FAIR VALUE MEASUREMENT - Items Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed and purchased under agreements to resell, Netting	$ (121,369)	$ (131,342)
Trading account assets	357,997	331,945
Investments	514,602	512,822
Loans held at fair value	5,732	6,082
Liabilities, Fair Value Disclosure [Abstract]
Federal funds purchased and securities loaned and sold under agreements to repurchase, Netting	(121,369)	(131,342)
Fair value
Liabilities, Fair Value Disclosure [Abstract]
Investments measured at net asset value excluded from Level 3	158	145
Recurring
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed and purchased under agreements to resell	347,532	342,261
Federal funds sold and securities borrowed and purchased under agreements to resell, Netting	(113,183)	(125,795)
Federal funds sold and securities borrowed and purchased under agreements to resell	234,349	216,466
Investments	265,573	289,409
Loans held at fair value	5,732	6,082
Mortgage servicing rights	520	404
Assets before netting	1,338,095	1,299,518
Netting, Assets, total of netting agreements and cash collateral received	(462,135)	(442,870)
Total assets	875,960	856,648
Liabilities, Fair Value Disclosure [Abstract]
Interest-bearing deposits	1,838	1,666
Federal funds purchased and securities loaned and sold under agreements to repurchase, Gross	168,353	174,961
Federal funds purchased and securities loaned and sold under agreements to repurchase, Netting	(102,810)	(118,267)
Federal funds purchased and securities loaned and sold under agreements to repurchase	65,543	56,694
Securities sold, not yet purchased	120,955	106,008
Trading liabilities	120,957	106,013
Short-term borrowings	7,367	7,358
Long-term debt	83,277	82,609
Total liabilities, Gross	797,861	753,632
Total liabilities, Netting	(448,109)	(440,201)
Total liabilities	349,752	313,431
Recurring | Trading account liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	412,401	377,450
Total trading derivatives and cash collateral, liability	412,401	377,450
Netting agreements	(319,683)	(292,628)
Netting of cash collateral paid	(25,616)	(29,306)
Netting, Liabilities, total of netting agreements and cash collateral received	(345,299)	(321,934)
Total derivative liabilities	67,102	55,516
Recurring | Trading account liabilities | Interest rate contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	155,154	150,074
Recurring | Trading account liabilities | Foreign exchange contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	148,976	135,298
Recurring | Trading account liabilities | Equity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	51,826	49,684
Recurring | Trading account liabilities | Commodity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	45,299	31,379
Recurring | Trading account liabilities | Credit derivatives
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	11,146	11,015
Recurring | Other financial liabilities measured on a recurring basis
Liabilities, Fair Value Disclosure [Abstract]
Netting of cash collateral paid		0
Netting, Liabilities, total of netting agreements and cash collateral received
Non-trading derivatives and other financial liabilities measured on a recurring basis, gross	3,668	3,575
Total other assets and cash collateral, gross	3,668	3,575
Recurring | Other trading liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	2	5
Recurring | Mortgage-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	31,108	36,637
Investments	37,231	33,621
Recurring | Mortgage securitizations - U.S. agency-sponsored
Assets, Fair Value Disclosure [Abstract]
Trading account assets	29,909	35,030
Investments	36,893	33,216
Recurring | Residential
Assets, Fair Value Disclosure [Abstract]
Trading account assets	533	748
Investments	320	380
Recurring | Commercial
Assets, Fair Value Disclosure [Abstract]
Trading account assets	666	859
Investments	18	25
Recurring | U.S. Treasury and federal agency securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	67,628	48,134
Investments	90,525	122,440
Recurring | State and municipal
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,858	2,032
Investments	2,504	2,621
Recurring | Foreign government
Assets, Fair Value Disclosure [Abstract]
Trading account assets	72,221	70,684
Investments	123,459	118,740
Recurring | Corporate
Assets, Fair Value Disclosure [Abstract]
Trading account assets	19,145	18,112
Investments	6,069	5,920
Recurring | Equity securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	64,880	64,054
Investments	483	543
Recurring | Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,432	1,594
Investments	296	303
Recurring | Other trading assets
Assets, Fair Value Disclosure [Abstract]
Trading account assets	20,736	20,922
Investments	4,690	4,877
Recurring | Non-marketable equity securities
