Long-Term debt and Equity Financings (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2024 USD ($) shares	Mar. 31, 2024 USD ($) shares	Sep. 30, 2023 USD ($) shares	Sep. 30, 2024 USD ($) $ / shares shares	Sep. 30, 2023 USD ($) shares	Oct. 31, 2024 USD ($)	Aug. 31, 2024 USD ($)	Jun. 30, 2024 USD ($)	Apr. 30, 2024 USD ($)	Jan. 31, 2024 USD ($)
Long-Term Debt And Equity Financings [Line Items]
Shares issued under the DRPlus and 401(k) plan | shares	0.1		0.2	0.4	0.4
Issuances of common stock				$ 30.0	$ 28.0
Stock Issued During Period, Shares, Other | shares	0.0	0.2	0.0	0.2	0.5
Stock Issued During Period, Value, Other		$ 16.0
Maximum Value Of Shares To Be Issued Under ATM Program	$ 615.0			$ 615.0
Forward Contract Indexed to Issuer's Equity, Basis Spread	75			75
Minimum
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares				$ 76.69
Maximum
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares				89.31
Weighted Average
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares				$ 80.96
Dividend reinvestment and 401 (k) plans
Long-Term Debt And Equity Financings [Line Items]
Issuances of common stock	$ 2.0			$ 23.0
Accrued Proceeds from Issuance of Common Stock				$ 7.0
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	4.7			4.7
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value	$ 386.0			$ 386.0
Period End Net Cash Settlement Price	29.0			29.0
Period End Net Share Settlement Price	$ 0.3			$ 0.3
Forward Sale Agreement Equity Offering Shares | shares	4.7			4.7
Forward Sale Agreement Gross Sales Price	$ 388.0			$ 388.0
Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Capital contributions from parent				350.0	$ 0.0
Union Electric Company | Other Paid-in Capital:
Long-Term Debt And Equity Financings [Line Items]
Capital contributions from parent	0.0		$ 0.0	350.0	0.0
Union Electric Company | Secured Debt | First Mortgage Bonds, 5.25%, Due 2054 - $350 Issuance
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount										$ 350.0
Debt Instrument, Interest Rate, Stated Percentage										5.25%
Union Electric Company | Secured Debt | Senior Secured Notes 5.20% Due 2034
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount									$ 500.0
Debt Instrument, Interest Rate, Stated Percentage									5.20%
Union Electric Company | Secured Debt | Senior Secured Notes350 Due2024
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount									$ 350.0
Debt Instrument, Interest Rate, Stated Percentage									3.50%
Union Electric Company | Secured Debt | First Mortgage Bonds, 5.125%, Due 2055 - $450 Issuance | Subsequent Event
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount						$ 450.0
Debt Instrument, Interest Rate, Stated Percentage						5.125%
Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Capital contributions from parent				0.0	50.0
Ameren Illinois Company | Other Paid-in Capital:
Long-Term Debt And Equity Financings [Line Items]
Capital contributions from parent	0.0		$ 50.0	0.0	$ 50.0
Ameren Illinois Company | Secured Debt | First Mortgage Bonds, 5.55%, Due 2054 - $625 Issuance
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount								$ 625.0
Debt Instrument, Interest Rate, Stated Percentage								5.55%
Ameren Transmission Company of Illinois | Unsecured Debt | Senior Unsecured Notes, 5.17%, Due 2039
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount							$ 70.0
Debt Instrument, Interest Rate, Stated Percentage							5.17%
Ameren Transmission Company of Illinois | Unsecured Debt | Senior Unsecured Notes, 5.42%, Due 2053
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount							$ 70.0
Debt Instrument, Interest Rate, Stated Percentage							5.42%
Ameren Transmission Company of Illinois | Unsecured Debt | Senior Unsecured Notes, 3.43%, Due 2050
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Interest Rate, Stated Percentage							3.43%
Long-Term Debt, Maturity, Remainder of Fiscal Year							$ 49.0
Ameren (parent) | Unsecured Debt | Senior unsecured Notes 2.50% Due 2024
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount	$ 450.0			$ 450.0
Debt Instrument, Interest Rate, Stated Percentage	2.50%			2.50%