v3.26.1
Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($)
$ in Millions
 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Short-term Debt [Line Items]    
Average daily amount outstanding $ 1,154 $ 975
Weighted-average interest rate 3.89% 4.61%
Short-term Debt, Maximum Amount Outstanding During Period $ 1,996 $ 1,603
Peak interest rate 4.05% 4.75%
Union Electric Company    
Short-term Debt [Line Items]    
Average daily amount outstanding $ 438 $ 226
Weighted-average interest rate 3.87% 4.60%
Short-term Debt, Maximum Amount Outstanding During Period $ 1,360 $ 650
Peak interest rate 4.05% 4.72%
Ameren Illinois Company    
Short-term Debt [Line Items]    
Average daily amount outstanding $ 101 $ 90
Weighted-average interest rate 3.89% 4.59%
Short-term Debt, Maximum Amount Outstanding During Period $ 312 $ 245
Peak interest rate 4.00% 4.70%
Ameren (parent)    
Short-term Debt [Line Items]    
Average daily amount outstanding $ 615 $ 659
Weighted-average interest rate 3.90% 4.63%
Short-term Debt, Maximum Amount Outstanding During Period $ 1,073 $ 1,139
Peak interest rate 4.00% 4.75%