Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	$ 654
Other comprehensive income (loss)	(539)	$ (394)	$ 379
Balance at end of the period	171	654
Net Effect of Exchange Rate Fluctuations
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(55)	229
Change before reclassifications	(513)	(284)
Other comprehensive income (loss)	(513)	(284)
Balance at end of the period	(568)	(55)	229
Change in Certain Derivative Instruments
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(11)	(12)
Change before reclassifications	(4)	3
Amounts reclassified from accumulated other comprehensive income	(1)	(2)
Tax effect	(1)
Other comprehensive income (loss)	(6)	1
Balance at end of the period	(17)	(11)	(12)
Employee Benefit Plans
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(1,428)	(1,338)
Change before reclassifications	(58)	(140)
Amounts reclassified from accumulated other comprehensive income	83	92
Translation effect	(31)	(32)
Tax effect	2	(10)
Other comprehensive income (loss)	(4)	(90)
Balance at end of the period	(1,432)	(1,428)	(1,338)
Accumulated Other Comprehensive Loss
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(1,494)	(1,121)
Change before reclassifications	(575)	(421)
Amounts reclassified from accumulated other comprehensive income	82	90
Translation effect	(31)	(32)
Tax effect	1	(10)
Other comprehensive income (loss)	(523)	(373)
Balance at end of the period	$ (2,017)	$ (1,494)	$ (1,121)