Other Comprehensive Income (Loss) (Schedule of Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of amended accounting standard					$ (14)
Other comprehensive (loss) income before reclassifications	$ 44	$ (387)	$ 79	$ (264)
Amounts reclassified from accumulated other comprehensive income	19	27	41	56
Other comprehensive income, net of tax	63	(360)	120	(208)
Unrealized Investment Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	0	0	0	14
Cumulative effect of amended accounting standard					(14)
Other comprehensive (loss) income before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive income, net of tax	0	0	0	0
Balance, ending of period	0	0	0	0
Pension/Post-Retirement Plans Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(2,990)	(2,963)	(2,953)	(2,892)
Cumulative effect of amended accounting standard					0
Other comprehensive (loss) income before reclassifications	29	129	(30)	29
Amounts reclassified from accumulated other comprehensive income	19	27	41	56
Other comprehensive income, net of tax	48	156	11	85
Balance, ending of period	(2,942)	(2,807)	(2,942)	(2,807)
Foreign Currency Translation Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(1,600)	(942)	(1,694)	(1,165)
Cumulative effect of amended accounting standard					$ 0
Other comprehensive (loss) income before reclassifications	15	(516)	109	(293)
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive income, net of tax	15	(516)	109	(293)
Balance, ending of period	(1,585)	(1,458)	(1,585)	(1,458)
AOCI Attributable to Parent
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(4,590)	(3,905)	(4,647)	(4,043)
Other comprehensive income, net of tax	63	(360)	120	(208)
Balance, ending of period	$ (4,527)	$ (4,265)	$ (4,527)	$ (4,265)