forwards/swaps ($/MWh)
32 – 65
41
Nodal basis ($/MWh)
(8) – (2)
(5)
2024
Power(c)
$6$(53)Discounted cash flowAverage forward peak and off-peak pricing – forwards/swaps ($/MWh)
32 – 69
45
Nodal basis ($/MWh)
(8) – (2)
(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, 2025, and December 31, 2024:
Long-Term Debt (Including Current Portion):
Carrying
Amount(a)
Fair Value
Level 2Level 3Total
March 31, 2025
Ameren(b)
$18,371 $16,277 $547 
(c) 
$16,824 
Ameren Missouri(d)
7,746 6,963 — 6,963 
Ameren Illinois(d)
5,900 5,310 — 5,310 
December 31, 2024
Ameren(b)
$17,579 $15,395 $538 
(c) 
$15,933 
Ameren Missouri(d)
7,745 6,926 — 6,926 
Ameren Illinois(d)
5,852 5,243 — 5,243 
(a)Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $133 million, $61 million, and $54 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of March 31, 2025. Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $129 million, $62 million, and $51 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2024.
(b)Amount excludes Ameren (parent)’s repurchase of Ameren Missouri’s senior secured notes and first mortgage bonds and Ameren Illinois’ first mortgage bonds in 2024.
(c)The Level 3 fair value amount consists of ATXI’s senior unsecured notes.
(d)Amount includes Ameren Missouri’s senior secured notes and first mortgage bonds and Ameren Illinois’ first mortgage bonds that were repurchased by Ameren (parent) in 2024.
v3.25.1
Related Party Transactions (Tables)
 3 Months Ended
Mar. 31, 2025
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, 2025, and December 31, 2024:
March 31, 2025December 31, 2024
Ameren MissouriAmeren IllinoisAmeren MissouriAmeren Illinois
Income taxes payable to parent(a)
$—$32$—$32
Income taxes receivable from parent(b)
29—28—
(a)Included in “Accounts payable – affiliates” on the balance sheet.
(b)Included in “Accounts receivable – affiliates” on the balance sheet.
Schedule of Related Party Transactions
The following table presents the impact on Ameren Missouri and Ameren Illinois of related-party transactions for the three months ended March 31, 2025 and 2024:
Three Months
AgreementIncome Statement
Line Item		Ameren
Missouri		Ameren
Illinois
Ameren Missouri power supplyOperating Revenues2025$(a)$(a)
agreements with Ameren Illinois
2024(b)(a)
Ameren Missouri and Ameren IllinoisOperating Revenues2025$7 $(b)
rent and facility services
20247 (b)
Ameren Missouri and Ameren Illinois miscellaneousOperating Revenues2025$(b)$2 
support services2024(b)1 
Total Operating Revenues2025$7 $2 
20247 1 
Ameren Illinois power supplyPurchased Power2025$(a)$(a)
agreements with Ameren Missouri
2024(a)(b)
Ameren Missouri and Ameren IllinoisPurchased Power2025$3 $(b)
transmission services from ATXI20242 (b)
Total Purchased Power2025$3 $(b)
20242 (b)
Ameren Missouri and Ameren IllinoisOther Operations and Maintenance2025$(b)$1 
rent and facility services
2024(b)(b)
Ameren Services support servicesOther Operations and Maintenance2025$44 $40 
agreement
202438 37 
Total Other Operations and2025$44 $41 
Maintenance202438 37 
Money pool interest(Interest Charges)/Other Income, Net2025$(b)$(b)
2024(3)(2)
Long-term debt, net - related parties(Interest Charges)2025(b)(b)
2024— — 
(a)Not applicable.
(b)Amount less than $1 million.
v3.25.1
Callaway Energy Center (Tables)
 3 Months Ended
Mar. 31, 2025
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, 2025:
Type and Source of CoverageMost Recent
Renewal Date		Maximum CoveragesMaximum Assessments
for Single Incidents
Public liability and nuclear worker liability:
American Nuclear InsurersJanuary 1, 2025$500 $— 
Pool participation(a)15,763 
(a) 
166 
(b) 
$16,263 
(c) 
$166 
Property damage:
NEIL and EMANIApril 1, 2025$3,200 
(d)
$22 
(e) 
Accidental outage:
NEILApril 1, 2025$490 
(f) 
$9 
(e) 
(a)Provided through mandatory participation in an industrywide retrospective premium assessment program. The maximum coverage available is dependent on the number of United States commercial reactors participating in the program.
(b)Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $500 million in the event of an incident at any licensed United States commercial reactor, payable at $25 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 retrospective 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.
v3.25.1
Retirement Benefits (Tables)
 3 Months Ended
Mar. 31, 2025
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, 2025 and 2024:
Pension BenefitsPostretirement Benefits
Three MonthsThree Months
2025202420252024
Service cost(a)
$21 $21 $2 $3 
Non-service cost components:
Interest cost58 55 11 11 
Expected return on plan assets(b)
(76)(82)(23)(23)
Amortization of(b):
Prior service cost (credit)— — (1)(1)
Actuarial (gain)(10)(17)(9)(10)
Total non-service cost components(c)
$(28)$(44)$(22)$(23)
Net periodic benefit income(d)
$(7)$(23)$(20)$(20)
(a)Service cost, net of capitalization, is reflected in “Operating Expenses – Other operations and maintenance” on Ameren’s statement of income.
(b)Prior service cost (credit) 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 customer 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, 2025 and 2024:
Pension BenefitsPostretirement Benefits
Three MonthsThree Months
2025202420252024
Ameren Missouri(a)
$(4)$(12)$(7)$(7)
Ameren Illinois(2)(9)(13)(13)
Other(1)(2)— — 
Ameren(a)
$(7)$(23)$(20)$(20)
(a)Does not include the impact of the tracker for the difference between the level of pension and postretirement benefit costs (income) incurred by Ameren Missouri under GAAP and the level of such costs included in customer rates.
v3.25.1
Income Taxes (Tables)
 3 Months Ended
Mar. 31, 2025
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, 2025 and 2024:
AmerenAmeren MissouriAmeren Illinois
202520242025202420252024
Three Months
Federal statutory corporate income tax rate21 %21 %21 %21 %21 %21 %
Increases (decreases) from:
Amortization of excess deferred taxes(a)
(7)(8)

(8)(12)

(3)(4)
Amortization of deferred investment tax credit(1)— (1)— — — 
Renewable and other tax credits(b)
(4)(4)(7)(8)— — 
State tax6 6 4 4 7 7 
Depreciation differences(1)(1)(1)(1)(1)— 
Stock-based compensation— 1 — — — — 
Other permanent items— (1)— — — — 
Effective income tax rate14 %14 %8 %4 %24 %24 %
(a)Reflects the amortization of amounts resulting from the revaluation of deferred income taxes subject to regulatory ratemaking, which are being refunded to customers.
(b)The benefit of the credits associated with Missouri renewable energy standard compliance is refunded to customers through the RESRAM. The benefit of the credits associated with the production and investment tax credit tracker will be refunded to customers based on MoPSC approval in a regulatory rate review.
v3.25.1
Supplemental Information (Tables)
 3 Months Ended
Mar. 31, 2025
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, 2025, and December 31, 2024:
March 31, 2025December 31, 2024
AmerenAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois
“Cash and cash equivalents”$23 $7 $4 $7 $— $— 
Restricted cash included in “Other current assets”40 32 5 15 7 6 
Restricted cash included in “Other assets”307 — 307 296 — 296 
Restricted cash included in “Nuclear decommissioning trust fund”6 6 — 10 10 — 
Total cash, cash equivalents, and restricted cash$376 $45 $316 $328 $17 $302 
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, 2025 and 2024:
Three Months
20252024
Ameren:
Beginning of period$30 $30 
Bad debt expense16 10 
Charged to other accounts(a)
1 3 
Net write-offs(6)(6)
End of period$41 $37 
Ameren Missouri:
Beginning of period$12 $12 
Bad debt expense2 1 
Net write-offs(2)(2)
End of period$12 $11 
Ameren Illinois:(b)
Beginning of period$18 $18 
Bad debt expense14 9 
Charged to other accounts(a)
1 3 
Net write-offs(4)(4)
End of period$29 $26 
(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, 2025 and 2024:
March 31, 2025March 31, 2024
AmerenAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois
Investing:
Accrued capital expenditures, including nuclear fuel expenditures$381 $214 $159 $310 $169 $122 
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund(40)(40)— 74 74 — 
Financing:
Issuance of common stock for stock-based compensation$25 $— $— $16 $— $— 
Issuance of common stock under the DRPlus9 — — 7 — — 
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, 2025:
Ameren
Missouri		Ameren
Illinois		Ameren
Balance at December 31, 2024
$823 
(a) 
$4 
(b) 
$827 
(a) 
Liabilities settled(1)— (1)
Accretion9 
(c) 
— 

9 
(c) 
Balance at March 31, 2025
$831 
(a) 
$4 
(b) 
$835 
(a) 
(a)Balance included $5 million in “Other current liabilities” on the balance sheet as of both March 31, 2025, and December 31, 2024.
