Retirement Benefits (Tables)

6 Months Ended

Jun. 30, 2017

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 six months ended June 30, 2017 and 2016:



	Pension Benefits												Postretirement Benefits
	Three Months						Six Months						Three Months						Six Months
	2017			2016			2017			2016			2017			2016			2017			2016
Service cost	$	23		$	20		$	46		$	40		$	5		$	5		$	10		$	10
Interest cost	45			45			90			92			11			12			23			24
Expected return on plan assets	(65		)	(63		)	(131		)	(126		)	(18		)	(18		)	(37		)	(36		)
Amortization of:
Prior service benefit	—			—			—			—			(1		)	(1		)	(2		)	(2		)
Actuarial loss (gain)	13			7			27			16			(1		)	(2		)	(3		)	(5		)
Net periodic benefit cost (benefit)	$	16		$	9		$	32		$	22		$	(4	)	$	(4	)	$	(9	)	$	(9	)

Summary Of Benefit Plan Costs Incurred

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 six months ended June 30, 2017 and 2016:



	Pension Benefits										Postretirement Benefits
	Three Months					Six Months					Three Months						Six Months
	2017		2016			2017		2016			2017			2016			2017			2016
Ameren Missouri^(a)	$	6	$	5		$	12	$	13		$	(1	)	$	(1	)	$	(2	)	$	(2	)
Ameren Illinois	10		6			20		11			(3		)	(3		)	(7		)	(7		)
Other	—		(2		)	—		(2		)	—			—			—			—
Ameren^(a)(b)	$	16	$	9		$	32	$	22		$	(4	)	$	(4	)	$	(9	)	$	(9	)


(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.