Employee Benefits - Net Postretirement Benefit Cost for Funded and Unfunded Plans (Detail) - Other Postretirement Benefit Plans [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Interest cost on APBO	$ 1	$ 1	$ 3	$ 3
Expected return on plan assets	(1)	(1)	(2)	(3)
Amortization of unrecognized prior service credit			(1)
Net benefit cost	$ 0	$ 0	$ 0	$ 0