(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, 2025 and 2024:
Three Months
20252024
Ameren Missouri$38 $35 
Ameren Illinois43 37 
Ameren$81 $72 
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, 2025 and 2024:
Three Months
20252024
Weighted-average Common Shares Outstanding – Basic270.0 266.4 
Assumed settlement of performance share units and restricted stock units1.0 0.4 
Dilutive effect of forward sale agreements0.4 — 
Weighted-average Common Shares Outstanding – Diluted(a)
271.4 266.8 
(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, 2025 and 2024. There were no anti-dilutive shares related to the outstanding forward sale agreements as of March 31, 2025 excluded from earnings per diluted share calculations for three months ended March 31, 2025. The outstanding forward sale agreements as of March 31, 2024 were anti-dilutive for the three months ended March 31, 2024, and were excluded from the earnings per diluted share calculation as calculated using the treasury stock method. For additional information about the outstanding forward sale agreements, see Note 4 – Long-term Debt and Equity Financings.
v3.25.1
Segment Information (Tables)
 3 Months Ended
Mar. 31, 2025
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, 2025 and 2024. 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 MissouriAmeren Illinois Electric DistributionAmeren Illinois Natural GasAmeren TransmissionOtherIntersegment EliminationsAmeren
Three Months 2025:
External revenues$950 $570 $411 $166 $— $— $2,097 
Intersegment revenues7 2 — 44 — (53)— 
Revenue957 572 411 210 — (53)2,097 
Fuel and purchased power(a)
(330)(212)— — — 40 (502)
Natural gas purchased for resale(a)
(30)— (139)— — — (169)
Other operations and maintenance expenses(a)
(250)(166)(55)(19)(8)13 (485)
Other segment items
Depreciation and amortization(194)(91)(32)(48)(2)— (367)
Taxes other than income taxes(89)(21)(29)(1)(4)— (144)
Other income, net43 23 5 7 8 (1)85 
Interest charges(60)(26)(15)(29)(46)1 (175)
Income (taxes) benefit(4)(16)(38)(31)39 — (50)
Noncontrolling interests – preferred stock dividends(1)— — — — — (1)
Net income (loss) attributable to Ameren common shareholders42 63 108 89 
(b)
(13)— 289 
Interest income2 8 — 1 1 (1)11 
Capital expenditures658 167 59 173 2 5 1,064 
Three Months 2024:
External revenues$768 $506 $391 $151 $— $— $1,816 
Intersegment revenues7 — — 34 — (41)— 
Revenue775 506 391 185 — (41)1,816 
Fuel and purchased power(a)
(166)(192)— — — 30 (328)
Natural gas purchased for resale(a)
(28)— (123)— — — (151)
Other operations and maintenance expenses(a)
(254)(136)(58)(19)(14)11 (470)
Other segment items
Depreciation and amortization(195)(93)(33)(39)(1)— (361)
Taxes other than income taxes(87)(17)(26)(2)(3)— (135)
Other income, net44 22 7 2 20 (6)89 
Interest charges(62)(22)(15)(29)(32)6 (154)
Income (taxes) benefit(1)(12)(37)(26)32 — (44)
Noncontrolling interests – preferred stock dividends(1)— — — — — (1)
Net income attributable to Ameren common shareholders25 56 106 72 
(b)
2 — 261 
Interest income2 6 — — 6 (6)8 
Capital expenditures466 184 60 166 2 12 890 
(a)Significant segment expense that is regularly provided to the CODMs. Intersegment expenses are included within the amounts shown.
(b)Ameren Transmission earnings reflect an allocation of financing costs from Ameren (parent).
Ameren Illinois
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionIntersegment EliminationsAmeren Illinois
Three Months 2025:
External revenues$572 $411 $117 $— $1,100 
Intersegment revenues— — 37 (37)— 
Revenue572 411 154 (37)1,100 
Purchased power(a)
(212)— — 37 (175)
Natural gas purchased for resale(a)
— (139)— — (139)
Other operations and maintenance expenses(a)
(166)(55)(15)— (236)
Other segment items
Depreciation and amortization(91)(32)(36)— (159)
Taxes other than income taxes(21)(29)(1)— (51)
Other income, net23 5 6 — 34 
Interest charges(26)(15)(21)— (62)
Income taxes(16)(38)(22)— (76)
Net income available to common shareholder63 108 65 — 236 
Interest income8 — 1 — 9 
Capital expenditures167 59 137 — 363 
Three Months 2024:
External revenues$506 $391 $103 $— $1,000 
Intersegment revenues— — 28 (28)— 
Revenue506 391 131 (28)1,000 
Purchased power(a)
(192)— — 28 (164)
Natural gas purchased for resale(a)
— (123)— — (123)
Other operations and maintenance expenses(a)
(136)(58)(16)— (210)
Other segment items
Depreciation and amortization(93)(33)(27)— (153)
Taxes other than income taxes(17)(26)(1)— (44)
Other income, net22 7 2 — 31 
Interest charges(22)(15)(18)— (55)
Income taxes(12)(37)(18)— (67)
Net income available to common shareholder56 106 53 — 215 
Interest income6 — — — 6 
Capital expenditures184 60 129 — 373 
(a)Significant segment expense that is regularly provided to the CODMs. Intersegment expenses are included within the amounts shown.
Disaggregation of Revenue
The following tables present disaggregated revenues by segment at Ameren and Ameren Illinois for the three months ended March 31, 2025 and 2024. 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 MissouriAmeren Illinois Electric DistributionAmeren Illinois Natural GasAmeren TransmissionIntersegment EliminationsAmeren
Three Months 2025:
Residential$376 $342 $— $— $— $718 
Commercial273 180 — — — 453 
Industrial66 50 — — — 116 
Other178 — — 210 (53)335 
Total electric revenues$893 $572 $— $210 $(53)$1,622 
Residential$43 $— $309 $— $— $352 
Commercial19 — 77 — — 96 
Industrial2 — 4 — — 6 
Other— — 21 — — 21 
Total natural gas revenues$64 $— $411 $— $— $475 
Total revenues(a)
$957 $572 $411 $210 $(53)$2,097 
Three Months 2024:
Residential$341 $297 $— $— $— $638 
Commercial259 165 — — — 424 
Industrial61 45 — — — 106 
Other53 (1)
(b)
— 185 (41)196 
Total electric revenues$714 $506 $— $185 $(41)$1,364 
Residential$40 $— $287 $— $— $327 
Commercial16 — 68 — — 84 
Industrial2 — 4 — — 6 
Other3 — 32 — — 35 
Total natural gas revenues$61 $— $391 $— $— $452 
Total revenues(a)
$775 $506 $391 $185 $(41)$1,816 
(a)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the three months ended March 31, 2025 and 2024:
Ameren MissouriAmeren Illinois Electric DistributionAmeren Illinois Natural GasAmeren TransmissionAmeren
Three Months 2025:
Revenues from alternative revenue programs$(5)$21 $3 $(1)$18 
Other revenues not from contracts with customers1 3 1 — 5 
Three Months 2024:
Revenues from alternative revenue programs$(6)$39 $19 $9 $61 
Other revenues not from contracts with customers1 2 1 — 4 
(b)Includes over-recoveries of various riders.
