Short-Term Debt and Liquidity (Short-Term Debt outstanding) (Details) - USD ($) $ in Millions |
Jun. 30, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Short-term Debt [Line Items] | ||
| Short-term debt | $ 1,141 | $ 1,143 |
| Union Electric Company | ||
| Short-term Debt [Line Items] | ||
| Short-term debt | 330 | 0 |
| Ameren Illinois Company | ||
| Short-term Debt [Line Items] | ||
| Short-term debt | 245 | 88 |
| Commercial Paper | ||
| Short-term Debt [Line Items] | ||
| Short-term debt | 1,141 | 1,143 |
| Commercial Paper | Parent Company | ||
| Short-term Debt [Line Items] | ||
| Short-term debt | 566 | 1,055 |
| Commercial Paper | Union Electric Company | ||
| Short-term Debt [Line Items] | ||
| Short-term debt | 330 | 0 |
| Commercial Paper | Ameren Illinois Company | ||
| Short-term Debt [Line Items] | ||
| Short-term debt | $ 245 | $ 88 |