AMEREN CORP, 10-Q filed on 5/8/2026
Quarterly Report
v3.26.1
Cover Page - shares
 3 Months Ended
Mar. 31, 2026
Apr. 30, 2026
Entity Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Mar. 31, 2026  
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   276,751,616
Entity Central Index Key 0001002910  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q1  
Amendment Flag false  
Union Electric Company    
Entity Information [Line Items]    
Entity File Number 1-2967  
Entity Registrant Name Union Electric Company  
Entity Tax Identification Number 43-0559760  
Entity Incorporation, State or Country Code MO  
Entity Address, Address Line One 1901 Chouteau Avenue  
Entity Address, City or Town St. Louis  
Entity Address, State or Province MO  
Entity Address, Postal Zip Code 63103  
City Area Code (314)  
Local Phone Number 621-3222  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business false  
Emerging growth company false  
Entity Shell Company false  
Shares outstanding   102,123,834
Entity Central Index Key 0000100826  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q1  
Amendment Flag false  
Ameren Illinois Company    
Entity Information [Line Items]    
Entity File Number 1-3672  
Entity Registrant Name Ameren Illinois Company  
Entity Tax Identification Number 37-0211380  
Entity Incorporation, State or Country Code IL  
Entity Address, Address Line One 10 Richard Mark Way  
Entity Address, City or Town Collinsville  
Entity Address, State or Province IL  
Entity Address, Postal Zip Code 62234  
City Area Code (618)  
Local Phone Number 343-8150  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business false  
Emerging growth company false  
Entity Shell Company false  
Shares outstanding   25,452,373
Entity Central Index Key 0000018654  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q1  
Amendment Flag false  
v3.26.1
Consolidated Statement of Income (Loss) and Comprehensive Income - USD ($)
shares in Millions, $ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Operating Revenues:    
Operating Revenues $ 2,176 $ 2,097
Operating Expenses:    
Fuel and purchased power 433 502
Natural gas purchased for resale 171 169
Other operations and maintenance 491 485
Depreciation and amortization 398 367
Taxes other than income taxes 151 144
Total operating expenses 1,644 1,667
Operating Income 532 430
Other Income, Net 90 85
Interest Charges 204 175
Income Before Income Taxes 418 340
Income Taxes 60 50
Net Income 358 290
Less: Net Income Attributable to Noncontrolling Interests 1 1
Preferred Stock Dividends 1 1
Net income attributable to Ameren common shareholders 357 289
Pension and other postretirement benefit plan activity, net of income taxes (benefit) 0 0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax (2) (4)
Comprehensive Income 356 286
Less: Comprehensive Income Attributable to Noncontrolling Interests 1 1
Comprehensive Income Attributable to Ameren Common Shareholders $ 355 $ 285
Earnings per Common Share - Basic $ 1.29 $ 1.07
Earnings per Common Share - Basic $ 1.28 $ 1.07
Weighted-average Common Shares Outstanding – Basic 276.5 270.0
Weighted-average Common Shares Outstanding – Diluted 278.4 271.4
Electric    
Operating Revenues:    
Operating Revenues $ 1,661 $ 1,622
Natural gas    
Operating Revenues:    
Operating Revenues 515 475
Union Electric Company    
Operating Revenues:    
Operating Revenues 930 957
Operating Expenses:    
Fuel and purchased power 214 330
Natural gas purchased for resale 34 30
Other operations and maintenance 264 250
Depreciation and amortization 214 194
Taxes other than income taxes 95 89
Total operating expenses 821 893
Operating Income 109 64
Other Income, Net 53 43
Interest Charges 82 60
Income Before Income Taxes 80 47
Income Taxes 3 4
Net Income 77 43
Preferred Stock Dividends 1 1
Net income attributable to Ameren common shareholders 76 42
Union Electric Company | Electric    
Operating Revenues:    
Operating Revenues 851 893
Union Electric Company | Natural gas    
Operating Revenues:    
Operating Revenues 79 64
Ameren Illinois Company    
Operating Revenues:    
Operating Revenues 1,199 1,100
Operating Expenses:    
Purchased Power 222 175
Natural gas purchased for resale 137 139
Other operations and maintenance 232 236
Depreciation and amortization 170 159
Taxes other than income taxes 52 51
Total operating expenses 813 760
Operating Income 386 340
Other Income, Net 29 34
Interest Charges 68 62
Income Before Income Taxes 347 312
Income Taxes 91 76
Net Income 256 236
Net income attributable to Ameren common shareholders 256 236
Ameren Illinois Company | Electric    
Operating Revenues:    
Operating Revenues 763 689
Ameren Illinois Company | Natural gas    
Operating Revenues:    
Operating Revenues $ 436 $ 411
v3.26.1
Consolidated Statement of Income (Loss) and Comprehensive Income (Parenthetical) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Income Statement [Abstract]    
Pension and other postretirement benefit plan activity, tax $ 0 $ 0
Unrealized net loss on derivative hedging instruments, tax $ (1) $ 0
v3.26.1
Consolidated Balance Sheet - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Current Assets:    
Cash and cash equivalents $ 13 $ 13
Accounts receivable - trade (less allowance for doubtful accounts) 703 665
Unbilled revenue 298 415
Miscellaneous accounts receivable 175 107
Inventories 733 774
Current regulatory assets 434 387
Other current assets 211 210
Total current assets 2,567 2,571
Property, Plant, and Equipment, Net 40,471 39,313
Investments and Other Assets:    
Nuclear decommissioning trust fund 1,478 1,526
Goodwill 411 411
Regulatory Asset 2,674 2,524
Pension and other postretirement benefits 991 977
Other assets 1,254 1,154
Total investments and other assets 6,808 6,592
TOTAL ASSETS 49,846 48,476
Current Liabilities:    
Current maturities of long-term debt 1,123 973
Short-term debt 1,178 643
Accounts and wages payable 733 1,254
Interest accrued 179 229
Customer deposits 239 238
Other current liabilities 674 570
Total current liabilities 4,126 3,907
Long-term debt, net 19,003 18,214
Deferred Credits and Other Liabilities:    
Accumulated deferred income taxes and tax credits, net 5,311 5,181
Regulatory liabilities 6,251 6,255
Asset retirement obligations 864 849
Other deferred credits and liabilities 606 540
Total deferred credits and other liabilities 13,032 12,825
Commitments and Contingencies
Shareholders’ Equity:    
Common Stock 3 3
Other paid-in capital, principally premium on common stock 8,114 8,106
Retained earnings 5,441 5,292
Accumulated other comprehensive loss (2) 0
Total shareholders’ equity 13,556 13,401
Noncontrolling Interests 129 129
Total equity 13,685 13,530
TOTAL LIABILITIES AND EQUITY 49,846 48,476
Variable Interest Entity, Primary Beneficiary    
Investments and Other Assets:    
Regulatory Asset 437 443
Current Liabilities:    
Current maturities of long-term debt 23 23
Long-term debt, net 426 426
Union Electric Company    
Current Assets:    
Cash and cash equivalents 0 6
Unbilled revenue 142 193
Miscellaneous accounts receivable 71 15
Inventories 509 492
Current regulatory assets 233 181
Other current assets 128 119
Total current assets 1,409 1,305
Property, Plant, and Equipment, Net 21,555 20,604
Investments and Other Assets:    
Nuclear decommissioning trust fund 1,478 1,526
Regulatory Asset 1,462 1,450
Pension and other postretirement benefits 273 271
Other assets 273 244
Total investments and other assets 3,486 3,491
TOTAL ASSETS 26,450 25,400
Current Liabilities:    
Current maturities of long-term debt 23 23
Short-term debt 280 471
Taxes accrued 82 34
Interest accrued 90 99
Retainage payable 118 28
Other current liabilities 154 150
Total current liabilities 1,199 1,562
Deferred Credits and Other Liabilities:    
Accumulated deferred income taxes and tax credits, net 2,800 2,702
Regulatory liabilities 3,250 3,324
Asset retirement obligations 859 844
Other deferred credits and liabilities 241 184
Total deferred credits and other liabilities 7,150 7,054
Commitments and Contingencies
Shareholders’ Equity:    
Common Stock 511 511
Other paid-in capital, principally premium on common stock 3,579 3,229
Preferred stock 80 80
Retained earnings 4,833 4,757
Total shareholders’ equity 9,003 8,577
TOTAL LIABILITIES AND EQUITY 26,450 25,400
Union Electric Company | Variable Interest Entity, Primary Beneficiary    
Investments and Other Assets:    
Regulatory Asset 437 443
Current Liabilities:    
Current maturities of long-term debt 23 23
Long-term debt, net 426 426
Union Electric Company | Nonrelated Party    
Current Assets:    
Accounts receivable - trade (less allowance for doubtful accounts) 263 284
Current Liabilities:    
Accounts and wages payable 395 696
Long-term debt, net 9,011 8,120
Union Electric Company | Related Party    
Current Assets:    
Accounts receivable - trade (less allowance for doubtful accounts) 63 15
Current Liabilities:    
Accounts and wages payable 57 61
Long-term debt, net 87 87
Ameren Illinois Company    
Current Assets:    
Cash and cash equivalents 0 3
Unbilled revenue 156 222
Miscellaneous accounts receivable 67 56
Inventories 220 278
Prepaid assets 60 68
Current regulatory assets 188 189
Other current assets 5 6
Total current assets 1,140 1,204
Property, Plant, and Equipment, Net 16,724 16,567
Investments and Other Assets:    
Goodwill 411 411
Regulatory Asset 1,194 1,059
Pension and other postretirement benefits 579 570
Other assets 859 789
Total investments and other assets 3,043 2,829
TOTAL ASSETS 20,907 20,600
Current Liabilities:    
Short-term debt 75 17
Interest accrued 59 69
Customer deposits 204 204
Mark-to-market derivative liabilities 59 45
Current regulatory liabilities 80 132
Other current liabilities 190 182
Total current liabilities 1,163 1,101
Deferred Credits and Other Liabilities:    
Accumulated deferred income taxes and tax credits, net 2,398 2,354
Regulatory liabilities 2,841 2,775
Other deferred credits and liabilities 276 268
Total deferred credits and other liabilities 5,515 5,397
Commitments and Contingencies
Shareholders’ Equity:    
Common Stock 0 0
Other paid-in capital, principally premium on common stock 3,058 3,058
Preferred stock 49 49
Retained earnings 4,862 4,736
Total shareholders’ equity 7,969 7,843
TOTAL LIABILITIES AND EQUITY 20,907 20,600
Ameren Illinois Company | Nonrelated Party    
Current Assets:    
Accounts receivable - trade (less allowance for doubtful accounts) 423 364
Current Liabilities:    
Accounts and wages payable 259 395
Long-term debt, net 6,255 6,254
Ameren Illinois Company | Related Party    
Current Assets:    
Accounts receivable - trade (less allowance for doubtful accounts) 21 18
Current Liabilities:    
Borrowings from money pool 130 0
Accounts and wages payable 107 57
Long-term debt, net $ 5 $ 5
v3.26.1
Consolidated Balance Sheet (Parenthetical) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Accounts Receivable, Allowance for Credit Loss, Current $ 41 $ 39
Other current assets 211 210
Regulatory Asset 2,674 2,524
Current maturities of long-term debt 1,123 973
Long-term debt, net $ 19,003 $ 18,214
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 276,700,000 276,400,000
Common Stock, Shares, Issued 276,700,000 276,400,000
Variable Interest Entity, Primary Beneficiary    
Regulatory Asset $ 437 $ 443
Current maturities of long-term debt 23 23
Long-term debt, net 426 426
Union Electric Company    
Accounts Receivable, Allowance for Credit Loss, Current 15 17
Other current assets 128 119
Regulatory Asset 1,462 1,450
Current maturities of long-term debt $ 23 $ 23
Common stock, par value (in dollars per share) $ 5 $ 5
Common stock, shares authorized (in shares) 150,000,000.0 150,000,000.0
Common Stock, Shares, Outstanding 102,100,000 102,100,000
Union Electric Company | Variable Interest Entity, Primary Beneficiary    
Regulatory Asset $ 437 $ 443
Current maturities of long-term debt 23 23
Long-term debt, net 426 426
Ameren Illinois Company    
Accounts Receivable, Allowance for Credit Loss, Current 26 22
Other current assets 5 6
Regulatory Asset $ 1,194 $ 1,059
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
v3.26.1
Consolidated Statement of Cash Flows - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Cash Flows From Operating Activities:    
Net income $ 358 $ 290
Adjustments to reconcile net income to net cash provided by operating activities:    
Depreciation and amortization 417 395
Amortization of nuclear fuel 21 20
Amortization of debt issuance costs and premium/discounts 5 5
Deferred income taxes and tax credits, net 56 116
Allowance for equity funds used during construction (31) (16)
Stock-based compensation costs 8 7
Other 9 7
Changes in assets and liabilities:    
Receivables 41 (68)
Inventories 41 93
Accounts and wages payable (308) (291)
Taxes accrued 75 (8)
Regulatory assets and liabilities (205) (70)
Assets, other (3) 0
Liabilities, other (30) (10)
Pension and other postretirement benefits (33) (39)
Net cash provided by operating activities 421 431
Cash Flows From Investing Activities:    
Capital expenditures (1,574) (1,064)
Nuclear fuel expenditures (22) (18)
Purchases of securities – nuclear decommissioning trust fund (87) (107)
Sales and maturities of securities – nuclear decommissioning trust fund 76 93
Other (7) 9
Net cash used in investing activities (1,614) (1,087)
Cash Flows From Financing Activities:    
Dividends on common stock (208) (191)
Dividends paid to noncontrolling interest holders (1) (1)
Short-term debt, net 534 108
Maturities of long-term debt (350) (300)
Issuances of long-term debt 1,297 1,099
Issuances of common stock 12 13
Employee payroll taxes related to stock-based compensation (14) (13)
Debt issuance costs (12) (11)
Net cash provided by financing activities 1,258 704
Net change in cash, cash equivalents, and restricted cash 65 48
Cash, cash equivalents, and restricted cash at beginning of year 420 328
Cash, cash equivalents, and restricted cash at end of period 485 376
Union Electric Company    
Cash Flows From Operating Activities:    
Net income 77 43
Adjustments to reconcile net income to net cash provided by operating activities:    
Depreciation and amortization 233 222
Amortization of nuclear fuel 21 20
Amortization of debt issuance costs and premium/discounts 3 2
Deferred income taxes and tax credits, net 43 104
Allowance for equity funds used during construction (23) (8)
Other 4 4
Changes in assets and liabilities:    
Receivables 38 0
Inventories (17) 42
Accounts and wages payable (234) (250)
Taxes accrued 36 (9)
Regulatory assets and liabilities (87) (81)
Assets, other 4 19
Liabilities, other (1) 3
Pension and other postretirement benefits (10) (14)
Net cash provided by operating activities 87 97
Cash Flows From Investing Activities:    
Capital expenditures (1,091) (658)
Nuclear fuel expenditures (22) (18)
Purchases of securities – nuclear decommissioning trust fund (87) (107)
Sales and maturities of securities – nuclear decommissioning trust fund 76 93
Money pool advances, net 0 43
Other (8) 0
Net cash used in investing activities (1,132) (647)
Cash Flows From Financing Activities:    
Dividends on common stock 0 (50)
Dividends on preferred stock (1) (1)
Short-term debt, net (191) 629
Issuances of long-term debt 898 0
Capital contributions from parent 350 0
Debt issuance costs (9) 0
Net cash provided by financing activities 1,047 578
Net change in cash, cash equivalents, and restricted cash 2 28
Cash, cash equivalents, and restricted cash at beginning of year 68 17
Cash, cash equivalents, and restricted cash at end of period 70 45
Ameren Illinois Company    
Cash Flows From Operating Activities:    
Net income 256 236
Adjustments to reconcile net income to net cash provided by operating activities:    
Depreciation and amortization 170 159
Amortization of debt issuance costs and premium/discounts 1 2
Deferred income taxes and tax credits, net 33 29
Allowance for equity funds used during construction (7) (7)
Other 6 3
Changes in assets and liabilities:    
Receivables (20) (78)
Inventories 58 51
Accounts and wages payable (36) (34)
Taxes accrued 53 0
Regulatory assets and liabilities (118) 8
Assets, other (5) (18)
Liabilities, other 9 8
Pension and other postretirement benefits (16) (17)
Net cash provided by operating activities 384 342
Cash Flows From Investing Activities:    
Capital expenditures (388) (363)
Net cash used in investing activities (388) (363)
Cash Flows From Financing Activities:    
Dividends on common stock (130) (75)
Short-term debt, net 58 101
Money pool borrowings, net 130 (37)
Maturities of long-term debt 0 (300)
Issuances of long-term debt 0 350
Debt issuance costs 0 (4)
Net cash provided by financing activities 58 35
Net change in cash, cash equivalents, and restricted cash 54 14
Cash, cash equivalents, and restricted cash at beginning of year 344 302
Cash, cash equivalents, and restricted cash at end of period $ 398 $ 316
v3.26.1
Consolidated Statement of Stockholders' Equity - USD ($)
$ in Millions
Total
Common Stock
Other Paid-in Capital:
Retained Earnings:
Derivative Financial Instruments
Deferred Retirement Benefit Costs
Accumulated Other Comprehensive Loss:
Total Shareholders’ Equity
Noncontrolling Interests:
Union Electric Company
Union Electric Company
Common Stock
Union Electric Company
Other Paid-in Capital:
Union Electric Company
Preferred Stock
Union Electric Company
Retained Earnings:
Ameren Illinois Company
Ameren Illinois Company
Common Stock
Ameren Illinois Company
Other Paid-in Capital:
Ameren Illinois Company
Preferred Stock
Ameren Illinois Company
Retained Earnings:
Beginning of year at Dec. 31, 2024     $ 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     15                                
Stock-based compensation activity     (4)                                
Capital contributions from parent                   $ 0   0              
Net income $ 290                 43         $ 236        
Net Income Available to Common Shareholder       289                     236        
Dividends on common stock       (191)                   (50)         (75)
Dividends on preferred stock                           (1)          
Change in derivative financial instruments         (4)                            
Change in deferred retirement benefit costs 0         0                          
Net income attributable to noncontrolling interest holders $ (1)               1                    
Dividends paid to noncontrolling interest holders                 (1)                    
Common stock shares outstanding at beginning of year at Dec. 31, 2024 269,900,000                                    
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Shares issued under the DRPlus and 401(k) plan 100,000                                    
Shares issued for stock-based compensation 300,000                                    
Common stock shares outstanding at end of period at Mar. 31, 2025 270,300,000                                    
End of period at Mar. 31, 2025 $ 12,348 $ 3 7,524 4,702 (1) (9) $ (10)   129   $ 511 3,201 $ 80 4,198   $ 0 $ 3,056 $ 49 4,427
Shareholders' equity, end of year at Mar. 31, 2025               $ 12,219   $ 7,990         $ 7,532        
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Dividends per common share $ 0.71                                    
Beginning of year at Dec. 31, 2024     7,513 4,604 3 (9)     129     3,201   4,206         4,266
Common stock shares outstanding at beginning of year at Dec. 31, 2024 269,900,000                                    
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Shares issued for stock-based compensation 200,000                                    
Common stock shares outstanding at end of period at Dec. 31, 2025 276,400,000                 102,100,000         25,500,000        
End of period at Dec. 31, 2025 $ 13,530   8,106 5,292 6 (6)     129     3,229   4,757         4,736
Shareholders' equity, end of year at Dec. 31, 2025 13,401                 $ 8,577         $ 7,843        
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Shares issued under the DRPlus and 401(k) plan     12                                
Stock-based compensation activity     (4)                                
Capital contributions from parent                   350   350              
Net income 358                 $ 77         256        
Net Income Available to Common Shareholder       357                     $ 256        
Dividends on common stock       (208)                   0         (130)
Dividends on preferred stock                           (1)          
Change in derivative financial instruments         (2)                            
Change in deferred retirement benefit costs 0         0                          
Net income attributable to noncontrolling interest holders $ (1)               1                    
Dividends paid to noncontrolling interest holders                 (1)                    
Shares issued under the DRPlus and 401(k) plan 100,000                                    
Shares issued for stock-based compensation 200,000                                    
Common stock shares outstanding at end of period at Mar. 31, 2026 276,700,000                 102,100,000         25,500,000        
End of period at Mar. 31, 2026 $ 13,685 $ 3 $ 8,114 $ 5,441 $ 4 $ (6) $ (2)   $ 129   $ 511 $ 3,579 $ 80 $ 4,833   $ 0 $ 3,058 $ 49 $ 4,862
Shareholders' equity, end of year at Mar. 31, 2026 $ 13,556             $ 13,556   $ 9,003         $ 7,969        
Increase (Decrease) in Stockholders' Equity [Roll Forward]                                      
Dividends per common share $ 0.75                                    
v3.26.1
Summary Of Significant Accounting Policies
 3 Months Ended
Mar. 31, 2026
Accounting Policies [Abstract]  
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
General
Ameren, headquartered in St. Louis, Missouri, is a public utility holding company whose primary assets are its equity interests in its subsidiaries. Ameren’s subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. Dividends on Ameren’s common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren’s principal subsidiaries are listed below. Ameren also has other subsidiaries that conduct other activities, such as providing shared services.
•Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri.
•Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois.
•ATXI operates a FERC rate-regulated electric transmission business in the MISO.
