Income Taxes - Reconciliation of Unrecognized Tax Benefits (Excluding Interest and Penalties) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 73	$ 28	$ 18
Additions for tax positions of the current year	0	23	12
Additions for tax positions of prior years	143	27	0
Reductions for tax positions of prior years	(42)	0	0
Settlements with tax authorities	0	0	(1)
Expiration of the statute of limitations	(6)	(5)	(1)
Foreign currency translation	(2)	0	0
Balance at end of year	$ 166	$ 73	$ 28