Other Comprehensive Income (Loss) (Schedule of Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of amended accounting standard			$ (14)
Other comprehensive (loss) income before reclassifications	$ 35	$ 123
Amounts reclassified from accumulated other comprehensive income	22	29
Other comprehensive income, net of tax	57	152
Unrealized Investment Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	0	14
Cumulative effect of amended accounting standard			(14)
Other comprehensive (loss) income before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	0	0
Other comprehensive income, net of tax	0	0
Balance, ending of period	0	0
Pension/Post-Retirement Plans Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(2,953)	(2,892)
Cumulative effect of amended accounting standard			0
Other comprehensive (loss) income before reclassifications	(59)	(100)
Amounts reclassified from accumulated other comprehensive income	22	29
Other comprehensive income, net of tax	(37)	(71)
Balance, ending of period	(2,990)	(2,963)
Foreign Currency Translation Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(1,694)	(1,165)
Cumulative effect of amended accounting standard			$ 0
Other comprehensive (loss) income before reclassifications	94	223
Amounts reclassified from accumulated other comprehensive income	0	0
Other comprehensive income, net of tax	94	223
Balance, ending of period	(1,600)	(942)
AOCI Attributable to Parent
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(4,647)	(4,043)
Other comprehensive income, net of tax	57	152
Balance, ending of period	$ (4,590)	$ (3,905)