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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Interest cost on PBO	$ 10	$ 12	$ 20	$ 24
Expected return on plan assets	(13)	(17)	(26)	(34)
Amortization of losses	4	4	8	8
Net pension/postretirement benefit cost	$ 1	$ (1)	$ 2	$ (2)