Segment Information (Tables)

12 Months Ended

Dec. 31, 2011

Segment Information [Abstract]

Schedule Of Segment Reporting Information, By Segment

	Ameren Missouri		Ameren Illinois Regulated Segment		Merchant Generation			Other			Intersegment Eliminations			Consolidated
2011
External revenues	$	3,358	$	2,774	$	1,394		$	5		$	-		$	7,531
Intersegment revenues		25		13		235			4			(277	)		-
Depreciation and amortization		408		215		143			19			-			785
Interest and dividend income		30		1		-			44			(43	)		32
Interest charges		209		136		105			44			(43	)		451
Income taxes (benefit)		161		127		32			(10	)		-			310
Net income (loss) attributable to Ameren Corporation(a)		287		193		45			(6	)		-			519
Capital expenditures		550		351		153			(24	)(b)		-			1,030
Total assets		12,757		7,213		3,833			1,211			(1,369	)		23,645
2010
External revenues	$	3,176	$	3,002	$	1,459		$	1		$	-		$	7,638
Intersegment revenues		21		12		234			13			(280	)		-
Depreciation and amortization		382		210		146			27			-			765
Interest and dividend income		31		1		1			25			(25	)		33
Interest charges		213		143		133			35			(27	)		497
Income taxes (benefit)		199		137		6			(17	)		-			325
Net income (loss) attributable to Ameren Corporation(a)		364		208		(409	)		(24	)		-			139
Capital expenditures		624		281		101			36			-			1,042
Total assets		12,504		7,406		3,934			1,354			(1,687	)		23,511
2009
External revenues	$	2,847	$	2,957	$	1,322		$	9		$	-		$	7,135
Intersegment revenues		27		27		390			19			(463	)		-
Depreciation and amortization		357		216		126			26			-			725
Interest and dividend income		29		6		-			33			(38	)		30
Interest charges		229		153		119			48			(41	)		508
Income taxes (benefit)		128		79		151			(26	)		-			332
Net income (loss) attributable to Ameren Corporation(a)		259		127		247			(21	)		-			612
Capital expenditures		882		352		408			68			-			1,710
Total assets		12,219		7,181		4,751			1,814			(2,263	)		23,702

(a) Represents net income (loss) available to common stockholders.

(b) Includes the elimination of intercompany transfers.