Accumulated Other Comprehensive Income - Activity in AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), pre-tax activity	$ (438)	$ (156)	$ (1,250)	$ 2,135
Other comprehensive income (loss), tax effect	101	36	286	(496)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	22,926	22,335	23,111	21,203
Other comprehensive (loss) income, net of tax	(337)	(120)	(964)	1,639
Ending Balance	22,524	22,951	22,524	22,951
Available-for-sale debt securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	(368)	(42)	(978)	1,715
Other comprehensive income (loss), before reclassifications, tax effect	87	10	230	(409)
Other comprehensive income (loss), before reclassifications, net activity	(281)	(32)	(748)	1,306
Reclassification adjustment, pre-tax activity	(1)	(45)	9	(45)
Reclassification adjustment, tax effect	0	11	(2)	11
Reclassification adjustment, net activity	(1)	(34)	7	(34)
Other comprehensive income (loss), pre-tax activity	(369)	(87)	(969)	1,670
Other comprehensive income (loss), tax effect	87	21	228	(398)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	1,472	2,150	1,931	812
Other comprehensive (loss) income, net of tax	(282)	(66)	(741)	1,272
Ending Balance	1,190	2,084	1,190	2,084
Cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	3	1	(67)	625
Other comprehensive income (loss), before reclassifications, tax effect	(1)	0	14	(131)
Other comprehensive income (loss), before reclassifications, net activity	2	1	(53)	494
Reclassification adjustment, pre-tax activity	(74)	(72)	(219)	(165)
Reclassification adjustment, tax effect	16	16	46	35
Reclassification adjustment, net activity	(58)	(56)	(173)	(130)
Other comprehensive income (loss), pre-tax activity	(71)	(71)	(286)	460
Other comprehensive income (loss), tax effect	15	16	60	(96)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	548	841	718	422
Other comprehensive (loss) income, net of tax	(56)	(55)	(226)	364
Ending Balance	492	786	492	786
Defined benefit pension plans, net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	(1)	(2)	(2)	(2)
Other comprehensive income (loss), before reclassifications, tax effect	0	0	0	0
Other comprehensive income (loss), before reclassifications, net activity	(1)	(2)	(2)	(2)
Reclassification adjustment, pre-tax activity	3	4	7	7
Reclassification adjustment, tax effect	(1)	(1)	(2)	(2)
Reclassification adjustment, net activity	2	3	5	5
Other comprehensive income (loss), pre-tax activity	2	2	5	5
Other comprehensive income (loss), tax effect	(1)	(1)	(2)	(2)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(42)	(40)	(44)	(42)
Other comprehensive (loss) income, net of tax	1	1	3	3
Ending Balance	(41)	(39)	(41)	(39)
Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), pre-tax activity	0		0
Other comprehensive income (loss), tax effect	0		0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(4)		(4)
Other comprehensive (loss) income, net of tax	0		0
Ending Balance	(4)		(4)
AOCI
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	1,974	2,951	2,601	1,192
Ending Balance	$ 1,637	$ 2,831	$ 1,637	$ 2,831