Ameren’s and Ameren Missouri’s financial statements are prepared on a consolidated basis and therefore include the accounts of their majority-owned subsidiaries. All intercompany transactions have been eliminated. Ameren Illinois has no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated.
Note 1 – Summary of Significant Accounting Policies applies to the Ameren Companies. The remaining notes to the consolidated financial statements apply to the registrants as indicated in each footnote disclosure. Registrants are named specifically for their related activities and disclosures.
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 entity, as well as the obligation to absorb losses or the right to receive benefits from the entity. 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 retired energy center, among other costs, and long-term debt. Ameren and Ameren Missouri consolidate AMF, which Ameren Missouri wholly owns, and both manages and controls the entity’s operating activities. For additional information on the securitization of the Rush Island Energy Center costs, see Note 2 – Rate and Regulatory Matters under Part II, Item 8, of the Form 10-K. For additional information on the securitized tariff bond issuance, see Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, of the Form 10‑K.
The following table presents the carrying values of AMF’s assets and liabilities included on Ameren’s and Ameren Missouri’s consolidated balance sheets as of March 31, 2026 and December 31, 2025:
20262025
Unbilled revenue(a)
$1 $2 
Other current assets(a)
31 21 
Noncurrent regulatory assets(a)
437 443 
Current maturities of long-term debt(b)
23 23 
Interest accrued(b)
11 6 
Current regulatory liabilities(c)
9 11 
Long-term debt, net(b)
426 426 
(a)Assets may be used only to meet AMF’s obligations and commitments.
(b)The securitized tariff bondholders have no recourse to Ameren Missouri.
(c)Included in “Other current liabilities” on Ameren’s and Ameren Missouri’s balance sheet.
Variable Interest Entities that are not Consolidated
As of March 31, 2026, and December 31, 2025, Ameren had unconsolidated variable interests in various equity method investments, primarily to advance innovative energy technologies, totaling $65 million and $64 million, respectively, included in “Other assets” on Ameren’s consolidated balance sheet. Any earnings or losses related to these investments are included in “Other Income, Net” on Ameren’s consolidated statement of income and comprehensive income. Ameren is not the primary beneficiary of these investments because it does not have the power to direct matters that most significantly affect the activities of these variable interest entities. As of March 31, 2026, Ameren’s maximum exposure to loss related to these variable interest entities is limited to the investment in these partnerships of $65 million plus associated outstanding funding commitments of $27 million.
COLI
Ameren (parent) and Ameren Illinois have COLI, which is recorded at the net cash surrender value. The net cash surrender value is the amount that can be realized under the insurance policies at the balance sheet date. As of March 31, 2026, the cash surrender value of COLI at Ameren and Ameren Illinois was $219 million (December 31, 2025 – $219 million) and $127 million (December 31, 2025 – $126 million), respectively, while total borrowings against the policies were $117 million (December 31, 2025 – $117 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
See Note 1 – Summary of Significant Accounting Policies under Part II, Item 8, of the Form 10-K for additional information about recently issued authoritative accounting standards related to internal-use software and government grants.
v3.26.1
Rate And Regulatory Matters
 3 Months Ended
Mar. 31, 2026
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
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 about each facility:
Agreement typeFacility sizeStatus of MoPSC CCN
In-service date(a)
Bowling Green Solar Project(b)
Self-build
50-MW
Approved March 2024March 2026
Split Rail Solar Project
Build-transfer(c)
300-MW
Approved March 2024Second quarter 2026
Castle Bluff Natural Gas Project(d)
Self-build
800-MW
Approved October 2024Fourth quarter 2027
Big Hollow Battery Energy Storage Project(e)
Self-build
400-MW
Approved February 2026Second quarter 2028
Big Hollow Natural Gas Project(e)
Self-build
800-MW
Approved February 2026Third quarter 2028
Reform Solar ProjectSelf-build
250-MW
Filed August 2025(f)
Fourth quarter 2028
(a)Future in-service dates are dependent on the timing of regulatory approvals and construction completion, among other things.
(b)This project represents approximately $0.1 billion of capital expenditures.
(c)Ameren Missouri received FERC approval for the acquisition in November 2024. In February 2026, Ameren Missouri acquired the Split Rail Solar Project, which includes solar panels, project design, land rights, and engineering, procurement, and construction agreements, for approximately $0.6 billion, and took over construction management of the project.
(d)This project represents approximately $0.9 billion of capital expenditures.
(e)These projects represent approximately $2 billion of capital expenditures.
(f)In March 2026, Ameren Missouri, the MoPSC staff, and certain intervenors filed a nonunanimous stipulation and agreement with the MoPSC, which recommends the MoPSC approve Ameren Missouri’s requested CCN. Ameren Missouri expects a decision by the MoPSC in the first half of 2026.
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 Order
In December 2025, the ICC issued an order approving Ameren Illinois’ 2024 electric distribution service revenue requirement reconciliation adjustment filing. This order approved an adjustment increasing the allowed revenue requirement by $48 million, which reflected Ameren Illinois’ actual 2024 recoverable costs, year-end rate base of $4.2 billion, and capital structure composed of 50% common equity. The approved reconciliation adjustment is being collected from customers in 2026. In February 2026, the ICC denied Ameren Illinois’ rehearing request to include an asset associated with other postretirement benefits in the rate base, among other things. In March 2026, Ameren Illinois filed an appeal of the December 2025 order with the Illinois Appellate Court for the Fifth Judicial District. The appellate court is under no deadline to address the appeal, and Ameren Illinois cannot predict the ultimate outcome of the appeal.
2025 Electric Distribution Service Revenue Requirement Reconciliation Adjustment Review
In April 2026, Ameren Illinois filed a reconciliation adjustment to its 2025 electric distribution service revenue requirement with the ICC, requesting recovery of $65 million. The adjustment reflects Ameren Illinois’ actual 2025 recoverable costs, 2025 year-end rate base, which includes assets associated with other postretirement benefits that are under appeal in Ameren Illinois’ MYRP and 2024 electric distribution service revenue requirement reconciliation adjustment proceedings, and a capital structure composed of 50% common equity. An ICC decision is required by December 2026, and any approved adjustment would be collected from customers in 2027.
2025 Natural Gas Delivery Service Rate Order
In November 2025, the ICC issued an order in Ameren Illinois’ January 2025 natural gas delivery service regulatory rate review, which resulted in an increase to Ameren Illinois’ annual revenues for natural gas delivery service of $79 million based on a 9.60% ROE, a capital structure composed of 50% common equity, a 2026 future test year, and a rate base of $3.2 billion. The order reflected a reduction of $75 million of planned distribution and transmission capital investments included in Ameren Illinois’ future test year request. The new rates became effective December 2025.
In January 2026, Ameren Illinois filed an appeal of the ICC’s November 2025 order to the Illinois Appellate Court for the Fifth Judicial District. The appeal challenged the inclusion of the non-service cost component of the net periodic benefit income related to other postretirement benefits in the annual revenue requirement and the $75 million reduction of planned capital investments, among other things. The court is under no deadline to address the appeal, and Ameren Illinois cannot predict the ultimate outcome of the appeal.
QIP Reconciliation Hearing
Pursuant to Illinois law, 2014 was the first year of the QIP. In 2021, Ameren Illinois filed a request with the ICC to initiate a reconciliation proceeding of natural gas capital investments recovered under the QIP rider during 2020. Ameren Illinois recovered similar investments in each of the 2014 to 2019 annual reconciliations. In September 2024, the Illinois Attorney General’s office challenged the recovery of capital investments that were made during 2020, alleging that the ICC should disallow $30 million in natural gas capital investments as imprudent, unsupported, or ineligible to be recovered through the QIP resulting in a potential over-recovery of an immaterial amount by Ameren Illinois in 2020. In 2023, and again in 2024, the ICC staff filed testimony that supports the prudence and reasonableness of the capital investments made during 2020. Ameren Illinois’ 2020 QIP rate recovery request under review by the ICC is within the rate increase limitations allowed by law. The ICC is under no deadline to issue an order in this proceeding. Ameren Illinois included $529 million of eligible natural gas capital investments in the QIP from 2021 to 2023. In addition, the 2021 through 2023 reconciliation proceedings are still ongoing. Ameren Illinois cannot predict the ultimate outcome of these regulatory proceedings.
Federal
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 and April 2025, the MISO transmission owners, including Ameren Missouri, Ameren Illinois, and ATXI, filed appeals of the October 2024 order and a March 2025 FERC order that rejected all rehearing requests to the United States Court of Appeals for the District of Columbia Circuit. The appellate court is under no deadline to address the appeals.
v3.26.1
Short-Term Debt And Liquidity
 3 Months Ended
Mar. 31, 2026
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 for the borrowers. As of March 31, 2026, 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 $2.0 billion, and does not include Ameren’s forward equity sale agreements discussed below in Note 4 – Long-term Debt and Equity Financings. The Ameren Companies were in compliance with the covenants in their Credit Agreements as of March 31, 2026. As of March 31, 2026, the ratios of consolidated indebtedness to consolidated total capitalization, calculated in accordance with the provisions of the Credit Agreements, were 61%, 50%, and 45% for Ameren, Ameren Missouri, and Ameren Illinois, respectively.
The following table presents commercial paper outstanding, net of issuance discounts, as of March 31, 2026, and December 31, 2025. There were no borrowings outstanding under the Credit Agreements as of March 31, 2026, or December 31, 2025.
March 31, 2026December 31, 2025
Ameren (parent)$823 $155 
Ameren Missouri280 471 
Ameren Illinois75 17 
Ameren consolidated$1,178 $643 
The following table summarizes the activity and relevant interest rates for Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper issuances under the Credit Agreements for the three months ended March 31, 2026 and 2025:
Ameren
(parent)		Ameren
Missouri		Ameren
Illinois		Ameren
Consolidated
2026
Average daily amount outstanding$464 $530 $36 $1,030 
Weighted-average interest rate3.86 %3.83 %3.82 %3.84 %
Peak amount outstanding during period(a)
$992 $1,360 $122 $1,996 
Peak interest rate4.00 %4.05 %4.00 %4.05 %
2025
Average daily amount outstanding$898 $313 $82 $1,293 
Weighted-average interest rate4.61 %4.59 %4.56 %4.60 %
Peak amount outstanding during period(a)
$1,139 $630 $189 $1,603 
Peak interest rate4.75 %4.70 %4.69 %4.75 %
(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.
Separate from the Credit Agreements, Ameren Missouri has an uncommitted bilateral letter of credit agreement for up to $75 million that expires in September 2026, renews annually, and is limited in use to support letters of credit. As of March 31, 2026, Ameren Missouri had $68 million of outstanding letters of credit under the agreement.
Money Pools
Ameren has money pool agreements with and among its subsidiaries to coordinate and provide for certain short-term cash and working capital requirements. The average interest rate for borrowings under the utility money pool for the three months ended March 31, 2026 was 3.84% (2025 – 4.52%). See Note 8 – Related-party Transactions for the amount of interest income and expense from the utility money pool agreements recorded by Ameren Missouri and Ameren Illinois for the three months ended March 31, 2026 and 2025.
v3.26.1
Long-Term Debt And Equity Financings
 3 Months Ended
Mar. 31, 2026
Long-Term Debt And Equity Financings [Abstract]  
LONG-TERM DEBT AND EQUITY FINANCINGS LONG-TERM DEBT AND EQUITY FINANCINGS
Ameren
For the three months ended March 31, 2026, Ameren issued a total of 0.1 million shares of common stock, under its DRPlus and 401(k) plan, and received proceeds of $5 million. As of March 31, 2026, 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 2026, Ameren issued 0.2 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. There were no shares issued under the ATM program during the three months ended March 31, 2026. As of March 31, 2026, Ameren had approximately $1 billion of common stock remaining available for sale under the ATM program.
Forward sale agreements outstanding as of March 31, 2026, under the ATM program for 3.9 million shares can be settled at Ameren’s discretion on or prior to dates ranging from January 20, 2028, to February 9, 2028. The initial forward sale price for the agreements ranged from $109.22 to $111.31, with an average initial forward sale price of $110.22. 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 March 31, 2026, Ameren could have settled the forward sale agreements with physical delivery of 10.3 million shares of common stock to the respective counterparties in exchange for cash of $1.0 billion. Alternatively, the forward sale agreements could have also been net settled at March 31, 2026, with delivery of approximately $116 million of cash or approximately 1.1 million shares of common stock to the counterparties. In connection with the forward sale agreements outstanding at March 31, 2026, the various counterparties, or their affiliates, borrowed from third parties and sold 10.3 million shares of common stock. The gross sales price of these shares totaled $1.0 billion. Ameren does not receive any proceeds from such sales of borrowed shares. The forward sale agreements have been classified as equity transactions.
In April 2026, Ameren entered into forward sale agreements under the ATM program relating to 1.4 million shares of common stock. The April 2026 forward sales can be settled at Ameren’s discretion on or prior to dates ranging from February 2, 2028, to February 9, 2028. The average forward sale price was initially $110.47 for the April 2026 forward sale agreements.
In March 2026, Ameren (parent) issued $400 million of 5.00% senior unsecured notes due May 2036, with interest payable semiannually on May 15 and November 15 of each year, beginning November 15, 2026. Net proceeds from this issuance were used to repay a portion of Ameren’s short-term debt, including short-term debt incurred to refinance $350 million of 3.65% senior unsecured notes that matured in February 2026.
Ameren Missouri
In February 2026, Ameren Missouri issued $450 million of 4.80% first mortgage bonds due March 2036 and $450 million of 5.55% first mortgage bonds due March 2056. Interest is payable semiannually for both issuances on March 15 and September 15 of each year, beginning September 15, 2026. Net proceeds from the February 2026 issuances were used for capital expenditures and to repay short-term debt.
Ameren Missouri received capital contributions totaling $350 million from Ameren (parent) during the three months ended March 31, 2026.
Indenture Provisions and Other Covenants
See Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, of the Form 10-K for a description of our indenture provisions and other covenants, as well as restrictions on the payment of dividends. At March 31, 2026, the Ameren Companies were in compliance with the provisions and covenants contained in their indentures and articles of incorporation, as applicable, and ATXI was in compliance with the provisions and covenants contained in its note purchase agreements.
Off-balance-sheet Arrangements
At March 31, 2026, 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 forward sale agreements relating to common stock. See Note 1 – Summary of Significant Accounting Policies for further detail concerning variable interest entities.
v3.26.1
Other Income, Net
 3 Months Ended
Mar. 31, 2026
Other Nonoperating Income (Expense) [Abstract]  
OTHER INCOME, NET OTHER INCOME, NET
The following table presents the components of “Other Income, Net” in the Ameren Companies’ statements of income for the three months ended March 31, 2026 and 2025:
Three Months
20262025
Ameren:
Allowance for equity funds used during construction
$31 $16 
Other interest income
9 11 
Non-service cost components of net periodic benefit income(a)
49 66 
Miscellaneous income
5 3 
Earnings (losses) related to equity method investments2 (4)
Donations
(2)(2)
Miscellaneous expense
(4)(5)
Total Other Income, Net$90 $85 
Ameren Missouri:
Allowance for equity funds used during construction
$23 $8 
Other interest income
3 2 
Non-service cost components of net periodic benefit income(a)
30 35 
Miscellaneous income
— 1 
Donations
(1)(1)
Miscellaneous expense
(2)(2)
Total Other Income, Net$53 $43 
Ameren Illinois:
Allowance for equity funds used during construction
$7 $7 
Other interest income6 9 
Non-service cost components of net periodic benefit income
15 20 
Miscellaneous income
4 2 
Donations
(1)(1)
Miscellaneous expense(2)(3)
Total Other Income, Net$29 $34 
(a)For the three months ended March 31, 2026 and 2025, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $(20) million and $(16) million, respectively, due to a regulatory tracking mechanism for the difference between the level of such costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates. See Note 11 – Retirement Benefits for additional information.
v3.26.1
Derivative Financial Instruments
 3 Months Ended
Mar. 31, 2026
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 that differ from the cost of this commodity in inventory;
•actual cash outlays for interest expense and the purchase of commodities that differ from anticipated cash outlays; and
•actual off-system sales revenues that differ from anticipated revenues.
The derivatives that we use to hedge these risks are governed by our risk management policies for forward contracts, futures, options, and swaps. Our net positions are continually assessed within our structured hedging programs to determine whether new or offsetting transactions are required. The goal of the hedging program is generally to mitigate financial risks while ensuring that sufficient volumes are available to meet our requirements. Contracts we enter into as part of our risk management program may be settled financially, settled by physical delivery, or net settled with the counterparty.
All contracts considered to be derivative instruments are required to be recorded on the balance sheet at their fair values, unless the NPNS exception applies. Many of our physical contracts, such as our purchased power contracts, qualify for the NPNS exception to derivative accounting rules. The revenue or expense on NPNS contracts is recognized at the contract price upon physical delivery. The following disclosures exclude NPNS contracts and other non-derivative commodity contracts that are accounted for under the accrual method of accounting.
If we determine that a contract meets the definition of a derivative and is not eligible for the NPNS exception, we review the contract to determine whether the resulting gains or losses qualify for regulatory deferral. Derivative contracts that qualify for regulatory deferral are recorded at fair value, with changes in fair value recorded as regulatory assets or liabilities in the period in which the change occurs. We believe derivative losses and gains deferred as regulatory assets and liabilities are probable of recovery, or refund, through future rates charged to customers. Regulatory assets and liabilities are amortized to operating income as related losses and gains are reflected in rates charged to customers. Therefore, gains and losses on these derivatives have no effect on operating income. As of March 31, 2026, and December 31, 2025, 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 March 31, 2026, and December 31, 2025, Ameren had unsettled interest rate swaps with notional amounts of $740 million and $820 million, respectively. Ameren recorded a loss, net of income tax benefits, on the change in fair value of interest rate swaps of $2 million and $4 million to "Accumulated other comprehensive loss" for the three months ended March 31, 2026 and 2025, respectively. The losses reclassified out of “Accumulated other comprehensive loss” to “Interest Charges” for the three months ended March 31, 2026 were immaterial.
The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of March 31, 2026, and December 31, 2025. As of March 31, 2026, these contracts extended through October 2029, October 2032 and May 2032 for fuel oils, natural gas, and power, respectively.
Quantity (in millions, except as indicated)
March 31, 2026December 31, 2025
CommodityAmeren MissouriAmeren IllinoisAmerenAmeren MissouriAmeren IllinoisAmeren
Fuel oils (in gallons)22 — 22 25 — 25 
Natural gas (in MMBtu)56 229 285 46 217 263 
Power (in MWhs)4 7 11 — 7 7 
The following table presents the carrying value and balance sheet location of all derivative commodity contracts, none of which were designated as hedging instruments because all qualify for regulatory deferral, as of March 31, 2026, and December 31, 2025:
March 31, 2026December 31, 2025
CommodityBalance Sheet LocationAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois		Ameren
Fuel oilsOther current assets$9 $— $9 $— $— $— 
Other assets3 — 3 — — — 
Natural gasOther current assets— — — 1 1 2 
Other assets— 1 1 — 3 3 
PowerOther current assets3 — 3 11 — 11 
Other assets3 — 3 — — — 
Total assets$18 $1 $19 $12 $4 $16 
Fuel oilsOther current liabilities$— $— $— $3 $— $3 
Other deferred credits and liabilities— — — 2 — 2 
Natural gasMark-to-market derivative liabilities(a)31 (a)(a)21 (a)
Other current liabilities9 — 40 5 — 26 
Other deferred credits and liabilities8 19 27 5 11 16 
PowerMark-to-market derivative liabilities(a)28 (a)(a)24 (a)
Other current liabilities— — 28 — — 24 
Other deferred credits and liabilities1 48 49 — 55 55 
Total liabilities$18 $126 $144 $15 $111 $126 
(a) Balance sheet line item not applicable to registrant.
The Ameren Companies elect to present the fair value amounts of derivative assets and derivative liabilities subject to an enforceable master netting arrangement or similar agreement at the gross amounts on the balance sheet. However, if the gross amounts recognized on the balance sheet were netted with derivative instruments and cash collateral received or posted, the net amounts would not be materially different from the gross amounts at March 31, 2026, and December 31, 2025.
Credit Risk
In determining our concentrations of credit risk related to derivative instruments, we review our individual counterparties and categorize each counterparty into groupings according to the primary business in which each engages. As of March 31, 2026, 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. The following table presents, as of March 31, 2026, 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:
Aggregate Fair Value of
Derivative Liabilities(a)
Cash
Collateral Posted
Potential Aggregate Amount of
Additional Collateral Required(b)
Ameren Missouri$17 $— $9 
Ameren Illinois50 — 50 
Ameren$67 $— $59 
(a)Before consideration of master netting arrangements or similar agreements.
(b)As collateral requirements with certain counterparties are based on master netting arrangements or similar agreements, the aggregate amount of additional collateral required to be posted is determined after consideration of the effects of such arrangements.
v3.26.1
Fair Value Measurements
 3 Months Ended
Mar. 31, 2026
Fair Value Disclosures [Abstract]  
Fair Value Disclosures FAIR VALUE MEASUREMENTS
Fair value is defined as the price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Fair value measurements are classified in three levels based on the fair value hierarchy as defined by GAAP. See Note 8 – Fair Value Measurements under Part II, Item 8, of the Form 10-K for information related to hierarchy levels and valuation techniques.