Assets, Fair Value Disclosure [Abstract]
Investments	316	344
Recurring | Trading non-derivative assets
Assets, Fair Value Disclosure [Abstract]
Trading account assets	279,008	262,169
Recurring | Trading account derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	427,941	386,851
Trading derivative, asset, gross net cash collateral paid	427,941	386,851
Netting agreements	(319,683)	(292,628)
Netting of cash collateral received	(29,269)	(24,447)
Total trading derivatives, netting	(348,952)	(317,075)
Trading derivatives	78,989	69,776
Recurring | Trading account derivatives | Interest rate contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	167,042	165,488
Recurring | Trading account derivatives | Foreign exchange contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	153,859	135,549
Recurring | Trading account derivatives | Equity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	46,185	45,252
Recurring | Trading account derivatives | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	49,612	30,344
Recurring | Trading account derivatives | Credit derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	11,243	10,218
Recurring | Non-trading derivatives and other financial assets measured on a recurring basis
Assets, Fair Value Disclosure [Abstract]
Total trading derivatives, netting	0	0
Total other assets and cash collateral, gross	11,789	12,342
Other assets	11,789	12,342
Recurring | Level 1
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed and purchased under agreements to resell	0	0
Investments	153,895	182,324
Loans held at fair value	0	0
Mortgage servicing rights	0	0
Assets before netting	$ 320,984	$ 325,984
Total as a percentage of gross assets	24.00%	25.10%
Liabilities, Fair Value Disclosure [Abstract]
Interest-bearing deposits	$ 0	$ 0
Federal funds purchased and securities loaned and sold under agreements to repurchase, Gross	0	0
Securities sold, not yet purchased	101,842	82,675
Trading liabilities	101,842	82,675
Short-term borrowings	0	0
Long-term debt	0	0
Total liabilities, Gross	$ 105,825	$ 86,365
Total as a percentage of gross liabilities	13.30%	11.50%
Recurring | Level 1 | Trading account liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	$ 315	$ 116
Recurring | Level 1 | Trading account liabilities | Interest rate contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	288	56
Recurring | Level 1 | Trading account liabilities | Foreign exchange contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	0	0
Recurring | Level 1 | Trading account liabilities | Equity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	25	60
Recurring | Level 1 | Trading account liabilities | Commodity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	2	0
Recurring | Level 1 | Trading account liabilities | Credit derivatives
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	0	0
Recurring | Level 1 | Other financial liabilities measured on a recurring basis
Liabilities, Fair Value Disclosure [Abstract]
Other liabilities, gross	3,668	3,574
Recurring | Level 1 | Other trading liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	0	0
Recurring | Level 1 | Mortgage-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	0	1
Investments	0	0
Recurring | Level 1 | Mortgage securitizations - U.S. agency-sponsored
Assets, Fair Value Disclosure [Abstract]
Trading account assets	0	0
Investments	0	0
Recurring | Level 1 | Residential
Assets, Fair Value Disclosure [Abstract]
Trading account assets	0	1
Investments	0	0
Recurring | Level 1 | Commercial
Assets, Fair Value Disclosure [Abstract]
Trading account assets	0	0
Investments	0	0
Recurring | Level 1 | U.S. Treasury and federal agency securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	64,273	44,900
Investments	90,466	122,271
Recurring | Level 1 | State and municipal
Assets, Fair Value Disclosure [Abstract]
Trading account assets	0	0
Investments	0	0
Recurring | Level 1 | Foreign government
Assets, Fair Value Disclosure [Abstract]
Trading account assets	41,456	39,176
Investments	60,498	56,842
Recurring | Level 1 | Corporate
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,500	1,544
Investments	2,646	2,861
Recurring | Level 1 | Equity securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	54,369	53,833
Investments	285	350
Recurring | Level 1 | Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	0	0
Investments	0	0
Recurring | Level 1 | Other trading assets
Assets, Fair Value Disclosure [Abstract]
Trading account assets	8	0
Investments	0	0
Recurring | Level 1 | Non-marketable equity securities
Assets, Fair Value Disclosure [Abstract]
Investments	0	0
Recurring | Level 1 | Trading non-derivative assets
Assets, Fair Value Disclosure [Abstract]
Trading account assets	161,606	139,454
Recurring | Level 1 | Trading account derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	462	131
