Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	$ (9,676)	$ (10,225)	$ (9,676)	$ (10,225)		$ (10,855)
Other Comprehensive Income (Loss), Net of Tax	237	304	1,179	21
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	72	40	72	40	$ 55	104	$ (36)	$ 64
Other Comprehensive Income (Loss), before Reclassifications, before Tax	39	122	(15)	4
Other Comprehensive Income (Loss), Tax	(9)	(27)	2	(2)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	30	95	(13)	2
Other Comprehensive Income (Loss), Net of Tax	17	76	(32)	(24)
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	(17)	(25)	(25)	(34)
Reclassification from AOCI, Current Period, Tax	4	6	6	8
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(13)	(19)	(19)	(26)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(1,118)	(1,235)	(1,118)	(1,235)	(1,183)	(930)	(1,298)	(1,135)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	67	63	(150)	(98)
Other Comprehensive Income (Loss), Tax	1	2	(35)	14
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	68	65	(185)	(84)
Other Comprehensive Income (Loss), Net of Tax	65	63	(188)	(100)
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	(3)	(2)	(3)	(16)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(8,276)	(8,498)	(8,276)	(8,498)	(8,425)	(9,559)	(8,639)	(8,781)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	0	0	1,268	0
Other Comprehensive Income (Loss), Tax	0	0	(298)	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0	970	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	194	184	392	369
Reclassification from AOCI, Current Period, Tax	(45)	(43)	(79)	(86)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	149	141	313	283
Other Comprehensive Income (Loss), Net of Tax	149	141	1,283	283
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(354)	(532)	(354)	(532)	$ (360)	$ (470)	$ (556)	$ (394)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(10)	17	112	(159)
Other Comprehensive Income (Loss), Tax	8	(2)	(1)	8
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(2)	15	111	(151)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	9	12	6	19
Reclassification from AOCI, Current Period, Tax	(1)	(3)	(1)	(6)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	8	9	5	13
Other Comprehensive Income (Loss), Net of Tax	$ 6	$ 24	$ 116	$ (138)