AMEREN CORP, 10-Q filed on 11/6/2025
Quarterly Report
v3.25.3
Cover Page - shares
 9 Months Ended
Sep. 30, 2025
Oct. 31, 2025
Entity Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Sep. 30, 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   270,494,916
Entity Central Index Key 0001002910  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2025  
Document Fiscal Period Focus Q3  
Amendment Flag false  
Union Electric Company    
Entity Information [Line Items]    
Entity File Number 1-2967  
Entity Registrant Name Union Electric Company  
Entity Tax Identification Number 43-0559760  
Entity Incorporation, State or Country Code MO  
Entity Address, Address Line One 1901 Chouteau Avenue  
Entity Address, City or Town St. Louis  
Entity Address, State or Province MO  
Entity Address, Postal Zip Code 63103  
City Area Code (314)  
Local Phone Number 621-3222  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business false  
Emerging growth company false  
Entity Shell Company false  
Shares outstanding   102,123,834
Entity Central Index Key 0000100826  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2025  
Document Fiscal Period Focus Q3  
Amendment Flag false  
Ameren Illinois Company    
Entity Information [Line Items]    
Entity File Number 1-3672  
Entity Registrant Name Ameren Illinois Company  
Entity Tax Identification Number 37-0211380  
Entity Incorporation, State or Country Code IL  
Entity Address, Address Line One 10 Richard Mark Way  
Entity Address, City or Town Collinsville  
Entity Address, State or Province IL  
Entity Address, Postal Zip Code 62234  
City Area Code (618)  
Local Phone Number 343-8150  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business false  
Emerging growth company false  
Entity Shell Company false  
Shares outstanding   25,452,373
Entity Central Index Key 0000018654  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2025  
Document Fiscal Period Focus Q3  
Amendment Flag false  
v3.25.3
Consolidated Statement of Income (Loss) and Comprehensive Income - USD ($)
shares in Millions, $ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Operating Revenues:        
Operating Revenues $ 2,699 $ 2,173 $ 7,017 $ 5,682
Operating Expenses:        
Fuel and purchased power 768 499 2,064 1,154
Natural gas purchased for resale 25 30 233 214
Other operations and maintenance 502 520 1,447 1,455
Depreciation and amortization 415 388 1,168 1,125
Taxes other than income taxes 164 150 439 416
Total operating expenses 1,874 1,587 5,351 4,364
Operating Income 825 586 1,666 1,318
Other Income, Net 76 101 257 293
Interest Charges 208 173 570 492
Income Before Income Taxes 693 514 1,353 1,119
Income Taxes 52 57 145 140
Net Income 641 457 1,208 979
Less: Net Income Attributable to Noncontrolling Interests 1 1 4 4
Preferred Stock Dividends 1 1 4 4
Net income attributable to Ameren common shareholders 640 456 1,204 975
Pension and other postretirement benefit plan activity, net of income taxes (benefit) 0 (1) (2) (4)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax 0 0 (6) 0
Comprehensive Income 641 456 1,200 975
Less: Comprehensive Income Attributable to Noncontrolling Interests 1 1 4 4
Comprehensive Income Attributable to Ameren Common Shareholders $ 640 $ 455 $ 1,196 $ 971
Earnings per Common Share - Basic $ 2.37 $ 1.71 $ 4.46 $ 3.66
Earnings per Common Share - Basic $ 2.35 $ 1.70 $ 4.43 $ 3.65
Weighted-average Common Shares Outstanding – Basic 270.4 266.8 270.2 266.6
Weighted-average Common Shares Outstanding – Diluted 272.2 267.3 271.7 266.9
Electric        
Operating Revenues:        
Operating Revenues $ 2,563 $ 2,035 $ 6,223 $ 4,920
Natural gas        
Operating Revenues:        
Operating Revenues 136 138 794 762
Union Electric Company        
Operating Revenues:        
Operating Revenues 1,705 1,342 4,002 3,005
Operating Expenses:        
Fuel and purchased power 487 334 1,431 689
Natural gas purchased for resale 6 4 45 41
Other operations and maintenance 260 288 748 789
Depreciation and amortization 239 220 642 623
Taxes other than income taxes 122 109 300 287
Total operating expenses 1,114 955 3,166 2,429
Operating Income 591 387 836 576
Other Income, Net 45 51 135 144
Interest Charges 85 62 215 187
Income Before Income Taxes 551 376 756 533
Income Taxes 32 (6) 43 (4)
Net Income 519 382 713 537
Preferred Stock Dividends 1 1 3 3
Net income attributable to Ameren common shareholders 518 381 710 534
Union Electric Company | Electric        
Operating Revenues:        
Operating Revenues 1,685 1,324 3,893 2,902
Union Electric Company | Natural gas        
Operating Revenues:        
Operating Revenues 20 18 109 103
Ameren Illinois Company        
Operating Revenues:        
Operating Revenues 946 793 2,889 2,559
Operating Expenses:        
Purchased Power 284 169 642 474
Natural gas purchased for resale 19 26 188 173
Other operations and maintenance 241 229 702 663
Depreciation and amortization 162 155 484 462
Taxes other than income taxes 38 37 126 116
Total operating expenses 744 616 2,142 1,888
Operating Income 202 177 747 671
Other Income, Net 30 37 101 105
Interest Charges 67 63 192 178
Income Before Income Taxes 165 151 656 598
Income Taxes 17 37 134 144
Net Income 148 114 522 454
Preferred Stock Dividends 0 0 1 1
Net income attributable to Ameren common shareholders 148 114 521 453
Ameren Illinois Company | Electric        
Operating Revenues:        
Operating Revenues 829 672 2,203 1,899
Ameren Illinois Company | Natural gas        
Operating Revenues:        
Operating Revenues $ 117 $ 121 $ 686 $ 660
v3.25.3
Consolidated Statement of Income (Loss) and Comprehensive Income (Parenthetical) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Income Statement [Abstract]        
Pension and other postretirement benefit plan activity, tax $ 0 $ 0 $ (1) $ (1)
Unrealized net loss on derivative hedging instruments, tax $ 0 $ 0 $ (1) $ 0
v3.25.3
Consolidated Balance Sheet - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Current Assets:    
Cash and cash equivalents $ 9 $ 7
Accounts receivable - trade (less allowance for doubtful accounts) 794 525
Unbilled revenue 413 346
Miscellaneous accounts receivable 78 96
Inventories 804 762
Current regulatory assets 260 366
Other current assets 252 162
Total current assets 2,610 2,264
Property, Plant, and Equipment, Net 38,411 36,304
Investments and Other Assets:    
Nuclear decommissioning trust fund 1,502 1,342
Goodwill 411 411
Regulatory Asset 2,611 2,397
Pension and other postretirement benefits 741 757
Other assets 1,130 1,123
Total investments and other assets 6,395 6,030
TOTAL ASSETS 47,416 44,598
Current Liabilities:    
Current maturities of long-term debt 29 317
Short-term debt 903 1,143
Accounts and wages payable 762 1,059
Taxes accrued 215 60
Interest accrued 183 196
Customer deposits 248 223
Current regulatory liabilities 142 120
Other current liabilities 323 295
Total current liabilities 2,805 3,413
Long-term debt, net 19,172 17,262
Deferred Credits and Other Liabilities:    
Accumulated deferred income taxes and tax credits, net 5,081 4,474
Regulatory liabilities 6,089 5,897
Asset retirement obligations 844 822
Other deferred credits and liabilities 516 487
Total deferred credits and other liabilities 12,530 11,680
Commitments and Contingencies
Shareholders’ Equity:    
Common Stock 3 3
Other paid-in capital, principally premium on common stock 7,559 7,513
Retained earnings 5,232 4,604
Accumulated other comprehensive loss (14) (6)
Total shareholders’ equity 12,780 12,114
Noncontrolling Interests 129 129
Total equity 12,909 12,243
TOTAL LIABILITIES AND EQUITY 47,416 44,598
Variable Interest Entity, Primary Beneficiary    
Current Assets:    
Other current assets 46 2
Investments and Other Assets:    
Regulatory Asset 449 465
Current Liabilities:    
Current maturities of long-term debt 29 17
Long-term debt, net 437 448
Union Electric Company    
Current Assets:    
Cash and cash equivalents 0 0
Restricted Cash 86 7
Advances to money pool 0 43
Unbilled revenue 267 170
Miscellaneous accounts receivable 9 33
Inventories 511 514
Current regulatory assets 149 66
Other current assets 70 63
Total current assets 1,475 1,145
Property, Plant, and Equipment, Net 20,083 18,788
Investments and Other Assets:    
Nuclear decommissioning trust fund 1,502 1,342
Regulatory Asset 1,454 1,366
Pension and other postretirement benefits 202 211
Other assets 235 254
Total investments and other assets 3,393 3,173
TOTAL ASSETS 24,951 23,106
Current Liabilities:    
Current maturities of long-term debt 29 17
Short-term debt 259 0
Borrowings from money pool 51 0
Taxes accrued 192 29
Interest accrued 94 88
Other current liabilities 204 206
Total current liabilities 1,264 1,019
Deferred Credits and Other Liabilities:    
Accumulated deferred income taxes and tax credits, net 2,622 2,217
Regulatory liabilities 3,260 3,176
Asset retirement obligations 839 818
Other deferred credits and liabilities 166 150
Total deferred credits and other liabilities 6,887 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 4,791 4,206
Total shareholders’ equity 8,583 7,998
TOTAL LIABILITIES AND EQUITY 24,951 23,106
Union Electric Company | Variable Interest Entity, Primary Beneficiary    
Current Assets:    
Restricted Cash 46 2
Investments and Other Assets:    
Regulatory Asset 449 465
Current Liabilities:    
Current maturities of long-term debt 29 17
Long-term debt, net 437 448
Union Electric Company | Nonrelated Party    
Current Assets:    
Accounts receivable - trade (less allowance for doubtful accounts) 359 209
Current Liabilities:    
Accounts and wages payable 355 629
Long-term debt, net 8,130 7,671
Union Electric Company | Related Party    
Current Assets:    
Accounts receivable - trade (less allowance for doubtful accounts) 24 40
Current Liabilities:    
Accounts and wages payable 80 50
Long-term debt, net 87 57
Ameren Illinois Company    
Current Assets:    
Cash and cash equivalents 0 0
Advances to money pool 51 0
Unbilled revenue 146 175
Miscellaneous accounts receivable 36 28
Inventories 289 244
Prepaid assets 65 59
Current regulatory assets 106 281
Other current assets 8 8
Total current assets 1,141 1,110
Property, Plant, and Equipment, Net 16,274 15,530
Investments and Other Assets:    
Goodwill 411 411
Regulatory Asset 1,124 1,011
Pension and other postretirement benefits 492 471
Other assets 756 697
Total investments and other assets 2,783 2,590
TOTAL ASSETS 20,198 19,230
Current Liabilities:    
Current maturities of long-term debt 0 300
Short-term debt 0 88
Borrowings from money pool 0 37
Interest accrued 59 59
Customer deposits 212 185
Purchase of receivables liabilities 55 43
Current regulatory liabilities 101 79
Other current liabilities 128 129
Total current liabilities 975 1,318
Deferred Credits and Other Liabilities:    
Accumulated deferred income taxes and tax credits, net 2,245 2,143
Regulatory liabilities 2,705 2,573
Other deferred credits and liabilities 308 273
Total deferred credits and other liabilities 5,258 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 4,602 4,266
Total shareholders’ equity 7,707 7,371
TOTAL LIABILITIES AND EQUITY 20,198 19,230
Ameren Illinois Company | Nonrelated Party    
Current Assets:    
Accounts receivable - trade (less allowance for doubtful accounts) 419 300
Current Liabilities:    
Accounts and wages payable 314 324
Long-term debt, net 6,253 5,549
Ameren Illinois Company | Related Party    
Current Assets:    
Accounts receivable - trade (less allowance for doubtful accounts) 21 15
Current Liabilities:    
Accounts and wages payable 106 74
Long-term debt, net $ 5 $ 3
v3.25.3
Consolidated Balance Sheet (Parenthetical) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Accounts Receivable, Allowance for Credit Loss, Current $ 38 $ 30
Other current assets 252 162
Regulatory Asset 2,611 2,397
Current maturities of long-term debt 29 317
Long-term debt, net $ 19,172 $ 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 270,500,000 269,900,000
Variable Interest Entity, Primary Beneficiary    
Other current assets $ 46 $ 2
Regulatory Asset 449 465
Current maturities of long-term debt 29 17
Long-term debt, net 437 448
Union Electric Company    
Restricted Cash 86 7
Accounts Receivable, Allowance for Credit Loss, Current 15 12
Other current assets 70 63
Regulatory Asset 1,454 1,366
Current maturities of long-term debt $ 29 $ 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    
Restricted Cash $ 46 $ 2
Regulatory Asset 449 465
Current maturities of long-term debt 29 17
Long-term debt, net 437 448
Ameren Illinois Company    
Accounts Receivable, Allowance for Credit Loss, Current 23 18
Other current assets 8 8
Regulatory Asset 1,124 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
v3.25.3
Consolidated Statement of Cash Flows - USD ($)
$ in Millions
 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Cash Flows From Operating Activities:    
Net income $ 1,208 $ 979
Adjustments to reconcile net income to net cash provided by operating activities:    
Depreciation and amortization 1,199 1,142
Amortization of nuclear fuel 39 59
Amortization of debt issuance costs and premium/discounts 14 14
Deferred income taxes and tax credits, net 255 145
Allowance for equity funds used during construction (60) (48)
Stock-based compensation costs 21 22
Other 29 84
Changes in assets and liabilities:    
Receivables (356) (183)
Inventories (41) (60)
Accounts and wages payable (244) (239)
Taxes accrued 307 176
Regulatory assets and liabilities 97 86
Assets, other (29) (59)
Liabilities, other 72 (4)
Pension and other postretirement benefits (114) (168)
Net cash provided by operating activities 2,397 1,946
Cash Flows From Investing Activities:    
Capital expenditures (3,118) (3,029)
Nuclear fuel expenditures (20) (57)
Purchases of securities – nuclear decommissioning trust fund (373) (499)
Sales and maturities of securities – nuclear decommissioning trust fund 348 480
Other 51 (1)
Net cash used in investing activities (3,112) (3,106)
Cash Flows From Financing Activities:    
Dividends on common stock (576) (535)
Dividends paid to noncontrolling interest holders (4) (4)
Short-term debt, net (239) 1,002
Maturities and extinguishment of long-term debt (324) (849)
Issuances of long-term debt 1,960 1,610
Issuances of common stock 35 30
Employee payroll taxes related to stock-based compensation (13) (8)
Debt issuance costs (17) (19)
Other 0 (15)
Net cash provided by financing activities 822 1,212
Net change in cash, cash equivalents, and restricted cash 107 52
Cash, cash equivalents, and restricted cash at beginning of year 328 272
Cash, cash equivalents, and restricted cash at end of period 435 324
Union Electric Company    
Cash Flows From Operating Activities:    
Net income 713 537
Adjustments to reconcile net income to net cash provided by operating activities:    
Depreciation and amortization 673 641
Amortization of nuclear fuel 39 59
Amortization of debt issuance costs and premium/discounts 7 5
Deferred income taxes and tax credits, net 167 2
Allowance for equity funds used during construction (37) (38)
Other 7 69
Changes in assets and liabilities:    
Receivables (245) (178)
Inventories 3 (21)
Accounts and wages payable (240) (223)
Taxes accrued 336 218
Regulatory assets and liabilities (155) (5)
Assets, other 21 (20)
Liabilities, other 26 10
Pension and other postretirement benefits (42) (59)
Net cash provided by operating activities 1,273 997
Cash Flows From Investing Activities:    
Capital expenditures (1,873) (1,839)
Nuclear fuel expenditures (20) (57)
Purchases of securities – nuclear decommissioning trust fund (373) (499)
Sales and maturities of securities – nuclear decommissioning trust fund 348 480
Money pool advances, net 43  
Money pool advances, net   (9)
Other 0 (8)
Net cash used in investing activities (1,875) (1,932)
Cash Flows From Financing Activities:    
Dividends on common stock (125) 0
Dividends on preferred stock (3) (3)
Short-term debt, net 259 406
Money pool borrowings, net 51 (289)
Maturities and extinguishment of long-term debt 0 (350)
Issuances of long-term debt 500 846
Capital contributions from parent 0 350
Debt issuance costs (4) (10)
Other 0 (15)
Net cash provided by financing activities 678 935
Net change in cash, cash equivalents, and restricted cash 76 0
Cash, cash equivalents, and restricted cash at beginning of year 17 10
Cash, cash equivalents, and restricted cash at end of period 93 10
Ameren Illinois Company    
Cash Flows From Operating Activities:    
Net income 522 454
Adjustments to reconcile net income to net cash provided by operating activities:    
Depreciation and amortization 484 461
Amortization of debt issuance costs and premium/discounts 3 3
Deferred income taxes and tax credits, net 30 72
Allowance for equity funds used during construction (21) (10)
Other 24 32
Changes in assets and liabilities:    
Receivables (129) (23)
Inventories (45) (35)
Accounts and wages payable (1) (8)
Taxes accrued 26 118
Regulatory assets and liabilities 255 96
Assets, other (49) (32)
Liabilities, other 68 5
Pension and other postretirement benefits (50) (66)
Net cash provided by operating activities 1,117 1,067
Cash Flows From Investing Activities:    
Capital expenditures (1,127) (1,091)
Money pool advances, net (51) 0
Other (3) 1
Net cash used in investing activities (1,181) (1,090)
Cash Flows From Financing Activities:    
Dividends on common stock (185) (50)
Dividends on preferred stock (1) (1)
Short-term debt, net (88) (349)
Money pool borrowings, net (37) (135)
Maturities and extinguishment of long-term debt (300) 0
Issuances of long-term debt 711 624
Debt issuance costs (8) (7)
Net cash provided by financing activities 92 82
Net change in cash, cash equivalents, and restricted cash 28 59
Cash, cash equivalents, and restricted cash at beginning of year 302 234
Cash, cash equivalents, and restricted cash at end of period $ 330 $ 293
v3.25.3
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 period at Dec. 31, 2023     $ 7,216 $ 4,136 $ 0 $ (6)     $ 129     $ 2,725   $ 3,647         $ 3,756
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Shares issued under the DRPlus and 401(k) plan     30                                
Stock-based compensation activity     18                                
Capital contributions from parent                   $ 350   350              
Net income $ 979                 537         $ 454        
Net Income Available to Common Shareholder       975                     453        
Dividends on common stock       (535)                   0         (50)
Dividends on preferred stock                           (3)         (1)
Change in derivative financial instruments         0                            
Change in deferred retirement benefit costs (4)         (4)                          
Net income attributable to noncontrolling interest holders $ (4)               4                    
Dividends paid to noncontrolling interest holders                 (4)                    
Common stock shares outstanding at beginning of period at Dec. 31, 2023 266,300,000                                    
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Shares issued under the DRPlus and 401(k) plan 400,000                                    
Shares issued for stock-based compensation 200,000                                    
Common stock shares outstanding at end of period at Sep. 30, 2024 266,900,000                                    
End of period at Sep. 30, 2024 $ 11,962 $ 3 7,264 4,576 0 (10) $ (10)   129   $ 511 3,075 $ 80 4,181   $ 0 $ 3,020 $ 49 4,159
Shareholders' equity, end of year at Sep. 30, 2024               $ 11,833   7,847         7,228        
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Dividends per common share $ 2.01                                    
Beginning of period at Jun. 30, 2024     7,246 4,299 0 (9)     129     3,075   3,800         4,070
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Shares issued under the DRPlus and 401(k) plan     9                                
Stock-based compensation activity     9                                
Capital contributions from parent                       0              
Net income $ 457                 382         114        
Net Income Available to Common Shareholder       456                     114        
Dividends on common stock       (179)                   0         (25)
Dividends on preferred stock                           (1)         0
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 period at Jun. 30, 2024 266,800,000                                    
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Shares issued under the DRPlus and 401(k) plan 100,000                                    
Shares issued for stock-based compensation 0                                    
Common stock shares outstanding at end of period at Sep. 30, 2024 266,900,000                                    
End of period at Sep. 30, 2024 $ 11,962 3 7,264 4,576 0 (10) (10)   129   511 3,075 80 4,181   0 3,020 49 4,159
Shareholders' equity, end of year at Sep. 30, 2024               11,833   $ 7,847         $ 7,228        
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Dividends per common share $ 0.67                                    
Beginning of period at Dec. 31, 2024 $ 12,243   7,513 4,604 3 (9)     129     3,201   4,206         4,266
Common stock shares outstanding at beginning of period at Dec. 31, 2024 269,900,000                 102,100,000         25,500,000        
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Shares issued for stock-based compensation 300,000                                    
Common stock shares outstanding at end of period at Jun. 30, 2025 270,400,000                                    
End of period at Jun. 30, 2025     7,541 4,784 (3) (11)     129     3,201   4,348         4,564
Beginning of period at Dec. 31, 2024 $ 12,243   7,513 4,604 3 (9)     129     3,201   4,206         4,266
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Shares issued under the DRPlus and 401(k) plan     35                                
Stock-based compensation activity     11                                
Capital contributions from parent                   $ 0   0              
Net income 1,208                 $ 713         $ 522        
Net Income Available to Common Shareholder       1,204                     $ 521        
Dividends on common stock       (576)                   (125)         (185)
Dividends on preferred stock                           (3)         (1)
Change in derivative financial instruments         (6)                            
Change in deferred retirement benefit costs (2)         (2)                          
Net income attributable to noncontrolling interest holders $ (4)               4                    
Dividends paid to noncontrolling interest holders                 (4)                    
Common stock shares outstanding at beginning of period at Dec. 31, 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 300,000                                    
Shares issued for stock-based compensation 300,000                                    
Common stock shares outstanding at end of period at Sep. 30, 2025 270,500,000                 102,100,000         25,500,000        
End of period at Sep. 30, 2025 $ 12,909 3 7,559 5,232 (3) (11) (14)   129   511 3,201 80 4,791   0 3,056 49 4,602
Shareholders' equity, end of year at Sep. 30, 2025 $ 12,780             12,780   $ 8,583         $ 7,707        
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Dividends per common share $ 2.13                                    
Beginning of period at Jun. 30, 2025     7,541 4,784 (3) (11)     129     3,201   4,348         4,564
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Shares issued under the DRPlus and 401(k) plan     10                                
Stock-based compensation activity     8                                
Capital contributions from parent                       0              
Net income $ 641                 $ 519         148        
Net Income Available to Common Shareholder       640                     $ 148        
Dividends on common stock       (192)                   (75)         (110)
Dividends on preferred stock                           (1)         0
Change in derivative financial instruments         0                            
Change in deferred retirement benefit costs 0         0                          
Net income attributable to noncontrolling interest holders $ (1)               1                    
Dividends paid to noncontrolling interest holders                 (1)                    
Common stock shares outstanding at beginning of period at Jun. 30, 2025 270,400,000                                    
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Shares issued under the DRPlus and 401(k) plan 100,000                                    
Shares issued for stock-based compensation 0                                    
Common stock shares outstanding at end of period at Sep. 30, 2025 270,500,000                 102,100,000         25,500,000        
End of period at Sep. 30, 2025 $ 12,909 $ 3 $ 7,559 $ 5,232 $ (3) $ (11) $ (14)   $ 129   $ 511 $ 3,201 $ 80 $ 4,791   $ 0 $ 3,056 $ 49 $ 4,602
Shareholders' equity, end of year at Sep. 30, 2025 $ 12,780             $ 12,780   $ 8,583         $ 7,707        
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Dividends per common share $ 0.71                                    
v3.25.3
Summary Of Significant Accounting Policies
 9 Months Ended
Sep. 30, 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 September 30, 2025 and December 31, 2024:
20252024
Unbilled revenue(a)
$4 $— 
Other current assets(a)(b)
46 2 
Noncurrent regulatory assets(a)
449 465 
Current maturities of long-term debt(c)
29 17 
Interest accrued(c)
18 1 
Current regulatory liabilities(d)
15 — 
Long-term debt, net(c)
437 448 
(a)Assets may be used only to meet AMF’s obligations and commitments.
