Summary Of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2013

Accounting Policies [Abstract]

Summary Of Nonvested Shares Related To Long-Term Incentive Plan

A summary of nonvested shares as of March 31, 2013, and changes during the three months ended March 31, 2013, under the 2006 Omnibus Incentive Compensation Plan (2006 Plan) is presented below:

	Performance Share Units
	Share Units		Weighted-average Fair Value Per Unit at Grant Date
Nonvested at January 1, 2013	1,192,487		$	33.56
Granted(a)	832,034		31.19
Forfeitures	(5,456	)	32.67
Vested(b)	(122,671	)	31.19
Nonvested at March 31, 2013	1,896,394		$	32.68

(a) Includes performance share units (share units) granted to certain executive and nonexecutive officers and other eligible employees in January 2013 under the 2006 Plan.

(b) Share units vested due to the attainment of retirement eligibility by certain employees. Actual shares issued for retirement-eligible employees will vary depending on actual performance over the three-year measurement period.

Schedule Of Amortization Expense Based On Usage Of Renewable Energy Credits And Emission Allowances

The following table presents amortization expense based on usage of renewable energy credits and emission allowances, net of gains from sales, for Ameren, Ameren Missouri, and Ameren Illinois, during the three months ended March 31, 2013, and 2012.

		Three Months
		2013		2012
Ameren Missouri	$	(a)	$	(a)
Ameren Illinois		4		(a)
Ameren	$	4	$	(a)

(a) Less than $1 million.

Schedule of Excise Taxes

The following table presents excise taxes recorded in “Operating Revenues - Electric,” “Operating Revenues - Gas” and “Operating Expenses - Taxes other than income taxes” for the three months ended March 31, 2013, and 2012:

	Three Months
	2013		2012
Ameren Missouri	$	33	$	27
Ameren Illinois	22		18
Ameren	$	55	$	45

Equity Changes Attributable To Noncontrolling Interest

A reconciliation of the equity changes attributable to the noncontrolling interests at Ameren for the three months ended March 31, 2013, and 2012, is shown below:

	Three Months
	2013			2012
Ameren:
Noncontrolling interests, beginning of period (a)	$	151		$	149
Net income from continuing operations attributable to noncontrolling interests	2			2
Net income (loss) from discontinued operations attributable to noncontrolling interests	—			(2		)
Dividends paid to noncontrolling interest holders	(2		)	(2		)
Noncontrolling interests, end of period (a)	$	151		$	147

(a) Includes the 20% EEI ownership interest not owned by Ameren. The assets and liabilities of EEI were consolidated in Ameren’s balance sheet at a 100% ownership level and were included in “Current assets of discontinued operations” and “Current liabilities of discontinued operations,” however, the 20% ownership interest not owned by Ameren was included in “Noncontrolling interests” on Ameren’s March 31, 2013, and December 31, 2012 balance sheet. See Note 2 - Divestiture Transactions and Discontinued Operations for additional information.