Investment Securities - Amortized Costs and Estimated Fair Values (Details) - USD ($)		3 Months Ended		6 Months Ended
	Jan. 01, 2023	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Available-for-sale securities
Amortized cost		$ 269,899,000,000		$ 269,899,000,000		$ 205,456,000,000
Unallocated portfolio layer fair value basis adjustments, Amortized cost		(1,285,000,000)		(1,285,000,000)		73,000,000
Gross unrealized gains		1,091,000,000		1,091,000,000		1,762,000,000
Unallocated portfolio layer fair value basis adjustments, Gross unrealized gains						(73,000,000)
Gross unrealized losses		4,738,000,000		4,738,000,000		5,514,000,000
Unallocated portfolio layer fair value basis adjustments, Gross unrealized losses		(1,285,000,000)		(1,285,000,000)
Fair value		266,252,000,000		266,252,000,000		201,704,000,000
Held-to-maturity securities
Amortized cost		323,746,000,000		323,746,000,000		369,848,000,000
Gross unrealized gains		183,000,000		183,000,000		178,000,000
Gross unrealized losses		29,126,000,000		29,126,000,000		27,272,000,000
Fair value		294,803,000,000		294,803,000,000		342,754,000,000
Total investment securities, net of allowance for credit losses
Amortized cost		593,645,000,000		593,645,000,000		575,304,000,000
Gross unrealized gains		1,274,000,000		1,274,000,000		1,940,000,000
Gross unrealized losses		33,864,000,000		33,864,000,000		32,786,000,000
Fair value		561,055,000,000		561,055,000,000		544,458,000,000
HTM securities purchased		555,000,000	$ 520,000,000	1,000,000,000	$ 4,100,000,000
Investment securities, allowance for credit losses		177,000,000	104,000,000	177,000,000	104,000,000	128,000,000
Accrued interest receivables on investment securities		3,400,000,000		3,400,000,000		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		84,779,000,000		84,779,000,000		95,001,000,000
Gross unrealized gains		448,000,000		448,000,000		896,000,000
Gross unrealized losses		4,330,000,000		4,330,000,000		4,285,000,000
Fair value		80,897,000,000		80,897,000,000		91,612,000,000
Held-to-maturity securities
Amortized cost		120,556,000,000		120,556,000,000		125,857,000,000
Gross unrealized gains		29,000,000		29,000,000		56,000,000
Gross unrealized losses		15,270,000,000		15,270,000,000		13,194,000,000
Fair value		105,315,000,000		105,315,000,000		112,719,000,000
U.S. GSEs and government agencies mortgage-backed securities
Available-for-sale securities
Amortized cost		78,806,000,000		78,806,000,000		88,377,000,000
Gross unrealized gains		428,000,000		428,000,000		870,000,000
Gross unrealized losses		4,182,000,000		4,182,000,000		4,077,000,000
Fair value		75,052,000,000		75,052,000,000		85,170,000,000
Held-to-maturity securities
Amortized cost		101,515,000,000		101,515,000,000		105,614,000,000
Gross unrealized gains		15,000,000		15,000,000		39,000,000
Gross unrealized losses		13,729,000,000		13,729,000,000		11,643,000,000
Fair value		87,801,000,000		87,801,000,000		94,010,000,000
Residential: U.S. Mortgage-backed securities
Available-for-sale securities
Amortized cost		2,326,000,000		2,326,000,000		2,086,000,000
Gross unrealized gains		8,000,000		8,000,000		10,000,000
Gross unrealized losses		62,000,000		62,000,000		68,000,000
Fair value		2,272,000,000		2,272,000,000		2,028,000,000
Held-to-maturity securities
Amortized cost		9,162,000,000		9,162,000,000		9,709,000,000
Gross unrealized gains		2,000,000		2,000,000		4,000,000
Gross unrealized losses		1,050,000,000		1,050,000,000		970,000,000
Fair value		8,114,000,000		8,114,000,000		8,743,000,000
Residential: Non-U.S. mortgage-backed securities
