| Three Months Ended September 30, | Nine Months Ended September 30, | ||||||||||||||||||||||
| 2026 | 2025 | 2026 | 2025 | ||||||||||||||||||||
| Operating Revenues: | |||||||||||||||||||||||
| Electric | $ | 2,722 | $ | 2,563 | $ | 6,270 | $ | 6,223 | |||||||||||||||
| Natural gas | 160 | 136 | 880 | 794 | |||||||||||||||||||
| Total operating revenues | 2,882 | 2,699 | 7,150 | 7,017 | |||||||||||||||||||
| Operating Expenses: | |||||||||||||||||||||||
| Fuel and purchased power | 809 | 768 | 1,749 | 2,064 | |||||||||||||||||||
| Natural gas purchased for resale | 28 | 25 | 238 | 233 | |||||||||||||||||||
| Other operations and maintenance | 535 | 502 | 1,547 | 1,447 | |||||||||||||||||||
| Depreciation and amortization | 436 | 415 | 1,254 | 1,168 | |||||||||||||||||||
| Taxes other than income taxes | 174 | 164 | 471 | 439 | |||||||||||||||||||
| Total operating expenses | 1,982 | 1,874 | 5,259 | 5,351 | |||||||||||||||||||
| Operating Income | 900 | 825 | 1,891 | 1,666 | |||||||||||||||||||
| Other Income, Net | 112 | 76 | 320 | 257 | |||||||||||||||||||
| Interest Charges | 216 | 208 | 629 | 570 | |||||||||||||||||||
| Income Before Income Taxes | 796 | 693 | 1,582 | 1,353 | |||||||||||||||||||
| Income Taxes | 119 | 52 | 231 | 145 | |||||||||||||||||||
| Net Income | 677 | 641 | 1,351 | 1,208 | |||||||||||||||||||
| Less: Net Income Attributable to Noncontrolling Interests | 1 | 1 | 4 | 4 | |||||||||||||||||||
| Net Income Attributable to Ameren Common Shareholders | $ | 676 | $ | 640 | $ | 1,347 | $ | 1,204 | |||||||||||||||
| Earnings per Common Share - Basic | $ | 2.44 | $ | 2.37 | $ | 4.87 | $ | 4.46 | |||||||||||||||
| Earnings per Common Share – Diluted | $ | 2.42 | $ | 2.35 | $ | 4.83 | $ | 4.43 | |||||||||||||||
| Weighted-average Common Shares Outstanding – Basic | 276.8 | 270.4 | 276.7 | 270.2 | |||||||||||||||||||
| Weighted-average Common Shares Outstanding – Diluted | 278.9 | 272.2 | 278.7 | 271.7 | |||||||||||||||||||
| September 30, 2026 | December 31, 2025 | ||||||||||
| ASSETS | |||||||||||
| Current Assets: | |||||||||||
| Cash and cash equivalents | $ | 40 | $ | 13 | |||||||
| Accounts receivable - trade (less allowance for doubtful accounts) | 853 | 665 | |||||||||
| Unbilled revenue | 511 | 415 | |||||||||
| Miscellaneous accounts receivable | 238 | 107 | |||||||||
| Inventories | 873 | 774 | |||||||||
| Current regulatory assets | 275 | 387 | |||||||||
| Other current assets | 329 | 210 | |||||||||
| Total current assets | 3,119 | 2,571 | |||||||||
| Property, Plant, and Equipment, Net | 42,239 | 39,313 | |||||||||
| Investments and Other Assets: | |||||||||||
| Nuclear decommissioning trust fund | 1,638 | 1,526 | |||||||||
| Goodwill | 411 | 411 | |||||||||
| Regulatory assets | 2,964 | 2,524 | |||||||||
| Pension and other postretirement benefits | 1,000 | 977 | |||||||||
| Other assets | 1,396 | 1,154 | |||||||||
| Total investments and other assets | 7,409 | 6,592 | |||||||||
| TOTAL ASSETS | $ | 52,767 | $ | 48,476 | |||||||
| LIABILITIES AND EQUITY | |||||||||||
| Current Liabilities: | |||||||||||
| Current maturities of long-term debt | $ | 1,574 | $ | 973 | |||||||
| Short-term debt | 496 | 643 | |||||||||
| Accounts and wages payable | 976 | 1,254 | |||||||||
| Taxes accrued | 235 | 66 | |||||||||
