Investment Securities - Amortized Costs and Estimated Fair Values (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Available-for-sale securities
Amortized cost	$ 492,300,000,000		$ 492,300,000,000		$ 411,045,000,000
Unallocated portfolio layer fair value basis adjustments, Amortized cost	1,172,000,000		1,172,000,000		(1,153,000,000)
Gross unrealized gains	2,236,000,000		2,236,000,000		1,115,000,000
Unallocated portfolio layer fair value basis adjustments, Gross unrealized gains	(1,172,000,000)		(1,172,000,000)		0
Gross unrealized losses	4,037,000,000		4,037,000,000		5,308,000,000
Unallocated portfolio layer fair value basis adjustments, Gross unrealized losses	0		0		(1,153,000,000)
Fair value	490,499,000,000		490,499,000,000		406,852,000,000
Held-to-maturity securities
Amortized cost	293,446,000,000		293,446,000,000		274,468,000,000
Gross unrealized gains	162,000,000		162,000,000		152,000,000
Gross unrealized losses	18,703,000,000		18,703,000,000		26,720,000,000
Fair value	274,905,000,000		274,905,000,000		247,900,000,000
Total investment securities, net of allowance for credit losses
Amortized cost	785,746,000,000		785,746,000,000		685,513,000,000
Gross unrealized gains	2,398,000,000		2,398,000,000		1,267,000,000
Gross unrealized losses	22,740,000,000		22,740,000,000		32,028,000,000
Fair value	765,404,000,000		765,404,000,000		654,752,000,000
HTM securities purchased	1,600,000,000	$ 1,400,000,000	4,800,000,000	$ 2,400,000,000
Investment securities, allowance for credit losses	105,000,000	175,000,000	105,000,000	175,000,000	152,000,000
Accrued interest receivables on investment securities	4,800,000,000		4,800,000,000		3,700,000,000
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	103,839,000,000		103,839,000,000		104,628,000,000
Gross unrealized gains	1,138,000,000		1,138,000,000		290,000,000
Gross unrealized losses	2,584,000,000		2,584,000,000		4,149,000,000
Fair value	102,393,000,000		102,393,000,000		100,769,000,000
Held-to-maturity securities
Amortized cost	106,160,000,000		106,160,000,000		114,599,000,000
Gross unrealized gains	70,000,000		70,000,000		34,000,000
Gross unrealized losses	10,829,000,000		10,829,000,000		14,824,000,000
Fair value	95,401,000,000		95,401,000,000		99,809,000,000
U.S. GSEs and government agencies mortgage-backed securities
Available-for-sale securities
Amortized cost	93,325,000,000		93,325,000,000		95,671,000,000
Gross unrealized gains	1,048,000,000		1,048,000,000		251,000,000
Gross unrealized losses	2,520,000,000		2,520,000,000		4,029,000,000
Fair value	91,853,000,000		91,853,000,000		91,893,000,000
Held-to-maturity securities
Amortized cost	91,146,000,000		91,146,000,000		97,177,000,000
Gross unrealized gains	47,000,000		47,000,000		6,000,000
Gross unrealized losses	9,939,000,000		9,939,000,000		13,531,000,000
Fair value	81,254,000,000		81,254,000,000		83,652,000,000
Residential: U.S. Mortgage-backed securities
Available-for-sale securities
Amortized cost	5,573,000,000		5,573,000,000		4,242,000,000
Gross unrealized gains	39,000,000		39,000,000		16,000,000
Gross unrealized losses	24,000,000		24,000,000		50,000,000
Fair value	5,588,000,000		5,588,000,000		4,208,000,000
Held-to-maturity securities
Amortized cost	7,792,000,000		7,792,000,000		8,605,000,000
Gross unrealized gains	5,000,000		5,000,000		4,000,000
Gross unrealized losses	642,000,000		642,000,000		904,000,000
Fair value	7,155,000,000		7,155,000,000		7,705,000,000
Residential: Non-U.S. mortgage-backed securities
Available-for-sale securities
Amortized cost	429,000,000		429,000,000		600,000,000
