Income Taxes - Reconciliation of the Beginning and Ending Amount of Gross Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Balance, beginning of year	$ 140	$ 136	$ 123
Increases to tax positions related to the current year	3	11	11
Increases to tax positions related to the prior year	1	1	2
Decreases to tax positions related to the prior year		(8)
Balance, end of year	$ 144	$ 140	$ 136