Accumulated Other Comprehensive Income - Activity in AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax unrealized losses	$ (525)	$ 1,131
Other comprehensive income (loss), tax effect	124	(266)
Other comprehensive (loss) income, net of tax	(401)	865
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	19,172	17,327
Other comprehensive income (loss), net of tax	(401)	865
Ending balance	19,018	18,364
AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive (loss) income, net of tax	(401)	865
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(4,487)	(5,110)
Other comprehensive income (loss), net of tax	(401)	865
Ending balance	(4,888)	(4,245)
Available-for-sale debt securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	236	(788)
Other comprehensive income (loss), before reclassifications, tax effect	(54)	188
Other comprehensive income (loss), before reclassifications, net activity	182	(600)
Reclassification adjustment, pre-tax activity	3	0
Reclassification adjustment, tax effect	0	0
Reclassification adjustment, net activity	3	0
Pretax unrealized losses	761	788
Other comprehensive income (loss), tax effect	(155)	(188)
Other comprehensive (loss) income, net of tax	606	600
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(4,094)	(4,589)
Other comprehensive income (loss), net of tax	606	600
Ending balance	(3,488)	(3,989)
Available-for-sale debt securities transferred to held-to-maturity securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	994
Other comprehensive income (loss), before reclassifications, tax effect	(209)
Other comprehensive income (loss), before reclassifications, net activity	785
Reclassification adjustment, pre-tax activity	32
Reclassification adjustment, tax effect	(7)
Reclassification adjustment, net activity	25
Pretax unrealized losses	(962)
Other comprehensive income (loss), tax effect	202
Other comprehensive (loss) income, net of tax	(760)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	0
Other comprehensive income (loss), net of tax	(760)
Ending balance	(760)
Cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	413	(278)
Other comprehensive income (loss), before reclassifications, tax effect	(97)	63
Other comprehensive income (loss), before reclassifications, net activity	316	(215)
Reclassification adjustment, pre-tax activity	89	65
Reclassification adjustment, tax effect	(20)	(15)
Reclassification adjustment, net activity	69	50
Pretax unrealized losses	(324)	343
Other comprehensive income (loss), tax effect	77	(78)
Other comprehensive (loss) income, net of tax	(247)	265
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(372)	(498)
Other comprehensive income (loss), net of tax	(247)	265
Ending balance	(619)	(233)
Defined benefit pension plants, net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification adjustment, pre-tax activity	0	0
Reclassification adjustment, tax effect	0	0
Reclassification adjustment, net activity	0	0
Pretax unrealized losses	0	0
Other comprehensive income (loss), tax effect	0	0
Other comprehensive (loss) income, net of tax	0	0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(17)	(19)
Other comprehensive income (loss), net of tax	0	0
Ending balance	(17)	(19)
Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax unrealized losses	0	0
Other comprehensive income (loss), tax effect	0	0
Other comprehensive (loss) income, net of tax	0	0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(4)	(4)
Other comprehensive income (loss), net of tax	0	0
Ending balance	$ (4)	$ (4)