Summary Of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2012

Summary Of Significant Accounting Policies [Abstract]

Summary Of Nonvested Shares

	Performance Share Units
	Share Units			Weighted-average Fair Value Per Unit at Grant Date
Nonvested at January 1, 2012		1,156,831		$	31.70
Granted(a)		717,151			35.68
Forfeitures		(3,897	)		32.94
Vested(b)		(110,729	)		35.68
Nonvested at March 31, 2012		1,759,356		$	33.07

(a) Includes performance share units (share units) granted to certain executive and nonexecutive officers and other eligible employees in January 2012 under the 2006 Plan.

(b) Share units vested due to 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 Excise Taxes

		XXXXXX		XXXXXX
	Three Months
	2012		2011
Ameren Missouri	$	27	$	29
Ameren Illinois		18		22
Ameren	$	45	$	51

Schedule Of Equity Changes To The Noncontrolling Interest

		XXXXXXX			XXXXXXX
	Three Months
	2012			2011
Ameren:
Noncontrolling interest, beginning of period	$	149		$	154
Net income attributable to noncontrolling interest		-			3
Dividends paid to noncontrolling interest holders		(2	)		(2	)
Noncontrolling interest, end of period	$	147		$	155
Genco:
Noncontrolling interest, beginning of period	$	7		$	11
Net income (loss) attributable to noncontrolling interest		(2	)		1
Noncontrolling interest, end of period	$	5		$	12