Pension and Other Postretirement Benefit Plans - Components of Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (loss) gain arising during the period	$ (2,085)	$ 2,676	$ (688)
Prior service (cost) credit arising during the period	(59)	(23)	(16)
Total	(2,144)	2,653	(704)
Net loss amortization included in benefit cost	135	318	217
Prior service (credit) cost amortization included in benefit cost	(61)	(67)	(68)
Total	74	251	149
International [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (loss) gain arising during the period	(779)	513	(1,219)
Prior service (cost) credit arising during the period	(8)	226	3
Total	(787)	739	(1,216)
Net loss amortization included in benefit cost	74	89	39
Prior service (credit) cost amortization included in benefit cost	(15)	(4)	(3)
Total	59	85	36
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (loss) gain arising during the period	(223)	499	(24)
Prior service (cost) credit arising during the period	(42)	26	78
Total	(265)	525	54
Net loss amortization included in benefit cost	1	23	31
Prior service (credit) cost amortization included in benefit cost	(72)	(73)	(66)
Total	$ (71)	$ (50)	$ (35)