Ameren Illinois
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionIntersegment EliminationsAmeren Illinois
Three Months 2025:
Residential$342 $309 $— $— $651 
Commercial180 77 — — 257 
Industrial50 4 — — 54 
Other— 21 154 (37)138 
Total revenues(a)
$572 $411 $154 $(37)$1,100 
Three Months 2024:
Residential$297 $287 $— $— $584 
Commercial165 68 — — 233 
Industrial45 4 — — 49 
Other(1)
(b)
32 131 (28)134 
Total revenues(a)
$506 $391 $131 $(28)$1,000 
(a)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the Ameren Illinois segments for the three months ended March 31, 2025 and 2024:
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionAmeren Illinois
Three Months 2025:
Revenues from alternative revenue programs$21 $3 $(1)$23 
Other revenues not from contracts with customers3 1 — 4 
Three Months 2024:
Revenues from alternative revenue programs$39 $19 $8 $66 
Other revenues not from contracts with customers2 1 — 3 
(b)Includes over-recoveries of various riders.
v3.25.1
Summary of Significant Accounting Policies (Narrative) (Details) - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Unconsolidated variable interest $ 71 $ 74
Cash Surrender Value of Life Insurance 259 260
Corporate owned life insurance, borrowings 110 110
Ameren Illinois Company    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Cash Surrender Value of Life Insurance 120 118
Corporate owned life insurance, borrowings 110 $ 110
Partnership Funding Commitment    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Outstanding funding commitments $ 34  
v3.25.1
Summary Of Significant Accounting Policies - Schedule of Other Assets and Other Liabilities (Details) - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Accounting Policies [Line Items]    
Unbilled revenue $ 253 $ 346
Other current assets 176 162
Regulatory Asset 2,569 2,397
Current maturities of long-term debt 17 317
Interest accrued 159 196
Long-term debt, net 18,354 17,262
Ameren Missouri Securitization Funding I, LLC    
Accounting Policies [Line Items]    
Unbilled revenue 2 0
Other current assets 15 2
Regulatory Asset 459 465
Current maturities of long-term debt 17 17
Interest accrued 6 1
Current regulatory liabilities 5 0
Long-term debt, net $ 449 $ 448
v3.25.1
Rate And Regulatory Matters (Narrative-Missouri) (Details)
$ in Millions
 3 Months Ended
Mar. 31, 2027
Dec. 31, 2025
Jun. 30, 2025
USD ($)
Mar. 31, 2025
USD ($)
Jun. 30, 2024
MWh
Mar. 31, 2024
USD ($)
Sep. 30, 2023
MWh
Dec. 31, 2022
MWh
Rate And Regulatory Matters [Line Items]                
Depreciation and amortization       $ 367   $ 361    
Capital expenditures       $ 1,064   890    
Union Electric Company                
Rate And Regulatory Matters [Line Items]                
PISA Deferral Percentage       85.00%        
Depreciation and amortization       $ 194   195    
Capital expenditures       $ 658   $ 466    
Union Electric Company | Maximum                
Rate And Regulatory Matters [Line Items]                
Public Utilities, Approved Rate Increase (Decrease), Percentage       2.50%        
Union Electric Company | Maximum | Subsequent Event                
Rate And Regulatory Matters [Line Items]                
Public Utilities, Approved Rate Increase (Decrease), Percentage   2.25%            
Union Electric Company | Generation Facilities                
Rate And Regulatory Matters [Line Items]                
Capital expenditures       $ 1,700        
Union Electric Company | Electric | Subsequent Event                
Rate And Regulatory Matters [Line Items]                
Frequency of Integrated Resource Plan Filings 4 years              
Union Electric Company | Electric | Final Rate Order | Subsequent Event                
Rate And Regulatory Matters [Line Items]                
Public Utilities, Approved Rate Increase (Decrease), Amount     $ 355          
Depreciation and amortization     70          
Union Electric Company | Build-transfer | Solar generation facility                
Rate And Regulatory Matters [Line Items]                
Amount of Megawatts | MWh             300  
Union Electric Company | Self-build | Solar generation facility                
Rate And Regulatory Matters [Line Items]                
Amount of Megawatts | MWh             50 50
Union Electric Company | Self-build | Natural Gas Generation Facility                
Rate And Regulatory Matters [Line Items]                
Amount of Megawatts | MWh         800      
Union Electric Company | Natural gas | Subsequent Event                
Rate And Regulatory Matters [Line Items]                
Number of days after end of test year to perform reconciliation when using a future test year 45 days              
Union Electric Company | Natural gas | Pending Rate Case                
Rate And Regulatory Matters [Line Items]                
Public Utilities, Requested Rate Increase (Decrease), Amount       $ 38        
Public Utilities, Requested Return on Equity, Percentage       10.25%        
Public Utilities, Requested Equity Capital Structure, Percentage       52.00%        
Rate Base       $ 525        
Months to complete a rate proceeding       11 months        
Union Electric Company | Natural gas | Pending Rate Case | Subsequent Event                
Rate And Regulatory Matters [Line Items]                
MoPSC Staff recommended rate increase (decrease)     $ 32          
MoPSC Staff's recommended ROE     9.64%          
MoPSC Staff's recommended capital structure     52.00%          
MoPSC Staff's recommended rate base     $ 482          
v3.25.1
Rate And Regulatory Matters (Narrative-Illinois) (Details) - Ameren Illinois Company - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Jun. 30, 2025
Mar. 31, 2025
Dec. 31, 2027
Dec. 31, 2026
Dec. 31, 2025
Dec. 31, 2024
Rate And Regulatory Matters [Line Items]            
Annual investment in energy-efficiency programs   $ 126        
IETL | Electric Distribution            
Rate And Regulatory Matters [Line Items]            
Multi-year rate plan approved revenue requirement           $ 1,206
Public Utilities, Approved Rate Increase (Decrease), Amount           $ 308
IETL | Electric Distribution | Forecast            
Rate And Regulatory Matters [Line Items]            
Multi-year rate plan approved revenue requirement     $ 1,421 $ 1,367 $ 1,287  
Pending Rate Case | Electric Distribution | Subsequent Event            
Rate And Regulatory Matters [Line Items]            
Public Utilities, Requested Rate Increase (Decrease), Amount $ 61          
Public Utilities, Requested Equity Capital Structure, Percentage 50.00%          
Pending Rate Case | Natural gas            
Rate And Regulatory Matters [Line Items]            
Public Utilities, Requested Rate Increase (Decrease), Amount   $ 140        
Public Utilities, Requested Equity Capital Structure, Percentage   52.00%        
Public Utilities, Requested Return on Equity, Percentage   10.70%        
Rate Base   $ 3,300        
v3.25.1
Rate And Regulatory Matters (Narrative-Federal) (Details) - USD ($)
$ in Millions
 1 Months Ended 3 Months Ended
Oct. 31, 2024
May 31, 2020
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Dec. 31, 2024
Rate And Regulatory Matters [Line Items]            
Capital expenditures       $ 1,064 $ 890  
Forecast            
Rate And Regulatory Matters [Line Items]            
Capital expenditures     $ 1,300      
Ameren Illinois Company            
Rate And Regulatory Matters [Line Items]            
Capital expenditures       363 $ 373  
Current regulatory liabilities       89   $ 79
Midwest Independent Transmission System Operator, Inc | Final Rate Order            
Rate And Regulatory Matters [Line Items]            
Approved return on equity percentage 9.98% 10.02%        
Current regulatory liabilities       11    
Midwest Independent Transmission System Operator, Inc | Final Rate Order | Ameren Illinois Company            
Rate And Regulatory Matters [Line Items]            
Current regulatory liabilities       $ 7    
v3.25.1
Short-Term Debt And Liquidity (Narrative) (Details)
$ in Billions
 3 Months Ended
Mar. 31, 2025
USD ($)
Mar. 31, 2024
Credit Agreements    
Short-term Debt [Line Items]    
Net Liquidity Available $ 1.3  
Actual debt-to-capital ratio 0.61  
Utilities    
Short-term Debt [Line Items]    
Short-term Debt, Weighted Average Interest Rate, over Time 4.52% 5.32%
Union Electric Company | Missouri Credit Agreement    
Short-term Debt [Line Items]    
Actual debt-to-capital ratio 0.50  
Ameren Illinois Company | Illinois Credit Agreement    
Short-term Debt [Line Items]    
Actual debt-to-capital ratio 0.45  
v3.25.1
Short-Term Debt and Liquidity (Short-Term Debt outstanding) (Details) - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Short-term Debt [Line Items]    
Short-term debt $ 1,252 $ 1,143
Union Electric Company    
Short-term Debt [Line Items]    
Short-term debt 629 0
Ameren Illinois Company    
Short-term Debt [Line Items]    
Short-term debt 189 88
Commercial Paper    
Short-term Debt [Line Items]    
Short-term debt 1,252 1,143
Commercial Paper | Parent Company    
Short-term Debt [Line Items]    
Short-term debt 434 1,055
Commercial Paper | Union Electric Company    
Short-term Debt [Line Items]    
Short-term debt 629 0
Commercial Paper | Ameren Illinois Company    
Short-term Debt [Line Items]    
Short-term debt $ 189 $ 88
v3.25.1
Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Short-term Debt [Line Items]    
Average daily amount outstanding $ 1,293 $ 471
Weighted-average interest rate 4.60% 5.57%
Short-term Debt, Maximum Amount Outstanding During Period $ 1,603 $ 869
Peak interest rate 4.75% 5.68%
Parent Company    
Short-term Debt [Line Items]    
Average daily amount outstanding $ 898 $ 0
Weighted-average interest rate 4.61% 0.00%
Short-term Debt, Maximum Amount Outstanding During Period $ 1,139 $ 0
Peak interest rate 4.75% 0.00%
Union Electric Company    
Short-term Debt [Line Items]    
Average daily amount outstanding $ 313 $ 135
Weighted-average interest rate 4.59% 5.53%
Short-term Debt, Maximum Amount Outstanding During Period $ 630 $ 444
Peak interest rate 4.70% 5.68%
Ameren Illinois Company    
Short-term Debt [Line Items]    
