Other Comprehensive Income (Loss) (Schedule of Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive (loss) income, net of tax	$ (19)	$ 12	$ 533	$ (69)
Unrealized Investment Gains
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	30	6	19	6
Other comprehensive (loss) income before reclassifications	(5)	1	6	1
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive (loss) income, net of tax	(5)	1	6	1
Balance, ending of period	25	7	25	7
Pension/Postretirement Plans Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(3,215)	(2,885)	(3,232)	(3,124)
Other comprehensive (loss) income before reclassifications	(173)	36	(219)	214
Amounts reclassified from accumulated other comprehensive income	33	29	96	90
Other comprehensive (loss) income, net of tax	(140)	65	(123)	304
Balance, ending of period	(3,355)	(2,820)	(3,355)	(2,820)
Foreign Currency Translation Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(1,356)	(1,422)	(1,880)	(1,102)
Other comprehensive (loss) income before reclassifications	126	(54)	650	(374)
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive (loss) income, net of tax	126	(54)	650	(374)
Balance, ending of period	(1,230)	(1,476)	(1,230)	(1,476)
AOCI Attributable to Parent
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(4,541)	(4,301)	(5,093)	(4,220)
Other comprehensive (loss) income before reclassifications	(52)	(17)	437	(159)
Amounts reclassified from accumulated other comprehensive income	33	29	96	90
Other comprehensive (loss) income, net of tax	(19)	12	533	(69)
Balance, ending of period	$ (4,560)	$ (4,289)	$ (4,560)	$ (4,289)