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- Definition

Common Stock Equity To Total Capitalization

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- Definition

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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-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

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- Definition

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

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

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The percentage rate used to calculate dividend payments on preferred stock.

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- Definition

The cash inflow from parent as a source of financing that is recorded as additional paid in capital.

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-Name Accounting Standards Codification

-Topic 230

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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

The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

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Long-Term Debt And Equity Financings (Narrative) (Detail) - USD ($)	1 Months Ended	9 Months Ended
	Apr. 30, 2015	Sep. 30, 2015	Sep. 30, 2014
Long-Term Debt And Equity Financings [Line Items]
Redemptions of Long-term Debt		$ 114,000,000	$ 692,000,000
Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Capital contribution from parent		224,000,000	0
Redemptions of Long-term Debt		$ 114,000,000	104,000,000
Ameren Missouri And Ameren Illinois
Long-Term Debt And Equity Financings [Line Items]
Assumed interest rate		5.00%
Dividend rate		6.00%
Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Redemptions of Long-term Debt		$ 0	$ 163,000,000
Ameren Illinois Company \| Federal Energy Regulatory Commission Restriction
Long-Term Debt And Equity Financings [Line Items]
Common stock equity to total capitalization		52.00%
Ameren Illinois Company \| Minimum \| Federal Energy Regulatory Commission Restriction
Long-Term Debt And Equity Financings [Line Items]
Common stock equity to total capitalization		30.00%
Secured Debt \| Senior Secured Notes, 3.65%, Due 2045 \| Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount	$ 250,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.65%
Proceeds from Issuance of Secured Debt	$ 247,000,000
Secured Debt \| Senior Secured Notes 4.75% Due 2015 \| Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Redemptions of Long-term Debt	$ 114,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.75%