Pension Plans, Postretirement and Other Employee Benefits - Amounts to be Reflected as Component of Net Periodic Cost (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 5
Prior service cost	(1)
Total	4
Postretirement
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	48	$ 49
Prior service cost	$ (4)	$ (6)