Employee Benefit Plans - Sources of Change in Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Sources of change in other comprehensive income
Net gain (loss) arising during the period	$ (840)	$ 688		$ (704)
Amortization of (gain) loss included in income	131	294		430
Prior service (cost) credit arising during the period	(3)	1		2
Reclassification adjustment for amortization of prior service cost included in net income	(6)	(5)		(5)
United States Pension Plans of US Entity, Defined Benefit [Member]
Sources of change in other comprehensive income
Net gain (loss) arising during the period	(456)	524
Amortization of (gain) loss included in income	77	218	[1]
Net change during the period	(379)	742
Reclassification adjustment for amortization of prior service cost included in net income	6	6
Net change during the period	6	6
Amounts included in accumulated other comprehensive income that are expected to be amortized into net periodic postretirement cost
Unrecognized net actuarial loss (gain)	115
Unrecognized prior service cost (credit)	6
Foreign Pension Plans, Defined Benefit [Member]
Sources of change in other comprehensive income
Net gain (loss) arising during the period	(331)	107
Amortization of (gain) loss included in income	57	73	[1]
Net change during the period	(274)	180
Prior service (cost) credit arising during the period	(3)	1
Reclassification adjustment for amortization of prior service cost included in net income	(8)	(7)
Net change during the period	(11)	(6)
Amounts included in accumulated other comprehensive income that are expected to be amortized into net periodic postretirement cost
Unrecognized net actuarial loss (gain)	86
Unrecognized prior service cost (credit)	(7)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Sources of change in other comprehensive income
Net gain (loss) arising during the period	(53)	57
Amortization of (gain) loss included in income	(3)	3
Net change during the period	(56)	60
Reclassification adjustment for amortization of prior service cost included in net income	(4)	(4)
Net change during the period	(4)	(4)
Amounts included in accumulated other comprehensive income that are expected to be amortized into net periodic postretirement cost
Unrecognized net actuarial loss (gain)	3
Unrecognized prior service cost (credit)	$ (4)

[1] *Includes settlement losses recognized in 2013.