Income Taxes - Reconciliation of Beginning and Ending Amounts of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Balance at January 1	$ 168	$ 205	$ 424
Additions based on tax positions taken in the current year	2	19	14
Additions based on tax positions of prior years	1	36	4
Reductions based on tax positions of prior years	(1)	(78)	(147)
Reductions due to settlements with taxing authorities	0	(10)	(85)
Reductions due to lapses in statutes of limitation	(2)	(4)	(5)
Balance at December 31	$ 168	$ 168	$ 205