Employee Benefits - Change in FVA (Other Post Retirement Benefit Plan Assets) (Detail) - Other Postretirement Benefit Plans [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
FVA at beginning of year	$ 49	$ 56
Employer contributions	0	0
Plan participants’ contributions	2	2
Benefit payments	(6)	(6)
Actual return on plan assets	5	(3)
FVA at end of year	$ 50	$ 49