Goodwill, Impairment And Other Charges (Tables)

12 Months Ended

Dec. 31, 2011

Goodwill, Impairment And Other Charges [Abstract]

Summary Of Goodwill And Other Asset Impairment Pretax Charges

	Goodwill		Long-Lived Assets and  Related Charges		Emission Allowances		Total
2011:
Ameren(a)	$	—	$	123	$	2	$	125
Ameren Missouri		—		89		—		89
Genco		—		34		1		35
2010:
Ameren(a)		420		101		68		589
Genco		65		64		41		170
2009:
Ameren(a)		—		7		—		7
Genco		—		6		—		6

(a) Includes amounts for registrant and nonregistrant subsidiaries.

Reconciliation Of Goodwill

Ameren

	2011		2010
	Ameren Illinois		Ameren Illinois		Merchant Generation		Total(a)
Gross goodwill at January 1	$	411	$	411	$	420	$	831
Accumulated impairment losses		—		—		—		—
Goodwill, net of accumulated impairment losses	$	411	$	411	$	420	$	831
Impairment losses during year		—		—		420		420
Goodwill, net of impairment losses at December 31	$	411	$	411	$	—	$	411

(a) Includes amounts for Ameren registrants and nonregistrant subsidiaries.