We consider nonperformance risk in our valuation of derivative instruments by analyzing our own credit standing and the credit standing of our counterparties, and by considering any credit enhancements (e.g., collateral). Included in our valuation, and based on current market conditions, is a valuation adjustment for counterparty default derived from market data such as the price of credit default swaps, bond yields, and credit ratings. No material gains or losses related to valuation adjustments for counterparty default risk were recorded at Ameren, Ameren Missouri, or Ameren Illinois in the three months ended March 31, 2026 or 2025. At March 31, 2026, and December 31, 2025, the counterparty default risk valuation adjustment related to derivative contracts was immaterial for Ameren, Ameren Missouri, and Ameren Illinois.
The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of March 31, 2026, and December 31, 2025:
March 31, 2026December 31, 2025
Level 1Level 2Level 3TotalLevel 1Level 2Level 3Total
Assets:
Ameren Missouri
Derivative assets – commodity contracts:
Fuel oils$12 $— $— $12 $— $— $— $— 
Natural gas— — — — — 1 — 1 
Power— 3 3 6 — — 11 11 
Total derivative assets – commodity contracts$12 $3 $3 $18 $— $1 $11 $12 
Nuclear decommissioning trust fund:
Equity securities:
U.S. large capitalization$981 $— $— $981 $1,028 $— $— $1,028 
Debt securities:
U.S. Treasury and agency securities— 218 — 218 — 225 — 225 
Corporate bonds— 184 — 184 — 177 — 177 
Other— 87 — 87 — 84 — 84 
Total nuclear decommissioning trust fund$981 $489 $— $1,470 
(a) 
$1,028 $486 $— $1,514 
(a) 
Total Ameren Missouri$993 $492 $3 $1,488 $1,028 $487 $11 $1,526 
Ameren Illinois
Derivative assets – commodity contracts:
Natural gas$— $— $1 $1 $— $2 $2 $4 
Total Ameren Illinois$— $— $1 $1 $— $2 $2 $4 
Ameren
Derivative assets – commodity contracts(b)
$12 $3 $4 $19 $— $3 $13 $16 
Nuclear decommissioning trust fund(c)
981 489 — 1,470 
(a) 
1,028 486 — 1,514 
(a) 
Total Ameren$993 $492 $4 $1,489 $1,028 $489 $13 $1,530 
Liabilities:
Ameren Missouri
Derivative liabilities – commodity contracts:
Fuel oils$— $— $— $— $5 $— $— $5 
Natural gas— 16 1 17 — 10 — 10 
Power— 1 — 1 — — — — 
Total Ameren Missouri$— $17 $1 $18 $5 $10 $— $15 
Ameren Illinois
Derivative liabilities – commodity contracts:
Natural gas$1 $43 $6 $50 $1 $28 $3 $32 
Power— 20 56 76 — 13 66 79 
Total Ameren Illinois$1 $63 $62 $126 $1 $41 $69 $111 
Ameren
Derivative liabilities – commodity contracts(b)
$1 $80 $63 $144 $6 $51 $69 $126 
(a)Balance excludes $8 million and $12 million of cash and cash equivalents, receivables, payables, and accrued income, net, for March 31, 2026, and December 31, 2025, 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 natural gas derivative contract assets and liabilities measured at fair value on a recurring basis were immaterial for all periods presented. The following table presents the fair value reconciliation of Level 3 power derivative contract assets and liabilities measured at fair value on a recurring basis for the three months ended March 31, 2026 and 2025:
20262025
Ameren MissouriAmeren IllinoisAmerenAmeren MissouriAmeren IllinoisAmeren
For the three months ended March 31:
Beginning balance at January 1
$11 $(66)$(55)$6 $(53)$(47)
Realized and unrealized gains/(losses) included in regulatory assets/liabilities(3)8 5 2 (16)(14)
Settlements(5)2 (3)(3)2 (1)
Ending balance at March 31
$3 $(56)$(53)$5 $(67)$(62)
Change in unrealized gains/(losses) related to assets/liabilities held at March 31
$(2)$7 $5 $2 $(16)$(14)
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 March 31, 2026, and December 31, 2025:
Fair Value
Weighted Average(b)
CommodityAssetsLiabilitiesValuation Technique(s)
Unobservable Input(a)
Range
2026
Power(c)
$3$(56)Discounted cash flow
Average forward peak and off-peak pricing – forwards/swaps ($/MWh)
32 – 71
44
Nodal basis ($/MWh)
(11) – (1)
(5)
2025
Power(c)
$11$(66)Discounted cash flowAverage forward peak and off-peak pricing – forwards/swaps ($/MWh)
33 – 72
43
Nodal basis ($/MWh)
(9) – (2)
(5)
(a)Generally, significant increases (decreases) in these inputs in isolation would result in a significantly higher (lower) fair value measurement.
(b)Unobservable inputs were weighted by relative fair value.
(c)Valuations use visible forward prices adjusted for nodal-to-hub basis differentials.
The following table sets forth the carrying amount and, by level within the fair value hierarchy, the fair value of long-term debt (including current portion) disclosed, but not recorded, at fair value as of March 31, 2026, and December 31, 2025:
Long-Term Debt (Including Current Portion):
Carrying
Amount(a)
Fair Value
Level 2Level 3Total
March 31, 2026
Ameren(b)
$20,126 $17,986 $547 
(c) 
$18,533 
Ameren Missouri(d)
9,121 8,314 — 8,314 
Ameren Illinois(d)
6,260 5,603 — 5,603 
December 31, 2025
Ameren(b)
$19,187 $17,433 $559 
(c) 
$17,992 
Ameren Missouri(d)
8,230 7,608 — 7,608 
Ameren Illinois(d)
6,259 5,753 — 5,753 
(a)Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $145 million, $69 million, and $55 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of March 31, 2026. Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $136 million, $62 million, and $56 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2025.
(b)Amount excludes 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. See Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, of the Form 10-K for additional information.
(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.
v3.26.1
Related Party Transactions
 3 Months Ended
Mar. 31, 2026
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 $35 million and $37 million, respectively, as of March 31, 2026, and $36 million and $38 million, respectively, as of December 31, 2025, related to Ameren Services’ allocated portion of Ameren’s pension and postretirement benefit plans.
Tax Allocation Agreement
See Note 1 – Summary of Significant Accounting Policies under Part II, Item 8, of the Form 10-K for a discussion of the tax allocation agreement. The following table presents the affiliate balances related to income taxes for Ameren Missouri and Ameren Illinois as of March 31, 2026, and December 31, 2025:
March 31, 2026December 31, 2025
Ameren MissouriAmeren IllinoisAmeren MissouriAmeren Illinois
Income taxes payable to parent(a)
$—$54$—$4
Income taxes receivable from parent(b)
38—37
(a)Included in “Accounts payable – affiliates” on the balance sheet.
(b)Included in “Accounts receivable – affiliates” on the balance sheet.
Effects of Related-party Transactions on the Statement of Income
The following table presents the impact on Ameren Missouri and Ameren Illinois of related-party transactions for the three months ended March 31, 2026 and 2025:
Three Months
AgreementIncome Statement
Line Item		Ameren
Missouri		Ameren
Illinois
Ameren Missouri and Ameren IllinoisOperating Revenues2026$10 $(a)
rent and facility services
20257 (a)
Ameren Illinois interconnection agreementOperating Revenues2026(b)(a)
with Ameren Missouri2025(b)(a)
Ameren Missouri and Ameren Illinois miscellaneousOperating Revenues2026$(a)$(a)
support services2025(a)2 
Total Operating Revenues2026$10 $(a)
20257 2 
Ameren Missouri and Ameren IllinoisPurchased Power2026$2 $1 
transmission services from ATXI20253 (b)
Ameren Missouri interconnection agreementPurchased Power2026(a)(b)
with Ameren Illinois2025(a)(b)
Total Purchased Power2026$2 $1 
20253 (a)
Ameren Missouri and Ameren IllinoisOther Operations and Maintenance2026$(a)$(a)
rent and facility services
2025(a)1 
Ameren Services support servicesOther Operations and Maintenance2026$48 $44 
agreement
202544 40 
Total Other Operations and2026$48 $44 
Maintenance202544 41 
Money pool interest (advances)(Interest Charges)/Other Income, Net2026$(a)$(a)
2025(a)(a)
Long-term debt, net - related parties(Interest Charges)2026$(1)$(a)
2025(a)(a)
(a)Amount less than $1 million
(b)Not applicable.
v3.26.1
Commitments And Contingencies
 3 Months Ended
Mar. 31, 2026
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 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 and 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, although the scope of covered pollutants can change. 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. Ameren Missouri does not anticipate these operating curtailments will have a material impact on its results of operations, financial position, or liquidity. In March 2026, Ameren Missouri submitted an application to the United States Fish and Wildlife Service for a new 30-year federal permit to operate the High Prairie Energy Center. Ameren Missouri’s current permit expires in May 2027.
Ameren and Ameren Missouri anticipate they may need to make estimated capital expenditures of $70 million to $100 million from 2026 through 2030 to comply with environmental regulations. Additional capital expenditures beyond 2030 could be required. This estimate includes surface impoundment closure and corrective action measures required by the 2015 and 2024 CCR rules 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 federal 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. In January 2026, the EPA issued a proposed rule to reconsider the Good Neighbor Rule which, if finalized as proposed, would resolve underlying litigation involving numerous states including Missouri. 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 a final rule is issued similar to the proposed 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. The EPA expects to issue a final rule by mid-2026. In addition, in February 2026, the EPA issued a final rule rescinding its 2009 Endangerment Finding for greenhouse gas emissions, which was the basis for implementing greenhouse gas emissions standards. Ameren and Ameren Missouri are assessing the final rule and, at this time, cannot predict the final impacts on their results of operations, financial position, and liquidity.
MATS
In February 2026, the EPA issued a final rule repealing an April 2024 rule that had revised the MATS and established more stringent standards for emissions of particulate matter and mercury and required the use of continuous emissions monitoring systems. As a result of the repeal, the April 2024 rule will not impact Ameren’s and Ameren Missouri’s results of operations, financial position, and liquidity.
NSPS
In January 2026, the EPA issued a final rule that established NOx emission standards for several subcategories of natural gas-fired stationary CTs that began construction after December 13, 2024, based on size, utilization, design efficiency, and fuel type. Ameren and Ameren Missouri are assessing the final rule and, at this time, cannot predict the final impacts on their results of operations, financial position, and liquidity.
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 had AROs of $56 million associated with CCR storage facilities recorded on their respective balance sheets as of March 31, 2026. This amount includes an immaterial incremental ARO related to the 2024 CCR Rule, which may be revised as additional site studies are performed. In April 2026, the EPA issued a proposed rule that reconsiders aspects of the existing CCR rules and proposes various amendments and compliance alternatives. Ameren and Ameren Missouri are monitoring the ongoing regulatory developments but, at this time, cannot predict the final impacts of the CCR rules or the EPA’s proposed revisions on their results of operations, financial position, and liquidity.
Remediation
The Ameren Companies are involved in a number of remediation actions to clean up sites impacted by the use or disposal of materials containing hazardous substances. Federal and state laws can require responsible parties to fund remediation regardless of their degree of fault, the legality of original disposal, or the ownership of a disposal site.
As of March 31, 2026, 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.
v3.26.1
Callaway Energy Center
 3 Months Ended
Mar. 31, 2026
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. Every three years, the MoPSC requires Ameren Missouri to file an updated cost study and funding analysis for decommissioning its Callaway Energy Center. In May 2025, the MoPSC issued an order approving 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 to zero, as the trust fund level exceeded the estimated present value of future decommissioning costs as outlined in the non-unanimous stipulation and agreement. This MoPSC order removed Ameren Missouri’s funding obligation effective in June 2025. An updated cost study and funding analysis is expected to be filed with the MoPSC in September 2026. See Note 13 – Supplemental Information for more information on Ameren Missouri’s AROs.
Insurance
The following table presents insurance coverage at Ameren Missouri’s Callaway Energy Center at April 1, 2026:
Type and Source of CoverageMost Recent
Renewal Date		Maximum CoveragesMaximum Assessments
for Single Incidents
Public liability and nuclear worker liability:
American Nuclear InsurersJanuary 1, 2026$500 $— 
Pool participation
(a)
15,763 
(a) 
166 
(b) 
$16,263 
(c) 
$166 
Property damage:
NEIL and EMANIApril 1, 2026$3,200 
(d)
$23 
(e) 
Accidental outage:
NEILApril 1, 2026$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, or are not covered by insurance, or if coverage is unavailable, Ameren Missouri is at risk for any uninsured losses. If a serious nuclear incident were to occur, it could have a material adverse effect on Ameren’s and Ameren Missouri’s results of operations, financial position, or liquidity.
v3.26.1
Retirement Benefits
 3 Months Ended
Mar. 31, 2026
Retirement Benefits [Abstract]  
RETIREMENT BENEFITS RETIREMENT BENEFITS
The following table presents the components of the net periodic benefit cost (income) incurred for Ameren’s pension and postretirement benefit plans for the three months ended March 31, 2026 and 2025:
Pension BenefitsPostretirement Benefits
Three MonthsThree Months
2026202520262025
Service cost(a)
$20 $21 $2 $2 
Non-service cost components:
Interest cost56 58 11 11 
Expected return on plan assets(b)
(66)(76)(23)(23)
Amortization of(b):
Prior service cost (credit)— — (1)(1)
Actuarial (gain) loss2 (10)(8)(9)
Total non-service cost components(c)
$(8)$(28)$(21)$(22)
Net periodic benefit cost (income)(d)
$12 $(7)$(19)$(20)
(a)Service cost, net of capitalization, is reflected in “Operating Expenses – Other operations and maintenance” on Ameren’s statement of income.
(b)Prior service cost (credit) is amortized on a straight-line basis over the average future service of active participants benefiting under a plan amendment. Net actuarial gains or losses subject to amortization are amortized over 10 years. Expected return on plan assets is based on a market-related value of assets that recognizes asset (gains) losses over 4 years.
(c)Non-service cost components are reflected in “Other Income, Net” on Ameren’s consolidated statement of income. See Note 5 – Other Income, Net for additional information.
(d)Does not include the impact of the tracker for the difference between the level of pension and postretirement benefit costs (income) incurred by Ameren Missouri under GAAP and the level of such costs included in customer rates.
Ameren Missouri and Ameren Illinois are responsible for their respective share of Ameren’s pension and other postretirement costs. The following table presents the respective share of net periodic pension and other postretirement benefit costs (income) incurred for the three months ended March 31, 2026 and 2025:
Pension BenefitsPostretirement Benefits
Three MonthsThree Months
2026202520262025
Ameren Missouri(a)
$5 $(4)$(6)$(7)
Ameren Illinois6 (2)(13)(13)
Other1 (1)— — 
Ameren(a)
$12 $(7)$(19)$(20)
(a)Does not include the impact of the tracker for the difference between the level of pension and postretirement benefit costs (income) incurred by Ameren Missouri under GAAP and the level of such costs included in customer rates.
v3.26.1
Income Taxes
 3 Months Ended
Mar. 31, 2026
Income Tax Disclosure [Abstract]  
Income Taxes INCOME TAXES
The following table presents the principal reasons for the difference between the effective income tax expense and rate and the federal statutory corporate income tax expense and rate for the three months ended March 31, 2026 and 2025:
Three MonthsThree Months
20262025
AmountEffective Tax RateAmountEffective Tax Rate
Ameren
Federal statutory corporate income tax expense and rate$88 21 %$72 21 %
State and local taxes, net of federal income tax(a)
21 5 20 6 
Tax credits
Renewable energy tax credits(b)
(15)(4)(12)(4)
Other(3)(1)(2)(1)
Nontaxable or nondeductible items(1)— (1)— 
Other adjustments
Amortization of excess deferred income taxes(c)
(24)(6)(24)(7)
Depreciation differences(6)(1)(3)(1)
Effective income tax expense and rate$60 14 %$50 14 %
Ameren Missouri
Federal statutory corporate income tax expense and rate$17 21 %$10 21 %
State and local taxes, net of federal income tax(a)
2 3 2 4 
Tax credits
Renewable energy tax credits(b)
(5)(6)(3)(7)
Other(2)(2)(1)(1)
Other adjustments
Amortization of excess deferred income taxes(c)
(8)(11)(3)(8)
Depreciation differences(1)(2)(1)(1)
Effective income tax expense and rate$3 3 %$4 8 %
Ameren Illinois
Federal statutory corporate income tax expense and rate$73 21 %$66 21 %
State and local taxes, net of federal income tax(a)
26 7 24 7 
Other adjustments
Amortization of excess deferred income taxes(c)
(5)(1)(11)(3)
Depreciation differences(3)(1)(3)(1)
Effective income tax expense and rate$91 26 %$76 24 %
(a)State taxes in Missouri and Illinois made up the majority of the tax effect in this category for Ameren, Ameren Missouri, and Ameren Illinois.
(b)The benefit of the credits associated with Missouri renewable energy standard compliance is refunded to customers through the RESRAM. The benefit of the credits associated with the production and investment tax credit tracker will be refunded to customers based on MoPSC approval in a regulatory rate review.
(c)Reflects the amortization of a regulatory liability resulting from the revaluation of accumulated deferred income taxes subject to regulatory ratemaking, which are being refunded to customers.
v3.26.1
Supplemental Information
 3 Months Ended
Mar. 31, 2026
Supplemental Information [Abstract]  
Supplemental Information SUPPLEMENTAL INFORMATION
Cash, Cash Equivalents, and Restricted Cash
The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows at March 31, 2026, and December 31, 2025:
March 31, 2026December 31, 2025
AmerenAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois
“Cash and cash equivalents”$13 $— $— $13 $6 $3 
Restricted cash included in “Other current assets”74 64 6 63 54 5 
Restricted cash included in “Other assets”392 — 392 336 — 336 
Restricted cash included in “Nuclear decommissioning trust fund”6 6 — 8 8 — 
Total cash, cash equivalents, and restricted cash$485 $70 $398 $420 $68 $344 
Restricted cash included in “Other current assets” represents funds held by an irrevocable Voluntary Employee Beneficiary Association (VEBA) trust, which provides health care benefits for active employees on Ameren’s, Ameren Missouri’s, and Ameren Illinois’ balance sheets, funds held in an escrow account for programs established as a result of a 2024 court order resolving outstanding claims in the NSR and Clean Air Act litigation on Ameren’s and Ameren Missouri’s balance sheets, and AMF’s restricted cash for payments for securitized utility tariff bonds on Ameren’s and Ameren Missouri’s balance sheets. Restricted cash included in “Other assets” on Ameren’s and Ameren Illinois’ balance sheets primarily represents amounts collected under a cost recovery rider restricted for use in the procurement of renewable energy credits and amounts in a trust fund restricted for the use of funding certain asbestos-related claims.
Accounts Receivable
“Accounts receivable – trade” on Ameren’s and Ameren Illinois’ balance sheets include certain receivables purchased at a discount from alternative retail electric suppliers that elect to participate in the utility consolidated billing program. At March 31, 2026, and December 31, 2025, “Other current liabilities” on Ameren’s and Ameren Illinois’ balance sheets included payables for purchased receivables of $46 million and $47 million, respectively.
The following table provides a reconciliation of the beginning and ending amount of the allowance for doubtful accounts for the three months ended March 31, 2026 and 2025:
Three Months
20262025
Ameren:
Beginning of period$39 $30 
Bad debt expense10 16 
Charged to other accounts(a)
1 1 
Net write-offs(9)(6)
End of period$41 $41 
Ameren Missouri:
Beginning of period$17 $12 
Bad debt expense2 2 
Net write-offs(4)(2)
End of period$15 $12 
Ameren Illinois:(b)
Beginning of period$22 $18 
Bad debt expense8 14 
Charged to other accounts(a)
1 1 
Net write-offs(5)(4)
End of period$26 $29 
(a)Amounts associated with the allowance for doubtful accounts related to receivables purchased by Ameren Illinois from alternative retail electric suppliers, as required by the Illinois Public Utilities Act.
(b)Ameren Illinois has rate-adjustment mechanisms that allow it to recover the difference between its actual net bad debt write-offs under GAAP, including those associated with receivables purchased from alternative retail electric suppliers, and the amount of net bad debt write-offs included in its base rates. The table above does not include the impact related to the riders.
Supplemental Cash Flow Information
The following table provides noncash financing and investing activity excluded from the statements of cash flows for the three months ended March 31, 2026 and 2025:
March 31, 2026March 31, 2025
AmerenAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois
Investing:
Accrued capital expenditures, including nuclear fuel expenditures$490 
(a)
$364 
(a)
$108 $381 $214 $159 
Net realized and unrealized loss – nuclear decommissioning trust fund(56)(56)— (40)(40)— 
Financing:
Issuance of common stock for stock-based compensation$25 $— $— $25 $— $— 
Issuance of common stock under the DRPlus7 — — 9 — — 
(a)Includes amounts associated with the February 2026 acquisition of the Split Rail Solar Project with payment contingent upon completion of the project.
Asset Retirement Obligations
The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the three months ended March 31, 2026:
Ameren
Missouri		Ameren
Illinois		Ameren
Balance at December 31, 2025
$849 
(a) 
$5 
(b) 
$854 
(a) 
Liabilities incurred7 — 7 
Liabilities settled(1)(c)(1)
Accretion9 
(d) 
(c)9 
(d) 
Balance at March 31, 2026
$864 
(a) 
$5 
(b) 
$869 
(a) 
(a)Balance included $5 million in “Other current liabilities” on the balance sheet as of both March 31, 2026, and December 31, 2025.
(b)Included in “Other deferred credits and liabilities” on the balance sheet.
