Employee Benefits - Changes in APBO (Detail) - Other Postretirement Benefit Plans [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
PBO/APBO at beginning of year	$ 67	$ 79
Service cost	1	1	$ 1
Interest cost	2	3	3
Plan participants’ contributions	2	2
Actuarial losses (gains)	(1)	(12)
Benefit payments	(6)	(6)
Plan acquisitions	4	0
PBO/APBO at end of year	$ 69	$ 67	$ 79