Accumulated Other Comprehensive Income - Activity in AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax unrealized losses	$ 1,909	$ (2,187)	$ 1,359	$ (2,260)
Other comprehensive income (loss), tax effect	(454)	514	(318)	531
Other comprehensive income (loss), net of tax	1,455	(1,673)	1,041	(1,729)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	19,226	17,809	19,172	17,327
Other comprehensive loss, net of tax	1,455	(1,673)	1,041	(1,729)
Ending balance	20,784	16,544	20,784	16,544
AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), net of tax	1,455	(1,673)	1,041	(1,729)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(4,901)	(5,166)	(4,487)	(5,110)
Other comprehensive loss, net of tax	1,455	(1,673)	1,041	(1,729)
Ending balance	(3,446)	(6,839)	(3,446)	(6,839)
Available-for-sale debt securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	1,241	(1,594)	1,001	(1,638)
Other comprehensive income (loss), before reclassifications, tax effect	(297)	376	(238)	386
Other comprehensive income (loss), before reclassifications, net activity	944	(1,218)	763	(1,252)
Reclassification adjustment, pre-tax activity	11	0	17	1
Reclassification adjustment, tax effect	(2)	0	(4)	0
Reclassification adjustment, net activity	9	0	13	1
Pretax unrealized losses	1,252	(1,594)	2,012	(1,637)
Other comprehensive income (loss), tax effect	(299)	376	(451)	386
Other comprehensive income (loss), net of tax	953	(1,218)	1,561	(1,251)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(3,486)	(4,622)	(4,094)	(4,589)
Other comprehensive loss, net of tax	953	(1,218)	1,561	(1,251)
Ending balance	(2,533)	(5,840)	(2,533)	(5,840)
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	33		97
Reclassification adjustment, tax effect	(7)		(21)
Reclassification adjustment, net activity	26		76
Pretax unrealized losses	33		(897)
Other comprehensive income (loss), tax effect	(7)		188
Other comprehensive income (loss), net of tax	26		(709)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(735)		0
Other comprehensive loss, net of tax	26		(709)
Ending balance	(709)		(709)
Cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, pre-tax activity	530	(687)	(29)	(864)
Other comprehensive income (loss), before reclassifications, tax effect	(127)	160	7	200
Other comprehensive income (loss), before reclassifications, net activity	403	(527)	(22)	(664)
Reclassification adjustment, pre-tax activity	91	94	270	240
Reclassification adjustment, tax effect	(21)	(22)	(62)	(55)
Reclassification adjustment, net activity	70	72	208	185
Pretax unrealized losses	621	(593)	241	(624)
Other comprehensive income (loss), tax effect	(148)	138	(55)	145
Other comprehensive income (loss), net of tax	473	(455)	186	(479)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(659)	(522)	(372)	(498)
Other comprehensive loss, net of tax	473	(455)	186	(479)
Ending balance	(186)	(977)	(186)	(977)
Defined benefit pension plants, net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification adjustment, pre-tax activity	1	0	1	1
Reclassification adjustment, tax effect	0	0	0	0
Reclassification adjustment, net activity	1	0	1	1
Pretax unrealized losses	1	0	1	1
Other comprehensive income (loss), tax effect	0	0	0	0
Other comprehensive income (loss), net of tax	1	0	1	1
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(17)	(18)	(17)	(19)
Other comprehensive loss, net of tax	1	0	1	1
Ending balance	(16)	(18)	(16)	(18)
Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax unrealized losses	2	0	2	0
Other comprehensive income (loss), tax effect	0	0	0	0
Other comprehensive income (loss), net of tax	2	0	2	0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(4)	(4)	(4)	(4)
Other comprehensive loss, net of tax	2	0	2	0
Ending balance	$ (2)	$ (4)	$ (2)	$ (4)