Accumulated Other Comprehensive Income - Activity in AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), pre-tax activity	$ (2,992)	$ (1,053)
Other comprehensive income (loss), tax effect	689	244
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	22,210	23,111
Other comprehensive loss, net of tax	(2,303)	(809)
Ending Balance	20,177	22,595
Available-for-sale debt securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	(2,505)	(914)
Other comprehensive income (loss), before reclassifications, tax effect	576	214
Other comprehensive income (loss), before reclassifications, net activity	(1,929)	(700)
Reclassification adjustment, pre-tax activity	(3)	15
Reclassification adjustment, tax effect	1	(4)
Reclassification adjustment, net activity	(2)	11
Other comprehensive income (loss), pre-tax activity	(2,508)	(899)
Other comprehensive income (loss), tax effect	577	210
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	891	1,931
Other comprehensive loss, net of tax	(1,931)	(689)
Ending Balance	(1,040)	1,242
Cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	(407)	(84)
Other comprehensive income (loss), before reclassifications, tax effect	94	20
Other comprehensive income (loss), before reclassifications, net activity	(313)	(64)
Reclassification adjustment, pre-tax activity	(78)	(72)
Reclassification adjustment, tax effect	18	15
Reclassification adjustment, net activity	(60)	(57)
Other comprehensive income (loss), pre-tax activity	(485)	(156)
Other comprehensive income (loss), tax effect	112	35
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	353	718
Other comprehensive loss, net of tax	(373)	(121)
Ending Balance	(20)	597
Defined benefit pension plans, net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification adjustment, pre-tax activity	1	2
Reclassification adjustment, tax effect	0	(1)
Reclassification adjustment, net activity	1	1
Other comprehensive income (loss), pre-tax activity	1	2
Other comprehensive income (loss), tax effect	0	(1)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(33)	(44)
Other comprehensive loss, net of tax	1	1
Ending Balance	(32)	(43)
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, net of tax	0	0
Ending Balance	(4)	(4)
AOCI
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	1,207	2,601
Ending Balance	$ (1,096)	$ 1,792