Investment Securities - Amortized Costs and Estimated Fair Values (Details) - USD ($)		3 Months Ended		9 Months Ended
	Jan. 01, 2023	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Available-for-sale securities
Amortized cost		$ 335,251,000,000		$ 335,251,000,000		$ 205,456,000,000
Unallocated portfolio layer fair value basis adjustments, Amortized cost		694,000,000		694,000,000		73,000,000
Gross unrealized gains		2,714,000,000		2,714,000,000		1,762,000,000
Unallocated portfolio layer fair value basis adjustments, Gross unrealized gains		(694,000,000)		(694,000,000)		(73,000,000)
Gross unrealized losses		3,417,000,000		3,417,000,000		5,514,000,000
Fair value		334,548,000,000		334,548,000,000		201,704,000,000
Held-to-maturity securities
Amortized cost		299,954,000,000		299,954,000,000		369,848,000,000
Gross unrealized gains		277,000,000		277,000,000		178,000,000
Gross unrealized losses		20,590,000,000		20,590,000,000		27,272,000,000
Fair value		279,641,000,000		279,641,000,000		342,754,000,000
Total investment securities, net of allowance for credit losses
Amortized cost		635,205,000,000		635,205,000,000		575,304,000,000
Gross unrealized gains		2,991,000,000		2,991,000,000		1,940,000,000
Gross unrealized losses		24,007,000,000		24,007,000,000		32,786,000,000
Fair value		614,189,000,000		614,189,000,000		544,458,000,000
HTM securities purchased		1,400,000,000	$ 0	2,400,000,000	$ 4,100,000,000
Investment securities, allowance for credit losses		175,000,000	117,000,000	175,000,000	117,000,000	128,000,000
Accrued interest receivables on investment securities		3,700,000,000		3,700,000,000		2,800,000,000
Accrued interest receivables reversed through interest income on AFS securities		0	0	0	0
Accrued interest receivables reversed through interest income on HTM securities		0	$ 0	0	$ 0
Total mortgage-backed securities
Available-for-sale securities
Amortized cost		90,786,000,000		90,786,000,000		95,001,000,000
Gross unrealized gains		1,348,000,000		1,348,000,000		896,000,000
Gross unrealized losses		2,605,000,000		2,605,000,000		4,285,000,000
Fair value		89,529,000,000		89,529,000,000		91,612,000,000
Held-to-maturity securities
Amortized cost		117,526,000,000		117,526,000,000		125,857,000,000
Gross unrealized gains		153,000,000		153,000,000		56,000,000
Gross unrealized losses		10,644,000,000		10,644,000,000		13,194,000,000
Fair value		107,035,000,000		107,035,000,000		112,719,000,000
U.S. GSEs and government agencies mortgage-backed securities
Available-for-sale securities
Amortized cost		83,081,000,000		83,081,000,000		88,377,000,000
Gross unrealized gains		1,280,000,000		1,280,000,000		870,000,000
Gross unrealized losses		2,498,000,000		2,498,000,000		4,077,000,000
Fair value		81,863,000,000		81,863,000,000		85,170,000,000
Held-to-maturity securities
Amortized cost		99,328,000,000		99,328,000,000		105,614,000,000
Gross unrealized gains		94,000,000		94,000,000		39,000,000
Gross unrealized losses		9,641,000,000		9,641,000,000		11,643,000,000
Fair value		89,781,000,000		89,781,000,000		94,010,000,000
Residential: U.S. Mortgage-backed securities
Available-for-sale securities
Amortized cost		3,321,000,000		3,321,000,000		2,086,000,000
Gross unrealized gains		33,000,000		33,000,000		10,000,000
Gross unrealized losses		33,000,000		33,000,000		68,000,000
Fair value		3,321,000,000		3,321,000,000		2,028,000,000
Held-to-maturity securities
Amortized cost		8,874,000,000		8,874,000,000		9,709,000,000
Gross unrealized gains		11,000,000		11,000,000		4,000,000
Gross unrealized losses		688,000,000		688,000,000		970,000,000
Fair value		8,197,000,000		8,197,000,000		8,743,000,000
Residential: Non-U.S. mortgage-backed securities
Available-for-sale securities
Amortized cost		733,000,000		733,000,000		1,608,000,000
Gross unrealized gains		3,000,000		3,000,000		4,000,000
