Short-Term Debt and Liquidity (Short-Term Debt outstanding) (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Short-term Debt [Line Items]
Short-term debt	$ 1,101	$ 545
Union Electric Company
Short-term Debt [Line Items]
Short-term debt	528	165
Ameren Illinois Company
Short-term Debt [Line Items]
Short-term debt	107	103
Commercial Paper
Short-term Debt [Line Items]
Short-term debt	1,101	545
Commercial Paper \| Parent Company
Short-term Debt [Line Items]
Short-term debt	466	277
Commercial Paper \| Union Electric Company
Short-term Debt [Line Items]
Short-term debt	528	165
Commercial Paper \| Ameren Illinois Company
Short-term Debt [Line Items]
Short-term debt	$ 107	$ 103

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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Name:	us-gaap_ShortTermBorrowings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant