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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 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) - USD ($) shares in Millions	1 Months Ended	3 Months Ended
	Apr. 30, 2020	Mar. 31, 2020	Mar. 31, 2019	Aug. 05, 2019
Long-Term Debt And Equity Financings [Line Items]
Stock Issued During Period, Shares, New Issues		0.2	0.3
Issuance of common stock		$ 13,000,000	$ 19,000,000
Stock Issued During Period, Shares, Other		0.5	0.8
Issuance of common stock for stock-based compensation		$ 38,000,000	$ 54,000,000
Forward Contract Indexed to Issuer's Equity, Indexed Shares (in shares)				7.5
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value		552,000,000
Period End Net Cash Settlement Price		$ 2,000,000
Period End Net Share Settlement Price (in shares)		0.1
Ameren (parent) \| Unsecured Debt [Member] \| Senior Unsecured Notes270 due 2020
Long-Term Debt And Equity Financings [Line Items]
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
Debt Instrument, Interest Rate, Stated Percentage		5.00%
Subsequent Event \| Unsecured Debt [Member] \| 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