(c)Amount less than $1 million.
(d)Accretion expense attributable to Ameren Missouri was recorded as a decrease to regulatory liabilities.
Deferred Compensation
At March 31, 2026, and December 31, 2025, the present value of benefits to be paid for deferred compensation obligations was $79 million and $79 million, respectively, which was primarily reflected in “Other deferred credits and liabilities” on Ameren’s consolidated balance sheet.
Operating Revenues
As of March 31, 2026 and 2025, our remaining performance obligations for contracts with a term greater than one year were immaterial. The Ameren Companies elected not to disclose the aggregate amount of the transaction price allocated to the performance obligations that are unsatisfied as of the end of the reporting period for contracts with an initial expected term of one year or less. See Note 14 – Segment Information for disaggregated revenue information.
Excise Taxes
Ameren Missouri and Ameren Illinois collect from their customers excise taxes, including municipal and state excise taxes and gross receipts taxes that are levied on the sale or distribution of natural gas and electricity. The following table presents the excise taxes recorded on a gross basis in “Operating Revenues – Electric,” “Operating Revenues – Natural gas” and “Operating Expenses – Taxes other than income taxes” on the statements of income for the three months ended March 31, 2026 and 2025:
Three Months
20262025
Ameren Missouri$40 $38 
Ameren Illinois45 43 
Ameren$85 $81 
Earnings per Share
The following table reconciles the basic weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the three months ended March 31, 2026 and 2025:
Three Months
20262025
Weighted-average Common Shares Outstanding – Basic276.5 270.0 
Assumed settlement of performance share units and restricted stock units1.0 1.0 
Dilutive effect of forward sale agreements0.9 0.4 
Weighted-average Common Shares Outstanding – Diluted(a)
278.4 271.4 
(a)There was an immaterial number of anti-dilutive performance share units excluded from the earnings per diluted share calculations for the three months ended March 31, 2026 and 2025. Outstanding forward sale agreements as of March 31, 2026 that were anti-dilutive for the three months ended March 31, 2026 were excluded from the earnings per diluted share calculation as calculated using the treasury stock method. There were no anti-dilutive shares related to the outstanding forward sale agreements as of March 31, 2025 excluded from earnings per diluted share calculations for the three months ended March 31, 2025. For additional information about the outstanding forward sale agreements, see Note 4 – Long-term Debt and Equity Financings.
v3.26.1
Segment Information
 3 Months Ended
Mar. 31, 2026
Segment Reporting [Abstract]  
SEGMENT INFORMATION SEGMENT INFORMATION
The following tables present revenues, net income attributable to common shareholders, and capital expenditures by segment at Ameren and Ameren Illinois for the three months ended March 31, 2026 and 2025. 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
Reportable Segments
Ameren MissouriAmeren Illinois Electric DistributionAmeren Illinois Natural GasAmeren TransmissionOtherIntersegment EliminationsAmeren
Three Months 2026:
External revenues$920 $643 $436 $177 $— $— $2,176 
Intersegment revenues10 — — 50 — (60)— 
Revenue930 643 436 227 — (60)2,176 
Fuel and purchased power(a)
(214)(266)— — — 47 (433)
Natural gas purchased for resale(a)
(34)— (137)— — — (171)
Other operations and maintenance expenses(a)
(264)(160)(57)(19)(4)13 (491)
Other segment items
Depreciation and amortization(214)(96)(34)(53)(1)— (398)
Taxes other than income taxes(95)(22)(29)(2)(3)— (151)
Other income (expense), net53 19 3 7 9 (1)90 
Interest charges(82)(28)(16)(30)(49)1 (204)
Income (taxes) benefit(3)(24)(44)(32)43 — (60)
Noncontrolling interests – preferred stock dividends(1)— — — — — (1)
Net income (loss) attributable to Ameren common shareholders$76 $66 $122 $98 $(5)$— $357 
Interest income$3 $6 $— $— $1 $(1)$9 
Capital expenditures1,091 196 72 204 1 10 1,574 
Three Months 2025:
External revenues$950 $570 $411 $166 $— $— $2,097 
Intersegment revenues7 2 — 44 — (53)— 
Revenue957 572 411 210 — (53)2,097 
Fuel and purchased power(a)
(330)(212)— — — 40 (502)
Natural gas purchased for resale(a)
(30)— (139)— — — (169)
Other operations and maintenance expenses(a)
(250)(166)(55)(19)(8)13 (485)
Other segment items
Depreciation and amortization(194)(91)(32)(48)(2)— (367)
Taxes other than income taxes(89)(21)(29)(1)(4)— (144)
Other income (expense), net43 23 5 7 8 (1)85 
Interest charges(60)(26)(15)(29)(46)1 (175)
Income (taxes) benefit(4)(16)(38)(31)39 — (50)
Noncontrolling interests – preferred stock dividends(1)— — — — — (1)
Net income (loss) attributable to Ameren common shareholders$42 $63 $108 $89 
(b)
$(13)$— $289 
Interest income$2 $8 $— $1 $1 $(1)$11 
Capital expenditures658 167 59 173 2 5 1,064 
(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
Reportable Segments
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionIntersegment EliminationsAmeren Illinois
Three Months 2026:
External revenues$643 $436 $120 $— $1,199 
Intersegment revenues— — 44 (44)— 
Revenue643 436 164 (44)1,199 
Purchased power(a)
(266)— — 44 (222)
Natural gas purchased for resale(a)
— (137)— — (137)
Other operations and maintenance expenses(a)
(160)(57)(15)— (232)
Other segment items
Depreciation and amortization(96)(34)(40)— (170)
Taxes other than income taxes(22)(29)(1)— (52)
Other income, net19 3 7 — 29 
Interest charges(28)(16)(24)— (68)
Income taxes(24)(44)(23)— (91)
Net income available to common shareholder$66 $122 $68 $— $256 
Interest income$6 $— $— $— $6 
Capital expenditures196 72 120 — 388 
Three Months 2025:
External revenues$572 $411 $117 $— $1,100 
Intersegment revenues— — 37 (37)— 
Revenue572 411 154 (37)1,100 
Purchased power(a)
(212)— — 37 (175)
Natural gas purchased for resale(a)
— (139)— — (139)
Other operations and maintenance expenses(a)
(166)(55)(15)— (236)
Other segment items
Depreciation and amortization(91)(32)(36)— (159)
Taxes other than income taxes(21)(29)(1)— (51)
Other income, net23 5 6 — 34 
Interest charges(26)(15)(21)— (62)
Income taxes(16)(38)(22)— (76)
Net income available to common shareholder$63 $108 $65 $— $236 
Interest income$8 $— $1 $— $9 
Capital expenditures167 59 137 — 363 
(a)Significant segment expense that is regularly provided to the CODMs. Intersegment expenses are included within the amounts shown.
The following tables present disaggregated revenues by segment at Ameren and Ameren Illinois for the three months ended March 31, 2026 and 2025. 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 2026:
Residential$399 $349 $— $— $— $748 
Commercial302 195 — — — 497 
Industrial72 55 — — — 127 
Other78 44 
(a)
— 227 (60)289 
Total electric revenues$851 $643 $— $227 $(60)$1,661 
Residential$48 $— $312 $— $— $360 
Commercial20 — 86 — — 106 
Industrial2 — 6 — — 8 
Other9 — 32 — — 41 
Total natural gas revenues$79 $— $436 $— $— $515 
Total revenues(b)
$930 $643 $436 $227 $(60)$2,176 
Three Months 2025:
Residential$376 $342 $— $— $— $718 
Commercial273 180 — — — 453 
Industrial66 50 — — — 116 
Other178 — 
(a)
— 210 (53)335 
Total electric revenues$893 $572 $— $210 $(53)$1,622 
Residential$43 $— $309 $— $— $352 
Commercial19 — 77 — — 96 
Industrial2 — 4 — — 6 
Other— — 21 — — 21 
Total natural gas revenues$64 $— $411 $— $— $475 
Total revenues(b)
$957 $572 $411 $210 $(53)$2,097 
(a)Includes over-recoveries of various riders.
(b)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the three months ended March 31, 2026 and 2025:
Ameren MissouriAmeren Illinois Electric DistributionAmeren Illinois Natural GasAmeren TransmissionAmeren
Three Months 2026:
Revenues from alternative revenue programs$(3)$46 $17 $(4)$56 
Other revenues not from contracts with customers2 3 1 — 6 
Three Months 2025:
Revenues from alternative revenue programs$(5)$21 $3 $(1)$18 
Other revenues not from contracts with customers1 3 1 — 5 
Ameren Illinois
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionIntersegment EliminationsAmeren Illinois
Three Months 2026:
Residential$349 $312 $— $— $661 
Commercial195 86 — — 281 
Industrial55 6 — — 61 
Other44 
(a)
32 164 (44)196 
Total revenues(b)
$643 $436 $164 $(44)$1,199 
Three Months 2025:
Residential$342 $309 $— $— $651 
Commercial180 77 — — 257 
Industrial50 4 — — 54 
Other— 
(a)
21 154 (37)138 
Total revenues(b)
$572 $411 $154 $(37)$1,100 
(a)Includes over-recoveries of various riders.
(b)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the Ameren Illinois segments for the three months ended March 31, 2026 and 2025:
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionAmeren Illinois
Three Months 2026:
Revenues from alternative revenue programs$46 $17 $(3)$60 
Other revenues not from contracts with customers3 1 — 4 
Three Months 2025:
Revenues from alternative revenue programs$21 $3 $(1)$23 
Other revenues not from contracts with customers3 1 — 4 
v3.26.1
Insider Trading Arrangements
 3 Months Ended
Mar. 31, 2026
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
Michael L. Moehn [Member]  
Trading Arrangements, by Individual  
Material Terms of Trading Arrangement
On February 24, 2026, Michael L. Moehn, Group President of Ameren Utilities and Interim Chairman and President of Ameren Missouri, adopted a Rule 10b5‑1 trading arrangement that provides for the sale of an aggregate of up to 26,000 shares of Ameren common stock, to be sold in four equal quarterly installments, beginning in August 2026 and continuing through May 2027, subject to certain price limitations set forth in the trading arrangement. Mr. Moehn’s Rule 10b5‑1 trading arrangement will terminate on the earlier of: (i) July 30, 2027; (ii) execution of all trades or expiration of all orders relating to such trades under the Rule 10b5‑1 trading arrangement; or (iii) such date as the Rule 10b5‑1 trading arrangement is otherwise terminated according to its terms.
Name Michael L. Moehn
Title Group President of Ameren Utilities and Interim Chairman and President of Ameren Missouri
Rule 10b5-1 Arrangement Adopted true
Adoption Date February 24, 2026
Expiration Date July 30, 2027
Arrangement Duration 521 days
Aggregate Available 26,000
Mark C. Lindgren [Member]  
Trading Arrangements, by Individual  
Material Terms of Trading Arrangement
On February 24, 2026, Mark C. Lindgren, Executive Vice President, Communications, and Chief Human Resources Officer of Ameren Services Company, adopted a Rule 10b5‑1 trading arrangement that provides for the sale of 50% of any net shares of Ameren common stock received, after tax withholding, in connection with certain previously awarded performance share units and restricted stock units that will vest upon payment in March 2027 and March 2028. The estimated maximum number of shares to be sold pursuant to the Rule 10b5-1 trading arrangement is 5,272 shares. The actual number of shares sold pursuant to the Rule 10b5-1 trading arrangement will depend on the actual number of shares earned pursuant to the awards, which is generally dependent on the Company's achievement of certain performance measures, the actual dividends paid by the Company during the applicable vesting periods, and Mr. Lindgren's continued employment during the applicable vesting periods. Mr. Lindgren’s Rule 10b5‑1 trading arrangement will terminate on the earlier of: (i) March 17, 2028; (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 Mark C. Lindgren
Title Executive Vice President, Communications, and Chief Human Resources Officer of Ameren Services Company
Rule 10b5-1 Arrangement Adopted true
Adoption Date February 24, 2026
Expiration Date March 17, 2028
Arrangement Duration 752 days
Aggregate Available 5,272
v3.26.1
Summary Of Significant Accounting Policies (Policies)
 3 Months Ended
Mar. 31, 2026
Accounting Policies [Abstract]  
Nature of Operations
Ameren, headquartered in St. Louis, Missouri, is a public utility holding company whose primary assets are its equity interests in its subsidiaries. Ameren’s subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. Dividends on Ameren’s common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren’s principal subsidiaries are listed below. Ameren also has other subsidiaries that conduct other activities, such as providing shared services.
•Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri.
•Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois.
•ATXI operates a FERC rate-regulated electric transmission business in the MISO.
Consolidation
Ameren’s and Ameren Missouri’s financial statements are prepared on a consolidated basis and therefore include the accounts of their majority-owned subsidiaries. All intercompany transactions have been eliminated. Ameren Illinois has no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated.
Note 1 – Summary of Significant Accounting Policies applies to the Ameren Companies. The remaining notes to the consolidated financial statements apply to the registrants as indicated in each footnote disclosure. Registrants are named specifically for their related activities and disclosures.
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 entity, as well as the obligation to absorb losses or the right to receive benefits from the entity. 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 retired energy center, among other costs, and long-term debt. Ameren and Ameren Missouri consolidate AMF, which Ameren Missouri wholly owns, and both manages and controls the entity’s operating activities. For additional information on the securitization of the Rush Island Energy Center costs, see Note 2 – Rate and Regulatory Matters under Part II, Item 8, of the Form 10-K. For additional information on the securitized tariff bond issuance, see Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, of the Form 10‑K.
The following table presents the carrying values of AMF’s assets and liabilities included on Ameren’s and Ameren Missouri’s consolidated balance sheets as of March 31, 2026 and December 31, 2025:
20262025
Unbilled revenue(a)
$1 $2 
Other current assets(a)
31 21 
Noncurrent regulatory assets(a)
437 443 
Current maturities of long-term debt(b)
23 23 
Interest accrued(b)
11 6 
Current regulatory liabilities(c)
9 11 
Long-term debt, net(b)
426 426 
(a)Assets may be used only to meet AMF’s obligations and commitments.
(b)The securitized tariff bondholders have no recourse to Ameren Missouri.
(c)Included in “Other current liabilities” on Ameren’s and Ameren Missouri’s balance sheet.
Variable Interest Entities that are not Consolidated
As of March 31, 2026, and December 31, 2025, Ameren had unconsolidated variable interests in various equity method investments, primarily to advance innovative energy technologies, totaling $65 million and $64 million, respectively, included in “Other assets” on Ameren’s consolidated balance sheet. Any earnings or losses related to these investments are included in “Other Income, Net” on Ameren’s consolidated statement of income and comprehensive income. Ameren is not the primary beneficiary of these investments because it does not have the power to direct matters that most significantly affect the activities of these variable interest entities. As of March 31, 2026, Ameren’s maximum exposure to loss related to these variable interest entities is limited to the investment in these partnerships of $65 million plus associated outstanding funding commitments of $27 million.
Life Insurance, Corporate Or Bank Owned
COLI
Ameren (parent) and Ameren Illinois have COLI, which is recorded at the net cash surrender value. The net cash surrender value is the amount that can be realized under the insurance policies at the balance sheet date.
Derivatives, Policy If we determine that a contract meets the definition of a derivative and is not eligible for the NPNS exception, we review the contract to determine whether the resulting gains or losses qualify for regulatory deferral. Derivative contracts that qualify for regulatory deferral are recorded at fair value, with changes in fair value recorded as regulatory assets or liabilities in the period in which the change occurs. We believe derivative losses and gains deferred as regulatory assets and liabilities are probable of recovery, or refund, through future rates charged to customers. Regulatory assets and liabilities are amortized to operating income as related losses and gains are reflected in rates charged to customers. Therefore, gains and losses on these derivatives have no effect on operating income.
Deferred Compensation
Deferred Compensation
At March 31, 2026, and December 31, 2025, the present value of benefits to be paid for deferred compensation obligations was $79 million and $79 million, respectively, which was primarily reflected in “Other deferred credits and liabilities” on Ameren’s consolidated balance sheet.
Revenue from Contract with Customer
Operating Revenues
As of March 31, 2026 and 2025, 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.
v3.26.1
Accounting Policies (Tables)
 3 Months Ended
Mar. 31, 2026
Accounting Policies [Abstract]  
Schedule of Other Assets and Other Liabilities
The following table presents the carrying values of AMF’s assets and liabilities included on Ameren’s and Ameren Missouri’s consolidated balance sheets as of March 31, 2026 and December 31, 2025:
20262025
Unbilled revenue(a)
$1 $2 
Other current assets(a)
31 21 
Noncurrent regulatory assets(a)
437 443 
Current maturities of long-term debt(b)
23 23 
Interest accrued(b)
11 6 
Current regulatory liabilities(c)
9 11 
Long-term debt, net(b)
426 426 
(a)Assets may be used only to meet AMF’s obligations and commitments.
(b)The securitized tariff bondholders have no recourse to Ameren Missouri.
(c)Included in “Other current liabilities” on Ameren’s and Ameren Missouri’s balance sheet.
v3.26.1
Rate and Regulatory Matters (Tables)
 3 Months Ended
Mar. 31, 2026
Regulated Operations [Abstract]  
Schedule of Generation Facilities The following table provides information about each facility:
Agreement typeFacility sizeStatus of MoPSC CCN
In-service date(a)
Bowling Green Solar Project(b)
Self-build
50-MW
Approved March 2024March 2026
Split Rail Solar Project
Build-transfer(c)
300-MW
Approved March 2024Second quarter 2026
Castle Bluff Natural Gas Project(d)
Self-build
800-MW
Approved October 2024Fourth quarter 2027
Big Hollow Battery Energy Storage Project(e)
Self-build
400-MW
Approved February 2026Second quarter 2028
Big Hollow Natural Gas Project(e)
Self-build
800-MW
Approved February 2026Third quarter 2028
Reform Solar ProjectSelf-build
250-MW
Filed August 2025(f)
Fourth quarter 2028
(a)Future in-service dates are dependent on the timing of regulatory approvals and construction completion, among other things.
(b)This project represents approximately $0.1 billion of capital expenditures.
(c)Ameren Missouri received FERC approval for the acquisition in November 2024. In February 2026, Ameren Missouri acquired the Split Rail Solar Project, which includes solar panels, project design, land rights, and engineering, procurement, and construction agreements, for approximately $0.6 billion, and took over construction management of the project.
(d)This project represents approximately $0.9 billion of capital expenditures.
(e)These projects represent approximately $2 billion of capital expenditures.
(f)In March 2026, Ameren Missouri, the MoPSC staff, and certain intervenors filed a nonunanimous stipulation and agreement with the MoPSC, which recommends the MoPSC approve Ameren Missouri’s requested CCN. Ameren Missouri expects a decision by the MoPSC in the first half of 2026.
v3.26.1
Short-Term Debt and Liquidity (Tables)
 3 Months Ended
Mar. 31, 2026
Debt Disclosure [Abstract]  
Schedule of Short-term Debt
The following table presents commercial paper outstanding, net of issuance discounts, as of March 31, 2026, and December 31, 2025. There were no borrowings outstanding under the Credit Agreements as of March 31, 2026, or December 31, 2025.
March 31, 2026December 31, 2025
Ameren (parent)$823 $155 
Ameren Missouri280 471 
Ameren Illinois75 17 
Ameren consolidated$1,178 $643 
The following table summarizes the activity and relevant interest rates for Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper issuances under the Credit Agreements for the three months ended March 31, 2026 and 2025:
Ameren
(parent)		Ameren
Missouri		Ameren
Illinois		Ameren
Consolidated
2026
Average daily amount outstanding$464 $530 $36 $1,030 
Weighted-average interest rate3.86 %3.83 %3.82 %3.84 %
Peak amount outstanding during period(a)
$992 $1,360 $122 $1,996 
Peak interest rate4.00 %4.05 %4.00 %4.05 %
2025
Average daily amount outstanding$898 $313 $82 $1,293 
Weighted-average interest rate4.61 %4.59 %4.56 %4.60 %
Peak amount outstanding during period(a)
$1,139 $630 $189 $1,603 
Peak interest rate4.75 %4.70 %4.69 %4.75 %
(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.
v3.26.1
Other Income, Net (Tables)
 3 Months Ended
Mar. 31, 2026
Other Nonoperating Income (Expense) [Abstract]  
Other Income And Expenses
The following table presents the components of “Other Income, Net” in the Ameren Companies’ statements of income for the three months ended March 31, 2026 and 2025:
Three Months
20262025
Ameren:
Allowance for equity funds used during construction
$31 $16 
Other interest income
9 11 
Non-service cost components of net periodic benefit income(a)
49 66 
Miscellaneous income
5 3 
Earnings (losses) related to equity method investments2 (4)
Donations
(2)(2)
Miscellaneous expense
(4)(5)
Total Other Income, Net$90 $85 
Ameren Missouri:
Allowance for equity funds used during construction
$23 $8 
Other interest income
3 2 
Non-service cost components of net periodic benefit income(a)
30 35 
Miscellaneous income
— 1 
Donations
(1)(1)
Miscellaneous expense
(2)(2)
Total Other Income, Net$53 $43 
Ameren Illinois:
Allowance for equity funds used during construction
$7 $7 
Other interest income6 9 
Non-service cost components of net periodic benefit income
15 20 
Miscellaneous income
4 2 
Donations
(1)(1)
Miscellaneous expense(2)(3)
Total Other Income, Net$29 $34 
(a)For the three months ended March 31, 2026 and 2025, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $(20) million and $(16) million, respectively, due to a regulatory tracking mechanism for the difference between the level of such costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates. See Note 11 – Retirement Benefits for additional information.
v3.26.1
Derivative Financial Instruments (Tables)
 3 Months Ended
Mar. 31, 2026
Derivative Instruments and Hedging Activities Disclosure [Abstract]  
Open Gross Derivative Volumes By Commodity Type
The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of March 31, 2026, and December 31, 2025. As of March 31, 2026, these contracts extended through October 2029, October 2032 and May 2032 for fuel oils, natural gas, and power, respectively.
