Income Taxes - Schedule of Changes in Valuation Allowance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation Allowance [Line Items]
Balance at beginning of year	$ 2,584	$ 1,940	$ 1,291
Increase to allowance	136	831	772
Release of allowance	(154)	(246)	(209)
Acquisitions and divestitures (F)	0	(1)	(1)
Tax apportionment, tax rate and tax law changes	(14)	(24)	106
Foreign currency translation	(66)	84	(19)
Balance at end of year	2,486	$ 2,584	$ 1,940
Other Net State Deferred Tax Asset
Valuation Allowance [Line Items]
Balance at end of year	$ 675