Income Taxes - Uncertain Tax Positions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning of year	$ 15	$ 14	$ 28
Effect of provision to tax return filing adjustments	0	5	1
Decrease in unrecognized tax positions as a result of settlement of positions taken during the prior period	(15)	0	0
Reductions to unrecognized tax benefits as a result of the applicable statute of limitations	0	(4)	(15)
Balance as of December 31,	$ 0	$ 15	$ 14