v3.26.3
Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($)
$ in Millions
 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Short-term Debt [Line Items]    
Average daily amount outstanding $ 1,142 $ 1,012
Weighted-average interest rate 3.89% 4.59%
Short-term Debt, Maximum Amount Outstanding During Period $ 1,996 $ 1,603
Peak interest rate 4.08% 4.75%
Ameren (parent)    
Short-term Debt [Line Items]    
Average daily amount outstanding $ 662 $ 637
Weighted-average interest rate 3.90% 4.60%
Short-term Debt, Maximum Amount Outstanding During Period $ 1,073 $ 1,139
Peak interest rate 4.08% 4.75%
Union Electric Company    
Short-term Debt [Line Items]    
Average daily amount outstanding $ 314 $ 245
Weighted-average interest rate 3.87% 4.58%
Short-term Debt, Maximum Amount Outstanding During Period $ 1,360 $ 650
Peak interest rate 4.08% 4.72%
Ameren Illinois Company    
Short-term Debt [Line Items]    
Average daily amount outstanding $ 166 $ 130
Weighted-average interest rate 3.89% 4.55%
Short-term Debt, Maximum Amount Outstanding During Period $ 503 $ 425
Peak interest rate 4.08% 4.70%