Accumulated Other Comprehensive Loss (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Other comprehensive income (loss)	$ (220)	$ 56
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	(253)	35
Other comprehensive income (loss)	(253)	35
Balance at end of the period	(308)	264
Change in Certain Derivative Instruments
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period		(12)	(11)
Change before reclassifications		2
Amounts reclassified from accumulated other comprehensive income		(1)
Other comprehensive income (loss)		1
Balance at end of the period	(11)	(11)	(11)
Employee Benefit Plans
Increase (Decrease) Accumulated Other Comprehensive Loss, Net of Tax
Balance at beginning of the period	(1,428)	(1,338)
Amounts reclassified from accumulated other comprehensive income	21	23
Translation effect	15	1
Tax effect	1	(1)
Other comprehensive income (loss)	37	23
Balance at end of the period	(1,391)	(1,315)
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	(253)	37
Amounts reclassified from accumulated other comprehensive income	21	22
Translation effect	15	1
Tax effect	1	(1)
Other comprehensive income (loss)	(216)	59
Balance at end of the period	$ (1,710)	$ (1,062)