Average daily amount outstanding $ 82 $ 336
Weighted-average interest rate 4.56% 5.58%
Short-term Debt, Maximum Amount Outstanding During Period $ 189 $ 425
Peak interest rate 4.69% 5.68%
v3.25.1
Long-Term debt and Equity Financings (Details)
$ / shares in Units, shares in Millions, $ in Millions
 3 Months Ended
Mar. 31, 2025
USD ($)
$ / shares
shares
Mar. 31, 2024
USD ($)
shares
Apr. 30, 2025
USD ($)
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 $ 13.0 $ 10.0  
Stock Issued During Period, Shares, Other | shares 0.3 0.2  
Stock Issued During Period, Value, Other $ 25.0    
Maximum Value Of Shares To Be Issued Under ATM Program $ 230.0    
Forward Contract Indexed to Issuer's Equity, Basis Spread 75    
Dividend reinvestment and 401 (k) plans      
Long-Term Debt And Equity Financings [Line Items]      
Issuances of common stock $ 6.0    
Accrued Proceeds from Issuance of Common Stock 9.0    
Senior unsecured Notes 5.375% Due 2035 | Unsecured Debt | Ameren (parent)      
Long-Term Debt And Equity Financings [Line Items]      
Debt Instrument, Face Amount $ 750.0    
Debt Instrument, Interest Rate, Stated Percentage 5.375%    
First Mortgage Bonds, 5.25%, Due 2035 - $500 Issuance | Secured Debt | Union Electric Company | Subsequent Event      
Long-Term Debt And Equity Financings [Line Items]      
Debt Instrument, Face Amount     $ 500.0
Debt Instrument, Interest Rate, Stated Percentage     5.25%
First Mortgage Bonds, 5.625%, Due 2055 - $350 Issuance | Secured Debt | Ameren Illinois Company      
Long-Term Debt And Equity Financings [Line Items]      
Debt Instrument, Face Amount $ 350.0    
Debt Instrument, Interest Rate, Stated Percentage 5.625%    
Senior Secured Notes, 3.25%, Due 2025 | Secured Debt | Ameren Illinois Company      
Long-Term Debt And Equity Financings [Line Items]      
Debt Instrument, Face Amount $ 300.0    
Debt Instrument, Interest Rate, Stated Percentage 3.25%    
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 5.8    
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value $ 530.0    
Period End Net Cash Settlement Price 55.0    
Period End Net Share Settlement Price $ 0.6    
Forward Sale Agreement Equity Offering Shares | shares 5.8    
Forward Sale Agreement Gross Sales Price $ 535.0    
Minimum      
Long-Term Debt And Equity Financings [Line Items]      
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares $ 81.00    
Maximum      
Long-Term Debt And Equity Financings [Line Items]      
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares 98.66    
Weighted Average      
Long-Term Debt And Equity Financings [Line Items]      
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares $ 91.02    
v3.25.1
Other Income, Net (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Other Nonoperating Income (Expense) [Line Items]    
Allowance for equity funds used during construction $ 16 $ 9
Other interest income 11 8
Non-service cost components of net periodic benefit income 66 76
Miscellaneous income 3 2
Income (Loss) from Equity Method Investments (4) 0
Donations (2) (2)
Miscellaneous expense (5) (4)
Total Other Income, Net 85 89
Union Electric Company    
Other Nonoperating Income (Expense) [Line Items]    
Allowance for equity funds used during construction 8 9
Other interest income 2 2
Non-service cost components of net periodic benefit income 35 35
Miscellaneous income 1 1
Donations (1) (1)
Miscellaneous expense (2) (2)
Total Other Income, Net 43 44
Defined Benefit Plan, Non-service Cost or Income Components - Tracker (16) (9)
Ameren Illinois Company    
Other Nonoperating Income (Expense) [Line Items]    
Allowance for equity funds used during construction 7 0
Other interest income 9 6
Non-service cost components of net periodic benefit income 20 27
Miscellaneous income 2 1
Donations (1) (1)
Miscellaneous expense (3) (2)
Total Other Income, Net $ 34 $ 31
v3.25.1
Derivative Financial Instruments (Narrative) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Dec. 31, 2024
Derivative [Line Items]      
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax $ (4) $ 0  
Interest Rate Swap      
Derivative [Line Items]      
Derivative, Notional Amount 280   $ 140
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax $ 4    
v3.25.1
Derivative Financial Instruments (Open Gross Derivative Volumes By Commodity Type) (Detail)
gal in Millions, MWh in Millions, MMBTU in Millions
 3 Months Ended 9 Months Ended
Mar. 31, 2025
MWh
MMBTU
gal
Sep. 30, 2024
MWh
MMBTU
gal
Fuel oils    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Volume | gal 24 23
Natural gas    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU 268 258
Power    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh 4 4
Union Electric Company | Fuel oils    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Volume | gal 24 23
Union Electric Company | Natural gas    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU 47 45
Union Electric Company | Power    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh 0 0
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 221 213
Ameren Illinois Company | Power    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh 4 4
v3.25.1
Derivative Financial Instruments (Derivative Instruments Carrying Value) (Detail) - Not Designated As Hedging Instrument - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Derivative [Line Items]    
Derivative Assets $ 27 $ 16
Derivative Liability 99 103
Fuel oils | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 2 2
Fuel oils | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 1 2
Natural gas | Other current assets    
Derivative [Line Items]    
Derivative Assets 15 4
Natural gas | Other assets    
Derivative [Line Items]    
Derivative Assets 7 6
Natural gas | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 8 27
Natural gas | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 21 19
Power | Other current assets    
Derivative [Line Items]    
Derivative Assets 5 6
Power | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 7 10
Power | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 60 43
Union Electric Company    
Derivative [Line Items]    
Derivative Assets 11 10
Derivative Liability 12 15
Union Electric Company | Fuel oils | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 2 2
Union Electric Company | Fuel oils | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 1 2
Union Electric Company | Natural gas | Other current assets    
Derivative [Line Items]    
Derivative Assets 4 2
Union Electric Company | Natural gas | Other assets    
Derivative [Line Items]    
Derivative Assets 2 2
Union Electric Company | Natural gas | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 2 5
Union Electric Company | Natural gas | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 7 6
Union Electric Company | Power | Other current assets    
Derivative [Line Items]    
Derivative Assets 5 6
Union Electric Company | Power | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 0 0
Union Electric Company | Power | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 0 0
Ameren Illinois Company    
Derivative [Line Items]    
Derivative Assets 16 6
Derivative Liability 87 88
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 11 2
Ameren Illinois Company | Natural gas | Other assets    
Derivative [Line Items]    
Derivative Assets 5 4
Ameren Illinois Company | Natural gas | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 6 22
Ameren Illinois Company | Natural gas | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 14 13
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 7 10
Ameren Illinois Company | Power | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability $ 60 $ 43
v3.25.1
Derivative Financial Instruments (Offsetting Assets and Liabilities) (Details) - Not Designated As Hedging Instrument - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Derivative [Line Items]    
Gross derivative asset amount recognized on the balance sheet $ 27 $ 16
Gross derivative liability amount recognized on the balance sheet 99 103
Union Electric Company    
Derivative [Line Items]    
Gross derivative asset amount recognized on the balance sheet 11 10
Gross derivative liability amount recognized on the balance sheet 12 15
Ameren Illinois Company    
Derivative [Line Items]    
Gross derivative asset amount recognized on the balance sheet 16 6
Gross derivative liability amount recognized on the balance sheet $ 87 $ 88
v3.25.1
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, 2025
Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: $ 1,304 $ 1,333
Assets fair value 1,331 1,349
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: 868 911
Assets fair value 870 911
Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 436 422
Assets fair value 450 429
Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 0 0
Assets fair value 11 9
Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 27 16
Derivative Liability 99 103
Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 2 0
Derivative Liability 3 5
Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 14 7
Derivative Liability 25 39
Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 11 9
Derivative Liability 71 59
Union Electric Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 1,304 1,333
Assets fair value 1,315 1,343
Union Electric Company | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 868 911
Assets fair value 868 911
Union Electric Company | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 436 422
Assets fair value 441 426
Union Electric Company | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 0 0
Assets fair value 6 6
Union Electric Company | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 11 10
Derivative Liability 12 15
Union Electric Company | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 0 0
Derivative Liability 3 4
Union Electric Company | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 5 4
Derivative Liability 8 11
Union Electric Company | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 6 6
Derivative Liability 1 0
Union Electric Company | Fuel oils | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 3 4