Gross unrealized gains	2,000,000		2,000,000		3,000,000
Gross unrealized losses	0		0		0
Fair value	431,000,000		431,000,000		603,000,000
Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost	4,512,000,000		4,512,000,000		4,115,000,000
Gross unrealized gains	49,000,000		49,000,000		20,000,000
Gross unrealized losses	40,000,000		40,000,000		70,000,000
Fair value	4,521,000,000		4,521,000,000		4,065,000,000
Held-to-maturity securities
Amortized cost	7,222,000,000		7,222,000,000		8,817,000,000
Gross unrealized gains	18,000,000		18,000,000		24,000,000
Gross unrealized losses	248,000,000		248,000,000		389,000,000
Fair value	6,992,000,000		6,992,000,000		8,452,000,000
U.S. Treasury and government agencies
Available-for-sale securities
Amortized cost	300,064,000,000		300,064,000,000		235,495,000,000
Gross unrealized gains	1,922,000,000		1,922,000,000		545,000,000
Gross unrealized losses	100,000,000		100,000,000		1,261,000,000
Fair value	301,886,000,000		301,886,000,000		234,779,000,000
Held-to-maturity securities
Amortized cost	148,837,000,000		148,837,000,000		108,632,000,000
Gross unrealized gains	37,000,000		37,000,000		0
Gross unrealized losses	7,144,000,000		7,144,000,000		11,212,000,000
Fair value	141,730,000,000		141,730,000,000		97,420,000,000
Obligations of U.S. states and municipalities
Available-for-sale securities
Amortized cost	20,817,000,000		20,817,000,000		18,337,000,000
Gross unrealized gains	111,000,000		111,000,000		110,000,000
Gross unrealized losses	960,000,000		960,000,000		534,000,000
Fair value	19,968,000,000		19,968,000,000		17,913,000,000
Held-to-maturity securities
Amortized cost	8,881,000,000		8,881,000,000		9,310,000,000
Gross unrealized gains	12,000,000		12,000,000		32,000,000
Gross unrealized losses	696,000,000		696,000,000		631,000,000
Fair value	8,197,000,000		8,197,000,000		8,711,000,000
Non-U.S. government debt securities
Available-for-sale securities
Amortized cost	44,516,000,000		44,516,000,000		36,655,000,000
Gross unrealized gains	148,000,000		148,000,000		94,000,000
Gross unrealized losses	385,000,000		385,000,000		504,000,000
Fair value	44,279,000,000		44,279,000,000		36,245,000,000
Corporate debt securities
Available-for-sale securities
Amortized cost	124,000,000		124,000,000		71,000,000
Gross unrealized gains	1,000,000		1,000,000		0
Gross unrealized losses	0		0		1,000,000
Fair value	125,000,000		125,000,000		70,000,000
Asset-backed securities: Collateralized loan obligations
Available-for-sale securities
Amortized cost	19,692,000,000		19,692,000,000		14,887,000,000
Gross unrealized gains	63,000,000		63,000,000		59,000,000
Gross unrealized losses	1,000,000		1,000,000		3,000,000
Fair value	19,754,000,000		19,754,000,000		14,943,000,000
Held-to-maturity securities
Amortized cost	28,483,000,000		28,483,000,000		40,573,000,000
Gross unrealized gains	41,000,000		41,000,000		84,000,000
Gross unrealized losses	11,000,000		11,000,000		14,000,000
Fair value	28,513,000,000		28,513,000,000		40,643,000,000
Asset-backed securities: Other
Available-for-sale securities
Amortized cost	2,076,000,000		2,076,000,000		2,125,000,000
Gross unrealized gains	25,000,000		25,000,000		17,000,000
Gross unrealized losses	7,000,000		7,000,000		9,000,000
Fair value	2,094,000,000		2,094,000,000		2,133,000,000
Held-to-maturity securities
Amortized cost	1,085,000,000		1,085,000,000		1,354,000,000
Gross unrealized gains	2,000,000		2,000,000		2,000,000
Gross unrealized losses	23,000,000		23,000,000		39,000,000
Fair value	$ 1,064,000,000		$ 1,064,000,000		$ 1,317,000,000