Selected Quarterly Information (Tables)

12 Months Ended

Dec. 31, 2012

Selected Quarterly Financial Information [Abstract]

Summary Of Selected Quarterly Information

Quarter Ended(a)	Operating Revenues		Operating Income (Loss)(b)			Net Income (Loss) Attributable to Ameren Corporation			Earnings (Loss) per Common Share - Basic and Diluted
Ameren
March 31, 2012	$	1,658	$	(422	)	$	(403	)	$	(1.66	)
March 31, 2011	1,904		227			71			0.29
June 30, 2012	1,660		363			211			0.87
June 30, 2011	1,781		316			138			0.57
September 30, 2012	2,001		635			374			1.54
September 30, 2011	2,268		550			285			1.18
December 31, 2012	1,509		(1,816		)	(1,156		)	(4.76		)
December 31, 2011	1,578		148			25			0.10

(a) The sum of quarterly amounts, including per share amounts, may not equal amounts reported for year-to-date periods. This is due to the effects of rounding and changes in the number of weighted-average shares outstanding each period.

(b) Includes pretax "Impairment and other charges" of $2,578 million and $125 million recorded at Ameren during the years ended December 31, 2012, and 2011, respectively. See Note 17 - Impairment and Other Charges under Part II, Item 8, for additional information.

Quarter Ended	Operating Revenues		Operating Income		Net Income (Loss)			Net Income (Loss) Available to Common Stockholder
Ameren Missouri
March 31, 2012	$	691	$	78	$	22		$	21
March 31, 2011	772		77		22			21
June 30, 2012	844		269		144			143
June 30, 2011	822		176		91			90
September 30, 2012	1,064		429		237			236
September 30, 2011	1,115		333		191			190
December 31, 2012	673		69		16			16
December 31, 2011	674		23		(14		)	(14		)

Quarter Ended	Operating Revenues		Operating Income		Net Income		Net Income Available to Common Stockholder
Ameren Illinois
March 31, 2012	$	724	$	89	$	28	$	27
March 31, 2011	808		88		34		33
June 30, 2012	564		86		33		32
June 30, 2011	623		99		38		37
September 30, 2012	648		151		71		71
September 30, 2011	745		196		98		98
December 31, 2012	589		51		12		11
December 31, 2011	611		75		26		25