Retirement Benefits (Tables)

9 Months Ended

Sep. 30, 2011

Retirement Benefits [Abstract]

Schedule of Defined Benefit Plans Disclosures

	Pension Benefits(a)												Postretirement Benefits(a)
	Three Months						Nine Months						Three Months						Nine Months
	2011			2010			2011			2010			2011			2010			2011			2010
Service cost	$	19		$	18		$	57		$	51		$	6		$	5		$	17		$	15
Interest cost		45			45			135			138			15			16			44			46
Expected return on plan assets		(54	)		(53	)		(162	)		(159	)		(14	)		(14	)		(41	)		(42	)
Amortization of:
Transition obligation		-			-			-			-			1			1			2			2
Prior service cost (benefit)		-			1			(1	)		5			(2	)		(2	)		(6	)		(6	)
Actuarial loss		10			5			31			14			1			-			3			1
Net periodic cost	$	20		$	16		$	60		$	49		$	7		$	6		$	19		$	16

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

Schedule Net Periodic Benefit Cost for Pension and Postretirement Benefit Plans by Company

	Pension Costs								Postretirement Costs
	Three Months				Nine Months				Three Months				Nine Months
	2011		2010		2011		2010		2011		2010		2011		2010
Ameren Missouri	$	13	$	10	$	39	$	31	$	3	$	3	$	8	$	8
Ameren Illinois		4		3		12		9		3		2		9		6
Genco		1		1		6		6		1		-		2		1
Other		2		2		3		3		-		1		-		1
Ameren(a)	$	20	$	16	$	60	$	49	$	7	$	6	$	19	$	16

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