v3.26.1
Short-Term Debt and Liquidity (Short-Term Debt outstanding) (Details) - USD ($)
$ in Millions
Jun. 30, 2026
Dec. 31, 2025
Short-term Debt [Line Items]    
Short-term debt $ 1,220 $ 643
Union Electric Company    
Short-term Debt [Line Items]    
Short-term debt 0 471
Ameren Illinois Company    
Short-term Debt [Line Items]    
Short-term debt 312 17
Commercial Paper    
Short-term Debt [Line Items]    
Short-term debt 1,220 643
Commercial Paper | Union Electric Company    
Short-term Debt [Line Items]    
Short-term debt 0 471
Commercial Paper | Ameren Illinois Company    
Short-term Debt [Line Items]    
Short-term debt 312 17
Commercial Paper | Ameren (parent)    
Short-term Debt [Line Items]    
Short-term debt $ 908 $ 155