Quantity (in millions, except as indicated)
March 31, 2026December 31, 2025
CommodityAmeren MissouriAmeren IllinoisAmerenAmeren MissouriAmeren IllinoisAmeren
Fuel oils (in gallons)22 — 22 25 — 25 
Natural gas (in MMBtu)56 229 285 46 217 263 
Power (in MWhs)4 7 11 — 7 7 
Derivative Instruments Carrying Value
The following table presents the carrying value and balance sheet location of all derivative commodity contracts, none of which were designated as hedging instruments because all qualify for regulatory deferral, as of March 31, 2026, and December 31, 2025:
March 31, 2026December 31, 2025
CommodityBalance Sheet LocationAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois		Ameren
Fuel oilsOther current assets$9 $— $9 $— $— $— 
Other assets3 — 3 — — — 
Natural gasOther current assets— — — 1 1 2 
Other assets— 1 1 — 3 3 
PowerOther current assets3 — 3 11 — 11 
Other assets3 — 3 — — — 
Total assets$18 $1 $19 $12 $4 $16 
Fuel oilsOther current liabilities$— $— $— $3 $— $3 
Other deferred credits and liabilities— — — 2 — 2 
Natural gasMark-to-market derivative liabilities(a)31 (a)(a)21 (a)
Other current liabilities9 — 40 5 — 26 
Other deferred credits and liabilities8 19 27 5 11 16 
PowerMark-to-market derivative liabilities(a)28 (a)(a)24 (a)
Other current liabilities— — 28 — — 24 
Other deferred credits and liabilities1 48 49 — 55 55 
Total liabilities$18 $126 $144 $15 $111 $126 
(a) Balance sheet line item not applicable to registrant.
Disclosure of Credit Derivatives The following table presents, as of March 31, 2026, 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:
Aggregate Fair Value of
Derivative Liabilities(a)
Cash
Collateral Posted
Potential Aggregate Amount of
Additional Collateral Required(b)
Ameren Missouri$17 $— $9 
Ameren Illinois50 — 50 
Ameren$67 $— $59 
(a)Before consideration of master netting arrangements or similar agreements.
(b)As collateral requirements with certain counterparties are based on master netting arrangements or similar agreements, the aggregate amount of additional collateral required to be posted is determined after consideration of the effects of such arrangements.
v3.26.1
Fair Value Measurements (Tables)
 3 Months Ended
Mar. 31, 2026
Fair Value Disclosures [Abstract]  
Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis
The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of March 31, 2026, and December 31, 2025:
March 31, 2026December 31, 2025
Level 1Level 2Level 3TotalLevel 1Level 2Level 3Total
Assets:
Ameren Missouri
Derivative assets – commodity contracts:
Fuel oils$12 $— $— $12 $— $— $— $— 
Natural gas— — — — — 1 — 1 
Power— 3 3 6 — — 11 11 
Total derivative assets – commodity contracts$12 $3 $3 $18 $— $1 $11 $12 
Nuclear decommissioning trust fund:
Equity securities:
U.S. large capitalization$981 $— $— $981 $1,028 $— $— $1,028 
Debt securities:
U.S. Treasury and agency securities— 218 — 218 — 225 — 225 
Corporate bonds— 184 — 184 — 177 — 177 
Other— 87 — 87 — 84 — 84 
Total nuclear decommissioning trust fund$981 $489 $— $1,470 
(a) 
$1,028 $486 $— $1,514 
(a) 
Total Ameren Missouri$993 $492 $3 $1,488 $1,028 $487 $11 $1,526 
Ameren Illinois
Derivative assets – commodity contracts:
Natural gas$— $— $1 $1 $— $2 $2 $4 
Total Ameren Illinois$— $— $1 $1 $— $2 $2 $4 
Ameren
Derivative assets – commodity contracts(b)
$12 $3 $4 $19 $— $3 $13 $16 
Nuclear decommissioning trust fund(c)
981 489 — 1,470 
(a) 
1,028 486 — 1,514 
(a) 
Total Ameren$993 $492 $4 $1,489 $1,028 $489 $13 $1,530 
Liabilities:
Ameren Missouri
Derivative liabilities – commodity contracts:
Fuel oils$— $— $— $— $5 $— $— $5 
Natural gas— 16 1 17 — 10 — 10 
Power— 1 — 1 — — — — 
Total Ameren Missouri$— $17 $1 $18 $5 $10 $— $15 
Ameren Illinois
Derivative liabilities – commodity contracts:
Natural gas$1 $43 $6 $50 $1 $28 $3 $32 
Power— 20 56 76 — 13 66 79 
Total Ameren Illinois$1 $63 $62 $126 $1 $41 $69 $111 
Ameren
Derivative liabilities – commodity contracts(b)
$1 $80 $63 $144 $6 $51 $69 $126 
(a)Balance excludes $8 million and $12 million of cash and cash equivalents, receivables, payables, and accrued income, net, for March 31, 2026, and December 31, 2025, respectively.
(b)See the Ameren Missouri and Ameren Illinois sections of the table for a breakout of the fair value of Ameren’s derivative assets and liabilities by type of commodity.
(c)See the Ameren Missouri section of the table for a breakout of the fair value of Ameren’s nuclear decommissioning trust fund by investment type.
Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level Three In The Fair Value Hierarchy The following table presents the fair value reconciliation of Level 3 power derivative contract assets and liabilities measured at fair value on a recurring basis for the three months ended March 31, 2026 and 2025:
20262025
Ameren MissouriAmeren IllinoisAmerenAmeren MissouriAmeren IllinoisAmeren
For the three months ended March 31:
Beginning balance at January 1
$11 $(66)$(55)$6 $(53)$(47)
Realized and unrealized gains/(losses) included in regulatory assets/liabilities(3)8 5 2 (16)(14)
Settlements(5)2 (3)(3)2 (1)
Ending balance at March 31
$3 $(56)$(53)$5 $(67)$(62)
Change in unrealized gains/(losses) related to assets/liabilities held at March 31
$(2)$7 $5 $2 $(16)$(14)
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis, Valuation Techniques
The following table describes the valuation techniques and significant unobservable inputs utilized for the fair value of our Level 3 power derivative contract assets and liabilities as of March 31, 2026, and December 31, 2025:
Fair Value
Weighted Average(b)
CommodityAssetsLiabilitiesValuation Technique(s)
Unobservable Input(a)
Range
2026
Power(c)
$3$(56)Discounted cash flow
Average forward peak and off-peak pricing – forwards/swaps ($/MWh)
32 – 71
44
Nodal basis ($/MWh)
(11) – (1)
(5)
2025
Power(c)
$11$(66)Discounted cash flowAverage forward peak and off-peak pricing – forwards/swaps ($/MWh)
33 – 72
43
Nodal basis ($/MWh)
(9) – (2)
(5)
(a)Generally, significant increases (decreases) in these inputs in isolation would result in a significantly higher (lower) fair value measurement.
(b)Unobservable inputs were weighted by relative fair value.
(c)Valuations use visible forward prices adjusted for nodal-to-hub basis differentials.
Schedule of Financial Assets and Liabilities
The following table sets forth the carrying amount and, by level within the fair value hierarchy, the fair value of long-term debt (including current portion) disclosed, but not recorded, at fair value as of March 31, 2026, and December 31, 2025:
Long-Term Debt (Including Current Portion):
Carrying
Amount(a)
Fair Value
Level 2Level 3Total
March 31, 2026
Ameren(b)
$20,126 $17,986 $547 
(c) 
$18,533 
Ameren Missouri(d)
9,121 8,314 — 8,314 
Ameren Illinois(d)
6,260 5,603 — 5,603 
December 31, 2025
Ameren(b)
$19,187 $17,433 $559 
(c) 
$17,992 
Ameren Missouri(d)
8,230 7,608 — 7,608 
Ameren Illinois(d)
6,259 5,753 — 5,753 
(a)Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $145 million, $69 million, and $55 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of March 31, 2026. Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $136 million, $62 million, and $56 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2025.
(b)Amount excludes 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. See Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, of the Form 10-K for additional information.
(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).
v3.26.1
Related Party Transactions (Tables)
 3 Months Ended
Mar. 31, 2026
Related Party Transactions [Abstract]  
Schedule of Affiliate Receivables and Payables The following table presents the affiliate balances related to income taxes for Ameren Missouri and Ameren Illinois as of March 31, 2026, and December 31, 2025:
March 31, 2026December 31, 2025
Ameren MissouriAmeren IllinoisAmeren MissouriAmeren Illinois
Income taxes payable to parent(a)
$—$54$—$4
Income taxes receivable from parent(b)
38—37
(a)Included in “Accounts payable – affiliates” on the balance sheet.
(b)Included in “Accounts receivable – affiliates” on the balance sheet.
Schedule of Related Party Transactions
The following table presents the impact on Ameren Missouri and Ameren Illinois of related-party transactions for the three months ended March 31, 2026 and 2025:
Three Months
AgreementIncome Statement
Line Item		Ameren
Missouri		Ameren
Illinois
Ameren Missouri and Ameren IllinoisOperating Revenues2026$10 $(a)
rent and facility services
20257 (a)
Ameren Illinois interconnection agreementOperating Revenues2026(b)(a)
with Ameren Missouri2025(b)(a)
Ameren Missouri and Ameren Illinois miscellaneousOperating Revenues2026$(a)$(a)
support services2025(a)2 
Total Operating Revenues2026$10 $(a)
20257 2 
Ameren Missouri and Ameren IllinoisPurchased Power2026$2 $1 
transmission services from ATXI20253 (b)
Ameren Missouri interconnection agreementPurchased Power2026(a)(b)
with Ameren Illinois2025(a)(b)
Total Purchased Power2026$2 $1 
20253 (a)
Ameren Missouri and Ameren IllinoisOther Operations and Maintenance2026$(a)$(a)
rent and facility services
2025(a)1 
Ameren Services support servicesOther Operations and Maintenance2026$48 $44 
agreement
202544 40 
Total Other Operations and2026$48 $44 
Maintenance202544 41 
Money pool interest (advances)(Interest Charges)/Other Income, Net2026$(a)$(a)
2025(a)(a)
Long-term debt, net - related parties(Interest Charges)2026$(1)$(a)
2025(a)(a)
(a)Amount less than $1 million
(b)Not applicable.
v3.26.1
Callaway Energy Center (Tables)
 3 Months Ended
Mar. 31, 2026
Nuclear Waste Matters [Abstract]  
Schedule of Insurance Coverage at Callaway Energy Center
The following table presents insurance coverage at Ameren Missouri’s Callaway Energy Center at April 1, 2026:
Type and Source of CoverageMost Recent
Renewal Date		Maximum CoveragesMaximum Assessments
for Single Incidents
Public liability and nuclear worker liability:
American Nuclear InsurersJanuary 1, 2026$500 $— 
Pool participation
(a)
15,763 
(a) 
166 
(b) 
$16,263 
(c) 
$166 
Property damage:
NEIL and EMANIApril 1, 2026$3,200 
(d)
$23 
(e) 
Accidental outage:
NEILApril 1, 2026$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.
v3.26.1
Retirement Benefits (Tables)
 3 Months Ended
Mar. 31, 2026
Retirement Benefits [Abstract]  
Components Of Net Periodic Benefit Cost
The following table presents the components of the net periodic benefit cost (income) incurred for Ameren’s pension and postretirement benefit plans for the three months ended March 31, 2026 and 2025:
Pension BenefitsPostretirement Benefits
Three MonthsThree Months
2026202520262025
Service cost(a)
$20 $21 $2 $2 
Non-service cost components:
Interest cost56 58 11 11 
Expected return on plan assets(b)
(66)(76)(23)(23)
Amortization of(b):
Prior service cost (credit)— — (1)(1)
Actuarial (gain) loss2 (10)(8)(9)
Total non-service cost components(c)
$(8)$(28)$(21)$(22)
Net periodic benefit cost (income)(d)
$12 $(7)$(19)$(20)
(a)Service cost, net of capitalization, is reflected in “Operating Expenses – Other operations and maintenance” on Ameren’s statement of income.
(b)Prior service cost (credit) is amortized on a straight-line basis over the average future service of active participants benefiting under a plan amendment. Net actuarial gains or losses subject to amortization are amortized over 10 years. Expected return on plan assets is based on a market-related value of assets that recognizes asset (gains) losses 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 months ended March 31, 2026 and 2025:
Pension BenefitsPostretirement Benefits
Three MonthsThree Months
2026202520262025
Ameren Missouri(a)
$5 $(4)$(6)$(7)
Ameren Illinois6 (2)(13)(13)
Other1 (1)— — 
Ameren(a)
$12 $(7)$(19)$(20)
(a)Does not include the impact of the tracker for the difference between the level of pension and postretirement benefit costs (income) incurred by Ameren Missouri under GAAP and the level of such costs included in customer rates.
v3.26.1
Income Taxes (Tables)
 3 Months Ended
Mar. 31, 2026
Income Tax Disclosure [Abstract]  
Schedule of Effective Income Tax Rate Reconciliation
The following table presents the principal reasons for the difference between the effective income tax expense and rate and the federal statutory corporate income tax expense and rate for the three months ended March 31, 2026 and 2025:
Three MonthsThree Months
20262025
AmountEffective Tax RateAmountEffective Tax Rate
Ameren
Federal statutory corporate income tax expense and rate$88 21 %$72 21 %
State and local taxes, net of federal income tax(a)
21 5 20 6 
Tax credits
Renewable energy tax credits(b)
(15)(4)(12)(4)
Other(3)(1)(2)(1)
Nontaxable or nondeductible items(1)— (1)— 
Other adjustments
Amortization of excess deferred income taxes(c)
(24)(6)(24)(7)
Depreciation differences(6)(1)(3)(1)
Effective income tax expense and rate$60 14 %$50 14 %
Ameren Missouri
Federal statutory corporate income tax expense and rate$17 21 %$10 21 %
State and local taxes, net of federal income tax(a)
2 3 2 4 
Tax credits
Renewable energy tax credits(b)
(5)(6)(3)(7)
Other(2)(2)(1)(1)
Other adjustments
Amortization of excess deferred income taxes(c)
(8)(11)(3)(8)
Depreciation differences(1)(2)(1)(1)
Effective income tax expense and rate$3 3 %$4 8 %
Ameren Illinois
Federal statutory corporate income tax expense and rate$73 21 %$66 21 %
State and local taxes, net of federal income tax(a)
26 7 24 7 
Other adjustments
Amortization of excess deferred income taxes(c)
(5)(1)(11)(3)
Depreciation differences(3)(1)(3)(1)
Effective income tax expense and rate$91 26 %$76 24 %
(a)State taxes in Missouri and Illinois made up the majority of the tax effect in this category for Ameren, Ameren Missouri, and Ameren Illinois.
(b)The benefit of the credits associated with Missouri renewable energy standard compliance is refunded to customers through the RESRAM. The benefit of the credits associated with the production and investment tax credit tracker will be refunded to customers based on MoPSC approval in a regulatory rate review.
(c)Reflects the amortization of a regulatory liability resulting from the revaluation of accumulated deferred income taxes subject to regulatory ratemaking, which are being refunded to customers.
v3.26.1
Supplemental Information (Tables)
 3 Months Ended
Mar. 31, 2026
Supplemental Information [Abstract]  
Schedule of Cash and Cash Equivalents Including Restricted Cash
The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows at March 31, 2026, and December 31, 2025:
March 31, 2026December 31, 2025
AmerenAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois
“Cash and cash equivalents”$13 $— $— $13 $6 $3 
Restricted cash included in “Other current assets”74 64 6 63 54 5 
Restricted cash included in “Other assets”392 — 392 336 — 336 
Restricted cash included in “Nuclear decommissioning trust fund”6 6 — 8 8 — 
Total cash, cash equivalents, and restricted cash$485 $70 $398 $420 $68 $344 
Schedule of Accounts, Notes, Loans and Financing Receivable
The following table provides a reconciliation of the beginning and ending amount of the allowance for doubtful accounts for the three months ended March 31, 2026 and 2025:
Three Months
20262025
Ameren:
Beginning of period$39 $30 
Bad debt expense10 16 
Charged to other accounts(a)
1 1 
Net write-offs(9)(6)
End of period$41 $41 
Ameren Missouri:
Beginning of period$17 $12 
Bad debt expense2 2 
Net write-offs(4)(2)
End of period$15 $12 
Ameren Illinois:(b)
Beginning of period$22 $18 
Bad debt expense8 14 
Charged to other accounts(a)
1 1 
Net write-offs(5)(4)
End of period$26 $29 
(a)Amounts associated with the allowance for doubtful accounts related to receivables purchased by Ameren Illinois from alternative retail electric suppliers, as required by the Illinois Public Utilities Act.
(b)Ameren Illinois has rate-adjustment mechanisms that allow it to recover the difference between its actual net bad debt write-offs under GAAP, including those associated with receivables purchased from alternative retail electric suppliers, and the amount of net bad debt write-offs included in its base rates. The table above does not include the impact related to the riders.
Schedule of Cash Flow, Supplemental Disclosures
The following table provides noncash financing and investing activity excluded from the statements of cash flows for the three months ended March 31, 2026 and 2025:
March 31, 2026March 31, 2025
AmerenAmeren
Missouri		Ameren
Illinois		AmerenAmeren
Missouri		Ameren
Illinois
Investing:
Accrued capital expenditures, including nuclear fuel expenditures$490 
(a)
$364 
(a)
$108 $381 $214 $159 
Net realized and unrealized loss – nuclear decommissioning trust fund(56)(56)— (40)(40)— 
Financing:
Issuance of common stock for stock-based compensation$25 $— $— $25 $— $— 
Issuance of common stock under the DRPlus7 — — 9 — — 
(a)Includes amounts associated with the February 2026 acquisition of the Split Rail Solar Project with payment contingent upon completion of the project.
Asset Retirement Obligation Disclosure
The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the three months ended March 31, 2026:
Ameren
Missouri		Ameren
Illinois		Ameren
Balance at December 31, 2025
$849 
(a) 
$5 
(b) 
$854 
(a) 
Liabilities incurred7 — 7 
Liabilities settled(1)(c)(1)
Accretion9 
(d) 
(c)9 
(d) 
Balance at March 31, 2026
$864 
(a) 
$5 
(b) 
$869 
(a) 
(a)Balance included $5 million in “Other current liabilities” on the balance sheet as of both March 31, 2026, and December 31, 2025.
(b)Included in “Other deferred credits and liabilities” on the balance sheet.
(c)Amount less than $1 million.
(d)Accretion expense attributable to Ameren Missouri was recorded as a decrease to regulatory liabilities.
