Long-Term debt and Equity Financings (Details) $ / shares in Units, shares in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2023 USD ($) shares	Mar. 31, 2023 USD ($) shares	Sep. 30, 2022 USD ($) shares	Sep. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2022 USD ($) shares
Long-Term Debt And Equity Financings [Line Items]
Shares issued under the DRPlus and 401(k) plan | shares	0.2		0.1	0.4	0.4
Issuances of common stock				$ 28,000,000	$ 29,000,000
Stock Issued During Period, Shares, Other | shares	0.0	0.5	0.0	0.5	0.4
Stock Issued During Period, Value, Other		$ 37,000,000
Common Stock, Shares Authorized Under DRPlus Plan | shares	3.0			3.0
Maximum Value Of Shares To Be Issued Under ATM Program	$ 910,000,000			$ 910,000,000
Forward Contract Indexed to Issuer's Equity, Basis Spread	75			75
Termination of a financing obligation				$ 240,000,000	$ 0
Minimum
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares				$ 81.83
Maximum
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares				94.63
Weighted Average
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares				$ 91.23
Dividend reinvestment and 401 (k) plans
Long-Term Debt And Equity Financings [Line Items]
Issuances of common stock	$ 5,000,000			$ 28,000,000
Accrued Proceeds from Issuance of Common Stock				$ 7,000,000
Forward Sale Agreements Outstanding
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Shares, at Fair Value | shares	4.3			4.3
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value	$ 390,000,000			$ 390,000,000
Period End Net Cash Settlement Price	72,000,000			72,000,000
Period End Net Share Settlement Price	1,000,000			1,000,000
Forward Sale Agreement Equity Offering Shares	4,300,000			4,300,000
Forward Sale Agreement Gross Sales Price	392,000,000			392,000,000
Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Termination of a financing obligation				240,000,000	0
Union Electric Company | Secured Debt | Senior Secured Notes 5.45% Due 2053
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount	$ 500,000,000			$ 500,000,000
Debt Instrument, Interest Rate, Stated Percentage	5.45%			5.45%
Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Capital contributions from parent				$ 50,000,000	0
Termination of a financing obligation				0	0
Ameren Illinois Company | Other Paid-in Capital:
Long-Term Debt And Equity Financings [Line Items]
Capital contributions from parent	$ 50,000,000		$ 0	50,000,000	$ 0
Ameren Illinois Company | Secured Debt | First Mortgage Bonds 0.375% Due 2023
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount	$ 100,000,000			$ 100,000,000
Debt Instrument, Interest Rate, Stated Percentage	0.375%			0.375%
Ameren Illinois Company | Secured Debt | First Mortgage Bonds 4.95% Due 2033
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount	$ 500,000,000			$ 500,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.95%			4.95%