(b)Included in “Restricted cash” on Ameren Missouri’s balance sheet.
(c)The securitized tariff bondholders have no recourse to Ameren Missouri.
(d)Included in “Other current liabilities” on Ameren Missouri’s balance sheet.
Variable Interest Entities that are Not Consolidated
As of September 30, 2025, and December 31, 2024, Ameren had unconsolidated variable interests in various equity method investments, primarily to advance innovative energy technologies, totaling $60 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 September 30, 2025, Ameren’s maximum exposure to loss related to these variable interest entities is limited to the investment in these partnerships of $60 million plus associated outstanding funding commitments of $31 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 September 30, 2025, the cash surrender value of COLI at Ameren and Ameren Illinois was $220 million (December 31, 2024 – $260 million) and $124 million (December 31, 2024 – $118 million), respectively, while total borrowings against the policies were $117 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.
Accounting and Reporting Developments
Improvements to the Accounting for Internal-Use Software
In September 2025, the FASB issued authoritative guidance that made targeted improvements to the accounting for internal-use software. The guidance requires an entity to capitalize internal-use software costs when management has authorized and committed to funding the software project, and it is probable that the project will be completed and the software will be used to perform its intended function. This guidance will be effective for the Ameren Companies in the first quarter of 2028. We are currently assessing the impacts of this guidance on our results of operations, financial position, and liquidity.
v3.25.3
Rate And Regulatory Matters
 9 Months Ended
Sep. 30, 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 became 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, require electric utilities to submit service tariff schedules for high-demand customers, 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 in effect was 2.5% and changed 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.
The law also requires an electric utility to develop and submit to the MoPSC schedules that include its service tariff applicable to customers projected to have 100 MWs or more of demand. These schedules must reasonably ensure that such high-demand customers’ rates reflect a representative share of the costs incurred to serve them and further, must prevent other lower-demand customer rates from reflecting any unjust or unreasonable costs arising from service provided to these high-demand customers.
In addition, the law 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 serving the utility's load 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 Order
In July 2025, the MoPSC issued an order in Ameren Missouri’s 2024 natural gas delivery service regulatory rate review, approving a unanimous stipulation and agreement. The order authorizes an increase of $32 million to Ameren Missouri’s annual revenue requirement for
natural gas delivery service, effective September 1, 2025. 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 of Ameren Missouri’s existing riders and trackers.
Large Load Customer Rate Plan
In November 2025, Ameren Missouri updated its May 2025 request with the MoPSC to modify its existing large primary service tariff to require customers requesting 75 MWs or more of demand and who are served at transmission level voltage to comply with additional tariff terms. The additional terms include a service term of 12 years plus a ramp period of up to five years to reach peak demand, minimum demand charges of 80% of contracted capacity, customer exit terms and fees, and customer credit and collateral requirements, among other terms. In addition, new customer programs would be available under this tariff, which allow customers to support renewable generation, battery storage, and/or nuclear generation through incremental payments. A decision by the MoPSC is expected by February 2026.
Generation and Storage Facilities
Ameren Missouri is party to agreements to acquire and/or construct various generation and storage facilities that are consistent with the 2025 Change to the 2023 PRP. The generation and storage facilities are eligible for recovery under the PISA. The following table provides information with respect to each facility:
Agreement typeFacility sizeStatus of MoPSC CCN
In-service date(a)
Vandalia Solar Project(b)
Self-build
50-MW
Approved March 2024Fourth quarter 2025
Bowling Green Solar Project(b)
Self-build
50-MW
Approved March 2024First quarter 2026
Split Rail Solar Project(b)
Build-transfer(c)
300-MW
Approved March 2024Mid-2026
Castle Bluff Natural Gas Project(d)
Self-build
800-MW
Approved October 2024Fourth quarter 2027
Big Hollow Battery Energy Storage ProjectSelf-build
400-MW
Filed June 2025(e)
Second quarter 2028
Big Hollow Natural Gas ProjectSelf-build
800-MW
Filed June 2025(e)
Third quarter 2028
Reform Solar ProjectSelf-build
250-MW
Filed August 2025(e)
Fourth quarter 2028
(a)In-service dates are dependent on the timing of regulatory approvals and construction completion, among other things.
(b)These projects collectively represent approximately $0.8 billion of capital expenditures.
(c)FERC approval of acquisition received November 2024.
(d)This project represents approximately $0.9 billion of capital expenditures.
(e)Ameren Missouri expects a decision by the MoPSC in the first half of 2026.
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. In July 2025, the MoPSC issued an order approving a CCN for a portion of the projects and a decision on the remaining projects is 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 March 2025, Ameren Illinois filed an appeal of the ICC’s December 2024 order to the Illinois Appellate Court for the Fifth Judicial District to revise the allowed ROE and to include an asset associated with other postretirement benefits in the rate base, among other things. 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 for a reconciliation adjustment to its 2024 electric distribution service revenue requirement with the ICC. In September 2025, Ameren Illinois filed a revised reconciliation adjustment, requesting recovery of $60 million. The adjustment reflects Ameren Illinois’ actual 2024 recoverable costs, 2024 year-end rate base, and a capital structure composed of 50% common equity. In September 2025, the ICC staff submitted its calculation of the reconciliation adjustment, recommending recovery of $47 million. The ICC staff’s recommendation excluded an asset associated with other postretirement benefits from the rate base. An ICC decision in this proceeding is required by December 2025, and any approved adjustment would be collected from customers in 2026.
Electric Customer Energy-Efficiency Investments
In May 2025, Ameren Illinois filed its annual electric energy-efficiency formula rate update to increase its annual revenues by $12 million with the ICC. In August 2025, the ICC staff filed a recommendation supporting Ameren Illinois’ requested increase. An ICC decision in this proceeding is required by December 2025, with new rates effective in January 2026.
Electric Energy Efficiency Plan
In August 2025, the ICC issued an order approving Ameren Illinois’ energy-efficiency plan that includes annual investments in electric energy-efficiency programs of approximately $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.
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. In July 2025, Ameren Illinois filed a revised request seeking to increase its annual revenues by $135 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. In August 2025, the ICC staff filed a revised recommendation to increase Ameren Illinois’ annual revenues for natural gas delivery service by $104 million. The recommendation is based on a 9.93% ROE, a capital structure composed of 50% common equity, and a rate base of $3.2 billion. In addition, in August 2025, the Illinois Attorney General's office recommended an increase to annual revenues for natural gas delivery service of $55 million, based on a 9.45% ROE, a capital structure composed of 50% common equity, and a rate base of $3.0 billion. In October 2025, the administrative law judge issued a proposed order for an increase to annual revenues of $91 million. The order was consistent with the ICC staff’s recommendation with the exception of the exclusion of the non-service cost component of the net periodic benefit income related to other postretirement benefits in the annual revenue requirement. A decision by the ICC in this proceeding is required by early December 2025, with new rates expected to be effective in early 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 July 2025, the ICC issued an order approving a request filed by Ameren Illinois and ATXI for a CCN, among other things, related to the portion of the MISO long-range transmission projects they will construct within the ICC’s jurisdiction.
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 July 2025, the FERC approved transmission rate incentives relating to the second tranche projects assigned to Ameren. The incentives will allow construction work in progress to be included in rate base for projects constructed by ATXI, thereby improving the timeliness of cash recovery, and would allow recovery of prudently incurred costs, subject to FERC approval, for any portion of the projects if they are abandoned for reasons beyond the control of Ameren. ATXI will not capitalize allowance for funds used during construction on the related projects.
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 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 of the October 2024 order. 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 September 30, 2025, Ameren and Ameren Illinois had recorded liabilities in "Current regulatory liabilities" on their balance sheets of $7 million and $4 million, respectively, to reflect the expected refunds, including interest, associated with the allowed base ROE set by the October 2024 order.
v3.25.3
Short-Term Debt And Liquidity
 9 Months Ended
Sep. 30, 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 September 30, 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 $1.6 billion. The Ameren Companies were in compliance with the covenants in their Credit Agreements as of September 30, 2025. As of September 30, 2025, the ratios of consolidated indebtedness to consolidated total capitalization, calculated in accordance with the provisions of the Credit Agreements, were 61%, 49%, and 45% for Ameren, Ameren Missouri, and Ameren Illinois, respectively.
The following table presents commercial paper outstanding, net of issuance discounts, as of September 30, 2025, and December 31, 2024. There were no borrowings outstanding under the Credit Agreements as of September 30, 2025, or December 31, 2024.
September 30, 2025December 31, 2024
Ameren (parent)$644 $1,055 
Ameren Missouri259 — 
Ameren Illinois— 88 
Ameren consolidated$903 $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 nine months ended September 30, 2025 and 2024:
Ameren
(parent)		Ameren
Missouri		Ameren
Illinois		Ameren
Consolidated
2025
Average daily amount outstanding$637 $245 $130 $1,012 
Weighted-average interest rate4.60 %4.58 %4.55 %4.59 %
Peak amount outstanding during period(a)
$1,139 $650 $425 $1,603 
Peak interest rate4.75 %4.72 %4.70 %4.75 %
2024
Average daily amount outstanding$177 $187 $256 $620 
Weighted-average interest rate5.46 %5.52 %5.57 %5.53 %
Peak amount outstanding during period(a)
$948 $576 $694 $1,542 
Peak interest rate5.60 %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 and nine months ended September 30, 2025, was 4.53% and 4.56%, respectively (2024 – 5.29% and 5.37%). 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 and nine months ended September 30, 2025 and 2024.
v3.25.3
Long-Term Debt And Equity Financings
 9 Months Ended
Sep. 30, 2025
Long-Term Debt And Equity Financings [Abstract]  
LONG-TERM DEBT AND EQUITY FINANCINGS LONG-TERM DEBT AND EQUITY FINANCINGS
Ameren
For the three and nine months ended September 30, 2025, Ameren issued a total of 0.1 million and 0.3 million shares of common stock, under its DRPlus and 401(k) plan, and received proceeds of $3 million and $28 million. As of September 30, 2025, Ameren had a receivable of $7 million related to issuances of common stock under its DRPlus and 401(k) plan. In addition, in the first quarter of 2025, Ameren issued 0.3 million shares of common stock valued at $25 million upon the settlement of stock-based compensation awards.
Ameren has entered into an equity distribution sales agreement pursuant to which Ameren may offer and sell from time to time its common stock through an ATM program, which includes the ability to enter into forward sale agreements. In August 2025, Ameren increased the amount of common stock available for sale under the ATM program by $1.25 billion to a total of $3 billion. There were no shares issued under the ATM program during the three and nine months ended September 30, 2025. As of September 30, 2025, Ameren had approximately $1.5 billion of common stock remaining available for sale under the ATM program.
Forward sale agreements outstanding as of September 30, 2025 under the ATM program for 5.8 million shares, can be settled at Ameren’s discretion on or prior to dates ranging from January 23, 2026, to March 6, 2026. 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. Additionally in May 2025, Ameren entered into forward sale agreements separate from the ATM program with multiple counterparties relating to 6.4 million shares of common stock. The forward sale agreements can be settled at Ameren’s discretion on or prior to January 15, 2027, and the initial forward sale price under these agreements was $91.89 per share. 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. 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 September 30, 2025, Ameren could have settled the forward sale agreements with physical delivery of 12.2 million shares of common stock to the respective counterparties in exchange for cash of $1.1 billion. Alternatively, the forward sale agreements could have also been net settled at September 30, 2025, with delivery of approximately $158 million of cash or approximately 1.5 million shares of common stock to the counterparties. In connection with the forward sale agreements outstanding at September 30, 2025, the various counterparties, or their affiliates, borrowed from third parties and sold 12.2 million shares of common stock. The gross sales price of these shares totaled $1.1 billion. 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.
In June 2025, Ameren (parent) purchased senior secured notes and first mortgage bonds issued by Ameren Missouri and first mortgage bonds issued by Ameren Illinois for $24 million in the aggregate. On a consolidated basis, Ameren (parent)’s repurchase of these senior secured notes and first mortgage bonds were accounted for as a debt extinguishment and resulted in a pre-tax gain of $8 million, which is reflected in “Other Income, Net” on Ameren’s consolidated statement of income. Interest expense related to repurchased bonds was $1 million and $2 million for the three and nine months ended September 30, 2025.
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 and September 2025, Ameren Illinois issued $350 million and $350 million, respectively, 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 and March 1, 2026, respectively. Net proceeds from the March 2025 issuance were used to repay $300 million principal amount of its 3.25% senior secured notes that matured in March 2025, and net proceeds of both issuances were used to repay a portion of its 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 September 30, 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 September 30, 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 relating to common stock. See Note 1 – Summary of Significant Accounting Policies for further detail concerning variable interest entities.
v3.25.3
Other Income, Net
 9 Months Ended
Sep. 30, 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 and nine months ended September 30, 2025 and 2024:
Three MonthsNine Months
2025202420252024
Ameren:
Allowance for equity funds used during construction
$21 $23 $60 $48 
Other interest income
10 8 31 29 
Non-service cost components of net periodic benefit income(a)
59 76 187 228 
Miscellaneous income
6 — 13 6 
Gain on the extinguishment of debt(b)
— — 8 — 
Losses related to equity method investments(9)(2)(19)(1)
Donations
(6)(1)(9)(5)
Miscellaneous expense
(5)(3)(14)(12)
Total Other Income, Net$76 $101 $257 $293 
Ameren Missouri:
Allowance for equity funds used during construction
$14 $15 $37 $38 
Other interest income
3 2 7 7 
Non-service cost components of net periodic benefit income(a)
29 35 96 104 
Miscellaneous income
4 1 6 3 
Donations
(2)— (4)(2)
Miscellaneous expense
(3)(2)(7)(6)
Total Other Income, Net$45 $51 $135 $144 
Ameren Illinois:
Allowance for equity funds used during construction
$6 $8 $21 $10 
Other interest income7 7 24 22 
Non-service cost components of net periodic benefit income
21 25 61 78 
Miscellaneous income
2 — 7 3 
Donations
(4)— (5)(2)
Miscellaneous expense(2)(3)(7)(6)
Total Other Income, Net$30 $37 $101 $105 
(a)For the three and nine months ended September 30, 2025, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $(9) million and $(41) million, respectively, due to a regulatory tracking mechanism for the difference between the level of such costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates. The deferral was $(11) million and $(31) million, respectively, for the three and nine months ended September 30, 2024. See Note 11 – Retirement Benefits for additional information.
(b)See Note 4 – Long-term Debt and Equity Financings for additional information on Ameren (parent)’s repurchase of Ameren Missouri’s senior secured notes and first mortgage bonds and Ameren Illinois’ first mortgage bonds that were accounted for as a debt extinguishment.
v3.25.3
Derivative Financial Instruments
 9 Months Ended
Sep. 30, 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 September 30, 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 entered into by Ameren (parent) and discussed below do not receive regulatory deferral and were included in accumulated OCI as Ameren (parent) is not a rate-regulated entity. The cash flows from our derivative financial instruments follow the cash flow classification of the hedged item.
Ameren (parent) entered into interest rate swaps to hedge a portion of its interest rate risk on cash flows related to certain forecasted debt issuances to occur in 2026 and 2027. 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 September 30, 2025, and December 31, 2024, Ameren had interest rate swaps with notional amounts of $660 million and $140 million, respectively. Ameren recorded an unrealized loss, net of income tax benefits, on the change in fair value of interest rate swaps of less than $1 million and $6 million to "Accumulated other comprehensive loss" for the three and nine months ended September 30, 2025.
The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of September 30, 2025, and December 31, 2024. As of September 30, 2025, these contracts extended through October 2028, October 2031 and May 2032 for fuel oils, natural gas, and power, respectively.
Quantity (in millions, except as indicated)
September 30, 2025December 31, 2024
CommodityAmeren MissouriAmeren IllinoisAmerenAmeren MissouriAmeren IllinoisAmeren
Fuel oils (in gallons)23 — 23 23 — 23 
Natural gas (in MMBtu)50 211 261 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 September 30, 2025, and December 31, 2024:
September 30, 2025December 31, 2024
Balance Sheet LocationAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois		Ameren
Natural gasOther current assets$1 $3 $4 $2 $2 $4 
Other assets1 5 6 2 4 6 
PowerOther current assets22 — 22 6 — 6 
Total assets$24 $8 $32 $10 $6 $16 
Fuel oilsOther current liabilities$2 $— $2 $2 $— $2 
Other deferred credits and liabilities1 — 1 2 — 2 
Natural gasOther current liabilities3 18 21 5 22 27 
Other deferred credits and liabilities5 8 13 6 13 19 
PowerOther current liabilities1 10 11 — 10 10 
Other deferred credits and liabilities— 52 52 — 43 43 
Total liabilities$12 $88 $100 $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 September 30, 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 September 30, 2025, if counterparty groups were to fail completely to perform on contracts, the Ameren Companies’ maximum exposure related to derivative assets 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 September 30, 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.
v3.25.3
Fair Value Measurements
 9 Months Ended
Sep. 30, 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 and nine months ended September 30, 2025 or 2024. At September 30, 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 September 30, 2025, and December 31, 2024:
September 30, 2025December 31, 2024
Level 1Level 2Level 3TotalLevel 1Level 2Level 3Total
Assets:
Ameren Missouri
Derivative assets – commodity contracts:
Natural gas$— $2 $— $2 $— $4 $— $4 
Power— — 22 22 — — 6 6 
Total derivative assets – commodity contracts$— $2 $22 $24 $— $4 $6 $10 
Nuclear decommissioning trust fund:
Equity securities:
U.S. large capitalization$1,001 $— $— $1,001 $911 $— $— $911 
Debt securities:
U.S. Treasury and agency securities— 235 — 235 — 191 — 191 
Corporate bonds— 174 — 174 — 145 — 145 
Other— 84 — 84 — 86 — 86 
Total nuclear decommissioning trust fund$1,001 $493 $— $1,494 
(a) 
$911 $422 $— $1,333 
(a) 
Total Ameren Missouri$1,001 $495 $22 $1,518 $911 $426 $6 $1,343 
Ameren Illinois
Derivative assets – commodity contracts:
Natural gas$— $4 $4 $8 $— $3 $3 $6 
Total Ameren Illinois$— $4 $4 $8 $— $3 $3 $6 
Ameren
Derivative assets – commodity contracts(b)
$— $6 $26 $32 $— $7 $9 $16 
Nuclear decommissioning trust fund(c)
1,001 493 — 1,494 
(a) 
911 422 — 1,333 
(a) 
Total Ameren$1,001 $499 $26 $1,526 $911 $429 $9 $1,349 
Liabilities:
Ameren Missouri
Derivative liabilities – commodity contracts:
Fuel oils$3 $— $— $3 $4 $— $— $4 
Natural gas— 8 — 8 — 11 — 11 
Power— — 1 1 — — — — 
Total Ameren Missouri$3 $8 $1 $12 $4 $11 $— $15 
Ameren Illinois
Derivative liabilities – commodity contracts:
Natural gas$1 $22 $3 $26 $1 $28 $6 $35 
Power— — 62 62 — — 53 53 
Total Ameren Illinois$1 $22 $65 $88 $1 $28 $59 $88 
Ameren
Derivative liabilities – commodity contracts(b)
$4 $30 $66 $100 $5 $39 $59 $103 
(a)Balance excludes $8 million and $9 million of cash and cash equivalents, receivables, payables, and accrued income, net, for September 30, 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 and nine months ended September 30, 2025 and 2024:
20252024
Ameren MissouriAmeren IllinoisAmerenAmeren MissouriAmeren IllinoisAmeren
For the three months ended September 30:
Beginning balance at July 1
$13 $(76)$(63)$14 $(61)$(47)
Realized and unrealized gains/(losses) included in regulatory assets/liabilities12 12 24 (1)(21)(22)
Settlements(4)2 (2)(3)4 1 
Ending balance at September 30
$21 $(62)$(41)$10 $(78)$(68)
Change in unrealized gains/(losses) related to assets/liabilities held at September 30
$11 $11 $22 $(1)$(19)$(20)
For the nine months ended September 30:
Beginning balance at January 1$6 $(53)$(47)$4 $(68)$(64)
Realized and unrealized gains/(losses) included in regulatory assets/liabilities28 (18)10 13 (23)(10)
Settlements(13)9 (4)(7)13 6 
Ending balance at September 30
$21 $(62)$(41)$10 $(78)$(68)
Change in unrealized gains/(losses) related to assets/liabilities held at September 30
$21 $(17)$4 $10 $(18)$(8)
All gains or losses related to our Level 3 derivative commodity contracts are expected to be collected or refunded through customer rates; therefore, there is no impact to either net income or other comprehensive income resulting from changes in the fair value of these instruments.
