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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) - USD ($) shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Aug. 05, 2019
Long-Term Debt And Equity Financings [Line Items]
Stock Issued During Period, Shares, New Issues	0.2	0.2	0.4	0.5
Issuance of common stock	$ 14,000,000		$ 27,000,000	$ 37,000,000
Stock Issued During Period, Shares, Other	0.0	0.0	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	$ 547,000,000		547,000,000
Period End Net Cash Settlement Price	$ 16,000,000		$ 16,000,000
Period End Net Share Settlement Price (in shares)	0.2		0.2
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		$ 800,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.50%		3.50%
Proceeds from Issuance of Debt			$ 793,000,000
Ameren (parent) \| Unsecured Debt \| Senior Unsecured Notes270 due 2020
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.70%		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		$ 465,000,000
Debt Instrument, Interest Rate, Stated Percentage	2.95%		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%
Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Issuance of common stock for stock-based compensation			$ 0	0
Capital contribution from parent			$ 350,000,000	$ 0