Short-Term Debt And Liquidity (Narrative) (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020	Jun. 30, 2021 USD ($)	Jun. 30, 2020	Dec. 31, 2020 USD ($)
Short-term Debt [Line Items]
Short-term debt	$ 431		$ 431		$ 490
Credit Agreements
Short-term Debt [Line Items]
Net Liquidity Available	$ 2,000		$ 2,000
Actual debt-to-capital ratio	0.57		0.57
Utilities
Short-term Debt [Line Items]
Short-term Debt, Weighted Average Interest Rate, over Time	0.22%	0.42%	0.22%	1.18%
Union Electric Company | Missouri Credit Agreement
Short-term Debt [Line Items]
Actual debt-to-capital ratio	0.49		0.49
Ameren Illinois Company | Illinois Credit Agreement
Short-term Debt [Line Items]
Actual debt-to-capital ratio	0.46		0.46
Ameren (parent) | Commercial Paper
Short-term Debt [Line Items]
Short-term debt	$ 431		$ 431		$ 490