Changes in Fair Value of Level 3 Plan Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Beginning Balance	$ 231	$ 61
Realized losses, net	(6)	(12)
Unrealized gains, net	3	7
Purchases, sales and settlements, net	(207)	(22)
Transfers into (out of) Level 3, net	5	197
Ending Balance	26	231
Private equity funds
Defined Benefit Plan Disclosure [Line Items]
Beginning Balance	200
Purchases, sales and settlements, net	(200)
Transfers into (out of) Level 3, net		200
Ending Balance		200
Other
Defined Benefit Plan Disclosure [Line Items]
Beginning Balance	31	61
Realized losses, net	(6)	(12)
Unrealized gains, net	3	7
Purchases, sales and settlements, net	(7)	(22)
Transfers into (out of) Level 3, net	5	(3)
Ending Balance	$ 26	$ 31