The following table describes the valuation techniques and significant unobservable inputs utilized for the fair value of our Level 3 power derivative contract assets and liabilities as of September 30, 2025, and December 31, 2024:
Fair Value
Weighted Average(b)
CommodityAssetsLiabilitiesValuation Technique(s)
Unobservable Input(a)
Range
2025
Power(c)
$22$(63)Discounted cash flow
Average forward peak and off-peak pricing – forwards/swaps ($/MWh)
33 – 67
43
Nodal basis ($/MWh)
(10) – 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 September 30, 2025, and December 31, 2024:
Long-Term Debt (Including Current Portion):
Carrying
Amount(a)
Fair Value
Level 2Level 3Total
September 30, 2025
Ameren(b)
$19,201 $17,532 $556 
(c) 
$18,088 
Ameren Missouri(d)
8,246 7,662 — 7,662 
Ameren Illinois(d)
6,258 5,815 — 5,815 
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 $139 million, $63 million, and $56 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of September 30, 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.
(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).
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.
v3.25.3
Related Party Transactions
 9 Months Ended
Sep. 30, 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 $18 million and $20 million, respectively, as of September 30, 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 September 30, 2025, and December 31, 2024:
September 30, 2025December 31, 2024
Ameren MissouriAmeren IllinoisAmeren MissouriAmeren Illinois
Income taxes payable to parent(a)
$3$67$—$32
Income taxes receivable from parent(b)
2—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 and nine months ended September 30, 2025 and 2024:
Three MonthsNine Months
AgreementIncome Statement
Line Item		Ameren
Missouri		Ameren
Illinois		Ameren
Missouri		Ameren
Illinois
Ameren Missouri and Ameren IllinoisOperating Revenues2025$8 $(b)$23 $1 
rent and facility services
20248 (b)23 (b)
Ameren Missouri and Ameren Illinois miscellaneousOperating Revenues2025$1 $(b)$1 $5 
support services20241 (b)2 1 
Total Operating Revenues2025$9 $(b)$24 $6 
20249 (b)25 1 
Ameren Missouri and Ameren IllinoisPurchased Power2025$2 $1 $7 $2 
transmission services from ATXI20243 1 7 2 
Ameren Missouri and Ameren IllinoisOther Operations and Maintenance2025$(b)$(b)$(b)$3 
rent and facility services
2024(b)(b)(b)(b)
Ameren Services support servicesOther Operations and Maintenance2025$42 $39 $130 $119 
agreement
202441 38 122 115 
Total Other Operations and2025$42 $39 $130 $122 
Maintenance202441 38 122 115 
Money pool interest(Interest Charges)/Other Income, Net2025$(b)$(b)$(b)$(b)
2024(b)(b)(3)(2)
Long-term debt, net - related parties(Interest Charges)2025$(1)$(b)$(2)$(b)
2024— — — — 
(a)Not applicable.
(b)Amount less than $1 million.
v3.25.3
Commitments And Contingencies
 9 Months Ended
Sep. 30, 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; regulate the handling and disposal of hazardous substances and waste materials; establish siting and land use requirements; and protect against 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 impact the electric utility industry and compliance obligations could be costly for Ameren Missouri, which operates coal-fired and natural gas-fired energy centers. Compliance obligations under the Clean Air Act stem from a variety of programs including the NSPS, the MATS, emission allowance programs, 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. To the extent our operations impact surface water bodies, including wetlands, the Clean Water Act requires permitting as well as evaluation of the ecological and biological impact of those operations. Implementation of requirements under the Clean Air Act and the Clean Water Act typically occurs through the issuance of permits by state regulators or resource agencies, and capital expenditures associated with compliance could be significant. The management and disposal of coal ash from our coal-fired energy centers must comply with federal regulations known as the CCR Rule issued under the Resource Conservation and Recovery Act and require the closure of surface impoundments at our coal-fired energy centers along with groundwater monitoring requirements and the implementations of corrective measures if necessary. The combined effects of compliance with existing and future environmental regulations could result in significant capital expenditures, increased operating costs, and the potential for 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 has 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.
Due to proposed rules issued by the EPA in June and July 2025, which are discussed below, Ameren and Ameren Missouri have revised capital expenditure estimates necessary to comply with environmental regulations to a range of $90 million to $120 million from 2025 through 2029. Additional capital expenditures beyond 2029 could be required. This estimate 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. 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 optimizing existing air pollution control equipment. Accordingly, the actual amount of capital expenditures required to comply with existing environmental regulations could vary from the above estimates because of uncertainty as to revisions to regulatory requirements by the EPA and/or state regulators 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 2022, the EPA proposed the Good Neighbor Rule to reduce the transport of ozone from power plants by reducing the amount of CSAPR NOx allowances available for compliance. The EPA subsequently rejected state implementation plans proposed by Missouri and other states to comply with the Good Neighbor Rule. The disapprovals for some state implementation plans, including Missouri’s, were stayed by multiple appellate courts, and in 2024, the United States Supreme Court issued a stay of a federal implementation plan. In March 2025, the EPA announced it would take steps to repeal the Good Neighbor Rule and work with states on their implementation plans. 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. If the EPA repeals the currently stayed Good Neighbor Rule, Ameren Missouri would not expect additional NOx controls at its coal-fired energy centers to be necessary.
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. In June 2025, the EPA issued a proposed rule to repeal all greenhouse gas emissions standards for fossil fuel-fired power plants, including the April 2024 rule. In addition, in July 2025, the EPA announced a proposed rule reconsidering its 2009 Endangerment Finding for greenhouse gas emissions, which was the basis for implementing greenhouse gas emissions standards. The EPA expects to issue final rules by the end of 2025.
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 presidential administration issued a proclamation through which it granted owners of coal-fired energy centers, including Ameren Missouri, a two-year extension of the compliance deadline. As such, the compliance deadline for the Labadie and Sioux energy centers is now set for July 2029. In June 2025, the EPA issued a proposed rule to repeal the April 2024 revisions to the MATS. The EPA expects to issue a final rule by the end of 2025.
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. As discussed above, in June 2025, the EPA issued a proposed rule to repeal all greenhouse gas emissions standards for fossil fuel-fired power plants, including the NSPS. The EPA expects to issue a final rule by the end of 2025.
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 $40 million associated with CCR storage facilities recorded on their respective balance sheets as of September 30, 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 September 30, 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 $45 million to $90 million. Ameren and Ameren Illinois recorded a liability of $45 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.
v3.25.3
Callaway Energy Center
 9 Months Ended
Sep. 30, 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 have historically been 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 May 2025, the MoPSC issued an order that approved a non-unanimous stipulation and agreement between Ameren Missouri and the MoPSC staff that reduced annual customer contributions for funding the Callaway Energy Center decommissioning costs from $7 million to zero, as the trust fund level exceeded the estimated present value of future decommissioning costs at the time of the agreement. This MoPSC order removed Ameren Missouri’s funding obligation effective in June 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 September 30, 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.
v3.25.3
Retirement Benefits
 9 Months Ended
Sep. 30, 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 and nine months ended September 30, 2025 and 2024:
Pension BenefitsPostretirement Benefits
Three MonthsNine MonthsThree MonthsNine Months
20252024202520242025202420252024
Service cost(a)
$21 $22 $62 $66 $3 $3 $8 $9 
Non-service cost components:
Interest cost58 56 175 167 11 11 33 33 
Expected return on plan assets(b)
(76)(82)(227)(246)(24)(23)(71)(69)
Amortization of(b):
Prior service cost (credit)— — — — (1)(1)(3)(3)
Actuarial (gain)(9)(17)(26)(50)(9)(9)(27)(29)
Total non-service cost components(c)
$(27)$(43)$(78)$(129)$(23)$(22)$(68)$(68)
Net periodic benefit income(d)
$(6)$(21)$(16)$(63)$(20)$(19)$(60)$(59)
(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 and nine months ended September 30, 2025 and 2024:
Pension BenefitsPostretirement Benefits
Three MonthsNine MonthsThree MonthsNine Months
20252024202520242025202420252024
Ameren Missouri(a)
$(4)$(11)$(11)$(33)$(7)$(6)$(21)$(20)
Ameren Illinois(1)(8)(3)(25)(13)(13)(39)(39)
Other(1)(2)(2)(5)— — — — 
Ameren(a)
$(6)$(21)$(16)$(63)$(20)$(19)$(60)$(59)
(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.
v3.25.3
Income Taxes
 9 Months Ended
Sep. 30, 2025
Income Tax Disclosure [Abstract]  
Income Taxes INCOME TAXES
OBBBA
The OBBBA was enacted in July 2025 and includes various income tax provisions, among other things. The OBBBA modified provisions of the IRA related to production and investment tax credits. The new law maintains production and investment tax credits for solar and wind projects that begin construction within one year of the OBBBA’s enactment and are placed in-service by the end of 2030. Projects that begin construction after one year from enactment of the OBBBA but are placed in service by the end of 2027 also remain eligible. The law provides investment tax credits for battery storage projects that begin construction by the end of 2033 and phase out by the end of 2035. Renewable energy projects that begin construction in 2026 and beyond that use a certain threshold percentage of materials from prohibited foreign entities, as defined in the OBBBA, are not eligible for the tax credits. Production tax credits associated with nuclear generation remain unchanged from the IRA and phase out by the end of 2032. Furthermore, the new law continues to allow for transferability of the production and investment tax credits to an unrelated party for cash but is restricted from being transferred to specified foreign entities, as defined in the OBBBA. Ameren is currently evaluating the OBBBA and guidance issued in connection with the OBBBA and does not expect any material impacts on its results of operations, financial position, and liquidity in 2025. Implementation of the OBBBA provisions is subject to additional guidance, regulations, interpretations, amendments, or technical corrections that may be issued by the IRS or United States Department of Treasury.
The following table presents a reconciliation of the federal statutory corporate income tax rate to the effective income tax rate for the three and nine months ended September 30, 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)(9)(9)(15)(4)(4)
Revaluation of excess deferred income taxes(b)
(7)— — — (14)— 
Amortization of deferred investment tax credit(1)— (1)— — — 
Renewable and other tax credits(c)
(3)(4)(7)(10)— — 
State tax5 4 3 3 7 7 
Depreciation differences(1)— (1)(1)(1)— 
Other permanent items— (1)— — 1 — 
Effective income tax rate7 %11 %6 %(2)%10 %24 %
Nine Months
Federal statutory corporate income tax rate21 %21 %21 %21 %21 %21 %
Increases (decreases) from:
Amortization of excess deferred taxes(a)
(7)(8)

(9)(14)

(4)(4)
Revaluation of excess deferred income taxes(b)
(3)— — — (4)— 
Amortization of deferred investment tax credit(1)— (1)— — — 
Renewable and other tax credits(c)
(3)(5)(7)(10)— — 
State tax5 5 3 3 7 7 
Depreciation differences(1)— (1)(1)— — 
Effective income tax rate11 %13 %6 %(1)%20 %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. Deferred income taxes are revalued when federal or state income tax rates change, and the offset to the revaluation of deferred income taxes subject to regulatory ratemaking is recorded to a regulatory asset or liability.
(b)In 2024, the IRS issued a series of private letter rulings to another taxpayer, which provided guidance on applying IRS normalization rules to the calculation of tax benefits applicable to the ratemaking treatment related to net operating loss carryforwards. The rulings concluded that, for ratemaking purposes, net operating loss carryforwards should be reflected on a separate company basis and should not be reduced by payments received for the utilization of losses by other affiliates under a tax allocation agreement. In 2025, the FERC issued an order reflecting implementation of the rules for the other taxpayer who had a similar fact pattern as Ameren Illinois and ATXI. Accordingly, in the third quarter of 2025, Ameren and Ameren Illinois decreased income tax expense by $48 million and $23 million, respectively, to reflect the revaluation of excess deferred income tax regulatory liabilities resulting from TCJA for FERC-regulated jurisdictions pursuant to IRS guidance and recent FERC order.
(c)The benefit of the renewable credits associated with Missouri renewable energy standard compliance is refunded to customers through the RESRAM. The benefit of the renewable credits associated with the production and investment tax credit tracker will be refunded to customers based on MoPSC approval in a regulatory rate review.
v3.25.3
Supplemental Information
 9 Months Ended
Sep. 30, 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 September 30, 2025, and December 31, 2024:
September 30, 2025December 31, 2024
AmerenAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois
“Cash and cash equivalents”$9 $— $— $7 $— $— 
Restricted cash included in “Other current assets” (a)
95 86 6 15 7 6 
Restricted cash included in “Other assets”324 — 324 296 — 296 
Restricted cash included in “Nuclear decommissioning trust fund”7 7 — 10 10 — 
Total cash, cash equivalents, and restricted cash$435 $93 $330 $328 $17 $302 
(a)Included in “Restricted cash” on Ameren Missouri’s balance sheet.
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 September 30, 2025, and December 31, 2024, Ameren’s and Ameren Illinois’ balance sheets included payables for purchased receivables of $55 million and $43 million, respectively. On Ameren’s balance sheet, these amounts were included in “Other current liabilities”.
The following table provides a reconciliation of the beginning and ending amount of the allowance for doubtful accounts for the three and nine months ended September 30, 2025 and 2024:
Three MonthsNine Months
2025202420252024
Ameren:
Beginning of period$39 $37 $30 $30 
Bad debt expense18 12 37 28 
Charged to other accounts(a)
2 2 5 6 
Net write-offs(21)(20)(34)(33)
End of period$38 $31 $38 $31 
Ameren Missouri:
Beginning of period$12 $12 $12 $12 
Bad debt expense7 3 11 8 
Net write-offs(4)(3)(8)(8)
End of period$15 $12 $15 $12 
Ameren Illinois:(b)
Beginning of period$27 $25 $18 $18 
Bad debt expense11 

9 26 20 
Charged to other accounts(a)
2 2 5 6 
Net write-offs(17)(17)(26)(25)
End of period$23 $19 $23 $19 
(a)Amounts associated with the allowance for doubtful accounts related to receivables purchased by Ameren Illinois from alternative retail electric suppliers, as required by the Illinois Public Utilities Act.
(b)Ameren Illinois has 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 nine months ended September 30, 2025 and 2024:
September 30, 2025September 30, 2024
AmerenAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois
Investing:
Accrued capital expenditures, including nuclear fuel expenditures$412 $277 $147 $404 $257 $127 
Net realized and unrealized gain – nuclear decommissioning trust fund136 136 — 163 163 — 
Financing:
Issuance of common stock for stock-based compensation$25 $— $— $16 $— $— 
Issuance of common stock under the DRPlus7 — — 7 — — 
Asset Retirement Obligations
The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the nine months ended September 30, 2025:
Ameren
Missouri		Ameren
Illinois		Ameren
Balance at December 31, 2024
$823 
(a) 
$4 
(b) 
$827 
(a) 
Liabilities settled(7)— (7)
Accretion27 
(c) 
— 

27 
(c) 
Change in estimates1 1 2 
Balance at September 30, 2025
$844 
(a) 
$5 
(b) 
$849 
(a) 
(a)Balance included $5 million in “Other current liabilities” on the balance sheet as of both September 30, 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 nine months ended September 30, 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 September 30, 2025, and December 31, 2024, the present value of benefits to be paid for deferred compensation obligations was $80 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 September 30, 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 and nine months ended September 30, 2025 and 2024:
Three MonthsNine Months
2025202420252024
Ameren Missouri$69 $60 $150 $136 
Ameren Illinois30 29 104 94 
Ameren$99 $89 $254 $230 
Earnings per Share
The following table reconciles the basic weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the three and nine months ended September 30, 2025 and 2024:
Three MonthsNine Months
2025202420252024
Weighted-average Common Shares Outstanding – Basic270.4 266.8 270.2 266.6 
Assumed settlement of performance share units and restricted stock units0.8 0.4 0.9 0.3 
Dilutive effect of forward sale agreements1.0 0.1 0.6 — 
Weighted-average Common Shares Outstanding – Diluted(a)
272.2 267.3 271.7 266.9 
(a)There was an immaterial number of anti-dilutive performance share units excluded from the earnings per diluted share calculations for the three and nine months ended September 30, 2025 and 2024. Outstanding forward sale agreements as of September 30, 2025 and 2024 that were anti-dilutive for the nine months ended September 30, 2025 and the three and nine months ended September 30, 2024 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.
