Common Stock Shares Issued Through Forward Sale Agreement

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Common Stock Value Issued Through Forward Sale Agreement

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Long-Term Debt And Equity Financings [Line Items]

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Maximum Value Of Shares To Be Issued Under ATM Program

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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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The cash outflow for reacquisition of callable preferred stock.

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The cash outflow for cost incurred directly with the issuance of an equity security.

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The percentage rate used to calculate dividend payments on preferred stock.

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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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The cash inflow from amounts received from issuance of long-term debt that is wholly or partially secured by collateral. Excludes proceeds from tax exempt secured debt.

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The cash inflow from the issuance of long-term debt that is not secured by collateral. Excludes proceeds from tax exempt unsecured debt.

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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 new stock issued during the period.

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

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Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

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Long-Term debt and Equity Financings (Narrative) (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	May 31, 2021	Feb. 11, 2021
Long-Term Debt And Equity Financings [Line Items]
Shares issued under the DRPlus and 401(k) plan	0.2		0.2	0.3	0.4
Stock Issued During Period, Shares, Other	0.0	0.5	0.0	0.5	0.5
Stock Issued During Period, Value, Other		$ 33
Shares issued under forward sale agreement (in shares)	0.0		0.0	1.6	0.0
Common Stock Value Issued Through Forward Sale Agreement							$ 113
Maximum Value Of Shares To Be Issued Under ATM Program						$ 750
Stock Issued During Period, Shares, New Issues	1.4		0.0	1.4	0.0
Shares issued under the ATM program				$ 121
Payments of Stock Issuance Costs				1
Other Paid-in Capital
Long-Term Debt And Equity Financings [Line Items]
Shares issued under the DRPlus and 401(k) plan	$ 12		$ 14	24	$ 27
Shares issued under the ATM program	121		0	121	0
Ameren (parent) \| Unsecured Debt \| Senior Secured Notes 1.75% Due 2028 [Domain]
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount	$ 450			$ 450
Debt Instrument, Interest Rate, Stated Percentage	1.75%			1.75%
Proceeds from Issuance of Debt				$ 447
Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Capital contributions from parent				183	0
Union Electric Company \| Other Paid-in Capital
Long-Term Debt And Equity Financings [Line Items]
Capital contributions from parent	$ (70)		0	(183)	0
Union Electric Company \| Secured Debt \| Senior Secured Notes 2.15% Due 2032
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount	$ 525			$ 525
Debt Instrument, Interest Rate, Stated Percentage	2.15%			2.15%
Proceeds from Issuance of Secured Debt				$ 521
Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Capital contributions from parent				70	350
Redemption of preferred stock				13	0
Ameren Illinois Company \| Other Paid-in Capital
Long-Term Debt And Equity Financings [Line Items]
Capital contributions from parent	$ (30)		$ (250)	$ (70)	$ (350)
Ameren Illinois Company \| Series6625
Long-Term Debt And Equity Financings [Line Items]
Preferred Stock, Dividend Rate, Percentage				6.625%
Redemption of preferred stock				$ 12
Ameren Illinois Company \| Series775
Long-Term Debt And Equity Financings [Line Items]
Preferred Stock, Dividend Rate, Percentage				7.75%
Redemption of preferred stock				$ 1
Ameren Illinois Company \| Secured Debt \| First Mortgage Bonds, 1.55%, 350 Million Due 2051
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount	$ 350			$ 350
Debt Instrument, Interest Rate, Stated Percentage	2.90%			2.90%
Proceeds from Issuance of Secured Debt				$ 345
Ameren Illinois Company \| Secured Debt \| First Mortgage Bonds, 0.375%, 100 Million Due 2023
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount	$ 100			$ 100
Debt Instrument, Interest Rate, Stated Percentage	0.375%			0.375%
Proceeds from Issuance of Secured Debt				$ 100