Other Comprehensive Income (Loss) (Components of Other Comprehensive Income Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 6,602	$ 7,133
Other comprehensive loss, net of tax	(873)	(373)	$ (1,226)
Ending balance	6,272	6,602	7,133
Foreign currency translation adjustments, tax portion	(9)	8
Net unrealized investment gains, tax portion	10	2
Net charges related to pension/ retiree plans, tax portion	(1,530)	(1,519)
Unrealized Investment Gains
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	6	5
Other comprehensive income (loss) before reclassifications	13	1
Amounts reclassified from accumulated other comprehensive loss	0	0
Other comprehensive loss, net of tax	13	1
Ending balance	19	6	5
Pension/Post-Retirement Plans Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(3,124)	(3,393)
Other comprehensive income (loss) before reclassifications	(294)	101
Amounts reclassified from accumulated other comprehensive loss	186	168
Other comprehensive loss, net of tax	(108)	269
Ending balance	(3,232)	(3,124)	(3,393)
Foreign Currency Translation Adjustments
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(1,102)	(459)
Other comprehensive income (loss) before reclassifications	(778)	(643)
Amounts reclassified from accumulated other comprehensive loss	0	0
Other comprehensive loss, net of tax	(778)	(643)
Ending balance	(1,880)	(1,102)	(459)
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(4,220)	(3,847)	(2,621)
Other comprehensive income (loss) before reclassifications	(1,059)	(541)
Amounts reclassified from accumulated other comprehensive loss	186	168
Other comprehensive loss, net of tax	(873)	(373)	(1,226)
Ending balance	$ (5,093)	$ (4,220)	$ (3,847)