| Three Months Ended December 31, | Year Ended December 31, | ||||||||||||||||||||||
| 2025 | 2024 | 2025 | 2024 | ||||||||||||||||||||
| Operating Revenues: | |||||||||||||||||||||||
| Electric | $ | 1,445 | $ | 1,620 | $ | 7,668 | $ | 6,540 | |||||||||||||||
| Natural gas | 337 | 321 | 1,131 | 1,083 | |||||||||||||||||||
| Total operating revenues | 1,782 | 1,941 | 8,799 | 7,623 | |||||||||||||||||||
| Operating Expenses: | |||||||||||||||||||||||
| Fuel and purchased power | 242 | 527 | 2,306 | 1,681 | |||||||||||||||||||
| Natural gas purchased for resale | 115 | 106 | 348 | 320 | |||||||||||||||||||
| Other operations and maintenance | 527 | 514 | 1,974 | 1,969 | |||||||||||||||||||
| Depreciation and amortization | 400 | 465 | 1,568 | 1,590 | |||||||||||||||||||
| Taxes other than income taxes | 138 | 131 | 577 | 547 | |||||||||||||||||||
| Total operating expenses | 1,422 | 1,743 | 6,773 | 6,107 | |||||||||||||||||||
| Operating Income | 360 | 198 | 2,026 | 1,516 | |||||||||||||||||||
| Other Income, Net | 90 | 124 | 347 | 417 | |||||||||||||||||||
| Interest Charges | 206 | 171 | 776 | 663 | |||||||||||||||||||
| Income Before Income Taxes | 244 | 151 | 1,597 | 1,270 | |||||||||||||||||||
| Income Taxes (Benefit) | (9) | (57) | 136 | 83 | |||||||||||||||||||
| Net Income | 253 | 208 | 1,461 | 1,187 | |||||||||||||||||||
| Less: Net Income Attributable to Noncontrolling Interests | 1 | 1 | 5 | 5 | |||||||||||||||||||
| Net Income Attributable to Ameren Common Shareholders | $ | 252 | $ | 207 | $ | 1,456 | $ | 1,182 | |||||||||||||||
| Earnings per Common Share – Basic | $ | 0.93 | $ | 0.77 | $ | 5.38 | $ | 4.43 | |||||||||||||||
| Earnings per Common Share – Diluted | $ | 0.92 | $ | 0.77 | $ | 5.35 | $ | 4.42 | |||||||||||||||
| Weighted-average Common Shares Outstanding – Basic | 271.5 | 267.4 | 270.5 | 266.8 | |||||||||||||||||||
| Weighted-average Common Shares Outstanding – Diluted | 273.7 | 268.9 | 272.2 | 267.4 | |||||||||||||||||||
| December 31, 2025 | December 31, 2024 | ||||||||||
| ASSETS | |||||||||||
| Current Assets: | |||||||||||
| Cash and cash equivalents | $ | 13 | $ | 7 | |||||||
| Accounts receivable - trade (less allowance for doubtful accounts) | 665 | 525 | |||||||||
| Unbilled revenue | 415 | 346 | |||||||||
| Miscellaneous accounts receivable | 107 | 96 | |||||||||
| Inventories | 774 | 762 | |||||||||
| Current regulatory assets | 387 | 366 | |||||||||
| Other current assets | 210 | 162 | |||||||||
| Total current assets | 2,571 | 2,264 | |||||||||
| Property, Plant, and Equipment, Net | 39,313 | 36,304 | |||||||||
| Investments and Other Assets: | |||||||||||
| Nuclear decommissioning trust fund | 1,526 | 1,342 | |||||||||
| Goodwill | 411 | 411 | |||||||||
| Regulatory assets | 2,524 | 2,397 | |||||||||
| Pension and other postretirement benefits | 977 | 757 | |||||||||
| Other assets | 1,154 | 1,123 | |||||||||
| Total investments and other assets | 6,592 | 6,030 | |||||||||
| TOTAL ASSETS | $ | 48,476 | $ | 44,598 | |||||||
| LIABILITIES AND EQUITY | |||||||||||
| Current Liabilities: | |||||||||||
| Current maturities of long-term debt | $ | 973 | $ | 317 | |||||||
| Short-term debt | 643 | 1,143 | |||||||||
| Accounts and wages payable | 1,254 | 1,059 | |||||||||
| Interest accrued | 229 | 196 | |||||||||
| Customer deposits | 238 | 223 | |||||||||
