Other Comprehensive Income (Loss) (Schedule of Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	$ 9,260
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(127)	$ (821)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	40	29
Other comprehensive loss, net of tax	(87)	(792)
Balance, end of period	9,596	7,451
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(5,110)	(5,055)
Other comprehensive loss, net of tax	(87)	(792)
Balance, end of period	(5,197)	(5,847)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(4,126)	(3,512)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(36)	109
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	40	29
Other comprehensive loss, net of tax	4	138
Balance, end of period	(4,122)	(3,374)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(984)	(1,543)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(91)	(930)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0
Other comprehensive loss, net of tax	(91)	(930)
Balance, end of period	$ (1,075)	$ (2,473)