Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits
Balance at beginning of period	$ 71	$ 52	$ 63
Increases related to prior year tax positions	24	9	2
Decreases related to prior year tax positions	0	(1)	(2)
Settlements	(11)	(2)	(8)
Foreign currency impact	(2)	(5)	0
Increases related to current year tax positions	0	21	0
Lapse of statute of limitations	0	(3)	(3)
Balance at end of period	$ 82	$ 71	$ 52