Retirement Benefits (Tables)

3 Months Ended

Mar. 31, 2013

Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]

Components Of Net Periodic Benefit Cost

The following table presents the components of the net periodic benefit cost for Ameren’s pension and postretirement benefit plans for the three months ended March 31, 2013, and 2012:

	Pension Benefits						Postretirement Benefits
	Three Months						Three Months
	2013			2012			2013			2012
Service cost	$	24		$	21		$	6		$	6
Interest cost	40			42			12			13
Expected return on plan assets	(54		)	(52		)	(16		)	(14		)
Amortization of:
Prior service cost (benefit)	(1		)	(1		)	(1		)	(1		)
Actuarial loss	22			19			2			3
Net periodic benefit cost	$	31		$	29		$	3		$	7

Summary Of Benefit Plan Costs Incurred

Ameren Missouri and Ameren Illinois are responsible for their share of the pension and postretirement costs. The following table presents the pension costs and the postretirement benefit costs incurred for the three months ended March 31, 2013, and 2012:

	Pension Costs				Postretirement Costs
	Three Months				Three Months
	2013		2012		2013		2012
Ameren Missouri	$	18	$	16	$	2	$	5
Ameren Illinois	10		10		1		2
Other	3		3		—		—
Ameren(a)	$	31	$	29	$	3	$	7

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