Gross unrealized losses		0		0		1,000,000
Fair value		736,000,000		736,000,000		1,611,000,000
Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost		3,651,000,000		3,651,000,000		2,930,000,000
Gross unrealized gains		32,000,000		32,000,000		12,000,000
Gross unrealized losses		74,000,000		74,000,000		139,000,000
Fair value		3,609,000,000		3,609,000,000		2,803,000,000
Held-to-maturity securities
Amortized cost		9,324,000,000		9,324,000,000		10,534,000,000
Gross unrealized gains		48,000,000		48,000,000		13,000,000
Gross unrealized losses		315,000,000		315,000,000		581,000,000
Fair value		9,057,000,000		9,057,000,000		9,966,000,000
U.S. Treasury and government agencies
Available-for-sale securities
Amortized cost		170,989,000,000		170,989,000,000		58,051,000,000
Gross unrealized gains		1,433,000,000		1,433,000,000		276,000,000
Gross unrealized losses		240,000,000		240,000,000		522,000,000
Fair value		172,182,000,000		172,182,000,000		57,805,000,000
Held-to-maturity securities
Amortized cost		123,504,000,000		123,504,000,000		173,666,000,000
Gross unrealized gains		0		0		0
Gross unrealized losses		9,343,000,000		9,343,000,000		13,074,000,000
Fair value		114,161,000,000		114,161,000,000		160,592,000,000
Obligations of U.S. states and municipalities
Available-for-sale securities
Amortized cost		18,112,000,000		18,112,000,000		21,243,000,000
Gross unrealized gains		340,000,000		340,000,000		390,000,000
Gross unrealized losses		247,000,000		247,000,000		266,000,000
Fair value		18,205,000,000		18,205,000,000		21,367,000,000
Held-to-maturity securities
Amortized cost		9,426,000,000		9,426,000,000		9,945,000,000
Gross unrealized gains		54,000,000		54,000,000		74,000,000
Gross unrealized losses		542,000,000		542,000,000		591,000,000
Fair value		8,938,000,000		8,938,000,000		9,428,000,000
Obligations of U.S. states and municipalities | Accounting Standards Update 2022-01
Total investment securities, net of allowance for credit losses
Amount of investment securities transferred from HTM to AFS	$ 7,100,000,000
Pre-tax unrealized losses recognized within AOCI for transfer of securities from HTM to AFS	$ 38,000,000
Non-U.S. government debt securities
Available-for-sale securities
Amortized cost		42,627,000,000		42,627,000,000		21,387,000,000
Gross unrealized gains		229,000,000		229,000,000		254,000,000
Gross unrealized losses		303,000,000		303,000,000		359,000,000
Fair value		42,553,000,000		42,553,000,000		21,282,000,000
Corporate debt securities
Available-for-sale securities
Amortized cost		70,000,000		70,000,000		128,000,000
Gross unrealized gains		0		0		0
Gross unrealized losses		9,000,000		9,000,000		28,000,000
Fair value		61,000,000		61,000,000		100,000,000
Asset-backed securities: Collateralized loan obligations
Available-for-sale securities
Amortized cost		9,655,000,000		9,655,000,000		6,769,000,000
Gross unrealized gains		32,000,000		32,000,000		11,000,000
Gross unrealized losses		5,000,000		5,000,000		28,000,000
Fair value		9,682,000,000		9,682,000,000		6,752,000,000
Held-to-maturity securities
Amortized cost		47,999,000,000		47,999,000,000		58,565,000,000
Gross unrealized gains		68,000,000		68,000,000		47,000,000
Gross unrealized losses		24,000,000		24,000,000		352,000,000
Fair value		48,043,000,000		48,043,000,000		58,260,000,000
Asset-backed securities: Other
Available-for-sale securities
Amortized cost		2,318,000,000		2,318,000,000		2,804,000,000
Gross unrealized gains		26,000,000		26,000,000		8,000,000
Gross unrealized losses		8,000,000		8,000,000		26,000,000
Fair value		2,336,000,000		2,336,000,000		2,786,000,000
Held-to-maturity securities
Amortized cost		1,499,000,000		1,499,000,000		1,815,000,000
Gross unrealized gains		2,000,000		2,000,000		1,000,000
Gross unrealized losses		37,000,000		37,000,000		61,000,000
Fair value		$ 1,464,000,000		$ 1,464,000,000		$ 1,755,000,000