Long-Term Debt And Equity Financings [Line Items]

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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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- Definition

Number of new stock issued during the period.

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Long-Term debt and Equity Financings (Narrative) (Details) - USD ($) shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2018	Jun. 30, 2017
Long-Term Debt And Equity Financings [Line Items]
Stock Issued During Period, Shares, New Issues	0.4	0.7	0.7
Noncash financing activity - Issuance of common stock for stock-based compensation		$ 35,000,000	$ 35,000,000	$ 0
Issuance of common stock	$ 23,000,000		40,000,000	$ 0
Union Electric Company \| First Mortgage Bonds, 4.00%, Due 2048 - $425 Issuance [Member] \| Secured Debt
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 \| Senior Secured Notes 6 Point 00 Due 2018 [Member] \| Secured Debt
Long-Term Debt And Equity Financings [Line Items]
State interest rate	6.00%		6.00%
Repayments of other long-term debt			$ 179,000,000
Ameren Illinois Company \| First Mortgage Bonds, 3.80%, Due 2028 [Member] \| Secured Debt
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 \| Senior Secured Notes6250 Due2018 [Member] \| Secured Debt
Long-Term Debt And Equity Financings [Line Items]
State interest rate	6.25%		6.25%
Repayments of other long-term debt			$ 144,000,000