Other Comprehensive Income (Loss) (Schedule of Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss), net of tax	$ 296	$ (204)	$ 552	$ (81)
Unrealized Investment Gains
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	16	6	19	6
Other comprehensive income (loss) before reclassifications	14	0	11	0
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive income (loss), net of tax	14	0	11	0
Balance, ending of period	30	6	30	6
Pension/Postretirement Plans Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(3,208)	(3,014)	(3,232)	(3,124)
Other comprehensive income (loss) before reclassifications	(40)	98	(46)	178
Amounts reclassified from accumulated other comprehensive income	33	31	63	61
Other comprehensive income (loss), net of tax	(7)	129	17	239
Balance, ending of period	(3,215)	(2,885)	(3,215)	(2,885)
Foreign Currency Translation Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(1,645)	(1,089)	(1,880)	(1,102)
Other comprehensive income (loss) before reclassifications	289	(333)	524	(320)
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive income (loss), net of tax	289	(333)	524	(320)
Balance, ending of period	(1,356)	(1,422)	(1,356)	(1,422)
AOCI Attributable to Parent
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(4,837)	(4,097)	(5,093)	(4,220)
Other comprehensive income (loss) before reclassifications	263	(235)	489	(142)
Amounts reclassified from accumulated other comprehensive income	33	31	63	61
Other comprehensive income (loss), net of tax	296	(204)	552	(81)
Balance, ending of period	$ (4,541)	$ (4,301)	$ (4,541)	$ (4,301)