Retirement Benefits

9 Months Ended

Sep. 30, 2016

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

The following table presents the components of the net periodic benefit cost (benefit) incurred for Ameren’s pension and postretirement benefit plans for the three and nine months ended September 30, 2016 and 2015:



	Pension Benefits												Postretirement Benefits
	Three Months						Nine Months						Three Months						Nine Months
	2016			2015			2016			2015			2016			2015			2016			2015
Service cost	$	20		$	23		$	60		$	69		$	5		$	6		$	15		$	17
Interest cost	46			43			138			130			12			12			36			36
Expected return on plan assets	(63		)	(62		)	(189		)	(186		)	(18		)	(17		)	(54		)	(51		)
Amortization of:
Prior service benefit	—			—			—			—			(1		)	(1		)	(3		)	(3		)
Actuarial loss (gain)	8			19			24			56			(3		)	1			(8		)	4
Settlement loss	—			—			—			1			—			—			—			—
Net periodic benefit cost (benefit)	$	11		$	23		$	33		$	70		$	(5	)	$	1		$	(14	)	$	3

Ameren Missouri and Ameren Illinois are responsible for their respective shares of Ameren’s pension and postretirement costs. The following table presents the pension costs and the postretirement benefit costs (benefit) incurred for the three and nine months ended September 30, 2016 and 2015:



	Pension Benefits										Postretirement Benefits
	Three Months					Nine Months					Three Months						Nine Months
	2016			2015		2016			2015		2016			2015			2016			2015
Ameren Missouri^(a)	$	6		$	14	$	19		$	42	$	(1	)	$	2		$	(3	)	$	6
Ameren Illinois	6			9		17			28		(3		)	—			(10		)	(2		)
Other	(1		)	—		(3		)	—		(1		)	(1		)	(1		)	(1		)
Ameren^(a)(b)	$	11		$	23	$	33		$	70	$	(5	)	$	1		$	(14	)	$	3


(a)	Does not include the impact of the regulatory tracking mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates.


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