Income Taxes - Reconciliation of our Uncertain Tax Positions (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Uncertain tax positions -
Balance January 1	$ 112	$ 111	$ 123
Gross increases in tax positions due to acquisition	110	0	0
Gross increases in tax positions in current period	8	6	6
Gross increases in tax positions in prior period	7	2	2
Gross decreases in tax positions in prior period	(1)	(2)	(5)
Gross decreases - settlements	(2)	0	0
Gross decreases - statute of limitations expired	(10)	(5)	(15)
Balance December 31	$ 224	$ 112	$ 111