| Interest accrued | 199 | 229 | |||||||||
| Customer deposits | 244 | 238 | |||||||||
| Other current liabilities | 469 | 504 | |||||||||
| Total current liabilities | 4,193 | 3,907 | |||||||||
| Long-term Debt, Net | 20,443 | 18,214 | |||||||||
| Deferred Credits and Other Liabilities: | |||||||||||
| Accumulated deferred income taxes and tax credits, net | 5,646 | 5,181 | |||||||||
| Regulatory liabilities | 6,606 | 6,255 | |||||||||
| Asset retirement obligations | 863 | 849 | |||||||||
| Other deferred credits and liabilities | 680 | 540 | |||||||||
| Total deferred credits and other liabilities | 13,795 | 12,825 | |||||||||
| Shareholders’ Equity: | |||||||||||
| Common stock | 3 | 3 | |||||||||
| Other paid-in capital, principally premium on common stock | 8,149 | 8,106 | |||||||||
| Retained earnings | 6,017 | 5,292 | |||||||||
| Accumulated other comprehensive income | 38 | — | |||||||||
| Total shareholders’ equity | 14,207 | 13,401 | |||||||||
| Noncontrolling Interests | 129 | 129 | |||||||||
| Total equity | 14,336 | 13,530 | |||||||||
| TOTAL LIABILITIES AND EQUITY | $ | 52,767 | $ | 48,476 | |||||||
| Nine Months Ended September 30, | |||||||||||
| 2026 | 2025 | ||||||||||
| Cash Flows From Operating Activities: | |||||||||||
| Net income | $ | 1,351 | $ | 1,208 | |||||||
| Adjustments to reconcile net income to net cash provided by operating activities: | |||||||||||
| Depreciation and amortization | 1,277 | 1,199 | |||||||||
| Amortization of nuclear fuel | 63 | 39 | |||||||||
| Amortization of debt issuance costs and premium/discounts | 15 | 14 | |||||||||
| Deferred income taxes and tax credits, net | 281 | 255 | |||||||||
| Allowance for equity funds used during construction | (104) | (60) | |||||||||
| Stock-based compensation costs | 24 | 21 | |||||||||
| Other | (7) | 29 | |||||||||
| Changes in assets and liabilities | (707) | (308) | |||||||||
| Net cash provided by operating activities | 2,193 | 2,397 | |||||||||
| Cash Flows From Investing Activities: | |||||||||||
| Capital expenditures | (4,089) | (3,118) | |||||||||
| Nuclear fuel expenditures | (26) | (20) | |||||||||
| Purchases of securities – nuclear decommissioning trust fund | (513) | (373) | |||||||||
| Sales and maturities of securities – nuclear decommissioning trust fund | 488 | 348 | |||||||||
| Other | (14) | 51 | |||||||||
| Net cash used in investing activities | (4,154) | (3,112) | |||||||||
| Cash Flows From Financing Activities: | |||||||||||
| Dividends on common stock | (622) | (576) | |||||||||
| Dividends paid to noncontrolling interest holders | (4) | (4) | |||||||||
| Short-term debt, net | (147) | (239) | |||||||||
| Maturities and extinguishment of long-term debt | (378) | (324) | |||||||||
| Issuances of long-term debt | 3,234 | 1,960 | |||||||||
| Issuances of common stock | 31 | 35 | |||||||||
| Employee payroll taxes related to stock-based compensation | (14) | (13) | |||||||||
| Debt issuance costs | (34) | (17) | |||||||||
| Net cash provided by financing activities | 2,066 | 822 | |||||||||
| Net change in cash, cash equivalents, and restricted cash | 105 | 107 | |||||||||
Cash, cash equivalents, and restricted cash at beginning of year(a) | 420 | 328 | |||||||||
Cash, cash equivalents, and restricted cash at end of period(b) | $ | 525 | $ | 435 | |||||||