Employee Benefits - Net Postretirement Benefit Cost and the Amount Recognized in OCI for All Funded and Unfunded Plans (Detail) - Other Postretirement Benefit Plans [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Service cost of benefits earned	$ 1	$ 1	$ 1
Interest cost on APBO	2	3	3
Expected return on plan assets	(2)	(3)	(3)
Amortization of prior service credit	(1)	(1)	(1)
Amortization of gains	0	0	(1)
Net pension cost (benefit)	0	0	(1)
Other changes in plan assets and benefit obligations recognized in OCI:
Net (gain) loss	(4)	(6)	13
Amortization of prior service credit	1	1	1
Amortization of losses	0	0	1
Total recognized in comprehensive income	(3)	(5)	15
Total recognized in net postretirement benefit cost and comprehensive income	$ (3)	$ (5)	$ 14