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Long-Term Debt And Equity Financings [Line Items]

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Fair value amount of debt instrument that was repurchased.

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Indicates type of variable interest rate on debt instrument.

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The per share price of the Company's stock at which the contract holder of the freestanding contract has the right to purchase or sell the Company's stock at a future date.

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The number of issuer's shares to which the forward contract is indexed.

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Amount that would be paid upon settlement of forward contract indexed to equity.

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Number of shares as a settlement alternative for each freestanding forward contract.

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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The cash inflow from parent as a source of financing that is recorded as additional paid in capital.

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For a forward contract or an option indexed to the issuer's equity shares, the number of issuer's shares to which the contract is indexed.

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Number of shares issued during the period from a dividend reinvestment plan (DRIP). A dividend reinvestment plan allows the shareholders to reinvest dividends paid to them by the entity on new issues of stock by the entity.

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Number of shares of stock issued attributable to transactions classified as other.

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Long-Term debt and Equity Financings (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	1 Months Ended		3 Months Ended			6 Months Ended	9 Months Ended
	Oct. 31, 2026	Sep. 30, 2026	Sep. 30, 2026	Jun. 30, 2026	Sep. 30, 2025	Jun. 30, 2026	Sep. 30, 2026	Sep. 30, 2025	May 31, 2026	Feb. 28, 2026
Long-Term Debt And Equity Financings [Line Items]
Shares issued under the DRPlus and 401(k) plan			100		100		300	300
Issuances of common stock							$ 31.0	$ 35.0
Stock Issued During Period, Shares, Other (in shares)			0		0	200	200	300
Stock Issued During Period, Value, Other				$ 25.0
Common Stock, Shares Authorized Under Dividend Reinvestment Plan									1,900
Increase To Total Common Stock Available For Sale Under ATM Program			$ 2,000.0
Total Common Stock Available For Sale Under ATM Program		$ 5,000.0	5,000.0				$ 5,000.0
Maximum Value Of Shares To Be Issued Under ATM Program		$ 2,000.0	$ 2,000.0				$ 2,000.0
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Number of Shares Indexed		13,000	13,000				13,000
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share							$ 91.89
Forward Contract Indexed to Issuer's Equity, Indexed Shares		6,400	6,400				6,400
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration]		US Treasury (UST) Interest Rate [Member]
Gain (Loss) on Extinguishment of Debt			$ 0.0		$ 0.0		$ 4.0	$ 8.0
Subsequent Event
Long-Term Debt And Equity Financings [Line Items]
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Number of Shares Indexed	2,100
Dividend reinvestment and 401 (k) plans
Long-Term Debt And Equity Financings [Line Items]
Issuances of common stock			2.0				24.0
Accrued Proceeds from Issuance of Common Stock							6.0
Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Capital contributions from parent			125.0				550.0	$ 0.0
First Mortgage Bonds 5.00% Due 2036 \| Unsecured Debt \| Ameren (parent)
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount										$ 400.0
Debt Instrument, Interest Rate, Stated Percentage										5.00%
Senior Unsecured Notes 3.65% Due 2026 \| Unsecured Debt \| Ameren (parent)
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount										$ 350.0
Debt Instrument, Interest Rate, Stated Percentage										3.65%
Junior Subordinated Notes 6.45% Due 2057 \| Unsecured Debt \| Ameren (parent)
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount		$ 900.0	$ 900.0				$ 900.0
Debt Instrument, Interest Rate, Stated Percentage		6.45%	6.45%				6.45%
Debt Instrument, Basis Spread on Variable Rate		1.868%
Senior Secured Notes and First Mortgage Bonds \| Secured Debt \| Ameren (parent) \| Related Party
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Repurchase Amount		$ 16.0	$ 16.0				$ 16.0
Gain (Loss) on Extinguishment of Debt							4.0
First Mortgage Bonds 4.80% Due 2036 \| Secured Debt \| Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount										$ 450.0
Debt Instrument, Interest Rate, Stated Percentage										4.80%
First Mortgage Bonds 5.55% Due 2056 \| Secured Debt \| Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount										$ 450.0
Debt Instrument, Interest Rate, Stated Percentage										5.55%
First Mortgage Bonds 5.75% Due 2056 \| Secured Debt \| Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount				$ 500.0		$ 500.0
Debt Instrument, Interest Rate, Stated Percentage				5.75%		5.75%
First Mortgage Bonds 5.50% Due 2036 \| Secured Debt \| Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount		$ 400.0	$ 400.0				$ 400.0
Debt Instrument, Interest Rate, Stated Percentage		5.50%	5.50%				5.50%
Senior Unsecured Notes 5.83% Due 2041 \| Unsecured Debt \| Ameren Illinois Transmission
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount		$ 140.0	$ 140.0				$ 140.0
Debt Instrument, Interest Rate, Stated Percentage		5.83%	5.83%				5.83%
Senior Unsecured Notes 6.24% Due 2054 \| Unsecured Debt \| Ameren Illinois Transmission
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount		$ 160.0	$ 160.0				$ 160.0
Debt Instrument, Interest Rate, Stated Percentage		6.24%	6.24%				6.24%
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		19,400	19,400				19,400
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value		$ 2,000.0	$ 2,000.0				$ 2,000.0
Period End Net Cash Settlement Price		80.0	80.0				80.0
Period End Net Share Settlement Price		$ 0.8	$ 0.8				$ 0.8
Forward Sale Agreement Equity Offering Shares		19,400	19,400				19,400
Forward Sale Agreement Gross Sales Price		$ 2,000.0	$ 2,000.0				$ 2,000.0
Minimum
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share							$ 104.39
Minimum \| Junior Subordinated Notes 6.45% Due 2057 \| Unsecured Debt \| Ameren (parent)
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Basis Spread on Variable Rate		6.45%
Maximum
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share							112.91
Weighted Average
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share							$ 109.51
Weighted Average \| Subsequent Event
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share	$ 99.59