Income Taxes - Reconciliation of our Uncertain Tax Positions (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Uncertain tax positions -
Balance January 1	$ 123	$ 114	$ 115
Gross increases in tax positions in current period	6	7	8
Gross increases in tax positions in prior period	2	14	5
Gross decreases in tax positions in prior period	(5)	(4)	(5)
Gross decreases - settlements	0	(1)	(2)
Gross decreases - statute of limitations expired	(15)	(7)	(7)
Balance December 31	$ 111	$ 123	$ 114