Other Comprehensive Income (Loss) (Components of Accumulated Other Comprehensive Income Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance as of January 1, 2015	$ (3,847)	$ (2,621)
Other comprehensive income (loss) before reclassifications	(541)	(1,331)
Amounts reclassified from accumulated other comprehensive loss	168	105
Other comprehensive (loss) income, net of tax	(373)	(1,226)	$ 686
Balance as of December 31, 2015	(4,220)	(3,847)	(2,621)
Foreign currency translation adjustments (net of deferred tax asset of $8 and $5 in 2015 and 2014, respectively)				$ (1,102)	$ (459)
Net unrealized investment gains (net of deferred tax liability of $2 in both 2015 and 2014)				6	5
Net charges related to pension / post-retirement plans (net of deferred tax asset of $1,519 and $1,587 in 2015 and 2014, respectively)				(3,124)	(3,393)
Accumulated other comprehensive income (loss)	(3,847)	(2,621)	(2,621)	(4,220)	(3,847)
Foreign currency translation adjustments, tax portion				(8)	(5)
Net unrealized investment gains, tax portion				2	2
Net charges related to pension/ retiree plans, tax portion				1,519	1,587
Unrealized Investment Gains
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance as of January 1, 2015	5	5
Other comprehensive income (loss) before reclassifications	1	0
Amounts reclassified from accumulated other comprehensive loss	0	0
Other comprehensive (loss) income, net of tax	1	0
Balance as of December 31, 2015	6	5	5
Accumulated other comprehensive income (loss)	5	5	5	6	5
Pension/Post-Retirement Plans Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance as of January 1, 2015	(3,393)	(2,682)
Other comprehensive income (loss) before reclassifications	101	(816)
Amounts reclassified from accumulated other comprehensive loss	168	105
Other comprehensive (loss) income, net of tax	269	(711)
Balance as of December 31, 2015	(3,124)	(3,393)	(2,682)
Accumulated other comprehensive income (loss)	(3,393)	(2,682)	(2,682)	(3,124)	(3,393)
Foreign Currency Translation Adjustments
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance as of January 1, 2015	(459)	56
Other comprehensive income (loss) before reclassifications	(643)	(515)
Amounts reclassified from accumulated other comprehensive loss	0	0
Other comprehensive (loss) income, net of tax	(643)	(515)
Balance as of December 31, 2015	(1,102)	(459)	56
Accumulated other comprehensive income (loss)	$ (459)	$ 56	$ 56	$ (1,102)	$ (459)