| Other current liabilities | 570 | 475 | |||||||||
| Total current liabilities | 3,907 | 3,413 | |||||||||
| Long-term Debt, Net | 18,214 | 17,262 | |||||||||
| Deferred Credits and Other Liabilities: | |||||||||||
| Accumulated deferred income taxes and production and investment tax credits, net | 5,181 | 4,474 | |||||||||
| Regulatory liabilities | 6,255 | 5,897 | |||||||||
| Asset retirement obligations | 849 | 822 | |||||||||
| Other deferred credits and liabilities | 540 | 487 | |||||||||
| Total deferred credits and other liabilities | 12,825 | 11,680 | |||||||||
| Shareholders’ Equity: | |||||||||||
| Common stock | 3 | 3 | |||||||||
| Other paid-in capital, principally premium on common stock | 8,106 | 7,513 | |||||||||
| Retained earnings | 5,292 | 4,604 | |||||||||
| Accumulated other comprehensive loss | — | (6) | |||||||||
| Total shareholders’ equity | 13,401 | 12,114 | |||||||||
| Noncontrolling Interests | 129 | 129 | |||||||||
| Total equity | 13,530 | 12,243 | |||||||||
| TOTAL LIABILITIES AND EQUITY | $ | 48,476 | $ | 44,598 | |||||||
| Year Ended December 31, | |||||||||||
| 2025 | 2024 | ||||||||||
| Cash Flows From Operating Activities: | |||||||||||
| Net income | $ | 1,461 | $ | 1,187 | |||||||
| Adjustments to reconcile net income to net cash provided by operating activities: | |||||||||||
| Depreciation and amortization | 1,612 | 1,524 | |||||||||
| Amortization of nuclear fuel | 56 | 81 | |||||||||
| Amortization of debt issuance costs and premium/discounts | 19 | 19 | |||||||||
| Deferred income taxes and production and investment tax credits, net | 253 | 127 | |||||||||
| Allowance for equity funds used during construction | (88) | (76) | |||||||||
| Stock-based compensation costs | 28 | 28 | |||||||||
| Other | 63 | 87 | |||||||||
| Changes in assets and liabilities | (51) | (214) | |||||||||
| Net cash provided by operating activities | 3,353 | 2,763 | |||||||||
| Cash Flows From Investing Activities: | |||||||||||
| Capital expenditures | (4,128) | (4,319) | |||||||||
| Nuclear fuel expenditures | (46) | (91) | |||||||||
| Purchases of securities – nuclear decommissioning trust fund | (440) | (584) | |||||||||
| Sales and maturities of securities – nuclear decommissioning trust fund | 416 | 564 | |||||||||
| Other | 53 | (26) | |||||||||
| Net cash used in investing activities | (4,145) | (4,456) | |||||||||
| Cash Flows From Financing Activities: | |||||||||||
| Dividends on common stock | (768) | (714) | |||||||||
| Dividends paid to noncontrolling interest holders | (5) | (5) | |||||||||
| Short-term debt, net | (499) | 607 | |||||||||
| Maturities and extinguishment of long-term debt | (341) | (893) | |||||||||
| Issuances of long-term debt | 1,960 | 2,535 | |||||||||
| Issuances of common stock | 574 | 273 | |||||||||
| Employee payroll taxes related to stock-based compensation | (13) | (8) | |||||||||
| Debt issuance costs | (24) | (31) | |||||||||
| Other | — | (15) | |||||||||
| Net cash provided by financing activities | 884 | 1,749 | |||||||||
| Net change in cash, cash equivalents, and restricted cash | 92 | 56 | |||||||||
Cash, cash equivalents, and restricted cash at beginning of year(a) | 328 | 272 | |||||||||
Cash, cash equivalents, and restricted cash at end of year(b) | $ | 420 | $ | 328 | |||||||