Short-Term Debt and Liquidity (Short-Term Debt outstanding) (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Short-term Debt [Line Items]
Short-term debt	$ 903	$ 1,143
Union Electric Company
Short-term Debt [Line Items]
Short-term debt	259	0
Ameren Illinois Company
Short-term Debt [Line Items]
Short-term debt	0	88
Commercial Paper
Short-term Debt [Line Items]
Short-term debt	903	1,143
Commercial Paper \| Parent Company
Short-term Debt [Line Items]
Short-term debt	644	1,055
Commercial Paper \| Union Electric Company
Short-term Debt [Line Items]
Short-term debt	259	0
Commercial Paper \| Ameren Illinois Company
Short-term Debt [Line Items]
Short-term debt	$ 0	$ 88

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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