v3.25.3
Segment Information
 9 Months Ended
Sep. 30, 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 and nine months ended September 30, 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$1,696 $698 $117 $188 $— $— $2,699 
Intersegment revenues9 1 — 52 — (62)— 
Revenue1,705 699 117 240 — (62)2,699 
Fuel and purchased power(a)
(487)(330)— — — 49 (768)
Natural gas purchased for resale(a)
(6)— (19)— — — (25)
Other operations and maintenance expenses(a)
(260)(171)(55)(19)(10)13 (502)
Other segment items
Depreciation and amortization(239)(92)(33)(49)(2)— (415)
Taxes other than income taxes(122)(22)(15)(3)(2)— (164)
Other income (expense), net45 20 4 (3)11 (1)76 
Interest charges(85)(28)(16)(31)(49)1 (208)
Income taxes (benefit)(32)(19)4 16 (21)— (52)
Noncontrolling interests – preferred stock dividends(1)— — — — — (1)
Net income (loss) attributable to Ameren common shareholders518 57 (13)151 
(b)
(73)— 640 
Interest income3 6 — 1 1 (1)10 
Capital expenditures548 163 78 174 1 24 988 
Three Months 2024:
External revenues$1,333 $551 $121 $168 $— $— $2,173 
Intersegment revenues9 1 — 42 — (52)— 
Revenue1,342 552 121 210 — (52)2,173 
Fuel and purchased power(a)
(334)(204)— — — 39 (499)
Natural gas purchased for resale(a)
(4)— (26)— — — (30)
Other operations and maintenance expenses(a)
(288)(163)(51)(19)(12)13 (520)
Other segment items
Depreciation and amortization(220)(92)(32)(42)(2)— (388)
Taxes other than income taxes(109)(21)(14)(2)(4)— (150)
Other income (expense), net51 23 6 8 16 (3)101 
Interest charges(62)(25)(16)(31)(42)3 (173)
Income taxes (benefit)6 (14)2 (34)(17)— (57)
Noncontrolling interests – preferred stock dividends(1)— — — — — (1)
Net income (loss) attributable to Ameren common shareholders381 56 (10)90 
(b)
(61)— 456 
Interest income2 6 1 — 2 (3)8 
Capital expenditures735 152 83 174 2 (9)1,137 
Ameren MissouriAmeren Illinois Electric DistributionAmeren Illinois Natural GasAmeren TransmissionOtherIntersegment EliminationsAmeren
Nine Months 2025:
External revenues$3,978 $1,838 $686 $515 $— $— $7,017 
Intersegment revenues24 6 — 143 — (173)— 
Revenue4,002 1,844 686 658 — (173)7,017 
Fuel and purchased power(a)
(1,431)(765)— — — 132 (2,064)
Natural gas purchased for resale(a)
(45)— (188)— — — (233)
Other operations and maintenance expenses(a)
(748)(493)(165)(56)(26)41 (1,447)
Other segment items
Depreciation and amortization(642)(276)(98)(146)(6)— (1,168)
Taxes other than income taxes(300)(63)(60)(7)(9)— (439)
Other income (expense), net135 66 14 14 31 (3)257 
Interest charges(215)(80)(47)(89)(142)3 (570)
Income (taxes) benefit(43)(48)(37)(48)31 — (145)
Noncontrolling interests – preferred stock dividends(3)(1)— — — — (4)
Net income (loss) attributable to Ameren common shareholders710 184 105 326 
(b)
(121)— 1,204 
Interest income7 22 — 2 3 (3)31 
Capital expenditures1,873 483 225 505 6 26 3,118 
Nine Months 2024:
External revenues$2,980 $1,566 $660 $476 $— $— $5,682 
Intersegment revenues25 1 — 110 — (136)— 
Revenue3,005 1,567 660 586 — (136)5,682 
Fuel and purchased power(a)
(689)(564)— — — 99 (1,154)
Natural gas purchased for resale(a)
(41)— (173)— — — (214)
Other operations and maintenance expenses(a)
(789)(452)(168)(54)(29)37 (1,455)
Other segment items
Depreciation and amortization(623)(278)(98)(121)(5)— (1,125)
Taxes other than income taxes(287)(57)(55)(6)(11)— (416)
Other income (expense), net144 72 20 14 54 (11)293 
Interest charges(187)(73)(46)(89)(108)11 (492)
Income (taxes) benefit4 (41)(38)(89)24 — (140)
Noncontrolling interests – preferred stock dividends(3)(1)— — — — (4)
Net income (loss) attributable to Ameren common shareholders534 173 102 241 
(b)
(75)— 975 
Interest income7 21 1 1 10 (11)29 
Capital expenditures1,839 468 202 515 6 (1)3,029 
(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$699 $117 $130 $— $946 
Intersegment revenues— — 46 (46)— 
Revenue699 117 176 (46)946 
Purchased power(a)
(330)— — 46 (284)
Natural gas purchased for resale(a)
— (19)— — (19)
Other operations and maintenance expenses(a)
(171)(55)(15)— (241)
Other segment items
Depreciation and amortization(92)(33)(37)— (162)
Taxes other than income taxes(22)(15)(1)— (38)
Other income, net20 4 6 — 30 
Interest charges(28)(16)(23)— (67)
Income taxes(19)4 (2)— (17)
Net income (loss) available to common shareholder57 (13)104 — 148 
Interest income6 — 1 — 7 
Capital expenditures163 78 144 — 385 
Three Months 2024:
External revenues$552 $121 $120 $— $793 
Intersegment revenues— — 35 (35)— 
Revenue552 121 155 (35)793 
Purchased power(a)
(204)— — 35 (169)
Natural gas purchased for resale(a)
— (26)— — (26)
Other operations and maintenance expenses(a)
(163)(51)(15)— (229)
Other segment items
Depreciation and amortization(92)(32)(31)— (155)
Taxes other than income taxes(21)(14)(2)— (37)
Other income, net23 6 8 — 37 
Interest charges(25)(16)(22)— (63)
Income taxes(14)2 (25)— (37)
Net income (loss) available to common shareholder56 (10)68 — 114 
Interest income6 1 — — 7 
Capital expenditures152 83 139 — 374 
Nine Months 2025:
External revenues$1,844 $686 $359 $— $2,889 
Intersegment revenues— — 123 (123)— 
Revenue1,844 686 482 (123)2,889 
Purchased power(a)
(765)— — 123 (642)
Natural gas purchased for resale(a)
— (188)— (188)
Other operations and maintenance expenses(a)
(493)(165)(44)(702)
Other segment items
Depreciation and amortization(276)(98)(110)(484)
Taxes other than income taxes(63)(60)(3)(126)
Other income, net66 14 21 101 
Interest charges(80)(47)(65)(192)
Income taxes(48)(37)(49)(134)
Noncontrolling interests – preferred stock dividends(1)— — (1)
Net income available to common shareholder184 105 232 — 521 
Interest income22 — 2 — 24 
Capital expenditures483 225 419 — 1,127 
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionIntersegment EliminationsAmeren Illinois
Nine Months 2024:
External revenues$1,567 $660 $332 $— $2,559 
Intersegment revenues— — 90 (90)— 
Revenue1,567 660 422 (90)2,559 
Purchased power(a)
(564)— — 90 (474)
Natural gas purchased for resale(a)
— (173)— (173)
Other operations and maintenance expenses(a)
(452)(168)(43)(663)
Other segment items
Depreciation and amortization(278)(98)(86)(462)
Taxes other than income taxes(57)(55)(4)(116)
Other income, net72 20 13 105 
Interest charges(73)(46)(59)(178)
Income taxes(41)(38)(65)(144)
Noncontrolling interests – preferred stock dividends(1)— — (1)
Net income available to common shareholder173 102 178 — 453 
Interest income21 1 — — 22 
Capital expenditures468 202 421 — 1,091 
(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 and nine months ended September 30, 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$702 $469 $— $— $— $1,171 
Commercial537 235 — — — 772 
Industrial119 46 — — — 165 
Other327 (51)
(a)
— 240 (61)455 
Total electric revenues$1,685 $699 $— $240 $(61)$2,563 
Residential$9 $— $70 $— $— $79 
Commercial5 — 21 — — 26 
Industrial— — 2 — — 2 
Other6 — 24 — (1)29 
Total natural gas revenues$20 $— $117 $— $(1)$136 
Total revenues(b)
$1,705 $699 $117 $240 $(62)$2,699 
Three Months 2024:
Residential$590 $339 $— $— $— $929 
Commercial465 184 — — — 649 
Industrial108 38 — — — 146 
Other161 (9)
(a)
— 210 (51)311 

Total electric revenues$1,324 $552 $— $210 $(51)$2,035 
Residential$9 $— $77 $— $— $86 
Commercial5 — 19 — — 24 
Industrial— — 2 — — 2 
Other4 — 23 — (1)26 
Total natural gas revenues$18 $— $121 $— $(1)$138 
Total revenues(b)
$1,342 $552 $121 $210 $(52)$2,173 
Nine Months 2025:
Residential$1,483 $1,132 $— $— $— $2,615 
Commercial1,154 596 — — — 1,750 
Industrial269 144 — — — 413 
Other987 (28)
(a)
— 658 (172)1,445 
Total electric revenues$3,893 $1,844 $— $658 $(172)$6,223 
Residential$65 $— $486 $— $— $551 
Commercial29 — 126 — — 155 
Industrial3 — 9 — — 12 
Other12 — 65 — (1)76 
Total natural gas revenues$109 $— $686 $— $(1)$794 
Total revenues(b)
$4,002 $1,844 $686 $658 $(173)$7,017 
Ameren MissouriAmeren Illinois Electric DistributionAmeren Illinois Natural GasAmeren TransmissionIntersegment EliminationsAmeren
Nine Months 2024:
Residential$1,326 $947 $— $— $— $2,273 
Commercial1,048 512 — — — 1,560 
Industrial246 130 — — — 376 
Other282 (22)
(a)
— 586 (135)711 
Total electric revenues$2,902 $1,567 $— $586 $(135)$4,920 
Residential$62 $— $466 $— $— $528 
Commercial26 — 111 — — 137 
Industrial3 — 7 — — 10 
Other12 — 76 — (1)87 
Total natural gas revenues$103 $— $660 $— $(1)$762 
Total revenues(b)
$3,005 $1,567 $660 $586 $(136)$5,682 
(a)Includes over-recoveries of various riders.
(b)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the three and nine months ended September 30, 2025 and 2024:
Ameren MissouriAmeren Illinois Electric DistributionAmeren Illinois Natural GasAmeren TransmissionIntersegment EliminationsAmeren
Three Months 2025:
Revenues from alternative revenue programs$— $(187)$(10)$(12)$— $(209)
Other revenues not from contracts with customers2 3 — — — 5 
Three Months 2024:
Revenues from alternative revenue programs$— $(144)$(9)$(2)$— $(155)
Other revenues not from contracts with customers2 2 — — — 4 
Nine Months 2025:
Revenues from alternative revenue programs$(4)$(174)$(6)$(21)$— $(205)
Other revenues not from contracts with customers5 11 2 — (4)14 
Nine Months 2024:
Revenues from alternative revenue programs$(7)$(83)$10 $11 $— $(69)
Other revenues not from contracts with customers4 5 2 — — 11 
Ameren Illinois
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionIntersegment EliminationsAmeren Illinois
Three Months 2025:
Residential$469 $70 $— $— $539 
Commercial235 21 — — 256 
Industrial46 2 — — 48 
Other(51)
(a)
24 176 (46)103 
Total revenues(b)
$699 $117 $176 $(46)$946 
Three Months 2024:
Residential$339 $77 $— $— $416 
Commercial184 19 — — 203 
Industrial38 2 — — 40 
Other(9)
(a)
23 155 (35)134 
Total revenues(b)
$552 $121 $155 $(35)$793 
Nine Months 2025:
Residential$1,132 $486 $— $— $1,618 
Commercial596 126 — — 722 
Industrial144 9 — — 153 
Other(28)
(a)
65 482 (123)396 
Total revenues(b)
$1,844 $686 $482 $(123)$2,889 
Nine Months 2024:
Residential$947 $466 $— $— $1,413 
Commercial512 111 — — 623 
Industrial130 7 — — 137 
Other(22)
(a)
76 422 (90)386 
Total revenues(b)
$1,567 $660 $422 $(90)$2,559 
(a)Includes over-recoveries of various riders.
(b)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the Ameren Illinois segments for the three and nine months ended September 30, 2025 and 2024:
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionAmeren Illinois
Three Months 2025:
Revenues from alternative revenue programs$(187)$(10)$(12)$(209)
Other revenues not from contracts with customers3 — — 3 
Three Months 2024:
Revenues from alternative revenue programs$(144)$(9)$(1)$(154)
Other revenues not from contracts with customers2 — — 2 
Nine Months 2025:
Revenues from alternative revenue programs$(174)$(6)$(20)$(200)
Other revenues not from contracts with customers11 2 — 13 
Nine Months 2024:
Revenues from alternative revenue programs$(83)$10 $9 $(64)
Other revenues not from contracts with customers5 2 — 7 
v3.25.3
Insider Trading Arrangements
 3 Months Ended
Sep. 30, 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
Theresa A. Shaw [Member]  
Trading Arrangements, by Individual  
Material Terms of Trading Arrangement
On August 13, 2025, Theresa A. Shaw, Senior Vice President, Finance and Chief Accounting Officer of Ameren, adopted a Rule 10b5-1 trading arrangement that provides for the sale of an aggregate of up to 1,300 shares to be sold in four equal quarterly installments between November 2025 and November 2026, subject to certain price limitations set forth in the trading arrangement. Ms. Shaw’s 10b5-1 trading arrangement will terminate on the earlier of: (i) November 13, 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 Theresa A. Shaw
Title Senior Vice President, Finance and Chief Accounting Officer of Ameren
Rule 10b5-1 Arrangement Adopted true
Adoption Date August 13, 2025
Expiration Date November 13, 2026
Arrangement Duration 365 days
Aggregate Available 1,300
v3.25.3
Summary Of Significant Accounting Policies (Policies)
 9 Months Ended
Sep. 30, 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 September 30, 2025 and December 31, 2024:
20252024
Unbilled revenue(a)
$4 $— 
Other current assets(a)(b)
46 2 
Noncurrent regulatory assets(a)
449 465 
Current maturities of long-term debt(c)
29 17 
Interest accrued(c)
18 1 
Current regulatory liabilities(d)
15 — 
Long-term debt, net(c)
437 448 
(a)Assets may be used only to meet AMF’s obligations and commitments.
(b)Included in “Restricted cash” on Ameren Missouri’s balance sheet.
(c)The securitized tariff bondholders have no recourse to Ameren Missouri.
(d)Included in “Other current liabilities” on Ameren Missouri’s balance sheet.
Variable Interest Entities that are Not Consolidated
As of September 30, 2025, and December 31, 2024, Ameren had unconsolidated variable interests in various equity method investments, primarily to advance innovative energy technologies, totaling $60 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 September 30, 2025, Ameren’s maximum exposure to loss related to these variable interest entities is limited to the investment in these partnerships of $60 million plus associated outstanding funding commitments of $31 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 September 30, 2025, and December 31, 2024, the present value of benefits to be paid for deferred compensation obligations was $80 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 September 30, 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.
v3.25.3
Accounting Policies (Tables)
 9 Months Ended
Sep. 30, 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 September 30, 2025 and December 31, 2024:
20252024
Unbilled revenue(a)
$4 $— 
Other current assets(a)(b)
46 2 
Noncurrent regulatory assets(a)
449 465 
Current maturities of long-term debt(c)
29 17 
Interest accrued(c)
18 1 
Current regulatory liabilities(d)
15 — 
Long-term debt, net(c)
437 448 
(a)Assets may be used only to meet AMF’s obligations and commitments.
(b)Included in “Restricted cash” on Ameren Missouri’s balance sheet.
(c)The securitized tariff bondholders have no recourse to Ameren Missouri.
(d)Included in “Other current liabilities” on Ameren Missouri’s balance sheet.
v3.25.3
Rate and Regulatory Matters (Tables)
 9 Months Ended
Sep. 30, 2025
Regulated Operations [Abstract]  
Schedule of Generation Facilities The following table provides information with respect to each facility:
Agreement typeFacility sizeStatus of MoPSC CCN
In-service date(a)
Vandalia Solar Project(b)
Self-build
50-MW
Approved March 2024Fourth quarter 2025
Bowling Green Solar Project(b)
Self-build
50-MW
Approved March 2024First quarter 2026
Split Rail Solar Project(b)
Build-transfer(c)
300-MW
Approved March 2024Mid-2026
Castle Bluff Natural Gas Project(d)
Self-build
800-MW
Approved October 2024Fourth quarter 2027
Big Hollow Battery Energy Storage ProjectSelf-build
400-MW
Filed June 2025(e)
Second quarter 2028
Big Hollow Natural Gas ProjectSelf-build
800-MW
Filed June 2025(e)
Third quarter 2028
Reform Solar ProjectSelf-build
250-MW
Filed August 2025(e)
Fourth quarter 2028
(a)In-service dates are dependent on the timing of regulatory approvals and construction completion, among other things.
(b)These projects collectively represent approximately $0.8 billion of capital expenditures.
(c)FERC approval of acquisition received November 2024.
(d)This project represents approximately $0.9 billion of capital expenditures.
(e)Ameren Missouri expects a decision by the MoPSC in the first half of 2026.
v3.25.3
Short-Term Debt and Liquidity (Tables)
 9 Months Ended
Sep. 30, 2025
Debt Disclosure [Abstract]  
Schedule of Short-term Debt
The following table presents commercial paper outstanding, net of issuance discounts, as of September 30, 2025, and December 31, 2024. There were no borrowings outstanding under the Credit Agreements as of September 30, 2025, or December 31, 2024.
September 30, 2025December 31, 2024
Ameren (parent)$644 $1,055 
Ameren Missouri259 — 
Ameren Illinois— 88 
Ameren consolidated$903 $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 nine months ended September 30, 2025 and 2024:
Ameren
(parent)		Ameren
Missouri		Ameren
Illinois		Ameren
Consolidated
2025
Average daily amount outstanding$637 $245 $130 $1,012 
Weighted-average interest rate4.60 %4.58 %4.55 %4.59 %
Peak amount outstanding during period(a)
$1,139 $650 $425 $1,603 
Peak interest rate4.75 %4.72 %4.70 %4.75 %
2024
Average daily amount outstanding$177 $187 $256 $620 
Weighted-average interest rate5.46 %5.52 %5.57 %5.53 %
Peak amount outstanding during period(a)
$948 $576 $694 $1,542 
Peak interest rate5.60 %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.
v3.25.3
Other Income, Net (Tables)
 9 Months Ended
Sep. 30, 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 and nine months ended September 30, 2025 and 2024:
Three MonthsNine Months
2025202420252024
Ameren:
Allowance for equity funds used during construction
$21 $23 $60 $48 
Other interest income
10 8 31 29 
Non-service cost components of net periodic benefit income(a)
59 76 187 228 
Miscellaneous income
6 — 13 6 
Gain on the extinguishment of debt(b)
— — 8 — 
Losses related to equity method investments(9)(2)(19)(1)
Donations
(6)(1)(9)(5)
Miscellaneous expense
(5)(3)(14)(12)
Total Other Income, Net$76 $101 $257 $293 
Ameren Missouri:
Allowance for equity funds used during construction
$14 $15 $37 $38 
Other interest income
3 2 7 7 
Non-service cost components of net periodic benefit income(a)
29 35 96 104 
Miscellaneous income
4 1 6 3 
Donations
(2)— (4)(2)
Miscellaneous expense
(3)(2)(7)(6)
Total Other Income, Net$45 $51 $135 $144 
Ameren Illinois:
Allowance for equity funds used during construction
$6 $8 $21 $10 
Other interest income7 7 24 22 
Non-service cost components of net periodic benefit income
21 25 61 78 
Miscellaneous income
2 — 7 3 
Donations
(4)— (5)(2)
Miscellaneous expense(2)(3)(7)(6)
Total Other Income, Net$30 $37 $101 $105 
(a)For the three and nine months ended September 30, 2025, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $(9) million and $(41) million, respectively, due to a regulatory tracking mechanism for the difference between the level of such costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates. The deferral was $(11) million and $(31) million, respectively, for the three and nine months ended September 30, 2024. See Note 11 – Retirement Benefits for additional information.
(b)See Note 4 – Long-term Debt and Equity Financings for additional information on Ameren (parent)’s repurchase of Ameren Missouri’s senior secured notes and first mortgage bonds and Ameren Illinois’ first mortgage bonds that were accounted for as a debt extinguishment.
v3.25.3
Derivative Financial Instruments (Tables)
 9 Months Ended
Sep. 30, 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 September 30, 2025, and December 31, 2024. As of September 30, 2025, these contracts extended through October 2028, October 2031 and May 2032 for fuel oils, natural gas, and power, respectively.
Quantity (in millions, except as indicated)
September 30, 2025December 31, 2024
CommodityAmeren MissouriAmeren IllinoisAmerenAmeren MissouriAmeren IllinoisAmeren
Fuel oils (in gallons)23 — 23 23 — 23 
Natural gas (in MMBtu)50 211 261 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 September 30, 2025, and December 31, 2024:
September 30, 2025December 31, 2024
Balance Sheet LocationAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois		Ameren
Natural gasOther current assets$1 $3 $4 $2 $2 $4 
Other assets1 5 6 2 4 6 
PowerOther current assets22 — 22 6 — 6 
Total assets$24 $8 $32 $10 $6 $16 
Fuel oilsOther current liabilities$2 $— $2 $2 $— $2 
Other deferred credits and liabilities1 — 1 2 — 2 
Natural gasOther current liabilities3 18 21 5 22 27 
Other deferred credits and liabilities5 8 13 6 13 19 
PowerOther current liabilities1 10 11 — 10 10 
Other deferred credits and liabilities— 52 52 — 43 43 
Total liabilities$12 $88 $100 $15 $88 $103 
v3.25.3
Fair Value Measurements (Tables)
 9 Months Ended
Sep. 30, 2025
Fair Value Disclosures [Abstract]  
Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis
The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of September 30, 2025, and December 31, 2024:
September 30, 2025December 31, 2024
Level 1Level 2Level 3TotalLevel 1Level 2Level 3Total
Assets:
Ameren Missouri
Derivative assets – commodity contracts:
Natural gas$— $2 $— $2 $— $4 $— $4 
Power— — 22 22 — — 6 6 
Total derivative assets – commodity contracts$— $2 $22 $24 $— $4 $6 $10 
Nuclear decommissioning trust fund:
Equity securities:
U.S. large capitalization$1,001 $— $— $1,001 $911 $— $— $911 
Debt securities:
U.S. Treasury and agency securities— 235 — 235 — 191 — 191 
Corporate bonds— 174 — 174 — 145 — 145 
Other— 84 — 84 — 86 — 86 
Total nuclear decommissioning trust fund$1,001 $493 $— $1,494 
(a) 
$911 $422 $— $1,333 
(a) 
Total Ameren Missouri$1,001 $495 $22 $1,518 $911 $426 $6 $1,343 
Ameren Illinois
Derivative assets – commodity contracts:
Natural gas$— $4 $4 $8 $— $3 $3 $6 
Total Ameren Illinois$— $4 $4 $8 $— $3 $3 $6 
Ameren
Derivative assets – commodity contracts(b)
$— $6 $26 $32 $— $7 $9 $16 
Nuclear decommissioning trust fund(c)
1,001 493 — 1,494 
(a) 
911 422 — 1,333 
(a) 
Total Ameren$1,001 $499 $26 $1,526 $911 $429 $9 $1,349 
Liabilities:
Ameren Missouri
Derivative liabilities – commodity contracts:
Fuel oils$3 $— $— $3 $4 $— $— $4 
Natural gas— 8 — 8 — 11 — 11 
Power— — 1 1 — — — — 
Total Ameren Missouri$3 $8 $1 $12 $4 $11 $— $15 
Ameren Illinois
Derivative liabilities – commodity contracts:
Natural gas$1 $22 $3 $26 $1 $28 $6 $35 
Power— — 62 62 — — 53 53 
Total Ameren Illinois$1 $22 $65 $88 $1 $28 $59 $88 
Ameren
Derivative liabilities – commodity contracts(b)
$4 $30 $66 $100 $5 $39 $59 $103 
(a)Balance excludes $8 million and $9 million of cash and cash equivalents, receivables, payables, and accrued income, net, for September 30, 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 and nine months ended September 30, 2025 and 2024:
20252024
Ameren MissouriAmeren IllinoisAmerenAmeren MissouriAmeren IllinoisAmeren
For the three months ended September 30:
Beginning balance at July 1
$13 $(76)$(63)$14 $(61)$(47)
Realized and unrealized gains/(losses) included in regulatory assets/liabilities12 12 24 (1)(21)(22)
Settlements(4)2 (2)(3)4 1 
Ending balance at September 30
$21 $(62)$(41)$10 $(78)$(68)
Change in unrealized gains/(losses) related to assets/liabilities held at September 30
$11 $11 $22 $(1)$(19)$(20)
For the nine months ended September 30:
Beginning balance at January 1$6 $(53)$(47)$4 $(68)$(64)
Realized and unrealized gains/(losses) included in regulatory assets/liabilities28 (18)10 13 (23)(10)
Settlements(13)9 (4)(7)13 6 
Ending balance at September 30
$21 $(62)$(41)$10 $(78)$(68)
Change in unrealized gains/(losses) related to assets/liabilities held at September 30
$21 $(17)$4 $10 $(18)$(8)
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis, Valuation Techniques
The following table describes the valuation techniques and significant unobservable inputs utilized for the fair value of our Level 3 power derivative contract assets and liabilities as of September 30, 2025, and December 31, 2024:
Fair Value
Weighted Average(b)
CommodityAssetsLiabilitiesValuation Technique(s)
Unobservable Input(a)
Range
2025
Power(c)
$22$(63)Discounted cash flow
Average forward peak and off-peak pricing – forwards/swaps ($/MWh)
33 – 67
43
Nodal basis ($/MWh)
(10) – 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 September 30, 2025, and December 31, 2024:
Long-Term Debt (Including Current Portion):
Carrying
Amount(a)
Fair Value
Level 2Level 3Total
September 30, 2025
Ameren(b)
$19,201 $17,532 $556 
(c) 
$18,088 
Ameren Missouri(d)
8,246 7,662 — 7,662 
Ameren Illinois(d)
6,258 5,815 — 5,815 
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 $139 million, $63 million, and $56 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of September 30, 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.
