Employee Benefits - Net Postretirement Benefit Cost for All Funded and Unfunded Plans (Detail) - Other Postretirement Benefit Plans [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 1	$ 0	$ 1	$ 0
Interest cost on APBO	0	1	2	3
Expected return on plan assets	0	(1)	(2)	(2)
Amortization of unrecognized prior service credit	(1)	0	(1)	(1)
Net pension/postretirement benefit cost	$ 0	$ 0	$ 0	$ 0