Income Taxes - Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Unrecognized Tax Benefits
Balance at beginning of year	$ 19	$ 4
Additions for tax positions related to the current year	2	1
Additions for tax positions related to prior years	15	2
Settlements for tax positions	(2)	0
Effective Income Tax Rate Reconciliation, Tax Settlement, Amount	1	0
Additions related to Acquisition	0	12
Balance at end of year	$ 33	$ 19