Accumulated Other Comprehensive Loss - Schedule of AOCI Components (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
AOCI Attributable to Parent, Net of Tax
Beginning balance (net of tax effect)	$ 12,287
Ending balance (net of tax effect)	14,001
AOCI beginning balance, tax effect	(1,458)	$ (1,222)
Changes in value, tax effect	4	(43)
Reclassifications into earnings, tax effect	63	51
AOCI ending balance, tax effect	(1,391)	(1,214)
Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax
Beginning balance (net of tax effect)	(7,636)	(7,275)
Changes in value (net of tax effect)	53	(26)
Reclassifications into earnings (net of tax effect)	107	89
Ending balance (net of tax effect)	(7,476)	(7,212)
Pension and Other Benefits Liabilities
AOCI Attributable to Parent, Net of Tax
Beginning balance (net of tax effect)	(7,714)	(7,354)
Changes in value (net of tax effect)	0	0
Reclassifications into earnings (net of tax effect)	122	111
Ending balance (net of tax effect)	(7,592)	(7,243)
Deferred income taxes related to pension obligation	1,900	1,900
Derivative Contracts
AOCI Attributable to Parent, Net of Tax
Beginning balance (net of tax effect)	97	140
Changes in value (net of tax effect)	(23)	(72)
Reclassifications into earnings (net of tax effect)	(7)	(22)
Ending balance (net of tax effect)	67	46
Investments
AOCI Attributable to Parent, Net of Tax
Beginning balance (net of tax effect)	(19)	(61)
Changes in value (net of tax effect)	76	46
Reclassifications into earnings (net of tax effect)	(8)	0
Ending balance (net of tax effect)	$ 49	$ (15)