Income Taxes - Reconciliation of Beginning and Ending Amount of Gross Unrecognized Tax Benefits, Including Accrued interest (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Balance beginning	$ 42	$ 49	$ 54
Additions based on tax positions related to the current year	18	9	6
Additions based on tax positions of prior years	21	2
Accrued interest	2	1	2
Reductions for tax positions of prior years	(1)		(7)
Settlements	(3)	(11)	(1)
Lapse of statute of limitations	(8)	(8)	(5)
Balance ending	$ 71	$ 42	$ 49