Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 17,877
Other comprehensive loss, net of tax	(5)	$ (163)
Amounts reclassified from accumulated other comprehensive loss		6
Net other comprehensive loss	(5)	(157)
Balance at end of period	13,832	18,610
Pension Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	5
Other comprehensive loss, net of tax	0
Net other comprehensive loss	0
Balance at end of period	5
Foreign Currency Translation Adjustment and Other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(176)	18
Other comprehensive loss, net of tax	(5)	(163)
Amounts reclassified from accumulated other comprehensive loss		6
Net other comprehensive loss	(5)	(157)
Balance at end of period	(181)	(139)
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(171)	18
Balance at end of period	$ (176)	$ (139)