Changes in Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Beginning Balance	$ 63	$ 59	$ 56
Additions based on tax positions related to the current year	8	6	3
Additions for tax positions for prior years	0	9	3
Reductions for tax positions for prior years	(6)	(10)	(3)
Settlements	(3)	0	0
Statute of limitations	(1)	(1)	0
Ending Balance	$ 61	$ 63	$ 59