(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).
v3.25.3
Related Party Transactions (Tables)
 9 Months Ended
Sep. 30, 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 September 30, 2025, and December 31, 2024:
September 30, 2025December 31, 2024
Ameren MissouriAmeren IllinoisAmeren MissouriAmeren Illinois
Income taxes payable to parent(a)
$3$67$—$32
Income taxes receivable from parent(b)
2—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 and nine months ended September 30, 2025 and 2024:
Three MonthsNine Months
AgreementIncome Statement
Line Item		Ameren
Missouri		Ameren
Illinois		Ameren
Missouri		Ameren
Illinois
Ameren Missouri and Ameren IllinoisOperating Revenues2025$8 $(b)$23 $1 
rent and facility services
20248 (b)23 (b)
Ameren Missouri and Ameren Illinois miscellaneousOperating Revenues2025$1 $(b)$1 $5 
support services20241 (b)2 1 
Total Operating Revenues2025$9 $(b)$24 $6 
20249 (b)25 1 
Ameren Missouri and Ameren IllinoisPurchased Power2025$2 $1 $7 $2 
transmission services from ATXI20243 1 7 2 
Ameren Missouri and Ameren IllinoisOther Operations and Maintenance2025$(b)$(b)$(b)$3 
rent and facility services
2024(b)(b)(b)(b)
Ameren Services support servicesOther Operations and Maintenance2025$42 $39 $130 $119 
agreement
202441 38 122 115 
Total Other Operations and2025$42 $39 $130 $122 
Maintenance202441 38 122 115 
Money pool interest(Interest Charges)/Other Income, Net2025$(b)$(b)$(b)$(b)
2024(b)(b)(3)(2)
Long-term debt, net - related parties(Interest Charges)2025$(1)$(b)$(2)$(b)
2024— — — — 
(a)Not applicable.
(b)Amount less than $1 million.
v3.25.3
Callaway Energy Center (Tables)
 9 Months Ended
Sep. 30, 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 September 30, 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.
v3.25.3
Retirement Benefits (Tables)
 9 Months Ended
Sep. 30, 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 and nine months ended September 30, 2025 and 2024:
Pension BenefitsPostretirement Benefits
Three MonthsNine MonthsThree MonthsNine Months
20252024202520242025202420252024
Service cost(a)
$21 $22 $62 $66 $3 $3 $8 $9 
Non-service cost components:
Interest cost58 56 175 167 11 11 33 33 
Expected return on plan assets(b)
(76)(82)(227)(246)(24)(23)(71)(69)
Amortization of(b):
Prior service cost (credit)— — — — (1)(1)(3)(3)
Actuarial (gain)(9)(17)(26)(50)(9)(9)(27)(29)
Total non-service cost components(c)
$(27)$(43)$(78)$(129)$(23)$(22)$(68)$(68)
Net periodic benefit income(d)
$(6)$(21)$(16)$(63)$(20)$(19)$(60)$(59)
(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 The following table presents the respective share of net periodic pension and other postretirement benefit costs (income) incurred for the three and nine months ended September 30, 2025 and 2024:
Pension BenefitsPostretirement Benefits
Three MonthsNine MonthsThree MonthsNine Months
20252024202520242025202420252024
Ameren Missouri(a)
$(4)$(11)$(11)$(33)$(7)$(6)$(21)$(20)
Ameren Illinois(1)(8)(3)(25)(13)(13)(39)(39)
Other(1)(2)(2)(5)— — — — 
Ameren(a)
$(6)$(21)$(16)$(63)$(20)$(19)$(60)$(59)
(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.
v3.25.3
Income Taxes (Tables)
 9 Months Ended
Sep. 30, 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 and nine months ended September 30, 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)(9)(9)(15)(4)(4)
Revaluation of excess deferred income taxes(b)
(7)— — — (14)— 
Amortization of deferred investment tax credit(1)— (1)— — — 
Renewable and other tax credits(c)
(3)(4)(7)(10)— — 
State tax5 4 3 3 7 7 
Depreciation differences(1)— (1)(1)(1)— 
Other permanent items— (1)— — 1 — 
Effective income tax rate7 %11 %6 %(2)%10 %24 %
Nine Months
Federal statutory corporate income tax rate21 %21 %21 %21 %21 %21 %
Increases (decreases) from:
Amortization of excess deferred taxes(a)
(7)(8)

(9)(14)

(4)(4)
Revaluation of excess deferred income taxes(b)
(3)— — — (4)— 
Amortization of deferred investment tax credit(1)— (1)— — — 
Renewable and other tax credits(c)
(3)(5)(7)(10)— — 
State tax5 5 3 3 7 7 
Depreciation differences(1)— (1)(1)— — 
Effective income tax rate11 %13 %6 %(1)%20 %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. Deferred income taxes are revalued when federal or state income tax rates change, and the offset to the revaluation of deferred income taxes subject to regulatory ratemaking is recorded to a regulatory asset or liability.
(b)In 2024, the IRS issued a series of private letter rulings to another taxpayer, which provided guidance on applying IRS normalization rules to the calculation of tax benefits applicable to the ratemaking treatment related to net operating loss carryforwards. The rulings concluded that, for ratemaking purposes, net operating loss carryforwards should be reflected on a separate company basis and should not be reduced by payments received for the utilization of losses by other affiliates under a tax allocation agreement. In 2025, the FERC issued an order reflecting implementation of the rules for the other taxpayer who had a similar fact pattern as Ameren Illinois and ATXI. Accordingly, in the third quarter of 2025, Ameren and Ameren Illinois decreased income tax expense by $48 million and $23 million, respectively, to reflect the revaluation of excess deferred income tax regulatory liabilities resulting from TCJA for FERC-regulated jurisdictions pursuant to IRS guidance and recent FERC order.
(c)The benefit of the renewable credits associated with Missouri renewable energy standard compliance is refunded to customers through the RESRAM. The benefit of the renewable credits associated with the production and investment tax credit tracker will be refunded to customers based on MoPSC approval in a regulatory rate review.
v3.25.3
Supplemental Information (Tables)
 9 Months Ended
Sep. 30, 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 September 30, 2025, and December 31, 2024:
September 30, 2025December 31, 2024
AmerenAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois
“Cash and cash equivalents”$9 $— $— $7 $— $— 
Restricted cash included in “Other current assets” (a)
95 86 6 15 7 6 
Restricted cash included in “Other assets”324 — 324 296 — 296 
Restricted cash included in “Nuclear decommissioning trust fund”7 7 — 10 10 — 
Total cash, cash equivalents, and restricted cash$435 $93 $330 $328 $17 $302 
(a)Included in “Restricted cash” on Ameren Missouri’s balance sheet.
Schedule of Accounts, Notes, Loans and Financing Receivable
The following table provides a reconciliation of the beginning and ending amount of the allowance for doubtful accounts for the three and nine months ended September 30, 2025 and 2024:
Three MonthsNine Months
2025202420252024
Ameren:
Beginning of period$39 $37 $30 $30 
Bad debt expense18 12 37 28 
Charged to other accounts(a)
2 2 5 6 
Net write-offs(21)(20)(34)(33)
End of period$38 $31 $38 $31 
Ameren Missouri:
Beginning of period$12 $12 $12 $12 
Bad debt expense7 3 11 8 
Net write-offs(4)(3)(8)(8)
End of period$15 $12 $15 $12 
Ameren Illinois:(b)
Beginning of period$27 $25 $18 $18 
Bad debt expense11 

9 26 20 
Charged to other accounts(a)
2 2 5 6 
Net write-offs(17)(17)(26)(25)
End of period$23 $19 $23 $19 
(a)Amounts associated with the allowance for doubtful accounts related to receivables purchased by Ameren Illinois from alternative retail electric suppliers, as required by the Illinois Public Utilities Act.
(b)Ameren Illinois has 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 nine months ended September 30, 2025 and 2024:
September 30, 2025September 30, 2024
AmerenAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois
Investing:
Accrued capital expenditures, including nuclear fuel expenditures$412 $277 $147 $404 $257 $127 
Net realized and unrealized gain – nuclear decommissioning trust fund136 136 — 163 163 — 
Financing:
Issuance of common stock for stock-based compensation$25 $— $— $16 $— $— 
Issuance of common stock under the DRPlus7 — — 7 — — 
Asset Retirement Obligation Disclosure
The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the nine months ended September 30, 2025:
Ameren
Missouri		Ameren
Illinois		Ameren
Balance at December 31, 2024
$823 
(a) 
$4 
(b) 
$827 
(a) 
Liabilities settled(7)— (7)
Accretion27 
(c) 
— 

27 
(c) 
Change in estimates1 1 2 
Balance at September 30, 2025
$844 
(a) 
$5 
(b) 
$849 
(a) 
(a)Balance included $5 million in “Other current liabilities” on the balance sheet as of both September 30, 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 and nine months ended September 30, 2025 and 2024:
Three MonthsNine Months
2025202420252024
Ameren Missouri$69 $60 $150 $136 
Ameren Illinois30 29 104 94 
Ameren$99 $89 $254 $230 
Schedule of Earnings Per Share, Basic and Diluted
The following table reconciles the basic weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the three and nine months ended September 30, 2025 and 2024:
Three MonthsNine Months
2025202420252024
Weighted-average Common Shares Outstanding – Basic270.4 266.8 270.2 266.6 
Assumed settlement of performance share units and restricted stock units0.8 0.4 0.9 0.3 
Dilutive effect of forward sale agreements1.0 0.1 0.6 — 
Weighted-average Common Shares Outstanding – Diluted(a)
272.2 267.3 271.7 266.9 
(a)There was an immaterial number of anti-dilutive performance share units excluded from the earnings per diluted share calculations for the three and nine months ended September 30, 2025 and 2024. Outstanding forward sale agreements as of September 30, 2025 and 2024 that were anti-dilutive for the nine months ended September 30, 2025 and the three and nine months ended September 30, 2024 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.
v3.25.3
Segment Information (Tables)
 9 Months Ended
Sep. 30, 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 and nine months ended September 30, 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$1,696 $698 $117 $188 $— $— $2,699 
Intersegment revenues9 1 — 52 — (62)— 
Revenue1,705 699 117 240 — (62)2,699 
Fuel and purchased power(a)
(487)(330)— — — 49 (768)
Natural gas purchased for resale(a)
(6)— (19)— — — (25)
Other operations and maintenance expenses(a)
(260)(171)(55)(19)(10)13 (502)
Other segment items
Depreciation and amortization(239)(92)(33)(49)(2)— (415)
Taxes other than income taxes(122)(22)(15)(3)(2)— (164)
Other income (expense), net45 20 4 (3)11 (1)76 
Interest charges(85)(28)(16)(31)(49)1 (208)
Income taxes (benefit)(32)(19)4 16 (21)— (52)
Noncontrolling interests – preferred stock dividends(1)— — — — — (1)
Net income (loss) attributable to Ameren common shareholders518 57 (13)151 
(b)
(73)— 640 
Interest income3 6 — 1 1 (1)10 
Capital expenditures548 163 78 174 1 24 988 
Three Months 2024:
External revenues$1,333 $551 $121 $168 $— $— $2,173 
Intersegment revenues9 1 — 42 — (52)— 
Revenue1,342 552 121 210 — (52)2,173 
Fuel and purchased power(a)
(334)(204)— — — 39 (499)
Natural gas purchased for resale(a)
(4)— (26)— — — (30)
Other operations and maintenance expenses(a)
(288)(163)(51)(19)(12)13 (520)
Other segment items
Depreciation and amortization(220)(92)(32)(42)(2)— (388)
Taxes other than income taxes(109)(21)(14)(2)(4)— (150)
Other income (expense), net51 23 6 8 16 (3)101 
Interest charges(62)(25)(16)(31)(42)3 (173)
Income taxes (benefit)6 (14)2 (34)(17)— (57)
Noncontrolling interests – preferred stock dividends(1)— — — — — (1)
Net income (loss) attributable to Ameren common shareholders381 56 (10)90 
(b)
(61)— 456 
Interest income2 6 1 — 2 (3)8 
Capital expenditures735 152 83 174 2 (9)1,137 
Ameren MissouriAmeren Illinois Electric DistributionAmeren Illinois Natural GasAmeren TransmissionOtherIntersegment EliminationsAmeren
Nine Months 2025:
External revenues$3,978 $1,838 $686 $515 $— $— $7,017 
Intersegment revenues24 6 — 143 — (173)— 
Revenue4,002 1,844 686 658 — (173)7,017 
Fuel and purchased power(a)
(1,431)(765)— — — 132 (2,064)
Natural gas purchased for resale(a)
(45)— (188)— — — (233)
Other operations and maintenance expenses(a)
(748)(493)(165)(56)(26)41 (1,447)
Other segment items
Depreciation and amortization(642)(276)(98)(146)(6)— (1,168)
Taxes other than income taxes(300)(63)(60)(7)(9)— (439)
Other income (expense), net135 66 14 14 31 (3)257 
Interest charges(215)(80)(47)(89)(142)3 (570)
Income (taxes) benefit(43)(48)(37)(48)31 — (145)
Noncontrolling interests – preferred stock dividends(3)(1)— — — — (4)
Net income (loss) attributable to Ameren common shareholders710 184 105 326 
(b)
(121)— 1,204 
Interest income7 22 — 2 3 (3)31 
Capital expenditures1,873 483 225 505 6 26 3,118 
Nine Months 2024:
External revenues$2,980 $1,566 $660 $476 $— $— $5,682 
Intersegment revenues25 1 — 110 — (136)— 
Revenue3,005 1,567 660 586 — (136)5,682 
Fuel and purchased power(a)
(689)(564)— — — 99 (1,154)
Natural gas purchased for resale(a)
(41)— (173)— — — (214)
Other operations and maintenance expenses(a)
(789)(452)(168)(54)(29)37 (1,455)
Other segment items
Depreciation and amortization(623)(278)(98)(121)(5)— (1,125)
Taxes other than income taxes(287)(57)(55)(6)(11)— (416)
Other income (expense), net144 72 20 14 54 (11)293 
Interest charges(187)(73)(46)(89)(108)11 (492)
Income (taxes) benefit4 (41)(38)(89)24 — (140)
Noncontrolling interests – preferred stock dividends(3)(1)— — — — (4)
Net income (loss) attributable to Ameren common shareholders534 173 102 241 
(b)
(75)— 975 
Interest income7 21 1 1 10 (11)29 
Capital expenditures1,839 468 202 515 6 (1)3,029 
(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$699 $117 $130 $— $946 
Intersegment revenues— — 46 (46)— 
Revenue699 117 176 (46)946 
Purchased power(a)
(330)— — 46 (284)
Natural gas purchased for resale(a)
— (19)— — (19)
Other operations and maintenance expenses(a)
(171)(55)(15)— (241)
Other segment items
Depreciation and amortization(92)(33)(37)— (162)
Taxes other than income taxes(22)(15)(1)— (38)
Other income, net20 4 6 — 30 
Interest charges(28)(16)(23)— (67)
Income taxes(19)4 (2)— (17)
Net income (loss) available to common shareholder57 (13)104 — 148 
Interest income6 — 1 — 7 
Capital expenditures163 78 144 — 385 
Three Months 2024:
External revenues$552 $121 $120 $— $793 
Intersegment revenues— — 35 (35)— 
Revenue552 121 155 (35)793 
Purchased power(a)
(204)— — 35 (169)
Natural gas purchased for resale(a)
— (26)— — (26)
Other operations and maintenance expenses(a)
(163)(51)(15)— (229)
Other segment items
Depreciation and amortization(92)(32)(31)— (155)
Taxes other than income taxes(21)(14)(2)— (37)
Other income, net23 6 8 — 37 
Interest charges(25)(16)(22)— (63)
Income taxes(14)2 (25)— (37)
Net income (loss) available to common shareholder56 (10)68 — 114 
Interest income6 1 — — 7 
Capital expenditures152 83 139 — 374 
Nine Months 2025:
External revenues$1,844 $686 $359 $— $2,889 
Intersegment revenues— — 123 (123)— 
Revenue1,844 686 482 (123)2,889 
Purchased power(a)
(765)— — 123 (642)
Natural gas purchased for resale(a)
— (188)— (188)
Other operations and maintenance expenses(a)
(493)(165)(44)(702)
Other segment items
Depreciation and amortization(276)(98)(110)(484)
Taxes other than income taxes(63)(60)(3)(126)
Other income, net66 14 21 101 
Interest charges(80)(47)(65)(192)
Income taxes(48)(37)(49)(134)
Noncontrolling interests – preferred stock dividends(1)— — (1)
Net income available to common shareholder184 105 232 — 521 
Interest income22 — 2 — 24 
Capital expenditures483 225 419 — 1,127 
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionIntersegment EliminationsAmeren Illinois
Nine Months 2024:
External revenues$1,567 $660 $332 $— $2,559 
Intersegment revenues— — 90 (90)— 
Revenue1,567 660 422 (90)2,559 
Purchased power(a)
(564)— — 90 (474)
Natural gas purchased for resale(a)
— (173)— (173)
Other operations and maintenance expenses(a)
(452)(168)(43)(663)
Other segment items
Depreciation and amortization(278)(98)(86)(462)
Taxes other than income taxes(57)(55)(4)(116)
Other income, net72 20 13 105 
Interest charges(73)(46)(59)(178)
Income taxes(41)(38)(65)(144)
Noncontrolling interests – preferred stock dividends(1)— — (1)
Net income available to common shareholder173 102 178 — 453 
Interest income21 1 — — 22 
Capital expenditures468 202 421 — 1,091 
(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 and nine months ended September 30, 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$702 $469 $— $— $— $1,171 
Commercial537 235 — — — 772 
Industrial119 46 — — — 165 
Other327 (51)
(a)
— 240 (61)455 
Total electric revenues$1,685 $699 $— $240 $(61)$2,563 
Residential$9 $— $70 $— $— $79 
Commercial5 — 21 — — 26 
Industrial— — 2 — — 2 
Other6 — 24 — (1)29 
Total natural gas revenues$20 $— $117 $— $(1)$136 
Total revenues(b)
$1,705 $699 $117 $240 $(62)$2,699 
Three Months 2024:
Residential$590 $339 $— $— $— $929 
Commercial465 184 — — — 649 
Industrial108 38 — — — 146 
Other161 (9)
(a)
— 210 (51)311 

Total electric revenues$1,324 $552 $— $210 $(51)$2,035 
Residential$9 $— $77 $— $— $86 
Commercial5 — 19 — — 24 
Industrial— — 2 — — 2 
Other4 — 23 — (1)26 
Total natural gas revenues$18 $— $121 $— $(1)$138 
Total revenues(b)
$1,342 $552 $121 $210 $(52)$2,173 
Nine Months 2025:
Residential$1,483 $1,132 $— $— $— $2,615 
Commercial1,154 596 — — — 1,750 
Industrial269 144 — — — 413 
Other987 (28)
(a)
— 658 (172)1,445 
Total electric revenues$3,893 $1,844 $— $658 $(172)$6,223 
Residential$65 $— $486 $— $— $551 
Commercial29 — 126 — — 155 
Industrial3 — 9 — — 12 
Other12 — 65 — (1)76 
Total natural gas revenues$109 $— $686 $— $(1)$794 
Total revenues(b)
$4,002 $1,844 $686 $658 $(173)$7,017 
Ameren MissouriAmeren Illinois Electric DistributionAmeren Illinois Natural GasAmeren TransmissionIntersegment EliminationsAmeren
Nine Months 2024:
Residential$1,326 $947 $— $— $— $2,273 
Commercial1,048 512 — — — 1,560 
Industrial246 130 — — — 376 
Other282 (22)
(a)
— 586 (135)711 
Total electric revenues$2,902 $1,567 $— $586 $(135)$4,920 
Residential$62 $— $466 $— $— $528 
Commercial26 — 111 — — 137 
Industrial3 — 7 — — 10 
Other12 — 76 — (1)87 
Total natural gas revenues$103 $— $660 $— $(1)$762 
Total revenues(b)
$3,005 $1,567 $660 $586 $(136)$5,682 
(a)Includes over-recoveries of various riders.
