Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Taxes [Line Items]
Statutory federal income tax rate:	35.00%	35.00%	35.00%
Depreciation differences			(1.00%)
Amortization of investment tax credit	(1.00%)	(1.00%)	(1.00%)
State tax	4.00%	4.00%	5.00%
Other permanent items	1.00%	0.00%	(1.00%)
Effective income tax rate	39.00%	38.00%	37.00%
Union Electric Company
Income Taxes [Line Items]
Statutory federal income tax rate:	35.00%	35.00%	35.00%
Depreciation differences		0.00%	(1.00%)
Amortization of investment tax credit	(1.00%)	(1.00%)	(1.00%)
State tax	3.00%	3.00%	3.00%
Other permanent items(a)			1.00%
Other permanent items	0.00%	1.00%	0.00%
Effective income tax rate	37.00%	38.00%	37.00%
Ameren Illinois Company
Income Taxes [Line Items]
Statutory federal income tax rate:	35.00%	35.00%	35.00%
Depreciation differences		(1.00%)
Amortization of investment tax credit	0.00%	0.00%	(1.00%)
State tax	6.00%	6.00%	6.00%
Effective income tax rate	41.00%	40.00%	40.00%

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to deductions. Including, but not limited to, extraterritorial income exclusion deduction, qualified production activity deduction, dividend deduction, deduction for dividend paid to employee stock ownership plan, Medicare prescription drug benefit subsidy deduction, and other deductions.

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