Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	$ (2,017)
Balance	279	$ 771	$ 1,010
Intraperiod tax allocation	(8)
Other comprehensive loss	(159)	(539)	(394)
Balance at end of the period	(2,172)	(2,017)
Balance	363	279	771
Net Effect of Exchange Rate Fluctuations
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(568)	(55)
Change before reclassifications	(220)	(513)
Other comprehensive loss	(220)	(513)
Balance at end of the period	(788)	(568)	(55)
Change in Certain Derivative Instruments
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(17)	(11)
Change before reclassifications	7	(4)
Amounts reclassified from accumulated other comprehensive income	6	(1)
Tax effect		(1)
Other comprehensive loss	13	(6)
Balance at end of the period	(4)	(17)	(11)
Employee Benefit Plans
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(1,432)	(1,428)
Change before reclassifications	(2)	(58)
Amounts reclassified from accumulated other comprehensive income	72	83
Translation effect	(25)	(31)
Tax effect	15	2
Intraperiod tax allocation	(8)
Other comprehensive loss	52	(4)
Balance at end of the period	(1,380)	(1,432)	(1,428)
Accumulated Other Comprehensive Loss
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(2,017)	(1,494)
Balance	(2,017)	(1,494)	(1,121)
Change before reclassifications	(215)	(575)
Amounts reclassified from accumulated other comprehensive income	78	82
Translation effect	(25)	(31)
Tax effect	15	1
Intraperiod tax allocation	(8)
Other comprehensive loss	(155)	(523)
Balance at end of the period	(2,172)	(2,017)	(1,494)
Balance	$ (2,172)	$ (2,017)	$ (1,494)