Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance		$ 416	$ 363	$ 279
Other comprehensive income (loss)	$ 14	(74)	207	(24)
Balance	779	458	779	458
Net Effect of Exchange Rate Fluctuations
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance	(602)	(478)	(788)	(568)
Change before reclassifications	24	(96)	210	(6)
Other comprehensive income (loss)	24	(96)	210	(6)
Balance	(578)	(574)	(578)	(574)
Change in Certain Derivative Instruments
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance	(10)	(19)	(4)	(17)
Amounts reclassified from accumulated other comprehensive income	(4)	7	(10)	5
Tax effect		1		1
Other comprehensive income (loss)	(4)	8	(10)	6
Balance	(14)	(11)	(14)	(11)
Employee Benefit Plans
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance	(1,369)	(1,474)	(1,380)	(1,432)
Change before reclassifications	(6)		(10)
Amounts reclassified from accumulated other comprehensive income	20	15	39	(28)
Translation effect	(10)	10	(14)	11
Tax effect		1		1
Other comprehensive income (loss)	4	26	15	(16)
Balance	(1,365)	(1,448)	(1,365)	(1,448)
Accumulated Other Comprehensive Loss.
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance	(1,981)	(1,971)	(2,172)	(2,017)
Change before reclassifications	18	(96)	200	(6)
Amounts reclassified from accumulated other comprehensive income	16	22	29	(23)
Translation effect	(10)	10	(14)	11
Tax effect		2		2
Other comprehensive income (loss)	24	(62)	215	(16)
Balance	$ (1,957)	$ (2,033)	$ (1,957)	$ (2,033)