Union Electric Company | Fuel oils | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 3 4
Union Electric Company | Fuel oils | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 0 0
Union Electric Company | Fuel oils | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 0 0
Union Electric Company | Natural gas | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 6 4
Derivative Liability 9 11
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 5 4
Derivative Liability 8 11
Union Electric Company | Natural gas | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 1 0
Derivative Liability 1 0
Union Electric Company | Power | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 5 6
Union Electric Company | Power | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 0 0
Union Electric Company | Power | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 0 0
Union Electric Company | Power | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 5 6
Union Electric Company | Equity securities: | U.S. large capitalization    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 868 911
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: 868 911
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: 188 191
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: 188 191
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: 156 145
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: 156 145
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: 92 86
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: 92 86
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 16 6
Ameren Illinois Company | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 2 0
Ameren Illinois Company | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 9 3
Ameren Illinois Company | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 5 3
Ameren Illinois Company | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 87 88
Ameren Illinois Company | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 0 1
Ameren Illinois Company | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 17 28
Ameren Illinois Company | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 70 59
Ameren Illinois Company | Natural gas | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 16 6
Derivative Liability 20 35
Ameren Illinois Company | Natural gas | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 2 0
Derivative Liability 0 1
Ameren Illinois Company | Natural gas | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 9 3
Derivative Liability 17 28
Ameren Illinois Company | Natural gas | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 5 3
Derivative Liability 3 6
Ameren Illinois Company | Power | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 67 53
Ameren Illinois Company | Power | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 0 0
Ameren Illinois Company | Power | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 0 0
Ameren Illinois Company | Power | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability $ 67 $ 53
v3.25.1
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, 2025
Mar. 31, 2024
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance $ (47) $ (64)
Included in regulatory assets/liabilities (14) 9
Settlements, assets   (3)
Settlement, liabilities 1  
Change in unrealized gains (losses) related to assets/liabilities held at period end (14) 11
Ending balance (62) (52)
Union Electric Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 6 4
Included in regulatory assets/liabilities 2 (1)
Settlement, liabilities (3) (1)
Change in unrealized gains (losses) related to assets/liabilities held at period end 2 0
Ending balance 5 2
Ameren Illinois Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance (53) (68)
Included in regulatory assets/liabilities (16) 10
Settlements, assets 2 4
Change in unrealized gains (losses) related to assets/liabilities held at period end (16) 11
Ending balance $ (67) $ (54)
v3.25.1
Fair Value Measurements (Schedule Of Valuation Process And Unobservable Inputs) (Details) - Power
$ in Millions
Mar. 31, 2025
USD ($)
$ / MWh
Dec. 31, 2024
USD ($)
$ / MWh
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative Assets | $ $ 5 $ 6
Derivative liabilities | $ $ (67) $ (53)
Commodity Forward Price | Discounted cash flow | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Measurement input 32 32
Commodity Forward Price | Discounted cash flow | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Measurement input 65 69
Commodity Forward Price | Discounted cash flow | Weighted Average    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Measurement input 41 45
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) (2)
Nodal Basis | Discounted cash flow | Weighted Average    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Measurement input (5) (5)
v3.25.1
Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Financial Assets and Liabilities) (Details) - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Carrying Amount(a)    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-Term Debt, Carrying Amount $ 18,371 $ 17,579
Debt Issuance Costs, Net 133 129
Carrying Amount(a) | Union Electric Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-Term Debt, Carrying Amount 7,746 7,745
Debt Issuance Costs, Net 61 62
Carrying Amount(a) | Ameren Illinois Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-Term Debt, Carrying Amount 5,900 5,852
Debt Issuance Costs, Net 54 51
Fair Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 16,824 15,933
Fair Value | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 16,277 15,395
Fair Value | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 547 538
Fair Value | Union Electric Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 6,963 6,926
Fair Value | Union Electric Company | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 6,963 6,926
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 5,310 5,243
Fair Value | Ameren Illinois Company | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 5,310 5,243
Fair Value | Ameren Illinois Company | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value $ 0 $ 0
v3.25.1
Related Party Transactions (Narrative) (Details) - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Related Party Transaction [Line Items]    
Other assets $ 1,143 $ 1,123
Union Electric Company    
Related Party Transaction [Line Items]    
Other assets 239 254
Ameren Illinois Company    
Related Party Transaction [Line Items]    
Other assets 731 697
Ameren Services Support Services Agreement | Union Electric Company | Related Party    
Related Party Transaction [Line Items]    
Other assets 27 29
Ameren Services Support Services Agreement | Ameren Illinois Company | Related Party    
Related Party Transaction [Line Items]    
Other assets $ 30 $ 32
v3.25.1
Related Party Transactions (Schedule of Affiliate Receivables and Payables) (Details) - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Related Party Transaction [Line Items]    
Accounts Payable, Related Parties, Current $ 702 $ 1,059
Accounts Receivable, Related Parties, Current 667 525
Union Electric Company | Related Party    
Related Party Transaction [Line Items]    
Accounts Payable, Related Parties, Current 42 50
Accounts Receivable, Related Parties, Current 44 40
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 29 28
Ameren Illinois Company | Related Party    
Related Party Transaction [Line Items]    
Accounts Payable, Related Parties, Current 71 74
Accounts Receivable, Related Parties, Current 22 15
Ameren Illinois Company | Income taxes payable to parent | Related Party    
Related Party Transaction [Line Items]    
Accounts Payable, Related Parties, Current 32 32
Ameren Illinois Company | Income taxes receivable from parent | Related Party    
Related Party Transaction [Line Items]    
Accounts Receivable, Related Parties, Current $ 0 $ 0
v3.25.1
Related Party Transactions (Effects of Related-party Transactions on the Statement of Income) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Related Party Transaction [Line Items]    
Operating Revenues $ 2,097 $ 1,816
Other operations and maintenance 485 470
Interest Charges 175 154
Union Electric Company    
Related Party Transaction [Line Items]    
Operating Revenues 957 775
Other operations and maintenance 250 254
Interest Charges 60 62
Union Electric Company | Ameren Missouri Power Supply Agreements with Ameren Illinois | Related Party    
Related Party Transaction [Line Items]    
Operating Revenues   1
Union Electric Company | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party    
Related Party Transaction [Line Items]    
Operating Revenues 7 7
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 7
Union Electric Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI | Related Party    
Related Party Transaction [Line Items]    
Purchased Power 3 2
Union Electric Company | Purchased Power | Related Party    
Related Party Transaction [Line Items]    
Purchased Power 3 2
Union Electric Company | Ameren Services Support Services Agreement | Related Party    
Related Party Transaction [Line Items]    
Other operations and maintenance 44 38
Union Electric Company | Total Related Party Other Operations and Maintenance | Related Party    
Related Party Transaction [Line Items]    
Other operations and maintenance 44 38
Union Electric Company | Money pool interest | Related Party    
Related Party Transaction [Line Items]    
Interest Charges 1 3
Union Electric Company | Long-Term Debt | Related Party    
Related Party Transaction [Line Items]    
Interest Charges 1 0
Ameren Illinois Company    
Related Party Transaction [Line Items]    
Operating Revenues 1,100 1,000
Purchased Power 175 164
Other operations and maintenance 236 210
Interest Charges 62 55
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 1
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Miscellaneous Support Services | Related Party    
Related Party Transaction [Line Items]    
Operating Revenues 2 1
Ameren Illinois Company | Total Related Party Operating Revenues | Related Party    
