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Number Of Acquired Wind Generation Facilities

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Period End Net Cash Settlement Price

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Period End Net Share Settlement Price

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

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Current fair value of each cash settlement alternative for each freestanding forward contract.

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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 the additional capital contribution to the entity.

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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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The fair value of stock issued in noncash financing activities.

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Number of new stock issued during the period.

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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 (Narrative) (Details) shares in Millions	1 Months Ended	3 Months Ended			9 Months Ended
	Oct. 31, 2020 USD ($)	Sep. 30, 2020 USD ($) shares	Mar. 31, 2020 USD ($) shares	Sep. 30, 2019 shares	Sep. 30, 2020 USD ($) shares	Sep. 30, 2019 USD ($) shares	Oct. 30, 2020 USD ($) numberOfWindGenerationFacilities	Apr. 30, 2020 USD ($)	Aug. 05, 2019 shares
Long-Term Debt And Equity Financings [Line Items]
Stock Issued During Period, Shares, New Issues \| shares		0.1		0.2	0.5	0.7
Issuance of common stock		$ 10,000,000			$ 37,000,000	$ 54,000,000
Stock Issued During Period, Shares, Other \| shares		0.0	0.5	0.0	0.5	0.8
Issuance of common stock for stock-based compensation			$ 38,000,000		$ 38,000,000	$ 54,000,000
Forward Contract Indexed to Issuer's Equity, Indexed Shares (in shares) \| shares									7.5
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value		$ 543,000,000			543,000,000
Period End Net Cash Settlement Price		$ 54,000,000			$ 54,000,000
Period End Net Share Settlement Price (in shares) \| shares		0.7			0.7
Ameren (parent) \| Unsecured Debt \| Senior Unsecured Notes 3.50% Due 2031
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount								$ 800,000,000
Debt Instrument, Interest Rate, Stated Percentage								3.50%
Proceeds from Issuance of Debt					$ 793,000,000
Ameren (parent) \| Unsecured Debt \| Senior Unsecured Notes270 due 2020 \| Subsequent Event
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount							$ 350,000,000
Debt Instrument, Interest Rate, Stated Percentage							2.70%
Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Issuance of common stock for stock-based compensation					0	0
Union Electric Company \| Secured Debt \| First Mortgage Bonds, 2.95%, Due 2030 - $465 Issuance
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount			$ 465,000,000
Debt Instrument, Interest Rate, Stated Percentage			2.95%
Proceeds from Issuance of Secured Debt					462,000,000
Union Electric Company \| Secured Debt \| Senior Secured Notes, 5.00%, Due 2020
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount		$ 85,000,000			$ 85,000,000
Debt Instrument, Interest Rate, Stated Percentage		5.00%			5.00%
Union Electric Company \| Secured Debt \| First Mortgage Bonds, 2.625%, Due 2051 - $550 Issuance [Member] \| Subsequent Event
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount							$ 550,000,000
Debt Instrument, Interest Rate, Stated Percentage							2.625%
Proceeds from Issuance of Secured Debt	$ 543,000,000
Number Of Wind Generation Facilities \| numberOfWindGenerationFacilities							2
Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Issuance of common stock for stock-based compensation					$ 0	0
Capital contributions from parent					$ 350,000,000	$ 0