Employee Benefits - Net Postretirement Benefit Cost for All Funded and Unfunded Plans (Detail) - Other Postretirement Benefit 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 APBO	$ 0	$ 1	$ 0	$ 2
Expected return on plan assets	0	(1)	0	(2)
Net pension/postretirement benefit cost	$ 0	$ 0	$ 0	$ 0