Related Party Transaction [Line Items]    
Operating Revenues 2 1
Ameren Illinois Company | Ameren Illinois Power Supply Agreements with Ameren Missouri | Related Party    
Related Party Transaction [Line Items]    
Purchased Power   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 40 37
Ameren Illinois Company | Total Related Party Other Operations and Maintenance | Related Party    
Related Party Transaction [Line Items]    
Other operations and maintenance 41 37
Ameren Illinois Company | Money pool interest | Related Party    
Related Party Transaction [Line Items]    
Interest Charges 1 2
Ameren Illinois Company | Long-Term Debt | Related Party    
Related Party Transaction [Line Items]    
Interest Charges $ 1 $ 0
v3.25.1
Commitments And Contingencies (Environmental Matters) (Detail)
$ in Millions
Mar. 31, 2025
USD ($)
scrubber
site
Dec. 31, 2024
USD ($)
Loss Contingencies [Line Items]    
Estimated capital costs to comply with existing and known federal CO2 emissions regulations $ 580  
Estimated capital costs to comply with existing and known federal MATS regulations 320  
Asset Retirement Obligation 835 $ 827
Minimum    
Loss Contingencies [Line Items]    
Estimated capital costs to comply with existing and known federal and state air emissions regulations 900  
Maximum    
Loss Contingencies [Line Items]    
Estimated capital costs to comply with existing and known federal and state air emissions regulations $ 1,000  
Union Electric Company    
Loss Contingencies [Line Items]    
Number of Energy Center Scrubbers | scrubber 2  
Estimated capital costs to comply with existing and known federal CO2 emissions regulations $ 580  
Estimated capital costs to comply with existing and known federal MATS regulations 320  
Asset Retirement Obligation 831 823
Union Electric Company | Minimum    
Loss Contingencies [Line Items]    
Estimated capital costs to comply with existing and known federal and state air emissions regulations 900  
Union Electric Company | Maximum    
Loss Contingencies [Line Items]    
Estimated capital costs to comply with existing and known federal and state air emissions regulations 1,000  
Ameren Illinois Company    
Loss Contingencies [Line Items]    
Asset Retirement Obligation $ 4 $ 4
Number of remediation sites | site 3  
Manufactured Gas Plant    
Loss Contingencies [Line Items]    
Accrual for environmental loss contingencies $ 47  
Manufactured Gas Plant | Ameren Illinois Company    
Loss Contingencies [Line Items]    
Number of remediation sites | site 44  
Accrual for environmental loss contingencies $ 47  
Manufactured Gas Plant | Ameren Illinois Company | Minimum    
Loss Contingencies [Line Items]    
Estimate of possible loss 47  
Manufactured Gas Plant | Ameren Illinois Company | Maximum    
Loss Contingencies [Line Items]    
Estimate of possible loss 91  
New CCR Rules Estimate    
Loss Contingencies [Line Items]    
Asset Retirement Obligation 46  
New CCR Rules Estimate | Union Electric Company    
Loss Contingencies [Line Items]    
Asset Retirement Obligation $ 46  
v3.25.1
Callaway Energy Center (Insurance Disclosure) (Details)
$ in Millions
 3 Months Ended
Mar. 31, 2025
USD ($)
yr
Nuclear Waste Matters [Line Items]  
Decommissioning Cost $ 7.0
Frequency of Decommissioning Cost Study 3 years
Future Decommissioning Cost $ 0.0
Number Of Years The Limit Of Liability And The Maximum Potential Annual Payments Are Adjusted 5 years
Number Of Weeks Of Coverage After The First Twelve Weeks Of An Outage | 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 $ 500.0
Insurance Maximum Coverage per Incident 0.0
Public Liability And Nuclear Worker Liability - Pool Participation  
Nuclear Waste Matters [Line Items]  
Insurance Aggregate Maximum Coverage 15,763.0
Insurance Maximum Coverage per Incident 166.0
Threshold Amount For Retrospective Insurance Assessment For Covered Loss Under Public Liability And Nuclear Worker Liability Insurance Policy 500.0
Maximum Annual Payment Per Incident At Licensed Commercial Nuclear Reactor 25.0
Public Liability  
Nuclear Waste Matters [Line Items]  
Insurance Aggregate Maximum Coverage 16,263.0
Insurance Maximum Coverage per Incident 166.0
Property Damage - Nuclear Electric Insurance Ltd  
Nuclear Waste Matters [Line Items]  
Insurance Aggregate Maximum Coverage 3,200.0
Insurance Maximum Coverage per Incident 22.0
Accidental Outage - Nuclear Electric Insurance Ltd  
Nuclear Waste Matters [Line Items]  
Insurance Aggregate Maximum Coverage 490.0
Insurance Maximum Coverage per Incident 9.0
Amount Of Weekly Indemnity Coverage Commencing Twelve Weeks After Power Outage 4.5
Amount Of Additional Weekly Indemnity Coverage Commencing After Initial Indemnity Coverage 3.6
Amount Of Weekly Indemnity Coverage Thereafter Not Exceeding Policy Limit 490.0
Sub-Limit Of Amount Of Weekly Indemnity Coverage Thereafter Not Exceeding Policy Limit For Non-Nuclear Events 291.0
Radiation Event  
Nuclear Waste Matters [Line Items]  
Insurance Aggregate Maximum Coverage 2,700.0
Aggregate Nuclear Power Industry Insurance Policy Limit For Losses From Terrorist Attacks Within Twelve Month Period 3,200.0
Non-Radiation Event  
Nuclear Waste Matters [Line Items]  
Insurance Aggregate Maximum Coverage 700.0
Aggregate Nuclear Power Industry Insurance Policy Limit For Losses From Terrorist Attacks Within Twelve Month Period 1,800.0
Property Damage European Mutual Association for Nuclear Insurance  
Nuclear Waste Matters [Line Items]  
Insurance Aggregate Maximum Coverage $ 490.0
v3.25.1
Retirement Benefits (Components Of Net Periodic Benefit Cost) (Detail) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Total non-service cost components $ (66) $ (76)
Pension Plan    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Service Cost 21 21
Interest cost 58 55
Defined Benefit Plan, Expected Return (Loss) on Plan Assets (76) (82)
Prior service cost (credit) 0 0
Actuarial (gain) (10) (17)
Total non-service cost components (28) (44)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total $ (7) (23)
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 $ 2 3
Interest cost 11 11
Defined Benefit Plan, Expected Return (Loss) on Plan Assets (23) (23)
Prior service cost (credit) (1) (1)
Actuarial (gain) (9) (10)
Total non-service cost components (22) (23)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total $ (20) $ (20)
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  
v3.25.1
Retirement Benefits (Summary of Benefit Plan Costs Incurred) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Pension Plan    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Net periodic benefit cost $ (7) $ (23)
Pension Plan | Union Electric Company    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Net periodic benefit cost (4) (12)
Pension Plan | Ameren Illinois Company    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Net periodic benefit cost (2) (9)
Pension Plan | Other Affiliated Entities And Intercompany Eliminations    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Net periodic benefit cost (1) (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) (20)
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) (7)
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
v3.25.1
Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details)
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Income Taxes [Line Items]    
Federal statutory corporate income tax rate 21.00% 21.00%
Increases (decreases) from:    
Amortization of excess deferred taxes (7.00%) (8.00%)
Amortization of deferred investment tax credit (1.00%) 0.00%
Renewable and other tax credits (4.00%) (4.00%)
State tax 6.00% 6.00%
Depreciation differences 1.00% 1.00%
Stock-based compensation 0.00% 1.00%
Other permanent items 0.00% (1.00%)
Effective income tax rate 14.00% 14.00%
Union Electric Company    
Income Taxes [Line Items]    
Federal statutory corporate income tax rate 21.00% 21.00%
Increases (decreases) from:    
Amortization of excess deferred taxes (8.00%) (12.00%)
Amortization of deferred investment tax credit (1.00%) 0.00%
Renewable and other tax credits (7.00%) (8.00%)
State tax 4.00% 4.00%
Depreciation differences 1.00% 1.00%
Stock-based compensation 0.00% 0.00%
Other permanent items 0.00% 0.00%
Effective income tax rate 8.00% 4.00%
Ameren Illinois Company    
Income Taxes [Line Items]    
Federal statutory corporate income tax rate 21.00% 21.00%
Increases (decreases) from:    
Amortization of excess deferred taxes (3.00%) (4.00%)
Amortization of deferred investment tax credit 0.00% 0.00%
Renewable and other tax credits 0.00% 0.00%
State tax 7.00% 7.00%
Depreciation differences 1.00% 0.00%
Stock-based compensation 0.00% 0.00%
Other permanent items 0.00% 0.00%
Effective income tax rate 24.00% 24.00%
v3.25.1
Supplemental Information (Cash and Cash Equivalents) (Details) - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Mar. 31, 2024
Dec. 31, 2023
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]        
Cash and cash equivalents $ 23 $ 7    
Restricted cash included in “Other current assets” 40 15    
Restricted cash included in “Other assets” 307 296    
Restricted cash included in “Nuclear decommissioning trust fund” 6 10    
Total cash, cash equivalents, and restricted cash 376 328 $ 355 $ 272
Union Electric Company        
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]        
Cash and cash equivalents 7 0    
Restricted cash included in “Other current assets” 32 7    
Restricted cash included in “Other assets” 0 0    
Restricted cash included in “Nuclear decommissioning trust fund” 6 10    
Total cash, cash equivalents, and restricted cash 45 17 16 10
Ameren Illinois Company        
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]        
Cash and cash equivalents 4 0    
Restricted cash included in “Other current assets” 5 6    
Restricted cash included in “Other assets” 307 296    
Restricted cash included in “Nuclear decommissioning trust fund” 0 0    
Total cash, cash equivalents, and restricted cash $ 316 $ 302 $ 254 $ 234
v3.25.1
Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Dec. 31, 2024
Allowance for Doubtful Accounts Receivable [Roll Forward]      