Available-for-sale securities
Amortized cost		749,000,000		749,000,000		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		752,000,000		752,000,000		1,611,000,000
Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost		2,898,000,000		2,898,000,000		2,930,000,000
Gross unrealized gains		9,000,000		9,000,000		12,000,000
Gross unrealized losses		86,000,000		86,000,000		139,000,000
Fair value		2,821,000,000		2,821,000,000		2,803,000,000
Held-to-maturity securities
Amortized cost		9,879,000,000		9,879,000,000		10,534,000,000
Gross unrealized gains		12,000,000		12,000,000		13,000,000
Gross unrealized losses		491,000,000		491,000,000		581,000,000
Fair value		9,400,000,000		9,400,000,000		9,966,000,000
U.S. Treasury and government agencies
Available-for-sale securities
Amortized cost		127,890,000,000		127,890,000,000		58,051,000,000
Gross unrealized gains		392,000,000		392,000,000		276,000,000
Gross unrealized losses		754,000,000		754,000,000		522,000,000
Fair value		127,528,000,000		127,528,000,000		57,805,000,000
Held-to-maturity securities
Amortized cost		140,281,000,000		140,281,000,000		173,666,000,000
Gross unrealized gains		0		0		0
Gross unrealized losses		13,104,000,000		13,104,000,000		13,074,000,000
Fair value		127,177,000,000		127,177,000,000		160,592,000,000
Obligations of U.S. states and municipalities
Available-for-sale securities
Amortized cost		17,546,000,000		17,546,000,000		21,243,000,000
Gross unrealized gains		132,000,000		132,000,000		390,000,000
Gross unrealized losses		490,000,000		490,000,000		266,000,000
Fair value		17,188,000,000		17,188,000,000		21,367,000,000
Held-to-maturity securities
Amortized cost		9,490,000,000		9,490,000,000		9,945,000,000
Gross unrealized gains		38,000,000		38,000,000		74,000,000
Gross unrealized losses		673,000,000		673,000,000		591,000,000
Fair value		8,855,000,000		8,855,000,000		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		31,442,000,000		31,442,000,000		21,387,000,000
Gross unrealized gains		76,000,000		76,000,000		254,000,000
Gross unrealized losses		419,000,000		419,000,000		359,000,000
Fair value		31,099,000,000		31,099,000,000		21,282,000,000
Corporate debt securities
Available-for-sale securities
Amortized cost		102,000,000		102,000,000		128,000,000
Gross unrealized gains		0		0		0
Gross unrealized losses		12,000,000		12,000,000		28,000,000
Fair value		90,000,000		90,000,000		100,000,000
Asset-backed securities: Collateralized loan obligations
Available-for-sale securities
Amortized cost		6,784,000,000		6,784,000,000		6,769,000,000
Gross unrealized gains		31,000,000		31,000,000		11,000,000
Gross unrealized losses		7,000,000		7,000,000		28,000,000
Fair value		6,808,000,000		6,808,000,000		6,752,000,000
Held-to-maturity securities
Amortized cost		51,822,000,000		51,822,000,000		58,565,000,000
Gross unrealized gains		113,000,000		113,000,000		47,000,000
Gross unrealized losses		30,000,000		30,000,000		352,000,000
Fair value		51,905,000,000		51,905,000,000		58,260,000,000
Asset-backed securities: Other
Available-for-sale securities
Amortized cost		2,641,000,000		2,641,000,000		2,804,000,000
Gross unrealized gains		12,000,000		12,000,000		8,000,000
Gross unrealized losses		11,000,000		11,000,000		26,000,000
Fair value		2,642,000,000		2,642,000,000		2,786,000,000
Held-to-maturity securities
Amortized cost		1,597,000,000		1,597,000,000		1,815,000,000
Gross unrealized gains		3,000,000		3,000,000		1,000,000
Gross unrealized losses		49,000,000		49,000,000		61,000,000
Fair value		$ 1,551,000,000		$ 1,551,000,000		$ 1,755,000,000