Long-Term debt and Equity Financings (Details) $ / shares in Units, shares in Thousands	1 Months Ended	3 Months Ended
	Apr. 30, 2023 $ / shares	Mar. 31, 2023 USD ($) $ / shares shares	Sep. 30, 2022 USD ($) shares	Mar. 31, 2022 USD ($) shares	Apr. 14, 2023 shares
Long-Term Debt And Equity Financings [Line Items]
Shares issued under the DRPlus and 401(k) plan | shares		100		100
Issuances of common stock		$ 5,000,000		$ 5,000,000
Stock Issued During Period, Shares, Other | shares		500	500	400
Stock Issued During Period, Value, Other			$ 37,000,000
Maximum Value Of Shares To Be Issued Under ATM Program		$ 980,000,000
Forward Contract Indexed to Issuer's Equity, Basis Spread		75
Subsequent Event
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Indexed Shares (in shares) | shares					400
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares	$ 89.11
Minimum
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares		$ 89.31
Maximum
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares		94.80
Weighted Average
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares		$ 92.66
Dividend reinvestment and 401 (k) plans
Long-Term Debt And Equity Financings [Line Items]
Issuances of common stock		$ 5,000,000
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, Indexed Shares (in shares) | shares		3,800
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Shares, at Fair Value | shares		3,400
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value		$ 317,000,000
Period End Net Cash Settlement Price		21,000,000
Period End Net Share Settlement Price		200,000
Forward Sale Agreement Equity Offering Shares		3,400,000
Forward Sale Agreement Gross Sales Price		321,000,000
Forward Sale Agreement, Compensation Received by Counterparty		3,000,000
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
Debt Instrument, Interest Rate, Stated Percentage		5.45%
Proceeds from Issuance of Secured Debt		$ 495,000,000