Other Comprehensive Income (Loss) (Schedule of Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive (loss) income, net of tax	$ (223)	$ (19)	$ (431)	$ 533
Unrealized Investment Gains
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	0	30	14	19
Cumulative effect of new accounting principle in period of adoption					$ (14)
Other comprehensive (loss) income before reclassifications	0	(5)	0	6
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive (loss) income, net of tax	0	(5)	0	6
Balance, ending of period	0	25	0	25
Pension/Postretirement Plans Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(2,807)	(3,215)	(2,892)	(3,232)
Cumulative effect of new accounting principle in period of adoption					0
Other comprehensive (loss) income before reclassifications	(13)	(173)	16	(219)
Amounts reclassified from accumulated other comprehensive income	32	33	88	96
Other comprehensive (loss) income, net of tax	19	(140)	104	(123)
Balance, ending of period	(2,788)	(3,355)	(2,788)	(3,355)
Foreign Currency Translation Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(1,458)	(1,356)	(1,165)	(1,880)
Cumulative effect of new accounting principle in period of adoption					0
Other comprehensive (loss) income before reclassifications	(242)	126	(535)	650
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive (loss) income, net of tax	(242)	126	(535)	650
Balance, ending of period	(1,700)	(1,230)	(1,700)	(1,230)
AOCI Attributable to Parent
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(4,265)	(4,541)	(4,043)	(5,093)
Cumulative effect of new accounting principle in period of adoption					$ (14)
Other comprehensive (loss) income before reclassifications	(255)	(52)	(519)	437
Amounts reclassified from accumulated other comprehensive income	32	33	88	96
Other comprehensive (loss) income, net of tax	(223)	(19)	(431)	533
Balance, ending of period	$ (4,488)	$ (4,560)	$ (4,488)	$ (4,560)