Investment Securities - Amortized Costs and Estimated Fair Values (Details) - USD ($)	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Available-for-sale securities
Amortized cost	$ 552,160,000,000		$ 507,226,000,000
Unallocated portfolio layer fair value basis adjustments, Amortized cost	179,000,000		641,000,000
Gross unrealized gains	1,518,000,000		3,314,000,000
Unallocated portfolio layer fair value basis adjustments, Gross unrealized gains	(179,000,000)		(641,000,000)
Gross unrealized losses	4,641,000,000		3,342,000,000
Unallocated portfolio layer fair value basis adjustments, Gross unrealized losses	0		0
Fair value	549,037,000,000		507,198,000,000
Held-to-maturity securities
Amortized cost	272,142,000,000		270,134,000,000
Gross unrealized gains	76,000,000		263,000,000
Gross unrealized losses	17,705,000,000		17,053,000,000
Fair value	254,513,000,000		253,344,000,000
Total investment securities, net of allowance for credit losses
Amortized cost	824,302,000,000		777,360,000,000
Gross unrealized gains	1,594,000,000		3,577,000,000
Gross unrealized losses	22,346,000,000		20,395,000,000
Fair value	803,550,000,000		760,542,000,000
HTM securities purchased	19,600,000,000	$ 1,600,000,000
Investment securities, allowance for credit losses	78,000,000	118,000,000	106,000,000
Accrued interest receivables on investment securities	5,200,000,000		4,600,000,000
Accrued interest receivables reversed through interest income on AFS securities	0	0
Accrued interest receivables reversed through interest income on HTM securities	0	$ 0
Total mortgage-backed securities
Available-for-sale securities
Amortized cost	98,140,000,000		102,547,000,000
Gross unrealized gains	699,000,000		1,162,000,000
Gross unrealized losses	2,156,000,000		2,262,000,000
Fair value	96,683,000,000		101,447,000,000
Held-to-maturity securities
Amortized cost	100,495,000,000		103,108,000,000
Gross unrealized gains	53,000,000		82,000,000
Gross unrealized losses	10,242,000,000		10,004,000,000
Fair value	90,306,000,000		93,186,000,000
U.S. GSEs and government agencies mortgage-backed securities
Available-for-sale securities
Amortized cost	88,354,000,000		92,112,000,000
Gross unrealized gains	654,000,000		1,075,000,000
Gross unrealized losses	2,109,000,000		2,215,000,000
Fair value	86,899,000,000		90,972,000,000
Held-to-maturity securities
Amortized cost	86,990,000,000		89,073,000,000
Gross unrealized gains	37,000,000		57,000,000
Gross unrealized losses	9,387,000,000		9,200,000,000
Fair value	77,640,000,000		79,930,000,000
Residential: U.S. Mortgage-backed securities
Available-for-sale securities
Amortized cost	5,171,000,000		5,564,000,000
Gross unrealized gains	17,000,000		38,000,000
Gross unrealized losses	22,000,000		17,000,000
Fair value	5,166,000,000		5,585,000,000
Held-to-maturity securities
Amortized cost	7,271,000,000		7,542,000,000
Gross unrealized gains	4,000,000		6,000,000
Gross unrealized losses	597,000,000		570,000,000
Fair value	6,678,000,000		6,978,000,000
Residential: Non-U.S. mortgage-backed securities
Available-for-sale securities
Amortized cost	300,000,000		405,000,000
Gross unrealized gains	1,000,000		1,000,000
Gross unrealized losses	0		0
Fair value	301,000,000		406,000,000
Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost	4,315,000,000		4,466,000,000
Gross unrealized gains	27,000,000		48,000,000
Gross unrealized losses	25,000,000		30,000,000
Fair value	4,317,000,000		4,484,000,000
Held-to-maturity securities
Amortized cost	6,234,000,000		6,493,000,000
Gross unrealized gains	12,000,000		19,000,000
Gross unrealized losses	258,000,000		234,000,000
Fair value	5,988,000,000		6,278,000,000
U.S. Treasury and government agencies
Available-for-sale securities
Amortized cost	356,193,000,000		313,470,000,000
Gross unrealized gains	843,000,000		2,384,000,000
Gross unrealized losses	778,000,000		32,000,000
Fair value	356,258,000,000		315,822,000,000
Held-to-maturity securities
Amortized cost	141,204,000,000		132,727,000,000
Gross unrealized gains	6,000,000		134,000,000
Gross unrealized losses	6,799,000,000		6,414,000,000
Fair value	134,411,000,000		126,447,000,000
Obligations of U.S. states and municipalities
Available-for-sale securities
Amortized cost	19,964,000,000		20,915,000,000
Gross unrealized gains	72,000,000		118,000,000
Gross unrealized losses	1,056,000,000		793,000,000
Fair value	18,980,000,000		20,240,000,000
Held-to-maturity securities
Amortized cost	8,245,000,000		8,600,000,000
Gross unrealized gains	7,000,000		17,000,000
Gross unrealized losses	625,000,000		609,000,000
Fair value	7,627,000,000		8,008,000,000
Non-U.S. government debt securities
Available-for-sale securities
Amortized cost	53,787,000,000		45,676,000,000
Gross unrealized gains	51,000,000		215,000,000
Gross unrealized losses	627,000,000		236,000,000
Fair value	53,211,000,000		45,655,000,000
Corporate debt securities
Available-for-sale securities
Amortized cost	132,000,000		139,000,000
Gross unrealized gains	0		0
Gross unrealized losses	8,000,000		11,000,000
Fair value	124,000,000		128,000,000
Asset-backed securities: Collateralized loan obligations
Available-for-sale securities
Amortized cost	21,989,000,000		21,897,000,000
Gross unrealized gains	15,000,000		51,000,000
Gross unrealized losses	9,000,000		1,000,000
Fair value	21,995,000,000		21,947,000,000
Held-to-maturity securities
Amortized cost	21,277,000,000		24,695,000,000
Gross unrealized gains	9,000,000		29,000,000
Gross unrealized losses	18,000,000		6,000,000
Fair value	21,268,000,000		24,718,000,000
Asset-backed securities: Other
Available-for-sale securities
Amortized cost	1,776,000,000		1,941,000,000
Gross unrealized gains	17,000,000		25,000,000
Gross unrealized losses	7,000,000		7,000,000
Fair value	1,786,000,000		1,959,000,000
Held-to-maturity securities
Amortized cost	921,000,000		1,004,000,000
Gross unrealized gains	1,000,000		1,000,000
Gross unrealized losses	21,000,000		20,000,000
Fair value	$ 901,000,000		$ 985,000,000