Accumulated Other Comprehensive Income - Activity in AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax unrealized losses	$ 974	$ (525)
Other comprehensive income (loss), tax effect	(233)	124
Other comprehensive income (loss), net of tax	741	(401)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	19,645	19,172
Other comprehensive loss, net of tax	741	(401)
Ending balance	20,403	19,018
AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), net of tax	741	(401)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(4,636)	(4,487)
Other comprehensive loss, net of tax	741	(401)
Ending balance	(3,895)	(4,888)
Available-for-sale debt securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	633	(236)
Other comprehensive income (loss), before reclassifications, tax effect	(152)	54
Other comprehensive income (loss), before reclassifications, net activity	481	(182)
Reclassification adjustment, pre-tax activity	0	3
Reclassification adjustment, tax effect	0	0
Reclassification adjustment, net activity	0	3
Pretax unrealized losses	633	761
Other comprehensive income (loss), tax effect	(152)	(155)
Other comprehensive income (loss), net of tax	481	606
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(3,280)	(4,094)
Other comprehensive loss, net of tax	481	606
Ending balance	(2,799)	(3,488)
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	32
Reclassification adjustment, tax effect	(7)	(7)
Reclassification adjustment, net activity	25	25
Pretax unrealized losses	32	(962)
Other comprehensive income (loss), tax effect	(7)	202
Other comprehensive income (loss), net of tax	25	(760)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(684)	0
Other comprehensive loss, net of tax	25	(760)
Ending balance	(659)	(760)
Cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	253	(413)
Other comprehensive income (loss), before reclassifications, tax effect	(60)	97
Other comprehensive income (loss), before reclassifications, net activity	193	(316)
Reclassification adjustment, pre-tax activity	56	89
Reclassification adjustment, tax effect	(14)	(20)
Reclassification adjustment, net activity	42	69
Pretax unrealized losses	309	(324)
Other comprehensive income (loss), tax effect	(74)	77
Other comprehensive income (loss), net of tax	235	(247)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(654)	(372)
Other comprehensive loss, net of tax	235	(247)
Ending balance	(419)	(619)
Defined benefit pension plants, net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax unrealized losses	0	0
Other comprehensive income (loss), tax effect	0	0
Other comprehensive income (loss), net of tax	0	0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(16)	(17)
Other comprehensive loss, net of tax	0	0
Ending balance	(16)	(17)
Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax unrealized losses	0	0
Other comprehensive income (loss), tax effect	0	0
Other comprehensive income (loss), net of tax	0	0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(2)	(4)
Other comprehensive loss, net of tax	0	0
Ending balance	$ (2)	$ (4)