Schedule of excise taxes The following table presents the excise taxes recorded on a gross basis in “Operating Revenues – Electric,” “Operating Revenues – Natural gas” and “Operating Expenses – Taxes other than income taxes” on the statements of income for the three months ended March 31, 2026 and 2025:
Three Months
20262025
Ameren Missouri$40 $38 
Ameren Illinois45 43 
Ameren$85 $81 
Schedule of Earnings Per Share, Basic and Diluted
The following table reconciles the basic weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the three months ended March 31, 2026 and 2025:
Three Months
20262025
Weighted-average Common Shares Outstanding – Basic276.5 270.0 
Assumed settlement of performance share units and restricted stock units1.0 1.0 
Dilutive effect of forward sale agreements0.9 0.4 
Weighted-average Common Shares Outstanding – Diluted(a)
278.4 271.4 
(a)There was an immaterial number of anti-dilutive performance share units excluded from the earnings per diluted share calculations for the three months ended March 31, 2026 and 2025. Outstanding forward sale agreements as of March 31, 2026 that were anti-dilutive for the three months ended March 31, 2026 were excluded from the earnings per diluted share calculation as calculated using the treasury stock method. There were no anti-dilutive shares related to the outstanding forward sale agreements as of March 31, 2025 excluded from earnings per diluted share calculations for the three months ended March 31, 2025. For additional information about the outstanding forward sale agreements, see Note 4 – Long-term Debt and Equity Financings.
v3.26.1
Segment Information (Tables)
 3 Months Ended
Mar. 31, 2026
Segment Reporting [Abstract]  
Schedule Of Segment Reporting Information By Segment
The following tables present revenues, net income attributable to common shareholders, and capital expenditures by segment at Ameren and Ameren Illinois for the three months ended March 31, 2026 and 2025. 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
Reportable Segments
Ameren MissouriAmeren Illinois Electric DistributionAmeren Illinois Natural GasAmeren TransmissionOtherIntersegment EliminationsAmeren
Three Months 2026:
External revenues$920 $643 $436 $177 $— $— $2,176 
Intersegment revenues10 — — 50 — (60)— 
Revenue930 643 436 227 — (60)2,176 
Fuel and purchased power(a)
(214)(266)— — — 47 (433)
Natural gas purchased for resale(a)
(34)— (137)— — — (171)
Other operations and maintenance expenses(a)
(264)(160)(57)(19)(4)13 (491)
Other segment items
Depreciation and amortization(214)(96)(34)(53)(1)— (398)
Taxes other than income taxes(95)(22)(29)(2)(3)— (151)
Other income (expense), net53 19 3 7 9 (1)90 
Interest charges(82)(28)(16)(30)(49)1 (204)
Income (taxes) benefit(3)(24)(44)(32)43 — (60)
Noncontrolling interests – preferred stock dividends(1)— — — — — (1)
Net income (loss) attributable to Ameren common shareholders$76 $66 $122 $98 $(5)$— $357 
Interest income$3 $6 $— $— $1 $(1)$9 
Capital expenditures1,091 196 72 204 1 10 1,574 
Three Months 2025:
External revenues$950 $570 $411 $166 $— $— $2,097 
Intersegment revenues7 2 — 44 — (53)— 
Revenue957 572 411 210 — (53)2,097 
Fuel and purchased power(a)
(330)(212)— — — 40 (502)
Natural gas purchased for resale(a)
(30)— (139)— — — (169)
Other operations and maintenance expenses(a)
(250)(166)(55)(19)(8)13 (485)
Other segment items
Depreciation and amortization(194)(91)(32)(48)(2)— (367)
Taxes other than income taxes(89)(21)(29)(1)(4)— (144)
Other income (expense), net43 23 5 7 8 (1)85 
Interest charges(60)(26)(15)(29)(46)1 (175)
Income (taxes) benefit(4)(16)(38)(31)39 — (50)
Noncontrolling interests – preferred stock dividends(1)— — — — — (1)
Net income (loss) attributable to Ameren common shareholders$42 $63 $108 $89 
(b)
$(13)$— $289 
Interest income$2 $8 $— $1 $1 $(1)$11 
Capital expenditures658 167 59 173 2 5 1,064 
(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
Reportable Segments
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionIntersegment EliminationsAmeren Illinois
Three Months 2026:
External revenues$643 $436 $120 $— $1,199 
Intersegment revenues— — 44 (44)— 
Revenue643 436 164 (44)1,199 
Purchased power(a)
(266)— — 44 (222)
Natural gas purchased for resale(a)
— (137)— — (137)
Other operations and maintenance expenses(a)
(160)(57)(15)— (232)
Other segment items
Depreciation and amortization(96)(34)(40)— (170)
Taxes other than income taxes(22)(29)(1)— (52)
Other income, net19 3 7 — 29 
Interest charges(28)(16)(24)— (68)
Income taxes(24)(44)(23)— (91)
Net income available to common shareholder$66 $122 $68 $— $256 
Interest income$6 $— $— $— $6 
Capital expenditures196 72 120 — 388 
Three Months 2025:
External revenues$572 $411 $117 $— $1,100 
Intersegment revenues— — 37 (37)— 
Revenue572 411 154 (37)1,100 
Purchased power(a)
(212)— — 37 (175)
Natural gas purchased for resale(a)
— (139)— — (139)
Other operations and maintenance expenses(a)
(166)(55)(15)— (236)
Other segment items
Depreciation and amortization(91)(32)(36)— (159)
Taxes other than income taxes(21)(29)(1)— (51)
Other income, net23 5 6 — 34 
Interest charges(26)(15)(21)— (62)
Income taxes(16)(38)(22)— (76)
Net income available to common shareholder$63 $108 $65 $— $236 
Interest income$8 $— $1 $— $9 
Capital expenditures167 59 137 — 363 
(a)Significant segment expense that is regularly provided to the CODMs. Intersegment expenses are included within the amounts shown.
Disaggregation of Revenue
The following tables present disaggregated revenues by segment at Ameren and Ameren Illinois for the three months ended March 31, 2026 and 2025. 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 2026:
Residential$399 $349 $— $— $— $748 
Commercial302 195 — — — 497 
Industrial72 55 — — — 127 
Other78 44 
(a)
— 227 (60)289 
Total electric revenues$851 $643 $— $227 $(60)$1,661 
Residential$48 $— $312 $— $— $360 
Commercial20 — 86 — — 106 
Industrial2 — 6 — — 8 
Other9 — 32 — — 41 
Total natural gas revenues$79 $— $436 $— $— $515 
Total revenues(b)
$930 $643 $436 $227 $(60)$2,176 
Three Months 2025:
Residential$376 $342 $— $— $— $718 
Commercial273 180 — — — 453 
Industrial66 50 — — — 116 
Other178 — 
(a)
— 210 (53)335 
Total electric revenues$893 $572 $— $210 $(53)$1,622 
Residential$43 $— $309 $— $— $352 
Commercial19 — 77 — — 96 
Industrial2 — 4 — — 6 
Other— — 21 — — 21 
Total natural gas revenues$64 $— $411 $— $— $475 
Total revenues(b)
$957 $572 $411 $210 $(53)$2,097 
(a)Includes over-recoveries of various riders.
(b)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the three months ended March 31, 2026 and 2025:
Ameren MissouriAmeren Illinois Electric DistributionAmeren Illinois Natural GasAmeren TransmissionAmeren
Three Months 2026:
Revenues from alternative revenue programs$(3)$46 $17 $(4)$56 
Other revenues not from contracts with customers2 3 1 — 6 
Three Months 2025:
Revenues from alternative revenue programs$(5)$21 $3 $(1)$18 
Other revenues not from contracts with customers1 3 1 — 5 
Ameren Illinois
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionIntersegment EliminationsAmeren Illinois
Three Months 2026:
Residential$349 $312 $— $— $661 
Commercial195 86 — — 281 
Industrial55 6 — — 61 
Other44 
(a)
32 164 (44)196 
Total revenues(b)
$643 $436 $164 $(44)$1,199 
Three Months 2025:
Residential$342 $309 $— $— $651 
Commercial180 77 — — 257 
Industrial50 4 — — 54 
Other— 
(a)
21 154 (37)138 
Total revenues(b)
$572 $411 $154 $(37)$1,100 
(a)Includes over-recoveries of various riders.
(b)The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the Ameren Illinois segments for the three months ended March 31, 2026 and 2025:
Ameren Illinois Electric DistributionAmeren Illinois Natural GasAmeren Illinois TransmissionAmeren Illinois
Three Months 2026:
Revenues from alternative revenue programs$46 $17 $(3)$60 
Other revenues not from contracts with customers3 1 — 4 
Three Months 2025:
Revenues from alternative revenue programs$21 $3 $(1)$23 
Other revenues not from contracts with customers3 1 — 4 
v3.26.1
Summary of Significant Accounting Policies (Narrative) (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Unconsolidated variable interest $ 65 $ 64
Cash Surrender Value of Life Insurance 219 219
Corporate owned life insurance, borrowings 117 117
Ameren Illinois Company    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Cash Surrender Value of Life Insurance 127 126
Corporate owned life insurance, borrowings 117 $ 117
Partnership Funding Commitment    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Outstanding funding commitments $ 27  
v3.26.1
Summary Of Significant Accounting Policies - Schedule of Other Assets and Other Liabilities (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Accounting Policies [Line Items]    
Unbilled revenue $ 298 $ 415
Other current assets 211 210
Regulatory Asset 2,674 2,524
Current maturities of long-term debt 1,123 973
Interest accrued 179 229
Long-term debt, net 19,003 18,214
Variable Interest Entity, Primary Beneficiary    
Accounting Policies [Line Items]    
Regulatory Asset 437 443
Current maturities of long-term debt 23 23
Long-term debt, net 426 426
Ameren Missouri Securitization Funding I, LLC | Variable Interest Entity, Primary Beneficiary    
Accounting Policies [Line Items]    
Unbilled revenue 1 2
Other current assets 31 21
Regulatory Asset 437 443
Current maturities of long-term debt 23 23
Interest accrued 11 6
Current regulatory liabilities 9 11
Long-term debt, net $ 426 $ 426
v3.26.1
Rate And Regulatory Matters (Narrative-Missouri) (Details)
$ in Millions
 3 Months Ended
Mar. 31, 2026
USD ($)
Sep. 30, 2025
MWh
Jun. 30, 2025
MWh
Mar. 31, 2025
USD ($)
Sep. 30, 2024
MWh
Dec. 31, 2023
MWh
Rate And Regulatory Matters [Line Items]            
Capital expenditures $ 1,574     $ 1,064    
Union Electric Company            
Rate And Regulatory Matters [Line Items]            
Capital expenditures 1,091     $ 658    
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 100          
Union Electric Company | Split Rail Solar Project            
Rate And Regulatory Matters [Line Items]            
Capital expenditures 600          
Union Electric Company | Big Hollow Energy Center            
Rate And Regulatory Matters [Line Items]            
Capital expenditures $ 2,000          
Union Electric Company | Self-build | Solar generation facility            
Rate And Regulatory Matters [Line Items]            
Amount of Megawatts | MWh   250       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
v3.26.1
Rate And Regulatory Matters (Narrative-Illinois) (Details) - USD ($)
$ in Millions
 1 Months Ended 3 Months Ended 12 Months Ended
Jan. 31, 2026
Nov. 30, 2025
Oct. 31, 2023
Jun. 30, 2026
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2028
Dec. 31, 2027
Dec. 31, 2026
Dec. 31, 2025
Rate And Regulatory Matters [Line Items]                    
Capital expenditures         $ 1,574 $ 1,064        
Ameren Illinois Company                    
Rate And Regulatory Matters [Line Items]                    
Capital expenditures         388 $ 363        
IETL | Ameren Illinois Company | 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 | Ameren Illinois Company | 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 | Ameren Illinois Company | Electric Distribution                    
Rate And Regulatory Matters [Line Items]                    
Public Utilities, Requested Rate Increase (Decrease), Amount         48          
Approved rate base         $ 4,200          
Public Utilities, Requested Equity Capital Structure, Percentage         50.00%          
Pending Rate Case | Ameren Illinois Company | Electric Distribution | Subsequent Event                    
Rate And Regulatory Matters [Line Items]                    
Public Utilities, Requested Rate Increase (Decrease), Amount       $ 65            
Public Utilities, Requested Equity Capital Structure, Percentage       50.00%            
Pending Rate Case | Ameren Illinois Company | Natural gas                    
Rate And Regulatory Matters [Line Items]                    
Capital expenditures $ 75   $ 30              
Eligible QIP investments     $ 529              
Final Rate Order | Ameren Illinois Company | Natural gas                    
Rate And Regulatory Matters [Line Items]                    
Public Utilities, Requested Rate Increase (Decrease), Amount   $ 79                
Approved rate base   $ 3,200                
Approved return on equity percentage   9.60%                
Public Utilities, Approved Equity Capital Structure, Percentage   50.00%                
Capital expenditures   $ 75                
v3.26.1
Rate And Regulatory Matters (Narrative-Federal) (Details)
 1 Months Ended
Oct. 31, 2024
May 31, 2020
Midwest Independent Transmission System Operator, Inc | Final Rate Order    
Rate And Regulatory Matters [Line Items]    
Approved return on equity percentage 9.98% 10.02%
v3.26.1
Short-Term Debt And Liquidity (Narrative) (Details)
$ in Millions
 3 Months Ended
Mar. 31, 2026
USD ($)
Mar. 31, 2025
Credit Agreements    
Short-term Debt [Line Items]    
Net Liquidity Available $ 2,000  
Actual debt-to-capital ratio 0.61  
Letter of Credit    
Short-term Debt [Line Items]    
Debt Instrument, Unused Borrowing Capacity, Amount $ 75  
Utilities    
Short-term Debt [Line Items]    
Short-term Debt, Weighted Average Interest Rate, over Time 3.84% 4.52%
Union Electric Company | Missouri Credit Agreement    
Short-term Debt [Line Items]    
Actual debt-to-capital ratio 0.50  
Union Electric Company | Letter of Credit    
Short-term Debt [Line Items]    
Debt Instrument, Unused Borrowing Capacity, Amount $ 68  
Ameren Illinois Company | Illinois Credit Agreement    
Short-term Debt [Line Items]    
Actual debt-to-capital ratio 0.45  
v3.26.1
Short-Term Debt and Liquidity (Short-Term Debt outstanding) (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Short-term Debt [Line Items]    
Short-term debt $ 1,178 $ 643
Union Electric Company    
Short-term Debt [Line Items]    
Short-term debt 280 471
Ameren Illinois Company    
Short-term Debt [Line Items]    
Short-term debt 75 17
Commercial Paper    
Short-term Debt [Line Items]    
Short-term debt 1,178 643
Commercial Paper | Union Electric Company    
Short-term Debt [Line Items]    
Short-term debt 280 471
Commercial Paper | Ameren Illinois Company    
Short-term Debt [Line Items]    
Short-term debt 75 17
Commercial Paper | Ameren (parent)    
Short-term Debt [Line Items]    
Short-term debt $ 823 $ 155
v3.26.1
Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Short-term Debt [Line Items]    
Average daily amount outstanding $ 1,030 $ 1,293
Weighted-average interest rate 3.84% 4.60%
Short-term Debt, Maximum Amount Outstanding During Period $ 1,996 $ 1,603
Peak interest rate 4.05% 4.75%
Union Electric Company    
Short-term Debt [Line Items]    
Average daily amount outstanding $ 530 $ 313
Weighted-average interest rate 3.83% 4.59%
Short-term Debt, Maximum Amount Outstanding During Period $ 1,360 $ 630
Peak interest rate 4.05% 4.70%
Ameren Illinois Company    
Short-term Debt [Line Items]    
Average daily amount outstanding $ 36 $ 82
Weighted-average interest rate 3.82% 4.56%
Short-term Debt, Maximum Amount Outstanding During Period $ 122 $ 189
Peak interest rate 4.00% 4.69%
Ameren (parent)    
Short-term Debt [Line Items]    
Average daily amount outstanding $ 464 $ 898
Weighted-average interest rate 3.86% 4.61%
Short-term Debt, Maximum Amount Outstanding During Period $ 992 $ 1,139
Peak interest rate 4.00% 4.75%
v3.26.1
Long-Term debt and Equity Financings (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Millions
 1 Months Ended 3 Months Ended 12 Months Ended
Apr. 30, 2026
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Feb. 28, 2026
Feb. 01, 2026
Long-Term Debt And Equity Financings [Line Items]            
Shares issued under the DRPlus and 401(k) plan   100 100      
Issuances of common stock   $ 12.0 $ 13.0      
Stock Issued During Period, Shares, Other (in shares)   200 300 200    
Stock Issued During Period, Value, Other   $ 25.0        
Maximum Value Of Shares To Be Issued Under ATM Program   $ 1,000.0        
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Number of Shares Indexed   3,900        
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share   $ 91.89        
Forward Contract Indexed to Issuer's Equity, Indexed Shares   6,400        
Subsequent Event            
Long-Term Debt And Equity Financings [Line Items]            
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Number of Shares Indexed 1,400          
Dividend reinvestment and 401 (k) plans            
Long-Term Debt And Equity Financings [Line Items]            
Issuances of common stock   $ 5.0        
Accrued Proceeds from Issuance of Common Stock   7.0        
Union Electric Company            
Long-Term Debt And Equity Financings [Line Items]            
Capital contributions from parent   $ 350.0 $ 0.0      
First Mortgage Bonds 5.00% Due 2036 | Secured Debt | Union Electric Company            
Long-Term Debt And Equity Financings [Line Items]            
Debt Instrument, Face Amount         $ 400.0  
Debt Instrument, Interest Rate, Stated Percentage         5.00%  
Senior Unsecured Notes 3.65% Due 2026 | Secured Debt | Union Electric Company            
Long-Term Debt And Equity Financings [Line Items]            
Debt Instrument, Face Amount         $ 350.0  
Debt Instrument, Interest Rate, Stated Percentage           3.65%
First Mortgage Bonds 4.80% Due 2036 | Secured Debt | Union Electric Company            
Long-Term Debt And Equity Financings [Line Items]            
Debt Instrument, Face Amount         $ 450.0  
Debt Instrument, Interest Rate, Stated Percentage         4.80%  
First Mortgage Bonds 5.55% Due 2056 | Secured Debt | Union Electric Company            
Long-Term Debt And Equity Financings [Line Items]            
Debt Instrument, Face Amount         $ 450.0  
Debt Instrument, Interest Rate, Stated Percentage         5.55%  
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   10,300        
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value   $ 1,000.0        
Period End Net Cash Settlement Price   116.0        
Period End Net Share Settlement Price   $ 1.1        
Forward Sale Agreement Equity Offering Shares   10,300        
Forward Sale Agreement Gross Sales Price   $ 1,000.0        
Minimum            
Long-Term Debt And Equity Financings [Line Items]            
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share   $ 109.22        
Maximum            
Long-Term Debt And Equity Financings [Line Items]            
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share   111.31        
Weighted Average            
Long-Term Debt And Equity Financings [Line Items]            
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share   $ 110.22        
Weighted Average | Subsequent Event            
Long-Term Debt And Equity Financings [Line Items]            
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share $ 110.47          
v3.26.1
Other Income, Net (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Other Nonoperating Income (Expense) [Line Items]    
Allowance for equity funds used during construction $ 31 $ 16
Other interest income 9 11
Non-service cost components of net periodic benefit income 49 66
Miscellaneous income 5 3
Income (Loss) from Equity Method Investments 2 (4)
Donations (2) (2)
Miscellaneous expense (4) (5)
Total Other Income, Net 90 85
Union Electric Company    
Other Nonoperating Income (Expense) [Line Items]    
Allowance for equity funds used during construction 23 8
Other interest income 3 2
Non-service cost components of net periodic benefit income 30 35
Miscellaneous income 0 1
Donations (1) (1)
Miscellaneous expense (2) (2)
Total Other Income, Net 53 43
Defined Benefit Plan, Non-service Cost or Income Components - Tracker (20) (16)
Ameren Illinois Company    
Other Nonoperating Income (Expense) [Line Items]    
Allowance for equity funds used during construction 7 7
Other interest income 6 9
Non-service cost components of net periodic benefit income 15 20
Miscellaneous income 4 2
Donations (1) (1)
Miscellaneous expense (2) (3)
Total Other Income, Net $ 29 $ 34
v3.26.1
Derivative Financial Instruments (Narrative) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Derivative [Line Items]      
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax $ (2) $ (4)  
Derivative, Net Liability Position, Aggregate Fair Value 67    
Current collateral assets 0    
Additional Collateral, Aggregate Fair Value 59    
Union Electric Company      
Derivative [Line Items]      
Derivative, Net Liability Position, Aggregate Fair Value 17    
Current collateral assets 0    
Additional Collateral, Aggregate Fair Value 9    
Ameren Illinois Company      
Derivative [Line Items]      
Derivative, Net Liability Position, Aggregate Fair Value 50    
Current collateral assets 0    
Additional Collateral, Aggregate Fair Value 50    
Interest Rate Swap      
Derivative [Line Items]      
Derivative, Notional Amount 740   $ 820
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax $ 2 $ 4  
v3.26.1
Derivative Financial Instruments (Open Gross Derivative Volumes By Commodity Type) (Detail)
gal in Millions, MWh in Millions, MMBTU in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2026
MWh
MMBTU
gal
Dec. 31, 2025
MWh
MMBTU
gal
Fuel oils    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Volume | gal 22 25
Natural gas    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU 285 263
Power    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh 11 7
Union Electric Company | Fuel oils    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Volume | gal 22 25
Union Electric Company | Natural gas    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU 56 46
Union Electric Company | Power    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh 4 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 229 217
Ameren Illinois Company | Power    
Derivative [Line Items]    
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh 7 7
v3.26.1
Derivative Financial Instruments (Derivative Instruments Carrying Value) (Detail) - Not Designated As Hedging Instrument - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Derivative [Line Items]    
Derivative Assets $ 19 $ 16
Derivative Liability 144 126
Natural gas | Other current assets    
Derivative [Line Items]    
Derivative Assets 0 2
Natural gas | Other assets    
Derivative [Line Items]    
Derivative Assets 1 3
Natural gas | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 40 26
Natural gas | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 27 16
Fuel oils | Other current assets    
Derivative [Line Items]    
Derivative Assets 9 0
Fuel oils | Other assets    
Derivative [Line Items]    
Derivative Assets 3 0
Fuel oils | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 0 3
Fuel oils | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 0 2
Power | Other current assets    
Derivative [Line Items]    
Derivative Assets 3 11
Power | Other assets    
Derivative [Line Items]    
Derivative Assets 3 0
Power | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 28 24
Power | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 49 55
Union Electric Company    
Derivative [Line Items]    
Derivative Assets 18 12
Derivative Liability 18 15
Union Electric Company | Natural gas | Other current assets    
Derivative [Line Items]    
Derivative Assets 0 1
Union Electric Company | Natural gas | Other assets    
Derivative [Line Items]    
Derivative Assets 0 0
Union Electric Company | Natural gas | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 9 5
Union Electric Company | Natural gas | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 8 5
Union Electric Company | Fuel oils | Other current assets    
Derivative [Line Items]    
Derivative Assets 9 0
Union Electric Company | Fuel oils | Other assets    
Derivative [Line Items]    
Derivative Assets 3 0
Union Electric Company | Fuel oils | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 0 3
Union Electric Company | Fuel oils | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 0 2
Union Electric Company | Power | Other current assets    
Derivative [Line Items]    
Derivative Assets 3 11
Union Electric Company | Power | Other assets    
Derivative [Line Items]    
Derivative Assets 3 0
Union Electric Company | Power | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 0 0
Union Electric Company | Power | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 1 0
Ameren Illinois Company    
Derivative [Line Items]    
Derivative Assets 1 4
Derivative Liability 126 111
Ameren Illinois Company | Natural gas | Other current assets    
Derivative [Line Items]    
Derivative Assets 0 1
Ameren Illinois Company | Natural gas | Other assets    
Derivative [Line Items]    
Derivative Assets 1 3
Ameren Illinois Company | Natural gas | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 0 0
