Employee Benefits - Net Pension Cost (Benefit) for All Funded and Unfunded Plans (Detail) - Pension Plans [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Interest cost on PBO	$ 12	$ 10	$ 36	$ 31
Expected return on plan assets	(17)	(13)	(51)	(39)
Amortization of losses	4	4	12	12
Net pension/postretirement benefit cost	$ (1)	$ 1	$ (3)	$ 4