(b)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the three and nine months ended September 30, 2025 and 2024:
Ameren MissouriAmeren Illinois Electric DistributionAmeren Illinois Natural GasAmeren TransmissionIntersegment EliminationsAmeren
Three Months 2025:
Revenues from alternative revenue programs$— $(187)$(10)$(12)$— $(209)
Other revenues not from contracts with customers2 3 — — — 5 
Three Months 2024:
Revenues from alternative revenue programs$— $(144)$(9)$(2)$— $(155)
Other revenues not from contracts with customers2 2 — — — 4 
Nine Months 2025:
Revenues from alternative revenue programs$(4)$(174)$(6)$(21)$— $(205)
Other revenues not from contracts with customers5 11 2 — (4)14 
Nine Months 2024:
Revenues from alternative revenue programs$(7)$(83)$10 $11 $— $(69)
Other revenues not from contracts with customers4 5 2 — — 11 
Ameren Illinois
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionIntersegment EliminationsAmeren Illinois
Three Months 2025:
Residential$469 $70 $— $— $539 
Commercial235 21 — — 256 
Industrial46 2 — — 48 
Other(51)
(a)
24 176 (46)103 
Total revenues(b)
$699 $117 $176 $(46)$946 
Three Months 2024:
Residential$339 $77 $— $— $416 
Commercial184 19 — — 203 
Industrial38 2 — — 40 
Other(9)
(a)
23 155 (35)134 
Total revenues(b)
$552 $121 $155 $(35)$793 
Nine Months 2025:
Residential$1,132 $486 $— $— $1,618 
Commercial596 126 — — 722 
Industrial144 9 — — 153 
Other(28)
(a)
65 482 (123)396 
Total revenues(b)
$1,844 $686 $482 $(123)$2,889 
Nine Months 2024:
Residential$947 $466 $— $— $1,413 
Commercial512 111 — — 623 
Industrial130 7 — — 137 
Other(22)
(a)
76 422 (90)386 
Total revenues(b)
$1,567 $660 $422 $(90)$2,559 
(a)Includes over-recoveries of various riders.
(b)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the Ameren Illinois segments for the three and nine months ended September 30, 2025 and 2024:
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionAmeren Illinois
Three Months 2025:
Revenues from alternative revenue programs$(187)$(10)$(12)$(209)
Other revenues not from contracts with customers3 — — 3 
Three Months 2024:
Revenues from alternative revenue programs$(144)$(9)$(1)$(154)
Other revenues not from contracts with customers2 — — 2 
Nine Months 2025:
Revenues from alternative revenue programs$(174)$(6)$(20)$(200)
Other revenues not from contracts with customers11 2 — 13 
Nine Months 2024:
Revenues from alternative revenue programs$(83)$10 $9 $(64)
Other revenues not from contracts with customers5 2 — 7 
v3.25.3
Summary of Significant Accounting Policies (Narrative) (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Unconsolidated variable interest $ 60 $ 74
Cash Surrender Value of Life Insurance 220 260
Corporate owned life insurance, borrowings 117 110
Ameren Illinois Company    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Cash Surrender Value of Life Insurance 124 118
Corporate owned life insurance, borrowings 117 $ 110
Partnership Funding Commitment    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Outstanding funding commitments $ 31  
v3.25.3
Summary Of Significant Accounting Policies - Schedule of Other Assets and Other Liabilities (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Accounting Policies [Line Items]    
Unbilled revenue $ 413 $ 346
Other current assets 252 162
Regulatory Asset 2,611 2,397
Current maturities of long-term debt 29 317
Interest accrued 183 196
Current regulatory liabilities 142 120
Long-term debt, net 19,172 17,262
Ameren Missouri Securitization Funding I, LLC    
Accounting Policies [Line Items]    
Unbilled revenue 4 0
Other current assets 46 2
Regulatory Asset 449 465
Current maturities of long-term debt 29 17
Interest accrued 18 1
Current regulatory liabilities 15 0
Long-term debt, net $ 437 $ 448
v3.25.3
Rate And Regulatory Matters (Narrative-Missouri) (Details)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
USD ($)
MWh
Jun. 30, 2025
MWh
Mar. 31, 2025
Sep. 30, 2024
USD ($)
Jun. 30, 2024
MWh
Jun. 30, 2023
MWh
Mar. 31, 2023
MWh
Sep. 30, 2025
USD ($)
MWh
Sep. 30, 2024
USD ($)
Rate And Regulatory Matters [Line Items]                  
Depreciation and amortization $ 415     $ 388       $ 1,168 $ 1,125
Capital expenditures               $ 3,118 3,029
Union Electric Company                  
Rate And Regulatory Matters [Line Items]                  
PISA Deferral Percentage               85.00%  
Depreciation and amortization $ 239     $ 220       $ 642 623
Capital expenditures               1,873 $ 1,839
Union Electric Company | Maximum                  
Rate And Regulatory Matters [Line Items]                  
Public Utilities, Approved Rate Increase (Decrease), Percentage 2.25%   2.50%            
Union Electric Company | Natural Gas Generation Facility                  
Rate And Regulatory Matters [Line Items]                  
Capital expenditures               900  
Union Electric Company | Solar Generation Facilities                  
Rate And Regulatory Matters [Line Items]                  
Capital expenditures               $ 800  
Union Electric Company | Electric                  
Rate And Regulatory Matters [Line Items]                  
Senate Bill 4 large service tariff threshold MWs | MWh               100  
Frequency of Integrated Resource Plan Filings               4 years  
Large load customer rate plan megawatts requested | MWh               75  
Minimum service term for large load customer rate plan               12 years  
Optional ramp up period for large load customer rate plan               5 years  
Minimum demand charges as percentage of contracted capacity for large load customer rate plan               80.00%  
Union Electric Company | Electric | Final Rate Order                  
Rate And Regulatory Matters [Line Items]                  
Public Utilities, Approved Rate Increase (Decrease), Amount               $ 355  
Depreciation and amortization               $ 70  
Union Electric Company | Natural gas                  
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 | Final Rate Order                  
Rate And Regulatory Matters [Line Items]                  
Public Utilities, Approved Rate Increase (Decrease), Amount               $ 32  
Union Electric Company | Self-build | Solar generation facility                  
Rate And Regulatory Matters [Line Items]                  
Amount of Megawatts | MWh 250         50 50    
Union Electric Company | Self-build | Natural Gas Generation Facility                  
Rate And Regulatory Matters [Line Items]                  
Amount of Megawatts | MWh   800     800        
Union Electric Company | Self-build | Energy Storage Facility                  
Rate And Regulatory Matters [Line Items]                  
Amount of Megawatts | MWh   400              
Union Electric Company | Build-transfer | Solar generation facility                  
Rate And Regulatory Matters [Line Items]                  
Amount of Megawatts | MWh           300      
v3.25.3
Rate And Regulatory Matters (Narrative-Illinois) (Details) - Ameren Illinois Company - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended 9 Months Ended
Dec. 31, 2025
Jun. 30, 2028
Jun. 30, 2027
Jun. 30, 2026
Jun. 30, 2025
Sep. 30, 2025
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            
Rate And Regulatory Matters [Line Items]            
Public Utilities, Requested Rate Increase (Decrease), Amount           $ 60
Public Utilities, Requested Equity Capital Structure, Percentage           50.00%
ICC Staff's recommended rate base           $ 47
Pending Rate Case | Electric Energy-Efficiency            
Rate And Regulatory Matters [Line Items]            
Public Utilities, Requested Rate Increase (Decrease), Amount           12
Pending Rate Case | Natural gas            
Rate And Regulatory Matters [Line Items]            
Public Utilities, Requested Rate Increase (Decrease), Amount           $ 135
Public Utilities, Requested Equity Capital Structure, Percentage           52.00%
Public Utilities, Requested Return on Equity, Percentage           10.70%
Rate Base           $ 3,300
ICC staff recommended rate increase           $ 104
ICC recommended ROE           9.93%
ICC Staff's recommended capital structure           50.00%
ICC Staff's recommended rate base           $ 3,200
Illinois Attorney General's office's recommended rate increase           $ 55
Illinois Attorney General's office's recommended ROE           9.45%
Illinois Attorney General's office's recommended capital structure           50.00%
Illinois Attorney General's office's recommended rate base           $ 3,000
Pending Rate Case | Natural gas | Subsequent Event            
Rate And Regulatory Matters [Line Items]            
Administrative law judge's recommended rate increase $ 91          
v3.25.3
Rate And Regulatory Matters (Narrative-Federal) (Details) - USD ($)
$ in Millions
 1 Months Ended 3 Months Ended 9 Months Ended
May 31, 2020
Dec. 31, 2024
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2024
Rate And Regulatory Matters [Line Items]          
Capital expenditures       $ 3,118 $ 3,029
Current regulatory liabilities   $ 120   142  
Forecast          
Rate And Regulatory Matters [Line Items]          
Capital expenditures     $ 1,300    
Ameren Illinois Company          
Rate And Regulatory Matters [Line Items]          
Capital expenditures       1,127 $ 1,091
Current regulatory liabilities   $ 79   101  
Midwest Independent Transmission System Operator, Inc | Final Rate Order          
Rate And Regulatory Matters [Line Items]          
Approved return on equity percentage 10.02% 9.98%      
Current regulatory liabilities       7  
Midwest Independent Transmission System Operator, Inc | Final Rate Order | Ameren Illinois Company          
Rate And Regulatory Matters [Line Items]          
Current regulatory liabilities       $ 4  
v3.25.3
Short-Term Debt And Liquidity (Narrative) (Details)
$ in Billions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
USD ($)
Sep. 30, 2024
Sep. 30, 2025
USD ($)
Sep. 30, 2024
Credit Agreements        
Short-term Debt [Line Items]        
Net Liquidity Available $ 1.6   $ 1.6  
Actual debt-to-capital ratio 0.61   0.61  
Utilities        
Short-term Debt [Line Items]        
Short-term Debt, Weighted Average Interest Rate, over Time 4.53% 5.29% 4.56% 5.37%
Union Electric Company | Missouri Credit Agreement        
Short-term Debt [Line Items]        
Actual debt-to-capital ratio 0.49   0.49  
Ameren Illinois Company | Illinois Credit Agreement        
Short-term Debt [Line Items]        
Actual debt-to-capital ratio 0.45   0.45  
v3.25.3
Short-Term Debt and Liquidity (Short-Term Debt outstanding) (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Short-term Debt [Line Items]    
Short-term debt $ 903 $ 1,143
Union Electric Company    
Short-term Debt [Line Items]    
Short-term debt 259 0
Ameren Illinois Company    
Short-term Debt [Line Items]    
Short-term debt 0 88
Commercial Paper    
Short-term Debt [Line Items]    
Short-term debt 903 1,143
Commercial Paper | Parent Company    
Short-term Debt [Line Items]    
Short-term debt 644 1,055
Commercial Paper | Union Electric Company    
Short-term Debt [Line Items]    
Short-term debt 259 0
Commercial Paper | Ameren Illinois Company    
Short-term Debt [Line Items]    
Short-term debt $ 0 $ 88
v3.25.3
Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($)
$ in Millions
 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Short-term Debt [Line Items]    
Average daily amount outstanding $ 1,012 $ 620
Weighted-average interest rate 4.59% 5.53%
Short-term Debt, Maximum Amount Outstanding During Period $ 1,603 $ 1,542
Peak interest rate 4.75% 5.68%
Parent Company    
Short-term Debt [Line Items]    
Average daily amount outstanding $ 637 $ 177
Weighted-average interest rate 4.60% 5.46%
Short-term Debt, Maximum Amount Outstanding During Period $ 1,139 $ 948
Peak interest rate 4.75% 5.60%
Union Electric Company    
Short-term Debt [Line Items]    
Average daily amount outstanding $ 245 $ 187
Weighted-average interest rate 4.58% 5.52%
Short-term Debt, Maximum Amount Outstanding During Period $ 650 $ 576
Peak interest rate 4.72% 5.68%
Ameren Illinois Company    
Short-term Debt [Line Items]    
Average daily amount outstanding $ 130 $ 256
Weighted-average interest rate 4.55% 5.57%
Short-term Debt, Maximum Amount Outstanding During Period $ 425 $ 694
Peak interest rate 4.70% 5.68%
v3.25.3
Long-Term debt and Equity Financings (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Millions
 3 Months Ended 6 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Jun. 30, 2025
Sep. 30, 2025
Sep. 30, 2024
Long-Term Debt And Equity Financings [Line Items]          
Shares issued under the DRPlus and 401(k) plan 100 100   300 400
Issuances of common stock       $ 35.0 $ 30.0
Stock Issued During Period, Shares, Other (in shares) 0 0 300 300 200
Stock Issued During Period, Value, Other $ 25.0        
Maximum Value Of Shares To Be Issued Under ATM Program $ 1,500.0     $ 1,500.0  
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Number of Shares Indexed 5,800     5,800  
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share       $ 91.89  
Forward Contract Indexed to Issuer's Equity, Indexed Shares 6,400     6,400  
Gain (Loss) on Extinguishment of Debt $ 0.0 $ 0.0   $ 8.0 $ 0.0
Total Common Stock Available For Sale Under ATM Program 3,000.0     3,000.0  
Increase To Total Common Stock Available For Sale Under ATM Program 1,250.0        
Dividend reinvestment and 401 (k) plans          
Long-Term Debt And Equity Financings [Line Items]          
Issuances of common stock 3.0     28.0  
Accrued Proceeds from Issuance of Common Stock       7.0  
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     $ 750.0  
Debt Instrument, Interest Rate, Stated Percentage 5.375%     5.375%  
Senior Secured Notes and First Mortgage Bonds | Secured Debt | Related Party          
Long-Term Debt And Equity Financings [Line Items]          
Gain (Loss) on Extinguishment of Debt       $ 8.0  
Interest Expense, Debt $ 1.0     2.0  
Senior Secured Notes and First Mortgage Bonds | Secured Debt | Ameren (parent) | Related Party          
Long-Term Debt And Equity Financings [Line Items]          
Repayments of Senior Secured Notes and First Mortgage Bonds       24.0  
First Mortgage Bonds, 5.25%, Due 2035 - $500 Issuance | Secured Debt | Union Electric Company          
Long-Term Debt And Equity Financings [Line Items]          
Debt Instrument, Face Amount $ 500.0     $ 500.0  
Debt Instrument, Interest Rate, Stated Percentage 5.25%     5.25%  
First Mortgage Bonds, 5.625%, Due 2055 - $350 March Issuance | Secured Debt | Ameren Illinois Company          
Long-Term Debt And Equity Financings [Line Items]          
Debt Instrument, Face Amount $ 350.0     $ 350.0  
Debt Instrument, Interest Rate, Stated Percentage 5.625%     5.625%  
First Mortgage Bonds, 5.625%, Due 2055 - $350 September Issuance | Secured Debt | Ameren Illinois Company          
Long-Term Debt And Equity Financings [Line Items]          
Debt Instrument, Face Amount $ 350.0     $ 350.0  
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     $ 300.0  
Debt Instrument, Interest Rate, Stated Percentage 3.25%     3.25%  
Gain (Loss) on Extinguishment of Debt       $ 300.0  
Forward Sale Agreements Outstanding          
Long-Term Debt And Equity Financings [Line Items]          
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Shares, at Fair Value 12,200     12,200  
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value $ 1,100.0     $ 1,100.0  
Period End Net Cash Settlement Price 158.0     158.0  
Period End Net Share Settlement Price $ 1.5     $ 1.5  
Forward Sale Agreement Equity Offering Shares 12,200     12,200  
Forward Sale Agreement Gross Sales Price $ 1,100.0     $ 1,100.0  
Minimum          
Long-Term Debt And Equity Financings [Line Items]          
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share       $ 81.00  
Maximum          
Long-Term Debt And Equity Financings [Line Items]          
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share       98.66  
Weighted Average          
Long-Term Debt And Equity Financings [Line Items]          
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share       $ 91.02  
v3.25.3
Other Income, Net (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Other Nonoperating Income (Expense) [Line Items]        
Allowance for equity funds used during construction $ 21 $ 23 $ 60 $ 48
Other interest income 10 8 31 29
Non-service cost components of net periodic benefit income 59 76 187 228
Miscellaneous income 6 0 13 6
Gain (Loss) on Extinguishment of Debt 0 0 8 0
Income (Loss) from Equity Method Investments (9) (2) (19) (1)
Donations (6) (1) (9) (5)
Miscellaneous expense (5) (3) (14) (12)
Total Other Income, Net 76 101 257 293
Union Electric Company        
Other Nonoperating Income (Expense) [Line Items]        
Allowance for equity funds used during construction 14 15 37 38
Other interest income 3 2 7 7
Non-service cost components of net periodic benefit income 29 35 96 104
Miscellaneous income 4 1 6 3
Donations (2) 0 (4) (2)
Miscellaneous expense (3) (2) (7) (6)
Total Other Income, Net 45 51 135 144
Defined Benefit Plan, Non-service Cost or Income Components - Tracker (9) (11) (41) (31)
Ameren Illinois Company        
Other Nonoperating Income (Expense) [Line Items]        
Allowance for equity funds used during construction 6 8 21 10
Other interest income 7 7 24 22
Non-service cost components of net periodic benefit income 21 25 61 78
Miscellaneous income 2 0 7 3
Donations (4) 0 (5) (2)
Miscellaneous expense (2) (3) (7) (6)
Total Other Income, Net $ 30 $ 37 $ 101 $ 105
v3.25.3
Derivative Financial Instruments (Narrative) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Dec. 31, 2024
Derivative [Line Items]          
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax $ 0 $ 0 $ (6) $ 0  
Interest Rate Swap          
Derivative [Line Items]          
Derivative, Notional Amount 660   660   $ 140
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax $ 1   $ 6    
v3.25.3
Derivative Financial Instruments (Open Gross Derivative Volumes By Commodity Type) (Detail)
gal in Millions, MWh in Millions, MMBTU in Millions
 9 Months Ended 12 Months Ended
Sep. 30, 2025
MWh
MMBTU
gal
Dec. 31, 2024
MMBTU
MWh
gal
Fuel oils    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Volume | gal 23 23
Natural gas    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU 261 258
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 23 23
Union Electric Company | Natural gas    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU 50 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 211 213
Ameren Illinois Company | Power    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh 4 4
v3.25.3
Derivative Financial Instruments (Derivative Instruments Carrying Value) (Detail) - Not Designated As Hedging Instrument - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Derivative [Line Items]    
Derivative Assets $ 32 $ 16
Derivative Liability 100 103
Natural gas | Other current assets    
Derivative [Line Items]    
Derivative Assets 4 4
Natural gas | Other assets    
Derivative [Line Items]    
Derivative Assets 6 6
Natural gas | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 21 27
Natural gas | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 13 19
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
Power | Other current assets    
Derivative [Line Items]    
Derivative Assets 22 6
Power | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 11 10
Power | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 52 43
Union Electric Company    
Derivative [Line Items]    
Derivative Assets 24 10
Derivative Liability 12 15
Union Electric Company | Natural gas | Other current assets    
Derivative [Line Items]    
Derivative Assets 1 2
Union Electric Company | Natural gas | Other assets    
Derivative [Line Items]    
Derivative Assets 1 2
Union Electric Company | Natural gas | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 3 5
Union Electric Company | Natural gas | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 5 6
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 | Power | Other current assets    
Derivative [Line Items]    
Derivative Assets 22 6
Union Electric Company | Power | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 1 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 8 6
Derivative Liability 88 88
Ameren Illinois Company | Natural gas | Other current assets    
Derivative [Line Items]    
Derivative Assets 3 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 18 22
Ameren Illinois Company | Natural gas | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 8 13
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 | Power | Other current assets    
Derivative [Line Items]    
Derivative Assets 0 0
Ameren Illinois Company | Power | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 10 10
Ameren Illinois Company | Power | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability $ 52 $ 43
v3.25.3
Fair Value Measurements (Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: $ 1,494 $ 1,333
Assets fair value 1,526 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: 1,001 911
Assets fair value 1,001 911
Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 493 422
Assets fair value 499 429
Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 0 0
Assets fair value 26 9
Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 32 16
Derivative Liability 100 103
Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 0 0
Derivative Liability 4 5
Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 6 7
Derivative Liability 30 39
Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 26 9
Derivative Liability 66 59
Union Electric Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 1,494 1,333
Assets fair value 1,518 1,343
Union Electric Company | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 1,001 911
Assets fair value 1,001 911
Union Electric Company | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 493 422
Assets fair value 495 426
Union Electric Company | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 0 0
Assets fair value 22 6
Union Electric Company | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 24 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 2 4
Derivative Liability 8 11
Union Electric Company | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 22 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 2 4
Derivative Liability 8 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 2 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 0 0
Derivative Liability 0 0
Union Electric Company | Power | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 22 6
Derivative Liability 1 0
Union Electric Company | Power | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 0 0
Derivative Liability 0 0
Union Electric Company | Power | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 0 0
Derivative Liability 0 0
Union Electric Company | Power | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 22 6
Derivative Liability 1 0
Union Electric Company | Equity securities: | U.S. large capitalization    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 1,001 911
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: 1,001 911
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: 235 191
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: 235 191
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: 174 145
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: 174 145
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: 84 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: 84 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 8 6
