Income Taxes - Reconciliation of our Uncertain Tax Positions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Uncertain tax positions -
Balance January 1	$ 215	$ 224	$ 112
Gross increases in tax positions due to acquisition	0	0	110
Gross increases in tax positions in current period	4	12	8
Gross increases in tax positions in prior period	14	4	7
Gross decreases in tax positions in prior period	(7)	(5)	(1)
Gross decreases - settlements	0	(12)	(2)
Gross decreases - statute of limitations expired	(18)	(8)	(10)
Balance December 31	$ 208	$ 215	$ 224