Employee Benefits - Net Pension Cost (Benefit) for All Funded and Unfunded Plans (Detail) - Pension Plans [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Interest cost on PBO	$ 12	$ 11	$ 24	$ 21
Expected return on plan assets	(17)	(13)	(34)	(26)
Amortization of losses	4	4	8	8
Net pension/postretirement benefit cost	$ (1)	$ 2	$ (2)	$ 3