Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	$ (10,529)	$ (9,783)	$ (10,246)
Other Comprehensive Income (Loss), Net of Tax	(283)	102
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(36)	16	64	$ (51)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(118)	86
Other Comprehensive Income (Loss), Tax	25	(18)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(93)	68
Other Comprehensive Income (Loss), Net of Tax	(100)	67
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(9)	(1)
Reclassification from AOCI, Current Period, Tax	2	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(7)	(1)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(1,298)	(1,844)	(1,135)	(1,813)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(161)	(12)
Other Comprehensive Income (Loss), Tax	12	(1)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(149)	(13)
Other Comprehensive Income (Loss), Net of Tax	(163)	(31)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(14)	(18)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(8,639)	(7,824)	(8,781)	(7,965)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	185	166
Reclassification from AOCI, Current Period, Tax	(43)	(25)
Other Comprehensive Income (Loss), Net of Tax	142	141
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(556)	(131)	$ (394)	$ (56)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(176)	(95)
Other Comprehensive Income (Loss), Tax	10	27
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(166)	(68)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	7	(7)
Reclassification from AOCI, Current Period, Tax	(3)	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	4	(7)
Other Comprehensive Income (Loss), Net of Tax	$ (162)	$ (75)