Accumulated Other Comprehensive Loss - Schedule of AOCI Components (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
AOCI Attributable to Parent, Net of Tax
Accumulated other comprehensive loss, beginning balance	$ (7,275)	$ (7,311)
Changes in value (net of tax effect)	(25)	10
Reclassifications into earnings (net of tax effect)	21	7
Accumulated other comprehensive loss, ending balance	(7,279)	(7,294)
Accumulated other comprehensive income tax portion, period start	1,222	1,279
Other comprehensive income tax affect	20	13
Reclassification into earnings tax effect	12	5
Accumulated other comprehensive income tax portion, period end	1,230	1,261
Deferred income taxes related to pension obligation	1,900	1,900
Pension and Other Benefits Liabilities
AOCI Attributable to Parent, Net of Tax
Accumulated other comprehensive loss, beginning balance	(7,354)	(7,517)
Reclassifications into earnings (net of tax effect)	36	39
Accumulated other comprehensive loss, ending balance	(7,318)	(7,478)
Derivative Contracts
AOCI Attributable to Parent, Net of Tax
Accumulated other comprehensive loss, beginning balance	140	222
Changes in value (net of tax effect)	(36)	22
Reclassifications into earnings (net of tax effect)	(15)	(32)
Accumulated other comprehensive loss, ending balance	89	212
Investments
AOCI Attributable to Parent, Net of Tax
Accumulated other comprehensive loss, beginning balance	(61)	(16)
Changes in value (net of tax effect)	11	(12)
Accumulated other comprehensive loss, ending balance	$ (50)	$ (28)