Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of unrecognized tax benefits
Balance at January 1,	$ 30	$ 24	$ 17
Additions based on tax positions related to the current year	0	0	2
Additions for tax positions of prior years	0	7	6
Reductions for tax positions of prior years	(1)	(1)	0
Reductions related to settlements with taxing authorities	(9)	0	(1)
Balance at December 31,	$ 20	$ 30	$ 24