Long-Term Debt And Equity Financings [Line Items]

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- Definition

The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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- Definition

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

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- Definition

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

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- Definition

The cash inflow from the additional capital contribution to the entity.

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- Definition

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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- Definition

Amount of cash outflow for the payment of debt classified as other, maturing after one year or the operating cycle, if longer.

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- Definition

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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Long-Term debt and Equity Financings (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Oct. 31, 2018	Dec. 31, 2017
Long-Term Debt And Equity Financings [Line Items]
Stock Issued During Period, Shares, New Issues	200,000	700,000	900,000
Issuance of common stock	$ 16,000,000		$ 56,000,000	$ 0
Noncash financing activity - Issuance of common stock for stock-based compensation		$ 35,000,000	$ 35,000,000	$ 0
Common stock, shares authorized (in shares)	400,000,000		400,000,000			400,000,000
Ameren (parent) \| Subsequent Event
Long-Term Debt And Equity Financings [Line Items]
Common stock, shares authorized (in shares)					4,000,000
Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Common stock, shares authorized (in shares)	150,000,000		150,000,000			150,000,000
Union Electric Company \| Secured Debt \| First Mortgage Bonds, 4.00%, Due 2048 - $425 Issuance
Long-Term Debt And Equity Financings [Line Items]
Total principal amount of notes	$ 425,000,000		$ 425,000,000
State interest rate	4.00%		4.00%
Proceeds from Issuance of Secured Debt			$ 419,000,000
Union Electric Company \| Secured Debt \| Senior Secured Notes 6 Point 00 Due 2018
Long-Term Debt And Equity Financings [Line Items]
State interest rate	6.00%		6.00%
Repayments of other long-term debt			$ 179,000,000
Union Electric Company \| Secured Debt \| Senior Secured Notes 5.10% Due 2018
Long-Term Debt And Equity Financings [Line Items]
State interest rate	5.10%		5.10%
Repayments of other long-term debt			$ 199,000,000
Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Common stock, shares authorized (in shares)	45,000,000		45,000,000			45,000,000
Ameren Illinois Company \| Secured Debt \| First Mortgage Bonds, 3.80%, Due 2028
Long-Term Debt And Equity Financings [Line Items]
Total principal amount of notes	$ 430,000,000		$ 430,000,000
State interest rate	3.80%		3.80%
Proceeds from Issuance of Secured Debt			$ 427,000,000
Ameren Illinois Company \| Secured Debt \| Senior Secured Notes6250 Due2018
Long-Term Debt And Equity Financings [Line Items]
State interest rate	6.25%		6.25%
Repayments of other long-term debt			$ 144,000,000