Beginning of period $ 30 $ 30  
Bad debt expense 16 10  
Charged to other accounts 1 3  
Net write-offs (6) (6)  
End of period 41 37  
Payables for purchased receivables 47   $ 43
Union Electric Company      
Allowance for Doubtful Accounts Receivable [Roll Forward]      
Beginning of period 12 12  
Bad debt expense 2 1  
Net write-offs (2) (2)  
End of period 12 11  
Ameren Illinois Company      
Allowance for Doubtful Accounts Receivable [Roll Forward]      
Beginning of period 18 18  
Bad debt expense 14 9  
Charged to other accounts 1 3  
Net write-offs (4) (4)  
End of period 29 $ 26  
Payables for purchased receivables $ 47   $ 43
v3.25.1
Supplemental Information (Supplemental Cash Flow Information) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Supplemental Cash Flow Information [Line Items]    
Accrued capital expenditures, including nuclear fuel expenditures $ 381 $ 310
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund (40) 74
Issuance of common stock for stock-based compensation    
Supplemental Cash Flow Information [Line Items]    
Stock Issued 25 16
Issuance of common stock under the DRPlus    
Supplemental Cash Flow Information [Line Items]    
Stock Issued 9 7
Union Electric Company    
Supplemental Cash Flow Information [Line Items]    
Accrued capital expenditures, including nuclear fuel expenditures 214 169
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund (40) 74
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 159 122
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund 0 0
Ameren Illinois Company | Issuance of common stock for stock-based compensation    
Supplemental Cash Flow Information [Line Items]    
Stock Issued 0 0
Ameren Illinois Company | Issuance of common stock under the DRPlus    
Supplemental Cash Flow Information [Line Items]    
Stock Issued $ 0 $ 0
v3.25.1
Supplemental Information (Schedule of Asset Retirement Obligations) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Dec. 31, 2024
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Asset Retirement Obligation, Beginning Balance $ 827  
Liabilities settled (1)  
Accretion 9  
Asset Retirement Obligation, Ending Balance 835  
Other current liabilities 510 $ 475
Union Electric Company    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Asset Retirement Obligation, Beginning Balance 823  
Liabilities settled (1)  
Accretion 9  
Asset Retirement Obligation, Ending Balance 831  
Other current liabilities 199 206
Ameren Illinois Company    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Asset Retirement Obligation, Beginning Balance 4  
Liabilities settled 0  
Accretion 0  
Asset Retirement Obligation, Ending Balance 4  
Other current liabilities 159 172
Asset Retirement Obligation Balance    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Other current liabilities $ 5 $ 5
v3.25.1
Supplemental Information (Narrative) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Dec. 31, 2024
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount $ (1) $ 1  
Deferred Compensation Liability, Classified, Noncurrent $ 79   $ 79
January 1, 2025      
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 | January 1, 2025      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares granted (in shares) 275,869    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Fair Value $ 33    
Stock Issued During Period Percentage Conversion Of Units, Low End 0.00%    
Stock Issued During Period Percentage Conversion Of Units, High End 200.00%    
Performance Shares | Market performance measures achievement | January 1, 2025      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares granted (in shares) 236,448    
Performance Shares | Renewable generation and energy storage installation targets | January 1, 2025      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares granted (in shares) 39,421    
Restricted Stock Units (RSUs) | January 1, 2025      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares granted (in shares) 118,213    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Fair Value $ 11    
v3.25.1
Supplemental Information (Schedule Of Excise Taxes) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Accounting Policies [Line Items]    
Excise tax expense $ 81 $ 72
Union Electric Company    
Accounting Policies [Line Items]    
Excise tax expense 38 35
Ameren Illinois Company    
Accounting Policies [Line Items]    
Excise tax expense $ 43 $ 37
v3.25.1
Supplemental Information (Earnings Per Share) (Details) - shares
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Earnings Per Share Reconciliation [Abstract]    
Weighted-average Common Shares Outstanding – Basic 270,000,000.0 266,400,000
Assumed settlement of performance share units and restricted stock units 1,000,000.0 400,000
Dilutive effect of forward sale agreements 400,000 0
Weighted-average Common Shares Outstanding – Diluted 271,400,000 266,800,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares) 0 0
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount - Forward Equity 0  
v3.25.1
Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Segment Reporting Information [Line Items]    
External revenues $ 2,097 $ 1,816
Revenues 2,097 1,816
Fuel and purchased power (502) (328)
Natural gas purchased for resale (169) (151)
Other operations and maintenance expenses (485) (470)
Depreciation and amortization (367) (361)
Taxes other than income taxes (144) (135)
Other Income, Net 85 89
Interest charges (175) (154)
Income taxes (50) (44)
Noncontrolling interests - preferred stock dividends (1) (1)
Net income attributable to Ameren common shareholders 289 261
Interest income 11 8
Capital expenditures 1,064 890
Union Electric Company    
Segment Reporting Information [Line Items]    
External revenues 957 775
Fuel and purchased power (330) (166)
Natural gas purchased for resale (30) (28)
Other operations and maintenance expenses (250) (254)
Taxes other than income taxes (89) (87)
Other Income, Net 43 44
Interest charges (60) (62)
Income taxes (4) (1)
Noncontrolling interests - preferred stock dividends (1) (1)
Net income attributable to Ameren common shareholders 42 25
Net income available to common shareholder 43 26
Ameren Illinois Company    
Segment Reporting Information [Line Items]    
External revenues 1,100 1,000
Revenues 1,100 1,000
Purchased Power (175) (164)
Natural gas purchased for resale (139) (123)
Other operations and maintenance expenses (236) (210)
Depreciation and amortization (159) (153)
Taxes other than income taxes (51) (44)
Other Income, Net 34 31
Interest charges (62) (55)
Income taxes (76) (67)
Net income attributable to Ameren common shareholders 236 215
Net income available to common shareholder 236 215
Interest income 9 6
Capital expenditures 363 373
Operating Segments | Union Electric Company    
Segment Reporting Information [Line Items]    
External revenues 950 768
Revenues 957 775
Fuel and purchased power (330) (166)
Natural gas purchased for resale (30) (28)
Other operations and maintenance expenses (250) (254)
Depreciation and amortization (194) (195)
Taxes other than income taxes (89) (87)
Other Income, Net 43 44
Interest charges (60) (62)
Income taxes (4) (1)
Noncontrolling interests - preferred stock dividends (1) (1)
Net income attributable to Ameren common shareholders 42 25
Interest income 2 2
Capital expenditures 658 466
Operating Segments | Ameren Illinois Electric Distribution    
Segment Reporting Information [Line Items]    
External revenues 570 506
Revenues 572 506
Fuel and purchased power (212) (192)
Natural gas purchased for resale 0 0
Other operations and maintenance expenses (166) (136)
Depreciation and amortization (91) (93)
Taxes other than income taxes (21) (17)
Other Income, Net 23 22
Interest charges (26) (22)
Income taxes (16) (12)
Noncontrolling interests - preferred stock dividends 0 0
Net income attributable to Ameren common shareholders 63 56
Interest income 8 6
Capital expenditures 167 184
Operating Segments | Ameren Illinois Natural Gas    
Segment Reporting Information [Line Items]    
External revenues 411 391
Revenues 411 391
Fuel and purchased power 0 0
Natural gas purchased for resale (139) (123)
Other operations and maintenance expenses (55) (58)
Depreciation and amortization (32) (33)
Taxes other than income taxes (29) (26)
Other Income, Net 5 7
Interest charges (15) (15)
Income taxes (38) (37)
Noncontrolling interests - preferred stock dividends 0 0
Net income attributable to Ameren common shareholders 108 106
Interest income 0 0
Capital expenditures 59 60
Operating Segments | Ameren Transmission    
Segment Reporting Information [Line Items]    
External revenues 166 151
Revenues 210 185
Fuel and purchased power 0 0
Natural gas purchased for resale 0 0
Other operations and maintenance expenses (19) (19)
Depreciation and amortization (48) (39)
Taxes other than income taxes (1) (2)
Other Income, Net 7 2
Interest charges (29) (29)
Income taxes (31) (26)
Noncontrolling interests - preferred stock dividends 0 0
Net income attributable to Ameren common shareholders 89 72
Interest income 1 0
Capital expenditures 173 166
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution    
Segment Reporting Information [Line Items]    
External revenues 572 506
Revenues 572 506
Purchased Power (212) (192)
Other operations and maintenance expenses (166) (136)
Depreciation and amortization (91) (93)
Taxes other than income taxes (21) (17)
Other Income, Net 23 22
Interest charges (26) (22)
Income taxes (16) (12)
Net income available to common shareholder 63 56
Interest income 8 6
Capital expenditures 167 184
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas    
Segment Reporting Information [Line Items]    
External revenues 411 391
Revenues 411 391
Natural gas purchased for resale (139) (123)
Other operations and maintenance expenses (55) (58)
Depreciation and amortization (32) (33)
Taxes other than income taxes (29) (26)
Other Income, Net 5 7
Interest charges (15) (15)
Income taxes (38) (37)
Net income available to common shareholder 108 106
Interest income 0 0
Capital expenditures 59 60
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission    
