Investment Securities - Amortized Costs and Estimated Fair Values (Details) - USD ($)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Available-for-sale securities
Amortized cost	$ 322,122,000,000		$ 308,254,000,000
Gross unrealized gains	1,220,000,000		2,614,000,000
Gross unrealized losses	10,467,000,000		2,343,000,000
Fair value	312,875,000,000		308,525,000,000
Held-to-maturity securities
Amortized cost	366,585,000,000		363,707,000,000
Gross unrealized gains	416,000,000		2,110,000,000
Gross unrealized losses	16,507,000,000		3,189,000,000
Fair value	350,494,000,000		362,628,000,000
Total investment securities, net of allowance for credit losses
Amortized cost	688,707,000,000		671,961,000,000
Gross unrealized gains	1,636,000,000		4,724,000,000
Gross unrealized losses	26,974,000,000		5,532,000,000
Fair value	663,369,000,000		671,153,000,000
HTM securities purchased	13,200,000,000	$ 31,300,000,000
Investment securities, allowance for credit losses	41,000,000	94,000,000	42,000,000
Accrued interest receivables on investment securities	2,000,000,000		1,900,000,000
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	104,825,000,000		83,754,000,000
Gross unrealized gains	329,000,000		821,000,000
Gross unrealized losses	4,834,000,000		1,013,000,000
Fair value	100,320,000,000		83,562,000,000
Held-to-maturity securities
Amortized cost	112,834,000,000		113,602,000,000
Gross unrealized gains	265,000,000		1,412,000,000
Gross unrealized losses	5,857,000,000		1,013,000,000
Fair value	107,242,000,000		114,001,000,000
U.S. GSEs and government agencies
Available-for-sale securities
Amortized cost	94,270,000,000		72,800,000,000
Gross unrealized gains	311,000,000		736,000,000
Gross unrealized losses	4,681,000,000		993,000,000
Fair value	89,900,000,000		72,543,000,000
Held-to-maturity securities
Amortized cost	98,079,000,000		102,556,000,000
Gross unrealized gains	258,000,000		1,400,000,000
Gross unrealized losses	5,117,000,000		853,000,000
Fair value	93,220,000,000		103,103,000,000
Residential: U.S.
Available-for-sale securities
Amortized cost	1,970,000,000		2,128,000,000
Gross unrealized gains	3,000,000		38,000,000
Gross unrealized losses	39,000,000		2,000,000
Fair value	1,934,000,000		2,164,000,000
Held-to-maturity securities
Amortized cost	9,377,000,000		7,316,000,000
Gross unrealized gains	1,000,000		1,000,000
Gross unrealized losses	462,000,000		106,000,000
Fair value	8,916,000,000		7,211,000,000
Residential: Non-U.S.
Available-for-sale securities
Amortized cost	3,572,000,000		3,882,000,000
Gross unrealized gains	15,000,000		25,000,000
Gross unrealized losses	6,000,000		1,000,000
Fair value	3,581,000,000		3,906,000,000
Commercial
Available-for-sale securities
Amortized cost	5,013,000,000		4,944,000,000
Gross unrealized gains	0		22,000,000
Gross unrealized losses	108,000,000		17,000,000
Fair value	4,905,000,000		4,949,000,000
Held-to-maturity securities
Amortized cost	5,378,000,000		3,730,000,000
Gross unrealized gains	6,000,000		11,000,000
Gross unrealized losses	278,000,000		54,000,000
Fair value	5,106,000,000		3,687,000,000
U.S. Treasury and government agencies
Available-for-sale securities
Amortized cost	170,683,000,000		178,038,000,000
Gross unrealized gains	417,000,000		668,000,000
Gross unrealized losses	5,138,000,000		1,243,000,000
Fair value	165,962,000,000		177,463,000,000
Held-to-maturity securities
Amortized cost	187,240,000,000		185,204,000,000
Gross unrealized gains	0		169,000,000
Gross unrealized losses	9,750,000,000		2,103,000,000
Fair value	177,490,000,000		183,270,000,000
Obligations of U.S. states and municipalities
Available-for-sale securities
Amortized cost	14,561,000,000		14,890,000,000
Gross unrealized gains	377,000,000		972,000,000
Gross unrealized losses	152,000,000		2,000,000
Fair value	14,786,000,000		15,860,000,000
Held-to-maturity securities
Amortized cost	14,812,000,000		13,985,000,000
Gross unrealized gains	124,000,000		453,000,000
Gross unrealized losses	492,000,000		44,000,000
Fair value	14,444,000,000		14,394,000,000
Non-U.S. government debt securities
Available-for-sale securities
Amortized cost	16,463,000,000		16,163,000,000
Gross unrealized gains	58,000,000		92,000,000
Gross unrealized losses	220,000,000		46,000,000
Fair value	16,301,000,000		16,209,000,000
Corporate debt securities
Available-for-sale securities
Amortized cost	376,000,000		332,000,000
Gross unrealized gains	0		8,000,000
Gross unrealized losses	20,000,000		19,000,000
Fair value	356,000,000		321,000,000
Asset-backed securities: Collateralized loan obligations
Available-for-sale securities
Amortized cost	10,554,000,000		9,674,000,000
Gross unrealized gains	4,000,000		6,000,000
Gross unrealized losses	85,000,000		18,000,000
Fair value	10,473,000,000		9,662,000,000
Held-to-maturity securities
Amortized cost	49,569,000,000		48,869,000,000
Gross unrealized gains	25,000,000		75,000,000
Gross unrealized losses	375,000,000		22,000,000
Fair value	49,219,000,000		48,922,000,000
Asset-backed securities: Other
Available-for-sale securities
Amortized cost	4,660,000,000		5,403,000,000
Gross unrealized gains	35,000,000		47,000,000
Gross unrealized losses	18,000,000		2,000,000
Fair value	4,677,000,000		5,448,000,000
Held-to-maturity securities
Amortized cost	2,130,000,000		2,047,000,000
Gross unrealized gains	2,000,000		1,000,000
Gross unrealized losses	33,000,000		7,000,000
Fair value	$ 2,099,000,000		$ 2,041,000,000