Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Unrecognized tax benefit at beginning of year	$ 38	$ 98	$ 132
Gross increase for current period tax positions			15
Gross increase for tax positions in prior years	25	10	31
Gross decrease for tax positions in prior years	(2)	(60)	(10)
Cash Settlements	(1)	(3)	(69)
Lapse of statute of limitations	(3)	(7)	(1)
Unrecognized tax benefit at end of year	$ 57	$ 38	$ 98