Ameren Illinois Company | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 0 0
Ameren Illinois Company | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 4 3
Ameren Illinois Company | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 4 3
Ameren Illinois Company | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 88 88
Ameren Illinois Company | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 1 1
Ameren Illinois Company | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 22 28
Ameren Illinois Company | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 65 59
Ameren Illinois Company | Natural gas | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 8 6
Derivative Liability 26 35
Ameren Illinois Company | Natural gas | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 0 0
Derivative Liability 1 1
Ameren Illinois Company | Natural gas | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 4 3
Derivative Liability 22 28
Ameren Illinois Company | Natural gas | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 4 3
Derivative Liability 3 6
Ameren Illinois Company | Power | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 62 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 $ 62 $ 53
v3.25.3
Fair Value Measurements (Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level Three In The Fair Value Hierarchy) (Details) - Power - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning balance $ (63) $ (47) $ (47) $ (64)
Included in regulatory assets/liabilities 24 (22) 10 (10)
Settlements, assets   1   6
Settlement, liabilities (2)   (4)  
Change in unrealized gains (losses) related to assets/liabilities held at period end 22 (20) 4 (8)
Ending balance (41) (68) (41) (68)
Union Electric Company        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning balance 13 14 6 4
Included in regulatory assets/liabilities 12 (1) 28 13
Settlement, liabilities (4) (3) (13) (7)
Change in unrealized gains (losses) related to assets/liabilities held at period end 11 (1) 21 10
Ending balance 21 10 21 10
Ameren Illinois Company        
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Beginning balance (76) (61) (53) (68)
Included in regulatory assets/liabilities 12 (21) (18) (23)
Settlements, assets 2 4 9 13
Change in unrealized gains (losses) related to assets/liabilities held at period end 11 (19) (17) (18)
Ending balance $ (62) $ (78) $ (62) $ (78)
v3.25.3
Fair Value Measurements (Schedule Of Valuation Process And Unobservable Inputs) (Details) - Power
$ in Millions
Sep. 30, 2025
USD ($)
$ / MWh
Dec. 31, 2024
USD ($)
$ / MWh
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative Assets | $ $ 22 $ 6
Derivative liabilities | $ $ (63) $ (53)
Commodity Forward Price | Discounted cash flow | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Measurement input 33 32
Commodity Forward Price | Discounted cash flow | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Measurement input 67 69
Commodity Forward Price | Discounted cash flow | Weighted Average    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Measurement input 43 45
Nodal Basis | Discounted cash flow | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Measurement input (10) (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)
v3.25.3
Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Financial Assets and Liabilities) (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Carrying Amount(a)    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-Term Debt, Carrying Amount $ 19,201 $ 17,579
Debt Issuance Costs, Net 139 129
Carrying Amount(a) | Union Electric Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-Term Debt, Carrying Amount 8,246 7,745
Debt Issuance Costs, Net 63 62
Carrying Amount(a) | Ameren Illinois Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-Term Debt, Carrying Amount 6,258 5,852
Debt Issuance Costs, Net 56 51
Fair Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 18,088 15,933
Fair Value | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 17,532 15,395
Fair Value | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 556 538
Fair Value | Union Electric Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 7,662 6,926
Fair Value | Union Electric Company | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 7,662 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 5,815 5,243
Fair Value | Ameren Illinois Company | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 5,815 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
v3.25.3
Related Party Transactions (Narrative) (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Related Party Transaction [Line Items]    
Other assets $ 1,130 $ 1,123
Union Electric Company    
Related Party Transaction [Line Items]    
Other assets 235 254
Ameren Illinois Company    
Related Party Transaction [Line Items]    
Other assets 756 697
Ameren Services Support Services Agreement | Union Electric Company | Related Party    
Related Party Transaction [Line Items]    
Other assets 18 29
Ameren Services Support Services Agreement | Ameren Illinois Company | Related Party    
Related Party Transaction [Line Items]    
Other assets $ 20 $ 32
v3.25.3
Related Party Transactions (Schedule of Affiliate Receivables and Payables) (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Related Party Transaction [Line Items]    
Accounts Payable, Related Parties, Current $ 762 $ 1,059
Accounts Receivable, Related Parties, Current 794 525
Union Electric Company | Related Party    
Related Party Transaction [Line Items]    
Accounts Payable, Related Parties, Current 80 50
Accounts Receivable, Related Parties, Current 24 40
Union Electric Company | Income taxes payable to parent | Related Party    
Related Party Transaction [Line Items]    
Accounts Payable, Related Parties, Current 3 0
Union Electric Company | Income taxes receivable from parent | Related Party    
Related Party Transaction [Line Items]    
Accounts Receivable, Related Parties, Current 2 28
Ameren Illinois Company | Related Party    
Related Party Transaction [Line Items]    
Accounts Payable, Related Parties, Current 106 74
Accounts Receivable, Related Parties, Current 21 15
Ameren Illinois Company | Income taxes payable to parent | Related Party    
Related Party Transaction [Line Items]    
Accounts Payable, Related Parties, Current 67 32
Ameren Illinois Company | Income taxes receivable from parent | Related Party    
Related Party Transaction [Line Items]    
Accounts Receivable, Related Parties, Current $ 0 $ 0
v3.25.3
Related Party Transactions (Effects of Related-party Transactions on the Statement of Income) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Related Party Transaction [Line Items]        
Operating Revenues $ 2,699 $ 2,173 $ 7,017 $ 5,682
Other operations and maintenance 502 520 1,447 1,455
Interest Charges 208 173 570 492
Union Electric Company        
Related Party Transaction [Line Items]        
Operating Revenues 1,705 1,342 4,002 3,005
Other operations and maintenance 260 288 748 789
Interest Charges 85 62 215 187
Union Electric Company | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party        
Related Party Transaction [Line Items]        
Operating Revenues 8 8 23 23
Other operations and maintenance 1 1 1 1
Union Electric Company | Ameren Missouri and Ameren Illinois Miscellaneous Support Services | Related Party        
Related Party Transaction [Line Items]        
Operating Revenues 1 1 1 2
Union Electric Company | Total Related Party Operating Revenues | Related Party        
Related Party Transaction [Line Items]        
Operating Revenues 9 9 24 25
Union Electric Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI | Related Party        
Related Party Transaction [Line Items]        
Purchased Power 2 3 7 7
Union Electric Company | Ameren Services Support Services Agreement | Related Party        
Related Party Transaction [Line Items]        
Other operations and maintenance 42 41 130 122
Union Electric Company | Total Related Party Other Operations and Maintenance | Related Party        
Related Party Transaction [Line Items]        
Other operations and maintenance 42 41 130 122
Union Electric Company | Money pool interest | Related Party        
Related Party Transaction [Line Items]        
Interest Charges 1 1 1 3
Union Electric Company | Long-Term Debt | Related Party        
Related Party Transaction [Line Items]        
Interest Charges 1 0 2 0
Ameren Illinois Company        
Related Party Transaction [Line Items]        
Operating Revenues 946 793 2,889 2,559
Purchased Power 284 169 642 474
Other operations and maintenance 241 229 702 663
Interest Charges 67 63 192 178
Ameren Illinois Company | Related Party        
Related Party Transaction [Line Items]        
Operating Revenues   1    
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party        
Related Party Transaction [Line Items]        
Operating Revenues 1 1 1 1
Other operations and maintenance   1 3 1
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Miscellaneous Support Services | Related Party        
Related Party Transaction [Line Items]        
Operating Revenues 1 1 5 1
Ameren Illinois Company | Total Related Party Operating Revenues | Related Party        
Related Party Transaction [Line Items]        
Operating Revenues 1   6 1
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI | Related Party        
Related Party Transaction [Line Items]        
Purchased Power 1 1 2 2
Ameren Illinois Company | Ameren Services Support Services Agreement | Related Party        
Related Party Transaction [Line Items]        
Other operations and maintenance 39 38 119 115
Ameren Illinois Company | Total Related Party Other Operations and Maintenance | Related Party        
Related Party Transaction [Line Items]        
Other operations and maintenance 39 38 122 115
Ameren Illinois Company | Money pool interest | Related Party        
Related Party Transaction [Line Items]        
Interest Charges 1 1 1 2
Ameren Illinois Company | Long-Term Debt | Related Party        
Related Party Transaction [Line Items]        
Interest Charges $ 1 $ 0 $ 1 $ 0
v3.25.3
Commitments And Contingencies (Environmental Matters) (Detail)
$ in Millions
Sep. 30, 2025
USD ($)
scrubber
site
Dec. 31, 2024
USD ($)
Loss Contingencies [Line Items]    
Asset Retirement Obligation $ 849 $ 827
Minimum    
Loss Contingencies [Line Items]    
Estimated capital costs to comply with existing and known federal and state air emissions regulations 90  
Maximum    
Loss Contingencies [Line Items]    
Estimated capital costs to comply with existing and known federal and state air emissions regulations $ 120  
Union Electric Company    
Loss Contingencies [Line Items]    
Number of Energy Center Scrubbers | scrubber 2  
Asset Retirement Obligation $ 844 823
Union Electric Company | Minimum    
Loss Contingencies [Line Items]    
Estimated capital costs to comply with existing and known federal and state air emissions regulations 90  
Union Electric Company | Maximum    
Loss Contingencies [Line Items]    
Estimated capital costs to comply with existing and known federal and state air emissions regulations 120  
Ameren Illinois Company    
Loss Contingencies [Line Items]    
Asset Retirement Obligation $ 5 $ 4
Number of remediation sites | site 3  
Manufactured Gas Plant    
Loss Contingencies [Line Items]    
Accrual for environmental loss contingencies $ 45  
Manufactured Gas Plant | Ameren Illinois Company    
Loss Contingencies [Line Items]    
Number of remediation sites | site 44  
Accrual for environmental loss contingencies $ 45  
Manufactured Gas Plant | Ameren Illinois Company | Minimum    
Loss Contingencies [Line Items]    
Estimate of possible loss 45  
Manufactured Gas Plant | Ameren Illinois Company | Maximum    
Loss Contingencies [Line Items]    
Estimate of possible loss 90  
New CCR Rules Estimate    
Loss Contingencies [Line Items]    
Asset Retirement Obligation 40  
New CCR Rules Estimate | Union Electric Company    
Loss Contingencies [Line Items]    
Asset Retirement Obligation $ 40  
v3.25.3
Callaway Energy Center (Insurance Disclosure) (Details)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
USD ($)
Sep. 30, 2025
USD ($)
yr
Nuclear Waste Matters [Line Items]    
Frequency of Decommissioning Cost Study   3 years
Number Of Years The Limit Of Liability And The Maximum Potential Annual Payments Are Adjusted   5 years
Number Of Weeks Of Coverage After The First Twelve Weeks Of An Outage | yr   1
Number Of Additional Weeks After Initial Indemnity Coverage For Power Outage | yr   1.365
Union Electric Company    
Nuclear Waste Matters [Line Items]    
Decommissioning Cost   $ 7.0
Future Decommissioning Cost $ 0.0  
Public Liability And Nuclear Worker Liability - American Nuclear Insurers | Union Electric Company    
Nuclear Waste Matters [Line Items]    
Insurance Aggregate Maximum Coverage 500.0 500.0
Insurance Maximum Coverage per Incident 0.0 0.0
Public Liability And Nuclear Worker Liability - Pool Participation | Union Electric Company    
Nuclear Waste Matters [Line Items]    
Insurance Aggregate Maximum Coverage 15,763.0 15,763.0
Insurance Maximum Coverage per Incident 166.0 166.0
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 | Union Electric Company    
Nuclear Waste Matters [Line Items]    
Insurance Aggregate Maximum Coverage 16,263.0 16,263.0
Insurance Maximum Coverage per Incident 166.0 166.0
Property Damage - Nuclear Electric Insurance Ltd | Union Electric Company    
Nuclear Waste Matters [Line Items]    
Insurance Aggregate Maximum Coverage 3,200.0 3,200.0
Insurance Maximum Coverage per Incident 22.0 22.0
Accidental Outage - Nuclear Electric Insurance Ltd | Union Electric Company    
Nuclear Waste Matters [Line Items]    
Insurance Aggregate Maximum Coverage 490.0 490.0
Insurance Maximum Coverage per Incident 9.0 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 | Union Electric Company    
Nuclear Waste Matters [Line Items]    
Insurance Aggregate Maximum Coverage 2,700.0 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 700.0 700.0
Non-Radiation Event | Union Electric Company    
Nuclear Waste Matters [Line Items]    
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 | Union Electric Company    
Nuclear Waste Matters [Line Items]    
Insurance Aggregate Maximum Coverage $ 490.0 $ 490.0
v3.25.3
Retirement Benefits (Components Of Net Periodic Benefit Cost) (Detail) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Total non-service cost components $ (59) $ (76) $ (187) $ (228)
Pension Plan        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service Cost 21 22 62 66
Interest cost 58 56 175 167
Defined Benefit Plan, Expected Return (Loss) on Plan Assets (76) (82) (227) (246)
Prior service cost (credit) 0 0 0 0
Actuarial (gain) (9) (17) (26) (50)
Total non-service cost components (27) (43) (78) (129)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total (6) (21) $ (16) (63)
Defined Benefit Plan, Amortization Period of Actuarial Gain (Loss)     10 years  
Defined Benefit Plan, Difference Between Actual and Expected Return (Loss) on Plan Assets Amortization Period     4 years  
Other Postretirement Benefit Plan, Defined Benefit        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Service Cost 3 3 $ 8 9
Interest cost 11 11 33 33
Defined Benefit Plan, Expected Return (Loss) on Plan Assets (24) (23) (71) (69)
Prior service cost (credit) (1) (1) (3) (3)
Actuarial (gain) (9) (9) (27) (29)
Total non-service cost components (23) (22) (68) (68)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total $ (20) $ (19) $ (60) $ (59)
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  
v3.25.3
Retirement Benefits (Summary of Benefit Plan Costs Incurred) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Pension Plan        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Net periodic benefit cost $ (6) $ (21) $ (16) $ (63)
Pension Plan | Union Electric Company        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Net periodic benefit cost (4) (11) (11) (33)
Pension Plan | Ameren Illinois Company        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Net periodic benefit cost (1) (8) (3) (25)
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) (2) (5)
Other Postretirement Benefit Plan, Defined Benefit        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Net periodic benefit cost (20) (19) (60) (59)
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) (6) (21) (20)
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) (39) (39)
Other Postretirement Benefit Plan, Defined Benefit | Other Affiliated Entities And Intercompany Eliminations        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Net periodic benefit cost $ 0 $ 0 $ 0 $ 0
v3.25.3
Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Income Taxes [Line Items]        
Federal statutory corporate income tax rate 21.00% 21.00% 21.00% 21.00%
Increases (decreases) from:        
Amortization of excess deferred taxes (7.00%) (9.00%) (7.00%) (8.00%)
Valuation allowance (7.00%) 0.00% (3.00%) 0.00%
Amortization of deferred investment tax credit (1.00%) 0.00% (1.00%) 0.00%
Renewable and other tax credits (3.00%) (4.00%) (3.00%) (5.00%)
State tax 5.00% 4.00% 5.00% 5.00%
Depreciation differences (1.00%) 0.00% (1.00%) 0.00%
Other permanent items 0.00% (1.00%)    
Effective income tax rate 7.00% 11.00% 11.00% 13.00%
Income Tax Expense (Benefit) $ 52 $ 57 $ 145 $ 140
TCJA - Private Letter Ruling        
Increases (decreases) from:        
Income Tax Expense (Benefit)     $ 48  
Union Electric Company        
Income Taxes [Line Items]        
Federal statutory corporate income tax rate 21.00% 21.00% 21.00% 21.00%
Increases (decreases) from:        
Amortization of excess deferred taxes (9.00%) (15.00%) (9.00%) (14.00%)
Valuation allowance 0.00% 0.00% 0.00% 0.00%
Amortization of deferred investment tax credit (1.00%) 0.00% (1.00%) 0.00%
Renewable and other tax credits (7.00%) (10.00%) (7.00%) (10.00%)
State tax 3.00% 3.00% 3.00% 3.00%
Depreciation differences (1.00%) (1.00%) (1.00%) (1.00%)
Other permanent items 0.00% 0.00%    
Effective income tax rate 6.00% (2.00%) 6.00% (1.00%)
Income Tax Expense (Benefit) $ 32 $ (6) $ 43 $ (4)
Ameren Illinois Company        
Income Taxes [Line Items]        
Federal statutory corporate income tax rate 21.00% 21.00% 21.00% 21.00%
Increases (decreases) from:        
Amortization of excess deferred taxes (4.00%) (4.00%) (4.00%) (4.00%)
Valuation allowance (14.00%) 0.00% (4.00%) 0.00%
Amortization of deferred investment tax credit 0.00% 0.00% 0.00% 0.00%
Renewable and other tax credits 0.00% 0.00% 0.00% 0.00%
State tax 7.00% 7.00% 7.00% 7.00%
Depreciation differences (1.00%) 0.00% 0.00% 0.00%
Other permanent items 1.00% 0.00%    
Effective income tax rate 10.00% 24.00% 20.00% 24.00%
Income Tax Expense (Benefit) $ 17 $ 37 $ 134 $ 144
Ameren Illinois Company | TCJA - Private Letter Ruling        
Increases (decreases) from:        
Income Tax Expense (Benefit)     $ 23  
v3.25.3
Supplemental Information (Cash and Cash Equivalents) (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Sep. 30, 2024
Dec. 31, 2023
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]        
Cash and cash equivalents $ 9 $ 7    
Restricted cash included in “Other current assets” (a) 95 15    
Restricted cash included in “Other assets” 324 296    
Restricted cash included in “Nuclear decommissioning trust fund” 7 10    
Total cash, cash equivalents, and restricted cash 435 328 $ 324 $ 272
Union Electric Company        
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]        
Cash and cash equivalents 0 0    
Restricted cash included in “Other current assets” (a) 86 7    
Restricted cash included in “Other assets” 0 0    
Restricted cash included in “Nuclear decommissioning trust fund” 7 10    
Total cash, cash equivalents, and restricted cash 93 17 10 10
Ameren Illinois Company        
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]        
Cash and cash equivalents 0 0    
Restricted cash included in “Other current assets” (a) 6 6    
Restricted cash included in “Other assets” 324 296    
Restricted cash included in “Nuclear decommissioning trust fund” 0 0    
Total cash, cash equivalents, and restricted cash $ 330 $ 302 $ 293 $ 234
v3.25.3
Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Dec. 31, 2024
Allowance for Doubtful Accounts Receivable [Roll Forward]          
Beginning of period $ 39 $ 37 $ 30 $ 30  
Bad debt expense 18 12 37 28  
Charged to other accounts 2 2 5 6  
Net write-offs (21) (20) (34) (33)  
End of period 38 31 38 31  
Payables for purchased receivables 55   55   $ 43
Union Electric Company          
Allowance for Doubtful Accounts Receivable [Roll Forward]          
Beginning of period 12 12 12 12  
Bad debt expense 7 3 11 8  
Net write-offs (4) (3) (8) (8)  
End of period 15 12 15 12  
Ameren Illinois Company          
Allowance for Doubtful Accounts Receivable [Roll Forward]          
Beginning of period 27 25 18 18  
Bad debt expense 11 9 26 20  
Charged to other accounts 2 2 5 6  
Net write-offs (17) (17) (26) (25)  
End of period 23 $ 19 23 $ 19  
Payables for purchased receivables $ 55   $ 55   $ 43
v3.25.3
Supplemental Information (Supplemental Cash Flow Information) (Details) - USD ($)
$ in Millions
 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Supplemental Cash Flow Information [Line Items]    
Accrued capital expenditures, including nuclear fuel expenditures $ 412 $ 404
Net realized and unrealized gain – nuclear decommissioning trust fund 136 163
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 7 7
Union Electric Company    
Supplemental Cash Flow Information [Line Items]    
Accrued capital expenditures, including nuclear fuel expenditures 277 257
Net realized and unrealized gain – nuclear decommissioning trust fund 136 163
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 147 127
Net realized and unrealized gain – 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
v3.25.3
Supplemental Information (Schedule of Asset Retirement Obligations) (Details) - USD ($)
$ in Millions
 9 Months Ended
Sep. 30, 2025
Dec. 31, 2024
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Asset Retirement Obligation, Beginning Balance $ 827  
Liabilities settled (7)  
Accretion 27  
Change in estimates 2  
Asset Retirement Obligation, Ending Balance 849  
Other current liabilities 323 $ 295
Union Electric Company    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Asset Retirement Obligation, Beginning Balance 823  
Liabilities settled (7)  
Accretion 27  
Change in estimates 1  
Asset Retirement Obligation, Ending Balance 844  
Other current liabilities 204 206
Ameren Illinois Company    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Asset Retirement Obligation, Beginning Balance 4  
Liabilities settled 0  
Accretion 0  
Change in estimates 1  
Asset Retirement Obligation, Ending Balance 5  
Other current liabilities 128 129
Asset Retirement Obligation Balance    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Other current liabilities $ 5 $ 5
v3.25.3
Supplemental Information (Narrative) (Details) - USD ($)
$ in Millions
 9 Months Ended
Sep. 30, 2025
Sep. 30, 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 $ 80   $ 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    
v3.25.3
Supplemental Information (Schedule Of Excise Taxes) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Accounting Policies [Line Items]        
Excise tax expense $ 99 $ 89 $ 254 $ 230
Union Electric Company        
Accounting Policies [Line Items]        
Excise tax expense 69 60 150 136
Ameren Illinois Company        
Accounting Policies [Line Items]        