Ameren Illinois Company | Natural gas | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 19 11
Ameren Illinois Company | Natural gas | Mark-to-Market Derivative Liabilities    
Derivative [Line Items]    
Derivative Liability 31 21
Ameren Illinois Company | Fuel oils | Other current assets    
Derivative [Line Items]    
Derivative Assets 0 0
Ameren Illinois Company | Fuel oils | Other assets    
Derivative [Line Items]    
Derivative Assets 0 0
Ameren Illinois Company | 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 assets    
Derivative [Line Items]    
Derivative Assets 0 0
Ameren Illinois Company | Power | Other current liabilities    
Derivative [Line Items]    
Derivative Liability 0 0
Ameren Illinois Company | Power | Other deferred credits and liabilities    
Derivative [Line Items]    
Derivative Liability 48 55
Ameren Illinois Company | Power | Mark-to-Market Derivative Liabilities    
Derivative [Line Items]    
Derivative Liability $ 28 $ 24
v3.26.1
Fair Value Measurements (Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: $ 1,470 $ 1,514
Assets fair value 1,489 1,530
Excluded receivables, payables, and accrued income, net 8 12
Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 981 1,028
Assets fair value 993 1,028
Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 489 486
Assets fair value 492 489
Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 0 0
Assets fair value 4 13
Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 19 16
Derivative Liability 144 126
Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 12 0
Derivative Liability 1 6
Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 3 3
Derivative Liability 80 51
Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 4 13
Derivative Liability 63 69
Union Electric Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 1,470 1,514
Assets fair value 1,488 1,526
Union Electric Company | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 981 1,028
Assets fair value 993 1,028
Union Electric Company | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 489 486
Assets fair value 492 487
Union Electric Company | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 0 0
Assets fair value 3 11
Union Electric Company | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 18 12
Derivative Liability 18 15
Union Electric Company | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 12 0
Derivative Liability 0 5
Union Electric Company | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 3 1
Derivative Liability 17 10
Union Electric Company | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 3 11
Derivative Liability 1 0
Union Electric Company | Fuel oils | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 12 0
Derivative Liability 0 5
Union Electric Company | Fuel oils | Commodity Contract | Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 12 0
Derivative Liability 0 5
Union Electric Company | Fuel oils | Commodity Contract | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 0 0
Derivative Liability 0 0
Union Electric Company | Fuel oils | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 0 0
Derivative Liability 0 0
Union Electric Company | Natural gas | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 0 1
Derivative Liability 17 10
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 0 1
Derivative Liability 16 10
Union Electric Company | Natural gas | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 0 0
Derivative Liability 1 0
Union Electric Company | Power | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 6 11
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 3 0
Derivative Liability 1 0
Union Electric Company | Power | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 3 11
Derivative Liability 0 0
Union Electric Company | Equity securities: | U.S. large capitalization    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Nuclear decommissioning trust fund: 981 1,028
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: 981 1,028
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: 218 225
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: 218 225
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: 184 177
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: 184 177
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: 87 84
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: 87 84
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 1 4
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 0 2
Ameren Illinois Company | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Assets fair value 1 2
Ameren Illinois Company | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 126 111
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 63 41
Ameren Illinois Company | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 62 69
Ameren Illinois Company | Natural gas | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 1 4
Derivative Liability 50 32
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 0 2
Derivative Liability 43 28
Ameren Illinois Company | Natural gas | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Assets 1 2
Derivative Liability 6 3
Ameren Illinois Company | Power | Commodity Contract    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability 76 79
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 20 13
Ameren Illinois Company | Power | Commodity Contract | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative Liability $ 56 $ 66
v3.26.1
Fair Value Measurements (Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level Three In The Fair Value Hierarchy) (Details) - Power - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance $ (55) $ (47)
Included in regulatory assets/liabilities 5 (14)
Settlement, liabilities (3) 1
Change in unrealized gains (losses) related to assets/liabilities held at period end 5 (14)
Ending balance (53) (62)
Union Electric Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 11 6
Included in regulatory assets/liabilities (3) 2
Settlement, liabilities (5) (3)
Change in unrealized gains (losses) related to assets/liabilities held at period end (2) 2
Ending balance 3 5
Ameren Illinois Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance (66) (53)
Included in regulatory assets/liabilities 8 (16)
Settlements, assets 2 2
Change in unrealized gains (losses) related to assets/liabilities held at period end 7 (16)
Ending balance $ (56) $ (67)
v3.26.1
Fair Value Measurements (Schedule Of Valuation Process And Unobservable Inputs) (Details) - Power
$ in Millions
Mar. 31, 2026
USD ($)
$ / MWh
Dec. 31, 2025
USD ($)
$ / MWh
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative Assets | $ $ 3 $ 11
Derivative liabilities | $ $ (56) $ (66)
Commodity Forward Price | Discounted cash flow | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Measurement input 32 33
Commodity Forward Price | Discounted cash flow | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Measurement input 71 72
Commodity Forward Price | Discounted cash flow | Weighted Average    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Measurement input 44 43
Nodal Basis | Discounted cash flow | Minimum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Measurement input (11) (9)
Nodal Basis | Discounted cash flow | Maximum    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Measurement input (1) (2)
Nodal Basis | Discounted cash flow | Weighted Average    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Measurement input (5) (5)
v3.26.1
Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Financial Assets and Liabilities) (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Carrying Amount(a)    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-Term Debt, Carrying Amount $ 20,126 $ 19,187
Debt Issuance Costs, Net 145 136
Carrying Amount(a) | Union Electric Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-Term Debt, Carrying Amount 9,121 8,230
Debt Issuance Costs, Net 69 62
Carrying Amount(a) | Ameren Illinois Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-Term Debt, Carrying Amount 6,260 6,259
Debt Issuance Costs, Net 55 56
Fair Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 18,533 17,992
Fair Value | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 17,986 17,433
Fair Value | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 547 559
Fair Value | Union Electric Company    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 8,314 7,608
Fair Value | Union Electric Company | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 8,314 7,608
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 5,603 5,753
Fair Value | Ameren Illinois Company | Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value 5,603 5,753
Fair Value | Ameren Illinois Company | Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt, Fair Value $ 0 $ 0
v3.26.1
Related Party Transactions (Narrative) (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Related Party Transaction [Line Items]    
Other assets $ 1,254 $ 1,154
Union Electric Company    
Related Party Transaction [Line Items]    
Other assets 273 244
Ameren Illinois Company    
Related Party Transaction [Line Items]    
Other assets 859 789
Ameren Services Support Services Agreement | Union Electric Company | Related Party    
Related Party Transaction [Line Items]    
Other assets 35 36
Ameren Services Support Services Agreement | Ameren Illinois Company | Related Party    
Related Party Transaction [Line Items]    
Other assets $ 37 $ 38
v3.26.1
Related Party Transactions (Schedule of Affiliate Receivables and Payables) (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Related Party Transaction [Line Items]    
Accounts Payable, Related Parties, Current $ 733 $ 1,254
Accounts Receivable, Related Parties, Current 703 665
Union Electric Company | Related Party    
Related Party Transaction [Line Items]    
Accounts Payable, Related Parties, Current 57 61
Accounts Receivable, Related Parties, Current 63 15
Union Electric Company | Income taxes payable to parent | Related Party    
Related Party Transaction [Line Items]    
Accounts Payable, Related Parties, Current 0 0
Union Electric Company | Income taxes receivable from parent | Related Party    
Related Party Transaction [Line Items]    
Accounts Receivable, Related Parties, Current 38 3
Ameren Illinois Company | Related Party    
Related Party Transaction [Line Items]    
Accounts Payable, Related Parties, Current 107 57
Accounts Receivable, Related Parties, Current 21 18
Ameren Illinois Company | Income taxes payable to parent | Related Party    
Related Party Transaction [Line Items]    
Accounts Payable, Related Parties, Current 54 4
Ameren Illinois Company | Income taxes receivable from parent | Related Party    
Related Party Transaction [Line Items]    
Accounts Receivable, Related Parties, Current $ 0 $ 7
v3.26.1
Related Party Transactions (Effects of Related-party Transactions on the Statement of Income) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Related Party Transaction [Line Items]    
Operating Revenues $ 2,176 $ 2,097
Other operations and maintenance 491 485
Interest Charges 204 175
Union Electric Company    
Related Party Transaction [Line Items]    
Operating Revenues 930 957
Other operations and maintenance 264 250
Interest Charges 82 60
Union Electric Company | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party    
Related Party Transaction [Line Items]    
Operating Revenues 10 7
Other operations and maintenance 1 1
Union Electric Company | Total Related Party Operating Revenues | Related Party    
Related Party Transaction [Line Items]    
Operating Revenues 10 7
Union Electric Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI | Related Party    
Related Party Transaction [Line Items]    
Purchased Power 2 3
Union Electric Company | Ameren Services Support Services Agreement | Related Party    
Related Party Transaction [Line Items]    
Other operations and maintenance 48 44
Union Electric Company | Total Related Party Other Operations and Maintenance | Related Party    
Related Party Transaction [Line Items]    
Other operations and maintenance 48 44
Union Electric Company | Money pool interest (advances) | Related Party    
Related Party Transaction [Line Items]    
Interest Charges 1 1
Union Electric Company | Long-Term Debt | Related Party    
Related Party Transaction [Line Items]    
Interest Charges 1 1
Union Electric Company | Purchased Power | Related Party    
Related Party Transaction [Line Items]    
Purchased Power 2 3
Union Electric Company | Ameren Missouri and Ameren Illinois miscellaneous support services and services provided to ATXI | Related Party    
Related Party Transaction [Line Items]    
Operating Revenues 1 1
Union Electric Company | Ameren Missouri Interconnection Agreement With Ameren Illinois | Related Party    
Related Party Transaction [Line Items]    
Purchased Power 1 1
Ameren Illinois Company    
Related Party Transaction [Line Items]    
Operating Revenues 1,199 1,100
Purchased Power 222 175
Other operations and maintenance 232 236
Interest Charges 68 62
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party    
Related Party Transaction [Line Items]    
Operating Revenues 1 1
Other operations and maintenance 1 1
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Miscellaneous Support Services | Related Party    
Related Party Transaction [Line Items]    
Operating Revenues   2
Ameren Illinois Company | Total Related Party Operating Revenues | Related Party    
Related Party Transaction [Line Items]    
Operating Revenues 1 2
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI | Related Party    
Related Party Transaction [Line Items]    
Purchased Power 1  
Ameren Illinois Company | Ameren Services Support Services Agreement | Related Party    
Related Party Transaction [Line Items]    
Other operations and maintenance 44 40
Ameren Illinois Company | Total Related Party Other Operations and Maintenance | Related Party    
Related Party Transaction [Line Items]    
Other operations and maintenance 44 41
Ameren Illinois Company | Money pool interest (advances) | Related Party    
Related Party Transaction [Line Items]    
Interest Charges 1 1
Ameren Illinois Company | Long-Term Debt | Related Party    
Related Party Transaction [Line Items]    
Interest Charges 1 1
Ameren Illinois Company | Purchased Power | Related Party    
Related Party Transaction [Line Items]    
Purchased Power 1 1
Ameren Illinois Company | Ameren Illinois Interconnection Agreement With Ameren Missouri | Related Party    
Related Party Transaction [Line Items]    
Operating Revenues 1 $ 1
Ameren Illinois Company | Ameren Missouri and Ameren Illinois miscellaneous support services and services provided to ATXI | Related Party    
Related Party Transaction [Line Items]    
Operating Revenues $ 1  
v3.26.1
Commitments And Contingencies (Environmental Matters) (Detail)
$ in Millions
Mar. 31, 2026
USD ($)
scrubber
site
Dec. 31, 2025
USD ($)
Loss Contingencies [Line Items]    
Asset Retirement Obligation $ 869 $ 854
Minimum    
Loss Contingencies [Line Items]    
Estimated capital costs to comply with existing and known federal and state air emissions regulations 70  
Maximum    
Loss Contingencies [Line Items]    
Estimated capital costs to comply with existing and known federal and state air emissions regulations $ 100  
Union Electric Company    
Loss Contingencies [Line Items]    
Number of Energy Center Scrubbers | scrubber 2  
Asset Retirement Obligation $ 864 849
Union Electric Company | Minimum    
Loss Contingencies [Line Items]    
Estimated capital costs to comply with existing and known federal and state air emissions regulations 70  
Union Electric Company | Maximum    
Loss Contingencies [Line Items]    
Estimated capital costs to comply with existing and known federal and state air emissions regulations 100  
Ameren Illinois Company    
Loss Contingencies [Line Items]    
Asset Retirement Obligation $ 5 $ 5
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 56  
New CCR Rules Estimate | Union Electric Company    
Loss Contingencies [Line Items]    
Asset Retirement Obligation $ 56  
v3.26.1
Callaway Energy Center (Insurance Disclosure) (Details)
$ in Millions
 3 Months Ended
Mar. 31, 2026
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]  
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
Insurance Maximum Coverage per Incident 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
Insurance Maximum Coverage per Incident 166.0
Threshold Amount For Retrospective Insurance Assessment For Covered Loss Under Public Liability And Nuclear Worker Liability Insurance Policy 500.0
Maximum Annual Payment Per Incident At Licensed Commercial Nuclear Reactor 25.0
Public Liability | Union Electric Company  
Nuclear Waste Matters [Line Items]  
Insurance Aggregate Maximum Coverage 16,263.0
Insurance Maximum Coverage per Incident 166.0
Property Damage - Nuclear Electric Insurance Ltd | Union Electric Company  
Nuclear Waste Matters [Line Items]  
Insurance Aggregate Maximum Coverage 3,200.0
Insurance Maximum Coverage per Incident 23.0
Accidental Outage - Nuclear Electric Insurance Ltd | Union Electric Company  
Nuclear Waste Matters [Line Items]  
Insurance Aggregate Maximum Coverage 490.0
Insurance Maximum Coverage per Incident 9.0
Amount Of Weekly Indemnity Coverage Commencing Twelve Weeks After Power Outage 4.5
Amount Of Additional Weekly Indemnity Coverage Commencing After Initial Indemnity Coverage 3.6
Amount Of Weekly Indemnity Coverage Thereafter Not Exceeding Policy Limit 490.0
Sub-Limit Of Amount Of Weekly Indemnity Coverage Thereafter Not Exceeding Policy Limit For Non-Nuclear Events 291.0
Radiation Event | Union Electric Company  
Nuclear Waste Matters [Line Items]  
Insurance Aggregate Maximum Coverage 2,700.0
Aggregate Nuclear Power Industry Insurance Policy Limit For Losses From Terrorist Attacks Within Twelve Month Period 3,200.0
Non-Radiation Event  
Nuclear Waste Matters [Line Items]  
Insurance Aggregate Maximum Coverage 700.0
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
v3.26.1
Retirement Benefits (Components Of Net Periodic Benefit Cost) (Detail) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Total non-service cost components $ (49) $ (66)
Pension Plan    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Service Cost 20 21
Interest cost 56 58
Defined Benefit Plan, Expected Return (Loss) on Plan Assets (66) (76)
Prior service cost (credit) 0 0
Actuarial (gain) loss 2 (10)
Total non-service cost components (8) (28)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total $ 12 (7)
Defined Benefit Plan, Amortization Period of Actuarial Gain (Loss) 10 years  
Defined Benefit Plan, Difference Between Actual and Expected Return (Loss) on Plan Assets Amortization Period 4 years  
Other Postretirement Benefit Plan, Defined Benefit    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Service Cost $ 2 2
Interest cost 11 11
Defined Benefit Plan, Expected Return (Loss) on Plan Assets (23) (23)
Prior service cost (credit) (1) (1)
Actuarial (gain) loss (8) (9)
Total non-service cost components (21) (22)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total $ (19) $ (20)
Defined Benefit Plan, Amortization Period of Actuarial Gain (Loss) 10 years  
Defined Benefit Plan, Difference Between Actual and Expected Return (Loss) on Plan Assets Amortization Period 4 years  
v3.26.1
Retirement Benefits (Summary of Benefit Plan Costs Incurred) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Pension Plan    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Net periodic benefit cost $ 12 $ (7)
Pension Plan | Union Electric Company    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Net periodic benefit cost 5 (4)
Pension Plan | Ameren Illinois Company    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Net periodic benefit cost 6 (2)
Pension Plan | Other Affiliated Entities And Intercompany Eliminations    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Net periodic benefit cost 1 (1)
Other Postretirement Benefit Plan, Defined Benefit    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Net periodic benefit cost (19) (20)
Other Postretirement Benefit Plan, Defined Benefit | Union Electric Company    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Net periodic benefit cost (6) (7)
Other Postretirement Benefit Plan, Defined Benefit | Ameren Illinois Company    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Net periodic benefit cost (13) (13)
Other Postretirement Benefit Plan, Defined Benefit | Other Affiliated Entities And Intercompany Eliminations    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Net periodic benefit cost $ 0 $ 0
v3.26.1
Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Effective Income Tax Rate Reconciliation, Percent [Abstract]    
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount $ 88 $ 72
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount 21 20
Effective Income Tax Rate Reconciliation, Tax Credit, Energy-Related, Amount 15 12
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount (3) (2)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amount (1) (1)
Effective Income Tax Rate Reconciliation, Other Adjustments, Amortization Of Excess Deferred Income Taxes. Amount (24) (24)
Effective Income Tax Rate Reconciliation, Other Adjustments, Depreciation Differences. Amount (6) (3)
Income Tax Expense (Benefit), Total $ 60 $ 50
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent 21.00% 21.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent 5.00% 6.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Energy-Related, Percent (4.00%) (4.00%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent (1.00%) (1.00%)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent 0.00% 0.00%
Effective Income Tax Rate Reconciliation, Other Adjustments, Amortization Of Excess Deferred Income Taxes. Percent (0.06) (0.07)
Effective Income Tax Rate Reconciliation, Other Adjustments, Depreciation Differences. Percent (0.01) (0.01)
Effective Income Tax Rate Reconciliation, Percent, Total 14.00% 14.00%
Union Electric Company    
Effective Income Tax Rate Reconciliation, Percent [Abstract]    
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount $ 17 $ 10
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount 2 2
Effective Income Tax Rate Reconciliation, Tax Credit, Energy-Related, Amount 5 3
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount (2) (1)
Effective Income Tax Rate Reconciliation, Other Adjustments, Amortization Of Excess Deferred Income Taxes. Amount (8) (3)
Effective Income Tax Rate Reconciliation, Other Adjustments, Depreciation Differences. Amount (1) (1)
Income Tax Expense (Benefit), Total $ 3 $ 4
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent 21.00% 21.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent 3.00% 4.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Energy-Related, Percent (6.00%) (7.00%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent (2.00%) (1.00%)
Effective Income Tax Rate Reconciliation, Other Adjustments, Amortization Of Excess Deferred Income Taxes. Percent (0.11) (0.08)
Effective Income Tax Rate Reconciliation, Other Adjustments, Depreciation Differences. Percent (0.02) (0.01)
Effective Income Tax Rate Reconciliation, Percent, Total 3.00% 8.00%
Ameren Illinois Company    
Effective Income Tax Rate Reconciliation, Percent [Abstract]    
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount $ 73 $ 66
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount 26 24
Effective Income Tax Rate Reconciliation, Other Adjustments, Amortization Of Excess Deferred Income Taxes. Amount (5) (11)
Effective Income Tax Rate Reconciliation, Other Adjustments, Depreciation Differences. Amount (3) (3)
Income Tax Expense (Benefit), Total $ 91 $ 76
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent 21.00% 21.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent 7.00% 7.00%
Effective Income Tax Rate Reconciliation, Other Adjustments, Amortization Of Excess Deferred Income Taxes. Percent (0.01) (0.03)
Effective Income Tax Rate Reconciliation, Other Adjustments, Depreciation Differences. Percent (0.01) (0.01)
Effective Income Tax Rate Reconciliation, Percent, Total 26.00% 24.00%
v3.26.1
Supplemental Information (Cash and Cash Equivalents) (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Dec. 31, 2024
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]        
Cash and cash equivalents $ 13 $ 13    
Restricted cash included in “Other current assets” 74 63    
Restricted cash included in “Other assets” 392 336    
Restricted cash included in “Nuclear decommissioning trust fund” 6 8    
Total cash, cash equivalents, and restricted cash 485 420 $ 376 $ 328
Union Electric Company        
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]        
Cash and cash equivalents 0 6    
Restricted cash included in “Other current assets” 64 54    
