Other Comprehensive Income (Loss) (Schedule of Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of amended accounting standard					$ (14)
Other comprehensive income before reclassifications	$ (419)	$ (255)	$ (340)	$ (519)
Amounts reclassified from accumulated other comprehensive income	15	32	56	88
Other comprehensive income (loss), net of tax	(404)	(223)	(284)	(431)
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(4,527)	(4,265)	(4,647)	(4,043)
Other comprehensive income (loss), net of tax	(404)	(223)	(284)	(431)
Balance, ending of period	(4,931)	(4,488)	(4,931)	(4,488)
Unrealized Investment Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	0	0	0	14
Cumulative effect of amended accounting standard					(14)
Other comprehensive income before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive income (loss), net of tax	0	0	0	0
Balance, ending of period	0	0	0	0
Pension/Post-Retirement Plans Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(2,942)	(2,807)	(2,953)	(2,892)
Cumulative effect of amended accounting standard					0
Other comprehensive income before reclassifications	56	(13)	26	16
Amounts reclassified from accumulated other comprehensive income	15	32	56	88
Other comprehensive income (loss), net of tax	71	19	82	104
Balance, ending of period	(2,871)	(2,788)	(2,871)	(2,788)
Foreign Currency Translation Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(1,585)	(1,458)	(1,694)	(1,165)
Cumulative effect of amended accounting standard					$ 0
Other comprehensive income before reclassifications	(475)	(242)	(366)	(535)
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive income (loss), net of tax	(475)	(242)	(366)	(535)
Balance, ending of period	$ (2,060)	$ (1,700)	$ (2,060)	$ (1,700)