Segment Reporting Information [Line Items]    
External revenues 117 103
Revenues 154 131
Other operations and maintenance expenses (15) (16)
Depreciation and amortization (36) (27)
Taxes other than income taxes (1) (1)
Other Income, Net 6 2
Interest charges (21) (18)
Income taxes (22) (18)
Net income available to common shareholder 65 53
Interest income 1 0
Capital expenditures 137 129
Other    
Segment Reporting Information [Line Items]    
Other operations and maintenance expenses (8) (14)
Depreciation and amortization (2) (1)
Taxes other than income taxes (4) (3)
Other Income, Net 8 20
Interest charges (46) (32)
Income taxes 39 32
Net income attributable to Ameren common shareholders (13) 2
Interest income 1 6
Capital expenditures 2 2
Intersegment Eliminations    
Segment Reporting Information [Line Items]    
Intersegment revenues (53) (41)
Revenues (53) (41)
Fuel and purchased power 40 30
Natural gas purchased for resale 0 0
Other operations and maintenance expenses 13 11
Depreciation and amortization 0 0
Taxes other than income taxes 0 0
Other Income, Net (1) (6)
Interest charges 1 6
Income taxes 0 0
Noncontrolling interests - preferred stock dividends 0 0
Interest income (1) (6)
Capital expenditures 5 12
Intersegment Eliminations | Union Electric Company    
Segment Reporting Information [Line Items]    
Intersegment revenues (7) (7)
Intersegment Eliminations | Ameren Illinois Electric Distribution    
Segment Reporting Information [Line Items]    
Intersegment revenues (2) 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 (44) (34)
Intersegment Eliminations | Ameren Illinois Company    
Segment Reporting Information [Line Items]    
Intersegment revenues (37) (28)
Revenues (37) (28)
Purchased Power (37) (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 $ (37) $ (28)
v3.25.1
Segment Information (Disaggregation of Revenue) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Disaggregation of Revenue [Line Items]    
Operating Revenues $ 2,097 $ 1,816
Revenues 2,097 1,816
Revenues from alternative revenue programs 18 61
Other revenues not from contracts with customers 5 4
Union Electric Company    
Disaggregation of Revenue [Line Items]    
Revenues from alternative revenue programs (5) (6)
Other revenues not from contracts with customers 1 1
Ameren Illinois Electric Distribution    
Disaggregation of Revenue [Line Items]    
Revenues from alternative revenue programs 21 39
Other revenues not from contracts with customers 3 2
Ameren Illinois Natural Gas    
Disaggregation of Revenue [Line Items]    
Revenues from alternative revenue programs 3 19
Other revenues not from contracts with customers 1 1
Ameren Transmission    
Disaggregation of Revenue [Line Items]    
Revenues from alternative revenue programs (1) 9
Other revenues not from contracts with customers 0 0
Electric    
Disaggregation of Revenue [Line Items]    
Operating Revenues 1,622 1,364
Revenues 1,622 1,364
Electric | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 718 638
Electric | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 453 424
Electric | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 116 106
Electric | Other    
Disaggregation of Revenue [Line Items]    
Revenues 335 196
Natural gas    
Disaggregation of Revenue [Line Items]    
Operating Revenues 475 452
Revenues 475 452
Natural gas | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 352 327
Natural gas | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 96 84
Natural gas | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 6 6
Natural gas | Other    
Disaggregation of Revenue [Line Items]    
Revenues 21 35
Ameren Illinois Company    
Disaggregation of Revenue [Line Items]    
Operating Revenues 1,100 1,000
Revenues 1,100 1,000
Revenues from alternative revenue programs 23 66
Other revenues not from contracts with customers 4 3
Ameren Illinois Company | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 651 584
Ameren Illinois Company | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 257 233
Ameren Illinois Company | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 54 49
Ameren Illinois Company | Other    
Disaggregation of Revenue [Line Items]    
Revenues 138 134
Ameren Illinois Company | Ameren Illinois Electric Distribution    
Disaggregation of Revenue [Line Items]    
Revenues from alternative revenue programs 21 39
Other revenues not from contracts with customers 3 2
Ameren Illinois Company | Ameren Illinois Natural Gas    
Disaggregation of Revenue [Line Items]    
Revenues from alternative revenue programs 3 19
Other revenues not from contracts with customers 1 1
Ameren Illinois Company | Ameren Illinois Transmission    
Disaggregation of Revenue [Line Items]    
Revenues from alternative revenue programs (1) 8
Other revenues not from contracts with customers 0 0
Ameren Illinois Company | Electric    
Disaggregation of Revenue [Line Items]    
Operating Revenues 689 609
Ameren Illinois Company | Natural gas    
Disaggregation of Revenue [Line Items]    
Operating Revenues 411 391
Operating Segments | Union Electric Company    
Disaggregation of Revenue [Line Items]    
Operating Revenues 950 768
Revenues 957 775
Operating Segments | Ameren Illinois Electric Distribution    
Disaggregation of Revenue [Line Items]    
Operating Revenues 570 506
Revenues 572 506
Operating Segments | Ameren Illinois Natural Gas    
Disaggregation of Revenue [Line Items]    
Operating Revenues 411 391
Revenues 411 391
Operating Segments | Ameren Transmission    
Disaggregation of Revenue [Line Items]    
Operating Revenues 166 151
Revenues 210 185
Operating Segments | Electric | Union Electric Company    
Disaggregation of Revenue [Line Items]    
Revenues 893 714
Operating Segments | Electric | Union Electric Company | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 376 341
Operating Segments | Electric | Union Electric Company | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 273 259
Operating Segments | Electric | Union Electric Company | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 66 61
Operating Segments | Electric | Union Electric Company | Other    
Disaggregation of Revenue [Line Items]    
Revenues 178 53
Operating Segments | Electric | Ameren Illinois Electric Distribution    
Disaggregation of Revenue [Line Items]    
Revenues 572 506
Operating Segments | Electric | Ameren Illinois Electric Distribution | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 342 297
Operating Segments | Electric | Ameren Illinois Electric Distribution | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 180 165
Operating Segments | Electric | Ameren Illinois Electric Distribution | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 50 45
Operating Segments | Electric | Ameren Illinois Electric Distribution | Other    
Disaggregation of Revenue [Line Items]    
Revenues 0 (1)
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 210 185
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 210 185
Operating Segments | Natural gas | Union Electric Company    
Disaggregation of Revenue [Line Items]    
Revenues 64 61
Operating Segments | Natural gas | Union Electric Company | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 43 40
Operating Segments | Natural gas | Union Electric Company | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 19 16
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 0 3
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 411 391
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 309 287
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 77 68
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 4 4
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Other    
Disaggregation of Revenue [Line Items]    
Revenues 21 32
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 572 506
Revenues 572 506
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas    
Disaggregation of Revenue [Line Items]    
Operating Revenues 411 391
Revenues 411 391
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission    
Disaggregation of Revenue [Line Items]    
Operating Revenues 117 103
Revenues 154 131
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution    
Disaggregation of Revenue [Line Items]    
Revenues 572 506
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 342 297
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 180 165
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 50 45
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Other    
Disaggregation of Revenue [Line Items]    
Revenues 0 (1)
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission    
Disaggregation of Revenue [Line Items]    
Revenues 154 131
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 154 131
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas    
Disaggregation of Revenue [Line Items]    
Revenues 411 391
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 309 287
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 77 68
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 4 4
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Other    
Disaggregation of Revenue [Line Items]    
Revenues 21 32
Intersegment Eliminations    
Disaggregation of Revenue [Line Items]    
Revenues (53) (41)
Revenues (53) (41)
Intersegment Eliminations | Union Electric Company    
Disaggregation of Revenue [Line Items]    
Revenues (7) (7)
Intersegment Eliminations | Ameren Illinois Electric Distribution    
Disaggregation of Revenue [Line Items]    
Revenues (2) 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 (44) (34)
Intersegment Eliminations | Electric    
Disaggregation of Revenue [Line Items]    
Revenues (53) (41)
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 (53) (41)
Intersegment Eliminations | Natural gas    
Disaggregation of Revenue [Line Items]    
Revenues 0 0
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 0
Intersegment Eliminations | Ameren Illinois Company    
Disaggregation of Revenue [Line Items]    
Revenues (37) (28)
Revenues (37) (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 (37) (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 $ (37) $ (28)