Restricted cash included in “Other assets” 0 0    
Restricted cash included in “Nuclear decommissioning trust fund” 6 8    
Total cash, cash equivalents, and restricted cash 70 68 45 17
Ameren Illinois Company        
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]        
Cash and cash equivalents 0 3    
Restricted cash included in “Other current assets” 6 5    
Restricted cash included in “Other assets” 392 336    
Restricted cash included in “Nuclear decommissioning trust fund” 0 0    
Total cash, cash equivalents, and restricted cash $ 398 $ 344 $ 316 $ 302
v3.26.1
Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Allowance for Doubtful Accounts Receivable [Roll Forward]      
Beginning of period $ 39 $ 30  
Bad debt expense 10 16  
Charged to other accounts 1 1  
Net write-offs (9) (6)  
End of period 41 41  
Payables for purchased receivables 46   $ 47
Union Electric Company      
Allowance for Doubtful Accounts Receivable [Roll Forward]      
Beginning of period 17 12  
Bad debt expense 2 2  
Net write-offs (4) (2)  
End of period 15 12  
Ameren Illinois Company      
Allowance for Doubtful Accounts Receivable [Roll Forward]      
Beginning of period 22 18  
Bad debt expense 8 14  
Charged to other accounts 1 1  
Net write-offs (5) (4)  
End of period 26 $ 29  
Payables for purchased receivables $ 46   $ 47
v3.26.1
Supplemental Information (Supplemental Cash Flow Information) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Supplemental Cash Flow Information [Line Items]    
Accrued capital expenditures, including nuclear fuel expenditures $ 490 $ 381
Net realized and unrealized loss – nuclear decommissioning trust fund (56) (40)
Issuance of common stock for stock-based compensation    
Supplemental Cash Flow Information [Line Items]    
Stock Issued 25 25
Issuance of common stock under the DRPlus    
Supplemental Cash Flow Information [Line Items]    
Stock Issued 7 9
Union Electric Company    
Supplemental Cash Flow Information [Line Items]    
Accrued capital expenditures, including nuclear fuel expenditures 364 214
Net realized and unrealized loss – nuclear decommissioning trust fund (56) (40)
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 108 159
Net realized and unrealized loss – nuclear decommissioning trust fund 0 0
Ameren Illinois Company | Issuance of common stock for stock-based compensation    
Supplemental Cash Flow Information [Line Items]    
Stock Issued 0 0
Ameren Illinois Company | Issuance of common stock under the DRPlus    
Supplemental Cash Flow Information [Line Items]    
Stock Issued $ 0 $ 0
v3.26.1
Supplemental Information (Schedule of Asset Retirement Obligations) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Dec. 31, 2025
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Asset Retirement Obligation, Beginning Balance $ 854  
Liabilities incurred 7  
Liabilities settled 1  
Accretion 9  
Asset Retirement Obligation, Ending Balance 869  
Other current liabilities 674 $ 570
Union Electric Company    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Asset Retirement Obligation, Beginning Balance 849  
Liabilities incurred 7  
Liabilities settled 1  
Accretion 9  
Asset Retirement Obligation, Ending Balance 864  
Other current liabilities 154 150
Ameren Illinois Company    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Asset Retirement Obligation, Beginning Balance 5  
Liabilities incurred 0  
Liabilities settled 1  
Accretion 1  
Asset Retirement Obligation, Ending Balance 5  
Other current liabilities 190 182
Asset Retirement Obligation Balance    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Other current liabilities $ 5 $ 5
v3.26.1
Supplemental Information (Narrative) (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Supplemental Information [Abstract]    
Deferred Compensation Liability, Classified, Noncurrent $ 79 $ 79
v3.26.1
Supplemental Information (Schedule Of Excise Taxes) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Accounting Policies [Line Items]    
Excise tax expense $ 85 $ 81
Union Electric Company    
Accounting Policies [Line Items]    
Excise tax expense 40 38
Ameren Illinois Company    
Accounting Policies [Line Items]    
Excise tax expense $ 45 $ 43
v3.26.1
Supplemental Information (Earnings Per Share) (Details) - shares
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Earnings Per Share Reconciliation [Abstract]    
Weighted-average Common Shares Outstanding – Basic 276,500,000 270,000,000.0
Assumed settlement of performance share units and restricted stock units 1,000,000.0 1,000,000.0
Dilutive effect of forward sale agreements 900,000 400,000
Weighted-average Common Shares Outstanding – Diluted 278,400,000 271,400,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares) 0 0
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount - Forward Equity   0
v3.26.1
Segment Information (Narrative) (Details)
 3 Months Ended
Mar. 31, 2026
segment
Segment Reporting Information [Line Items]  
Number of reportable segments 4
Union Electric Company  
Segment Reporting Information [Line Items]  
Number of reportable segments 1
Ameren Illinois Company  
Segment Reporting Information [Line Items]  
Number of reportable segments 3
v3.26.1
Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Segment Reporting Information [Line Items]    
External revenues $ 2,176 $ 2,097
Revenues 2,176 2,097
Fuel and purchased power (433) (502)
Natural gas purchased for resale (171) (169)
Other operations and maintenance expenses (491) (485)
Depreciation and amortization (398) (367)
Taxes other than income taxes (151) (144)
Other Income, Net 90 85
Interest charges (204) (175)
Income taxes (60) (50)
Noncontrolling interests - preferred stock dividends (1) (1)
Net income attributable to Ameren common shareholders 357 289
Interest income 9 11
Capital expenditures 1,574 1,064
Union Electric Company    
Segment Reporting Information [Line Items]    
External revenues 930 957
Fuel and purchased power (214) (330)
Natural gas purchased for resale (34) (30)
Other operations and maintenance expenses (264) (250)
Taxes other than income taxes (95) (89)
Other Income, Net 53 43
Interest charges (82) (60)
Income taxes (3) (4)
Noncontrolling interests - preferred stock dividends (1) (1)
Net income attributable to Ameren common shareholders 76 42
Ameren Illinois Company    
Segment Reporting Information [Line Items]    
External revenues 1,199 1,100
Revenues 1,199 1,100
Purchased Power (222) (175)
Natural gas purchased for resale (137) (139)
Other operations and maintenance expenses (232) (236)
Depreciation and amortization (170) (159)
Taxes other than income taxes (52) (51)
Other Income, Net 29 34
Interest charges (68) (62)
Income taxes (91) (76)
Net Income Available to Common Shareholder 256 236
Net income attributable to Ameren common shareholders 256 236
Interest income 6 9
Capital expenditures 388 363
Operating Segments | Union Electric Company    
Segment Reporting Information [Line Items]    
External revenues 920 950
Revenues 930 957
Fuel and purchased power (214) (330)
Natural gas purchased for resale (34) (30)
Other operations and maintenance expenses (264) (250)
Depreciation and amortization (214) (194)
Taxes other than income taxes (95) (89)
Other Income, Net 53 43
Interest charges (82) (60)
Income taxes (3) (4)
Noncontrolling interests - preferred stock dividends (1) (1)
Net Income Available to Common Shareholder 76 42
Interest income 3 2
Capital expenditures 1,091 658
Operating Segments | Ameren Illinois Electric Distribution    
Segment Reporting Information [Line Items]    
External revenues 643 570
Revenues 643 572
Fuel and purchased power (266) (212)
Natural gas purchased for resale 0 0
Other operations and maintenance expenses (160) (166)
Depreciation and amortization (96) (91)
Taxes other than income taxes (22) (21)
Other Income, Net 19 23
Interest charges (28) (26)
Income taxes (24) (16)
Noncontrolling interests - preferred stock dividends 0 0
Net Income Available to Common Shareholder 66 63
Interest income 6 8
Capital expenditures 196 167
Operating Segments | Ameren Illinois Natural Gas    
Segment Reporting Information [Line Items]    
External revenues 436 411
Revenues 436 411
Fuel and purchased power 0 0
Natural gas purchased for resale (137) (139)
Other operations and maintenance expenses (57) (55)
Depreciation and amortization (34) (32)
Taxes other than income taxes (29) (29)
Other Income, Net 3 5
Interest charges (16) (15)
Income taxes (44) (38)
Noncontrolling interests - preferred stock dividends 0 0
Net Income Available to Common Shareholder 122 108
Interest income 0 0
Capital expenditures 72 59
Operating Segments | Ameren Transmission    
Segment Reporting Information [Line Items]    
External revenues 177 166
Revenues 227 210
Fuel and purchased power 0 0
Natural gas purchased for resale 0 0
Other operations and maintenance expenses (19) (19)
Depreciation and amortization (53) (48)
Taxes other than income taxes (2) (1)
Other Income, Net 7 7
Interest charges (30) (29)
Income taxes (32) (31)
Noncontrolling interests - preferred stock dividends 0 0
Net Income Available to Common Shareholder 98 89
Interest income 0 1
Capital expenditures 204 173
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution    
Segment Reporting Information [Line Items]    
External revenues 643 572
Revenues 643 572
Purchased Power (266) (212)
Natural gas purchased for resale 0 0
Other operations and maintenance expenses (160) (166)
Depreciation and amortization (96) (91)
Taxes other than income taxes (22) (21)
Other Income, Net 19 23
Interest charges (28) (26)
Income taxes (24) (16)
Net Income Available to Common Shareholder 66 63
Interest income 6 8
Capital expenditures 196 167
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas    
Segment Reporting Information [Line Items]    
External revenues 436 411
Revenues 436 411
Purchased Power 0 0
Natural gas purchased for resale (137) (139)
Other operations and maintenance expenses (57) (55)
Depreciation and amortization (34) (32)
Taxes other than income taxes (29) (29)
Other Income, Net 3 5
Interest charges (16) (15)
Income taxes (44) (38)
Net Income Available to Common Shareholder 122 108
Interest income 0 0
Capital expenditures 72 59
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission    
Segment Reporting Information [Line Items]    
External revenues 120 117
Revenues 164 154
Purchased Power 0 0
Natural gas purchased for resale 0 0
Other operations and maintenance expenses (15) (15)
Depreciation and amortization (40) (36)
Taxes other than income taxes (1) (1)
Other Income, Net 7 6
Interest charges (24) (21)
Income taxes (23) (22)
Net Income Available to Common Shareholder 68 65
Interest income 0 1
Capital expenditures 120 137
Other    
Segment Reporting Information [Line Items]    
Other operations and maintenance expenses (4) (8)
Depreciation and amortization (1) (2)
Taxes other than income taxes (3) (4)
Other Income, Net 9 8
Interest charges (49) (46)
Income taxes 43 39
Noncontrolling interests - preferred stock dividends 0 0
Net Income Available to Common Shareholder (5) (13)
Interest income 1 1
Capital expenditures 1 2
Intersegment Eliminations    
Segment Reporting Information [Line Items]    
Intersegment revenues (60) (53)
Revenues (60) (53)
Fuel and purchased power 47 40
Natural gas purchased for resale 0 0
Other operations and maintenance expenses 13 13
Depreciation and amortization 0 0
Taxes other than income taxes 0 0
Other Income, Net (1) (1)
Interest charges 1 1
Income taxes 0 0
Noncontrolling interests - preferred stock dividends 0 0
Interest income (1) (1)
Capital expenditures 10 5
Intersegment Eliminations | Union Electric Company    
Segment Reporting Information [Line Items]    
Intersegment revenues (10) (7)
Intersegment Eliminations | Ameren Illinois Electric Distribution    
Segment Reporting Information [Line Items]    
Intersegment revenues 0 (2)
Intersegment Eliminations | Ameren Illinois Natural Gas    
Segment Reporting Information [Line Items]    
Intersegment revenues 0 0
Intersegment Eliminations | Ameren Transmission    
Segment Reporting Information [Line Items]    
Intersegment revenues (50) (44)
Intersegment Eliminations | Ameren Illinois Company    
Segment Reporting Information [Line Items]    
Intersegment revenues (44) (37)
Revenues (44) (37)
Purchased Power (44) (37)
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Electric Distribution    
Segment Reporting Information [Line Items]    
Intersegment revenues 0 0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Natural Gas    
Segment Reporting Information [Line Items]    
Intersegment revenues 0 0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Transmission    
Segment Reporting Information [Line Items]    
Intersegment revenues $ (44) $ (37)
v3.26.1
Segment Information (Disaggregation of Revenue) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Disaggregation of Revenue [Line Items]    
Operating Revenues $ 2,176 $ 2,097
Revenues 2,176 2,097
Revenues from alternative revenue programs 56 18
Other revenues not from contracts with customers 6 5
Union Electric Company    
Disaggregation of Revenue [Line Items]    
Revenues from alternative revenue programs (3) (5)
Ameren Illinois Electric Distribution    
Disaggregation of Revenue [Line Items]    
Revenues from alternative revenue programs 46 21
Ameren Illinois Natural Gas    
Disaggregation of Revenue [Line Items]    
Revenues from alternative revenue programs 17 3
Ameren Transmission    
Disaggregation of Revenue [Line Items]    
Revenues from alternative revenue programs (4) (1)
Electric    
Disaggregation of Revenue [Line Items]    
Operating Revenues 1,661 1,622
Revenues 1,661 1,622
Electric | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 748 718
Electric | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 497 453
Electric | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 127 116
Electric | Other    
Disaggregation of Revenue [Line Items]    
Revenues 289 335
Natural gas    
Disaggregation of Revenue [Line Items]    
Operating Revenues 515 475
Revenues 515 475
Natural gas | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 360 352
Natural gas | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 106 96
Natural gas | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 8 6
Natural gas | Other    
Disaggregation of Revenue [Line Items]    
Revenues 41 21
Ameren Illinois Company    
Disaggregation of Revenue [Line Items]    
Operating Revenues 1,199 1,100
Revenues 1,199 1,100
Revenues from alternative revenue programs 60 23
Other revenues not from contracts with customers 4 4
Ameren Illinois Company | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 661 651
Ameren Illinois Company | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 281 257
Ameren Illinois Company | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 61 54
Ameren Illinois Company | Other    
Disaggregation of Revenue [Line Items]    
Revenues 196 138
Ameren Illinois Company | Ameren Illinois Electric Distribution    
Disaggregation of Revenue [Line Items]    
Revenues from alternative revenue programs 46 21
Other revenues not from contracts with customers 3 3
Ameren Illinois Company | Ameren Illinois Natural Gas    
Disaggregation of Revenue [Line Items]    
Revenues from alternative revenue programs 17 3
Other revenues not from contracts with customers 1 1
Ameren Illinois Company | Ameren Illinois Transmission    
Disaggregation of Revenue [Line Items]    
Revenues from alternative revenue programs (3) (1)
Other revenues not from contracts with customers 0 0
Ameren Illinois Company | Electric    
Disaggregation of Revenue [Line Items]    
Operating Revenues 763 689
Ameren Illinois Company | Natural gas    
Disaggregation of Revenue [Line Items]    
Operating Revenues 436 411
Operating Segments | Union Electric Company    
Disaggregation of Revenue [Line Items]    
Operating Revenues 920 950
Revenues 930 957
Other revenues not from contracts with customers 2 1
Operating Segments | Ameren Illinois Electric Distribution    
Disaggregation of Revenue [Line Items]    
Operating Revenues 643 570
Revenues 643 572
Other revenues not from contracts with customers 3 3
Operating Segments | Ameren Illinois Natural Gas    
Disaggregation of Revenue [Line Items]    
Operating Revenues 436 411
Revenues 436 411
Other revenues not from contracts with customers 1 1
Operating Segments | Ameren Transmission    
Disaggregation of Revenue [Line Items]    
Operating Revenues 177 166
Revenues 227 210
Other revenues not from contracts with customers 0 0
Operating Segments | Electric | Union Electric Company    
Disaggregation of Revenue [Line Items]    
Revenues 851 893
Operating Segments | Electric | Union Electric Company | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 399 376
Operating Segments | Electric | Union Electric Company | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 302 273
Operating Segments | Electric | Union Electric Company | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 72 66
Operating Segments | Electric | Union Electric Company | Other    
Disaggregation of Revenue [Line Items]    
Revenues 78 178
Operating Segments | Electric | Ameren Illinois Electric Distribution    
Disaggregation of Revenue [Line Items]    
Revenues 643 572
Operating Segments | Electric | Ameren Illinois Electric Distribution | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 349 342
Operating Segments | Electric | Ameren Illinois Electric Distribution | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 195 180
Operating Segments | Electric | Ameren Illinois Electric Distribution | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 55 50
Operating Segments | Electric | Ameren Illinois Electric Distribution | Other    
Disaggregation of Revenue [Line Items]    
Revenues 44 0
Operating Segments | Electric | Ameren Illinois Natural Gas    
Disaggregation of Revenue [Line Items]    
Revenues 0 0
Operating Segments | Electric | Ameren Illinois Natural Gas | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Operating Segments | Electric | Ameren Illinois Natural Gas | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Operating Segments | Electric | Ameren Illinois Natural Gas | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Operating Segments | Electric | Ameren Illinois Natural Gas | Other    
Disaggregation of Revenue [Line Items]    
Revenues 0 0
Operating Segments | Electric | Ameren Transmission    
Disaggregation of Revenue [Line Items]    
Revenues 227 210
Operating Segments | Electric | Ameren Transmission | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Operating Segments | Electric | Ameren Transmission | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Operating Segments | Electric | Ameren Transmission | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Operating Segments | Electric | Ameren Transmission | Other    
Disaggregation of Revenue [Line Items]    
Revenues 227 210
Operating Segments | Natural gas | Union Electric Company    
Disaggregation of Revenue [Line Items]    
Revenues 79 64
Operating Segments | Natural gas | Union Electric Company | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 48 43
Operating Segments | Natural gas | Union Electric Company | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 20 19
Operating Segments | Natural gas | Union Electric Company | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 2 2
Operating Segments | Natural gas | Union Electric Company | Other    
Disaggregation of Revenue [Line Items]    
Revenues 9 0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution    
Disaggregation of Revenue [Line Items]    
Revenues 0 0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Other    
Disaggregation of Revenue [Line Items]    
Revenues 0 0
Operating Segments | Natural gas | Ameren Illinois Natural Gas    
Disaggregation of Revenue [Line Items]    
Revenues 436 411
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 312 309
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 86 77
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 6 4
Operating Segments | Natural gas | Ameren Illinois Natural Gas | Other    
Disaggregation of Revenue [Line Items]    
Revenues 32 21
Operating Segments | Natural gas | Ameren Transmission    
Disaggregation of Revenue [Line Items]    
Revenues 0 0
Operating Segments | Natural gas | Ameren Transmission | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Operating Segments | Natural gas | Ameren Transmission | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Operating Segments | Natural gas | Ameren Transmission | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Operating Segments | Natural gas | Ameren Transmission | Other    
Disaggregation of Revenue [Line Items]    
Revenues 0 0
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution    
Disaggregation of Revenue [Line Items]    
Operating Revenues 643 572
Revenues 643 572
Operating Segments | Ameren Illinois Company | Ameren Illinois Natural Gas    
Disaggregation of Revenue [Line Items]    
Operating Revenues 436 411
Revenues 436 411
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission    
Disaggregation of Revenue [Line Items]    
Operating Revenues 120 117
Revenues 164 154
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution    
Disaggregation of Revenue [Line Items]    
Revenues 643 572
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 349 342
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 195 180
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 55 50
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Other    
Disaggregation of Revenue [Line Items]    
Revenues 44 0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission    
Disaggregation of Revenue [Line Items]    
Revenues 164 154
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Other    
Disaggregation of Revenue [Line Items]    
Revenues 164 154
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas    
Disaggregation of Revenue [Line Items]    
Revenues 436 411
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 312 309
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 86 77
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 6 4
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Natural Gas | Other    
Disaggregation of Revenue [Line Items]    
Revenues 32 21
Intersegment Eliminations    
Disaggregation of Revenue [Line Items]    
Revenues (60) (53)
Revenues (60) (53)
Intersegment Eliminations | Union Electric Company    
Disaggregation of Revenue [Line Items]    
Revenues (10) (7)
Intersegment Eliminations | Ameren Illinois Electric Distribution    
Disaggregation of Revenue [Line Items]    
Revenues 0 (2)
Intersegment Eliminations | Ameren Illinois Natural Gas    
Disaggregation of Revenue [Line Items]    
Revenues 0 0
Intersegment Eliminations | Ameren Transmission    
Disaggregation of Revenue [Line Items]    
Revenues (50) (44)
Intersegment Eliminations | Electric    
Disaggregation of Revenue [Line Items]    
Revenues (60) (53)
Intersegment Eliminations | Electric | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Intersegment Eliminations | Electric | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Intersegment Eliminations | Electric | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Intersegment Eliminations | Electric | Other    
Disaggregation of Revenue [Line Items]    
Revenues (60) (53)
Intersegment Eliminations | Natural gas    
Disaggregation of Revenue [Line Items]    
Revenues 0 0
Intersegment Eliminations | Natural gas | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Intersegment Eliminations | Natural gas | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Intersegment Eliminations | Natural gas | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Intersegment Eliminations | Natural gas | Other    
Disaggregation of Revenue [Line Items]    
Revenues 0 0
Intersegment Eliminations | Ameren Illinois Company    
Disaggregation of Revenue [Line Items]    
Revenues (44) (37)
Revenues (44) (37)
Intersegment Eliminations | Ameren Illinois Company | Residential    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Intersegment Eliminations | Ameren Illinois Company | Commercial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Intersegment Eliminations | Ameren Illinois Company | Industrial    
Disaggregation of Revenue [Line Items]    
Operating Revenues 0 0
Intersegment Eliminations | Ameren Illinois Company | Other    
Disaggregation of Revenue [Line Items]    
Revenues (44) (37)
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Electric Distribution    
Disaggregation of Revenue [Line Items]    
Revenues 0 0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Natural Gas    
Disaggregation of Revenue [Line Items]    
Revenues 0 0
Intersegment Eliminations | Ameren Illinois Company | Ameren Illinois Transmission    
Disaggregation of Revenue [Line Items]    
Revenues $ (44) $ (37)