Employee Benefits - Changes in FVA (Detail) - Pension 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	$ 869	$ 957
Actual return on plan assets	42	(15)
Employer contributions	14	14
Benefit payments	(85)	(87)
Plan acquisitions	293	0
FVA at end of year	$ 1,133	$ 869