Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ 4,589
Adoption of new accounting guidance related to reclassification of certain tax effects	(45)	$ 0
Ending balance	4,163
AOCI
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(1,287)	(1,807)
Ending balance	(1,240)	(1,643)
Accumulated Foreign Currency Translation Adjustment
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), adjustments during the period	69	144
Income taxes	14	10
Other comprehensive income (loss), net of tax	83	154
Accumulated Pension and Other Postretirement Benefit Adjustments
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Other comprehensive income (loss), adjustments during the period	1	0
Other comprehensive income (loss), adjustments reclassified to income	10	14
Income taxes	(2)	(4)
Other comprehensive income (loss), net of tax	$ 9	$ 10