Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
AOCI Attributable to Parent, Net of Tax
Beginning balance	$ 10,850	$ 8,813	$ 11,643
Change in value (net of tax effect)	(459)	8	(2,174)
Reclassification into earnings (net of tax effect)	98	28	(7)
Ending balance	12,287	10,850	8,813
Other comprehensive income, tax effect	293	41	1,276
Non cash income tax expense recorded in other comprehensive income	57	16	4
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax
Beginning balance	(7,275)	(7,311)	(5,130)
Ending balance	(7,636)	(7,275)	(7,311)
Pension and Other Benefits Liabilities
AOCI Attributable to Parent, Net of Tax
Beginning balance	(7,354)	(7,517)	(5,323)
Change in value (net of tax effect)	(482)	10	(2,267)
Reclassification into earnings (net of tax effect)	122	153	73
Ending balance	(7,714)	(7,354)	(7,517)
Deferred income taxes, pension obligation	1,900
Derivative Contracts
AOCI Attributable to Parent, Net of Tax
Beginning balance	140	222	219
Change in value (net of tax effect)	(19)	43	83
Reclassification into earnings (net of tax effect)	(24)	(125)	(80)
Ending balance	97	140	222
Investments
AOCI Attributable to Parent, Net of Tax
Beginning balance	(61)	(16)	(26)
Change in value (net of tax effect)	42	(45)	10
Reclassification into earnings (net of tax effect)	0	0	0
Ending balance	$ (19)	$ (61)	$ (16)