Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance	$ 779	$ 458	$ 363	$ 279
Other comprehensive income (loss)	20	(59)	227	(83)
Balance	939	515	939	515
Net Effect of Exchange Rate Fluctuations
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance	(578)	(574)	(788)	(568)
Change before reclassifications	9	(77)	219	(83)
Other comprehensive income (loss)	9	(77)	219	(83)
Balance	(569)	(651)	(569)	(651)
Change in Certain Derivative Instruments
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance	(14)	(11)	(4)	(17)
Amounts reclassified from accumulated other comprehensive income		(1)	(10)	4
Tax effect				1
Other comprehensive income (loss)		(1)	(10)	5
Balance	(14)	(12)	(14)	(12)
Employee Benefit Plans
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance	(1,365)	(1,448)	(1,380)	(1,432)
Change before reclassifications	(2)		(12)
Amounts reclassified from accumulated other comprehensive income	19	26	58	(2)
Translation effect	(7)	(5)	(21)	6
Tax effect				1
Other comprehensive income (loss)	10	21	25	5
Balance	(1,355)	(1,427)	(1,355)	(1,427)
Accumulated Other Comprehensive Loss.
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance	(1,957)	(2,033)	(2,172)	(2,017)
Change before reclassifications	7	(77)	207	(83)
Amounts reclassified from accumulated other comprehensive income	19	25	48	2
Translation effect	(7)	(5)	(21)	6
Tax effect				2
Other comprehensive income (loss)	19	(57)	234	(73)
Balance	$ (1,938)	$ (2,090)	$ (1,938)	$ (2,090)