Selected Quarterly Information (Tables)

12 Months Ended

Dec. 31, 2012

Selected Quarterly Financial Information [Abstract]

Summary Of Selected Quarterly Information

	2012										2011
Quarter ended (a)	March 31			June 30		September 30		December 31			March 31		June 30		September 30		December 31
Operating Revenues	$	1,412		$	1,402	$	1,709	$	1,258		$	1,597	$	1,458	$	1,876	$	1,296
Operating Income (b)	158			344		578		111			156		270		494		91
Net Income (Loss)	(403		)	210		374		(1,155		)	74		139		287		26
Net Income (Loss) Attributable to Ameren Corporation - Continuing Operations	$	37		$	161	$	305	$	15		$	38	$	116	$	265	$	(1	)
Net Income (Loss) Attributable to Ameren Corporation - Discontinued Operations (c)	(440		)	50		69		(1,171		)	33		22		20		26
Net Income (Loss) Attributable to Ameren Corporation	$	(403	)	$	211	$	374	$	(1,156	)	$	71	$	138	$	285	$	25
Earnings (Loss) per Common Share - Basic and Diluted - Continuing Operations	$	0.15		$	0.66	$	1.26	$	0.06		$	0.16	$	0.48	$	1.10	$	(0.01	)
Earnings (Loss) per Common Share - Basic and Diluted - Discontinued Operations	(1.81		)	0.21		0.28		(4.82		)	0.13		0.09		0.08		0.11
Earnings (Loss) per Common Share - Basic and Diluted	$	(1.66	)	$	0.87	$	1.54	$	(4.76	)	$	0.29	$	0.57	$	1.18	$	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 $123 million recorded to continuing operations during the year ended December 31, 2011. See Note 17 - Impairment and Other Charges for additional information.

(c) Includes a pretax asset impairment charge of $2.578 billion recorded to discontinued operations during the year ended December 31, 2012. See Note 16 - Divestiture Transactions and Discontinued Operations for additional information.