Excise tax expense $ 30 $ 29 $ 104 $ 94
v3.25.3
Supplemental Information (Earnings Per Share) (Details) - shares
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Earnings Per Share Reconciliation [Abstract]        
Weighted-average Common Shares Outstanding – Basic 270,400,000 266,800,000 270,200,000 266,600,000
Assumed settlement of performance share units and restricted stock units 800,000 400,000 900,000 300,000
Dilutive effect of forward sale agreements 1,000,000.0 100,000 600,000 0
Weighted-average Common Shares Outstanding – Diluted 272,200,000 267,300,000 271,700,000 266,900,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares) 0 0 0 0
v3.25.3
Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Segment Reporting Information [Line Items]        
External revenues $ 2,699 $ 2,173 $ 7,017 $ 5,682
Revenues 2,699 2,173 7,017 5,682
Fuel and purchased power (768) (499) (2,064) (1,154)
Natural gas purchased for resale (25) (30) (233) (214)
Other operations and maintenance expenses (502) (520) (1,447) (1,455)
Depreciation and amortization (415) (388) (1,168) (1,125)
Taxes other than income taxes (164) (150) (439) (416)
Other Income, Net 76 101 257 293
Interest charges (208) (173) (570) (492)
Income taxes (52) (57) (145) (140)
Noncontrolling interests - preferred stock dividends (1) (1) (4) (4)
Net income attributable to Ameren common shareholders 640 456 1,204 975
Interest income 10 8 31 29
Capital expenditures 988 1,137 3,118 3,029
Union Electric Company        
Segment Reporting Information [Line Items]        
External revenues 1,705 1,342 4,002 3,005
Fuel and purchased power (487) (334) (1,431) (689)
Natural gas purchased for resale (6) (4) (45) (41)
Other operations and maintenance expenses (260) (288) (748) (789)
Taxes other than income taxes (122) (109) (300) (287)
Other Income, Net 45 51 135 144
Interest charges (85) (62) (215) (187)
Income taxes (32) 6 (43) 4
Noncontrolling interests - preferred stock dividends (1) (1) (3) (3)
Net income attributable to Ameren common shareholders 518 381 710 534
Ameren Illinois Company        
Segment Reporting Information [Line Items]        
External revenues 946 793 2,889 2,559
Revenues 946 793 2,889 2,559
Purchased Power (284) (169) (642) (474)
Natural gas purchased for resale (19) (26) (188) (173)
Other operations and maintenance expenses (241) (229) (702) (663)
Depreciation and amortization (162) (155) (484) (462)
Taxes other than income taxes (38) (37) (126) (116)
Other Income, Net 30 37 101 105
Interest charges (67) (63) (192) (178)
Income taxes (17) (37) (134) (144)
Noncontrolling interests - preferred stock dividends 0 0 (1) (1)
Net Income Available to Common Shareholder 148 114 521 453
Net income attributable to Ameren common shareholders 148 114 521 453
Interest income 7 7 24 22
Capital expenditures 385 374 1,127 1,091
Operating Segments | Union Electric Company        
Segment Reporting Information [Line Items]        
External revenues 1,696 1,333 3,978 2,980
Revenues 1,705 1,342 4,002 3,005
Fuel and purchased power (487) (334) (1,431) (689)
Natural gas purchased for resale (6) (4) (45) (41)
Other operations and maintenance expenses (260) (288) (748) (789)
Depreciation and amortization (239) (220) (642) (623)
Taxes other than income taxes (122) (109) (300) (287)
Other Income, Net 45 51 135 144
Interest charges (85) (62) (215) (187)
Income taxes (32) 6 (43) 4
Noncontrolling interests - preferred stock dividends (1) (1) (3) (3)
Net Income Available to Common Shareholder 518 381 710 534
Interest income 3 2 7 7
Capital expenditures 548 735 1,873 1,839
Operating Segments | Ameren Illinois Electric Distribution        
Segment Reporting Information [Line Items]        
External revenues 698 551 1,838 1,566
Revenues 699 552 1,844 1,567
Fuel and purchased power (330) (204) (765) (564)
Natural gas purchased for resale 0 0 0 0
Other operations and maintenance expenses (171) (163) (493) (452)
Depreciation and amortization (92) (92) (276) (278)
Taxes other than income taxes (22) (21) (63) (57)
Other Income, Net 20 23 66 72
Interest charges (28) (25) (80) (73)
Income taxes (19) (14) (48) (41)
Noncontrolling interests - preferred stock dividends 0 0 (1) (1)
Net Income Available to Common Shareholder 57 56 184 173
Interest income 6 6 22 21
Capital expenditures 163 152 483 468
Operating Segments | Ameren Illinois Natural Gas        
Segment Reporting Information [Line Items]        
External revenues 117 121 686 660
Revenues 117 121 686 660
Fuel and purchased power 0 0 0 0
Natural gas purchased for resale (19) (26) (188) (173)
Other operations and maintenance expenses (55) (51) (165) (168)
Depreciation and amortization (33) (32) (98) (98)
Taxes other than income taxes (15) (14) (60) (55)
Other Income, Net 4 6 14 20
Interest charges (16) (16) (47) (46)
Income taxes 4 2 (37) (38)
Noncontrolling interests - preferred stock dividends 0 0 0 0
Net Income Available to Common Shareholder (13) (10) 105 102
Interest income 0 1 0 1
Capital expenditures 78 83 225 202
Operating Segments | Ameren Transmission        
Segment Reporting Information [Line Items]        
External revenues 188 168 515 476
Revenues 240 210 658 586
Fuel and purchased power 0 0 0 0
Natural gas purchased for resale 0 0 0 0
Other operations and maintenance expenses (19) (19) (56) (54)
Depreciation and amortization (49) (42) (146) (121)
Taxes other than income taxes (3) (2) (7) (6)
Other Income, Net (3) 8 14 14
Interest charges (31) (31) (89) (89)
Income taxes 16 (34) (48) (89)
Noncontrolling interests - preferred stock dividends 0 0 0 0
Net Income Available to Common Shareholder 151 90 326 241
Interest income 1 0 2 1
Capital expenditures 174 174 505 515
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution        
Segment Reporting Information [Line Items]        
External revenues 699 552 1,844 1,567
Revenues 699 552 1,844 1,567
Purchased Power (330) (204) (765) (564)
Natural gas purchased for resale 0 0 0 0
Other operations and maintenance expenses (171) (163) (493) (452)
Depreciation and amortization (92) (92) (276) (278)
Taxes other than income taxes (22) (21) (63) (57)
Other Income, Net 20 23 66 72
Interest charges (28) (25) (80) (73)
Income taxes (19) (14) (48) (41)
Noncontrolling interests - preferred stock dividends     (1) (1)
Net Income Available to Common Shareholder 57 56 184 173
Interest income 6 6 22 21
Capital expenditures 163 152 483 468
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas        
Segment Reporting Information [Line Items]        
External revenues 117 121 686 660
Revenues 117 121 686 660
Purchased Power 0 0 0 0
Natural gas purchased for resale (19) (26) (188) (173)
Other operations and maintenance expenses (55) (51) (165) (168)
Depreciation and amortization (33) (32) (98) (98)
Taxes other than income taxes (15) (14) (60) (55)
Other Income, Net 4 6 14 20
Interest charges (16) (16) (47) (46)
Income taxes 4 2 (37) (38)
Noncontrolling interests - preferred stock dividends     0 0
Net Income Available to Common Shareholder (13) (10) 105 102
Interest income 0 1 0 1
Capital expenditures 78 83 225 202
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission        
Segment Reporting Information [Line Items]        
External revenues 130 120 359 332
Revenues 176 155 482 422
Purchased Power 0 0 0 0
Natural gas purchased for resale 0 0 0 0
Other operations and maintenance expenses (15) (15) (44) (43)
Depreciation and amortization (37) (31) (110) (86)
Taxes other than income taxes (1) (2) (3) (4)
Other Income, Net 6 8 21 13
Interest charges (23) (22) (65) (59)
Income taxes (2) (25) (49) (65)
Noncontrolling interests - preferred stock dividends     0 0
Net Income Available to Common Shareholder 104 68 232 178
Interest income 1 0 2 0
Capital expenditures 144 139 419 421
Other        
Segment Reporting Information [Line Items]        
Other operations and maintenance expenses (10) (12) (26) (29)
Depreciation and amortization (2) (2) (6) (5)
Taxes other than income taxes (2) (4) (9) (11)
Other Income, Net 11 16 31 54
Interest charges (49) (42) (142) (108)
Income taxes (21) (17) 31 24
Noncontrolling interests - preferred stock dividends 0 0 0 0
Net Income Available to Common Shareholder (73) (61) (121) (75)
Interest income 1 2 3 10
Capital expenditures 1 2 6 6
Intersegment Eliminations        
Segment Reporting Information [Line Items]        
Intersegment revenues (62) (52) (173) (136)
Revenues (62) (52) (173) (136)
Fuel and purchased power 49 39 132 99
Natural gas purchased for resale 0 0 0 0
Other operations and maintenance expenses 13 13 41 37
Depreciation and amortization 0 0 0 0
Taxes other than income taxes 0 0 0 0
Other Income, Net (1) (3) (3) (11)
Interest charges 1 3 3 11
Income taxes 0 0 0 0
Noncontrolling interests - preferred stock dividends 0 0 0 0
Interest income (1) (3) (3) (11)
Capital expenditures 24 (9) 26 (1)
Intersegment Eliminations | Union Electric Company        
Segment Reporting Information [Line Items]        
Intersegment revenues (9) (9) (24) (25)
Intersegment Eliminations | Ameren Illinois Electric Distribution        
Segment Reporting Information [Line Items]        
Intersegment revenues (1) (1) (6) (1)
Intersegment Eliminations | Ameren Illinois Natural Gas        
Segment Reporting Information [Line Items]        
Intersegment revenues 0 0 0 0
Intersegment Eliminations | Ameren Transmission        
Segment Reporting Information [Line Items]        
Intersegment revenues (52) (42) (143) (110)
Intersegment Eliminations | Ameren Illinois Company        
Segment Reporting Information [Line Items]        
Intersegment revenues (46) (35) (123) (90)
Revenues (46) (35) (123) (90)
Purchased Power (46) (35) (123) (90)
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Electric Distribution        
Segment Reporting Information [Line Items]        
Intersegment revenues 0 0 0 0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Natural Gas        
Segment Reporting Information [Line Items]        
Intersegment revenues 0 0 0 0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Transmission        
Segment Reporting Information [Line Items]        
Intersegment revenues $ (46) $ (35) $ (123) $ (90)
v3.25.3
Segment Information (Disaggregation of Revenue) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Disaggregation of Revenue [Line Items]        
Operating Revenues $ 2,699 $ 2,173 $ 7,017 $ 5,682
Revenues 2,699 2,173 7,017 5,682
Revenues from alternative revenue programs (209) (155) (205) (69)
Other revenues not from contracts with customers 5 4 14 11
Union Electric Company        
Disaggregation of Revenue [Line Items]        
Revenues from alternative revenue programs 0 0 (4) (7)
Ameren Illinois Electric Distribution        
Disaggregation of Revenue [Line Items]        
Revenues from alternative revenue programs (187) (144) (174) (83)
Ameren Illinois Natural Gas        
Disaggregation of Revenue [Line Items]        
Revenues from alternative revenue programs (10) (9) (6) 10
Ameren Transmission        
Disaggregation of Revenue [Line Items]        
Revenues from alternative revenue programs (12) (2) (21) 11
Electric        
Disaggregation of Revenue [Line Items]        
Operating Revenues 2,563 2,035 6,223 4,920
Revenues 2,563 2,035 6,223 4,920
Electric | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 1,171 929 2,615 2,273
Electric | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 772 649 1,750 1,560
Electric | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 165 146 413 376
Electric | Other        
Disaggregation of Revenue [Line Items]        
Revenues 455 311 1,445 711
Natural gas        
Disaggregation of Revenue [Line Items]        
Operating Revenues 136 138 794 762
Revenues 136 138 794 762
Natural gas | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 79 86 551 528
Natural gas | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 26 24 155 137
Natural gas | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 2 2 12 10
Natural gas | Other        
Disaggregation of Revenue [Line Items]        
Revenues 29 26 76 87
Ameren Illinois Company        
Disaggregation of Revenue [Line Items]        
Operating Revenues 946 793 2,889 2,559
Revenues 946 793 2,889 2,559
Revenues from alternative revenue programs (209) (154) (200) (64)
Other revenues not from contracts with customers 3 2 13 7
Ameren Illinois Company | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 539 416 1,618 1,413
Ameren Illinois Company | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 256 203 722 623
Ameren Illinois Company | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 48 40 153 137
Ameren Illinois Company | Other        
Disaggregation of Revenue [Line Items]        
Revenues 103 134 396 386
Ameren Illinois Company | Ameren Illinois Electric Distribution        
Disaggregation of Revenue [Line Items]        
Revenues from alternative revenue programs (187) (144) (174) (83)
Other revenues not from contracts with customers 3 2 11 5
Ameren Illinois Company | Ameren Illinois Natural Gas        
Disaggregation of Revenue [Line Items]        
Revenues from alternative revenue programs (10) (9) (6) 10
Other revenues not from contracts with customers 0 0 2 2
Ameren Illinois Company | Ameren Illinois Transmission        
Disaggregation of Revenue [Line Items]        
Revenues from alternative revenue programs (12) (1) (20) 9
Other revenues not from contracts with customers 0 0 0 0
Ameren Illinois Company | Electric        
Disaggregation of Revenue [Line Items]        
Operating Revenues 829 672 2,203 1,899
Ameren Illinois Company | Natural gas        
Disaggregation of Revenue [Line Items]        
Operating Revenues 117 121 686 660
Operating Segments | Union Electric Company        
Disaggregation of Revenue [Line Items]        
Operating Revenues 1,696 1,333 3,978 2,980
Revenues 1,705 1,342 4,002 3,005
Other revenues not from contracts with customers 2 2 5 4
Operating Segments | Ameren Illinois Electric Distribution        
Disaggregation of Revenue [Line Items]        
Operating Revenues 698 551 1,838 1,566
Revenues 699 552 1,844 1,567
Other revenues not from contracts with customers 3 2 11 5
Operating Segments | Ameren Illinois Natural Gas        
Disaggregation of Revenue [Line Items]        
Operating Revenues 117 121 686 660
Revenues 117 121 686 660
Other revenues not from contracts with customers 0 0 2 2
Operating Segments | Ameren Transmission        
Disaggregation of Revenue [Line Items]        
Operating Revenues 188 168 515 476
Revenues 240 210 658 586
Other revenues not from contracts with customers 0 0 0 0
Operating Segments | Electric | Union Electric Company        
Disaggregation of Revenue [Line Items]        
Revenues 1,685 1,324 3,893 2,902
Operating Segments | Electric | Union Electric Company | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 702 590 1,483 1,326
Operating Segments | Electric | Union Electric Company | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 537 465 1,154 1,048
Operating Segments | Electric | Union Electric Company | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 119 108 269 246
Operating Segments | Electric | Union Electric Company | Other        
Disaggregation of Revenue [Line Items]        
Revenues 327 161 987 282
Operating Segments | Electric | Ameren Illinois Electric Distribution        
Disaggregation of Revenue [Line Items]        
Revenues 699 552 1,844 1,567
Operating Segments | Electric | Ameren Illinois Electric Distribution | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 469 339 1,132 947
Operating Segments | Electric | Ameren Illinois Electric Distribution | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 235 184 596 512
Operating Segments | Electric | Ameren Illinois Electric Distribution | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 46 38 144 130
Operating Segments | Electric | Ameren Illinois Electric Distribution | Other        
Disaggregation of Revenue [Line Items]        
Revenues (51) (9) (28) (22)
Operating Segments | Electric | Ameren Illinois Natural Gas        
Disaggregation of Revenue [Line Items]        
Revenues 0 0 0 0
Operating Segments | Electric | Ameren Illinois Natural Gas | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Operating Segments | Electric | Ameren Illinois Natural Gas | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Operating Segments | Electric | Ameren Illinois Natural Gas | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Operating Segments | Electric | Ameren Illinois Natural Gas | Other        
Disaggregation of Revenue [Line Items]        
Revenues 0 0 0 0
Operating Segments | Electric | Ameren Transmission        
Disaggregation of Revenue [Line Items]        
Revenues 240 210 658 586
Operating Segments | Electric | Ameren Transmission | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Operating Segments | Electric | Ameren Transmission | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Operating Segments | Electric | Ameren Transmission | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Operating Segments | Electric | Ameren Transmission | Other        
Disaggregation of Revenue [Line Items]        
Revenues 240 210 658 586
Operating Segments | Natural gas | Union Electric Company        
Disaggregation of Revenue [Line Items]        
Revenues 20 18 109 103
Operating Segments | Natural gas | Union Electric Company | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 9 9 65 62
Operating Segments | Natural gas | Union Electric Company | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 5 5 29 26
Operating Segments | Natural gas | Union Electric Company | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 3 3
Operating Segments | Natural gas | Union Electric Company | Other        
Disaggregation of Revenue [Line Items]        
Revenues 6 4 12 12
Operating Segments | Natural gas | Ameren Illinois Electric Distribution        
Disaggregation of Revenue [Line Items]        
Revenues 0 0 0 0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Other        
Disaggregation of Revenue [Line Items]        
Revenues 0 0 0 0
Operating Segments | Natural gas | Ameren Illinois Natural Gas        
Disaggregation of Revenue [Line Items]        
Revenues 117 121 686 660
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 70 77 486 466
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 21 19 126 111
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 2 2 9 7
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Other        
Disaggregation of Revenue [Line Items]        
Revenues 24 23 65 76
Operating Segments | Natural gas | Ameren Transmission        
Disaggregation of Revenue [Line Items]        
Revenues 0 0 0 0
Operating Segments | Natural gas | Ameren Transmission | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Operating Segments | Natural gas | Ameren Transmission | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Operating Segments | Natural gas | Ameren Transmission | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Operating Segments | Natural gas | Ameren Transmission | Other        
Disaggregation of Revenue [Line Items]        
Revenues 0 0 0 0
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution        
Disaggregation of Revenue [Line Items]        
Operating Revenues 699 552 1,844 1,567
Revenues 699 552 1,844 1,567
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas        
Disaggregation of Revenue [Line Items]        
Operating Revenues 117 121 686 660
Revenues 117 121 686 660
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission        
Disaggregation of Revenue [Line Items]        
Operating Revenues 130 120 359 332
Revenues 176 155 482 422
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution        
Disaggregation of Revenue [Line Items]        
Revenues 699 552 1,844 1,567
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 469 339 1,132 947
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 235 184 596 512
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 46 38 144 130
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Other        
Disaggregation of Revenue [Line Items]        
Revenues (51) (9) (28) (22)
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission        
Disaggregation of Revenue [Line Items]        
Revenues 176 155 482 422
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Other        
Disaggregation of Revenue [Line Items]        
Revenues 176 155 482 422
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas        
Disaggregation of Revenue [Line Items]        
Revenues 117 121 686 660
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 70 77 486 466
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 21 19 126 111
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 2 2 9 7
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Other        
Disaggregation of Revenue [Line Items]        
Revenues 24 23 65 76
Intersegment Eliminations        
Disaggregation of Revenue [Line Items]        
Revenues (62) (52) (173) (136)
Revenues (62) (52) (173) (136)
Other revenues not from contracts with customers 0 0 (4) 0
Intersegment Eliminations | Union Electric Company        
Disaggregation of Revenue [Line Items]        
Revenues (9) (9) (24) (25)
Intersegment Eliminations | Ameren Illinois Electric Distribution        
Disaggregation of Revenue [Line Items]        
Revenues (1) (1) (6) (1)
Intersegment Eliminations | Ameren Illinois Natural Gas        
Disaggregation of Revenue [Line Items]        
Revenues 0 0 0 0
Intersegment Eliminations | Ameren Transmission        
Disaggregation of Revenue [Line Items]        
Revenues (52) (42) (143) (110)
Intersegment Eliminations | Electric        
Disaggregation of Revenue [Line Items]        
Revenues (61) (51) (172) (135)
Intersegment Eliminations | Electric | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Intersegment Eliminations | Electric | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Intersegment Eliminations | Electric | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Intersegment Eliminations | Electric | Other        
Disaggregation of Revenue [Line Items]        
Revenues (61) (51) (172) (135)
Intersegment Eliminations | Natural gas        
Disaggregation of Revenue [Line Items]        
Revenues (1) (1) (1) (1)
Intersegment Eliminations | Natural gas | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Intersegment Eliminations | Natural gas | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Intersegment Eliminations | Natural gas | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Intersegment Eliminations | Natural gas | Other        
Disaggregation of Revenue [Line Items]        
Revenues (1) (1) (1) (1)
Intersegment Eliminations | Ameren Illinois Company        
Disaggregation of Revenue [Line Items]        
Revenues (46) (35) (123) (90)
Revenues (46) (35) (123) (90)
Intersegment Eliminations | Ameren Illinois Company | Residential        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Intersegment Eliminations | Ameren Illinois Company | Commercial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Intersegment Eliminations | Ameren Illinois Company | Industrial        
Disaggregation of Revenue [Line Items]        
Operating Revenues 0 0 0 0
Intersegment Eliminations | Ameren Illinois Company | Other        
Disaggregation of Revenue [Line Items]        
Revenues (46) (35) (123) (90)
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Electric Distribution        
Disaggregation of Revenue [Line Items]        
Revenues 0 0 0 0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Natural Gas        
Disaggregation of Revenue [Line Items]        
Revenues 0 0 0 0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Transmission        
Disaggregation of Revenue [Line Items]        
Revenues $ (46) $ (35) $ (123) $ (90)