Recurring | Level 1 | Trading account derivatives | Interest rate contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	411	90
Recurring | Level 1 | Trading account derivatives | Foreign exchange contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	0	0
Recurring | Level 1 | Trading account derivatives | Equity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	51	41
Recurring | Level 1 | Trading account derivatives | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	0	0
Recurring | Level 1 | Trading account derivatives | Credit derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	0	0
Recurring | Level 1 | Non-trading derivatives and other financial assets measured on a recurring basis
Assets, Fair Value Disclosure [Abstract]
Other assets, gross	5,021	4,075
Recurring | Level 2
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed and purchased under agreements to resell	347,330	342,030
Investments	109,300	104,858
Loans held at fair value	5,110	5,371
Mortgage servicing rights	0	0
Assets before netting	$ 1,002,021	$ 958,810
Total as a percentage of gross assets	74.90%	73.80%
Liabilities, Fair Value Disclosure [Abstract]
Interest-bearing deposits	$ 1,647	$ 1,483
Federal funds purchased and securities loaned and sold under agreements to repurchase, Gross	167,741	174,318
Securities sold, not yet purchased	19,075	23,268
Trading liabilities	19,077	23,273
Short-term borrowings	7,331	7,253
Long-term debt	55,845	57,100
Total liabilities, Gross	$ 654,664	$ 632,091
Total as a percentage of gross liabilities	82.10%	83.90%
Recurring | Level 2 | Trading account liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	$ 403,023	$ 368,664
Recurring | Level 2 | Trading account liabilities | Interest rate contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	152,640	147,846
Recurring | Level 2 | Trading account liabilities | Foreign exchange contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	147,960	134,572
Recurring | Level 2 | Trading account liabilities | Equity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	48,499	46,177
Recurring | Level 2 | Trading account liabilities | Commodity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	43,851	30,004
Recurring | Level 2 | Trading account liabilities | Credit derivatives
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	10,073	10,065
Recurring | Level 2 | Other financial liabilities measured on a recurring basis
Liabilities, Fair Value Disclosure [Abstract]
Other liabilities, gross	0	0
Recurring | Level 2 | Other trading liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	2	5
Recurring | Level 2 | Mortgage-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	30,440	35,955
Investments	37,141	33,476
Recurring | Level 2 | Mortgage securitizations - U.S. agency-sponsored
Assets, Fair Value Disclosure [Abstract]
Trading account assets	29,411	34,534
Investments	36,847	33,165
Recurring | Level 2 | Residential
Assets, Fair Value Disclosure [Abstract]
Trading account assets	415	643
Investments	276	286
Recurring | Level 2 | Commercial
Assets, Fair Value Disclosure [Abstract]
Trading account assets	614	778
Investments	18	25
Recurring | Level 2 | U.S. Treasury and federal agency securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	3,353	3,230
Investments	58	168
Recurring | Level 2 | State and municipal
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,852	1,995
Investments	1,799	1,849
Recurring | Level 2 | Foreign government
Assets, Fair Value Disclosure [Abstract]
Trading account assets	30,671	31,485
Investments	61,932	61,112
Recurring | Level 2 | Corporate
Assets, Fair Value Disclosure [Abstract]
Trading account assets	16,632	16,156
Investments	3,186	2,871
Recurring | Level 2 | Equity securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	10,312	10,047
Investments	182	177
Recurring | Level 2 | Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	966	981
Investments	294	300
Recurring | Level 2 | Other trading assets
Assets, Fair Value Disclosure [Abstract]
Trading account assets	20,236	20,346
Investments	4,690	4,877
Recurring | Level 2 | Non-marketable equity securities
Assets, Fair Value Disclosure [Abstract]
Investments	18	28
Recurring | Level 2 | Trading non-derivative assets
Assets, Fair Value Disclosure [Abstract]
Trading account assets	114,462	120,195
Recurring | Level 2 | Trading account derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	419,119	378,162
Recurring | Level 2 | Trading account derivatives | Interest rate contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	163,626	161,500
Recurring | Level 2 | Trading account derivatives | Foreign exchange contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	152,974	134,912
Recurring | Level 2 | Trading account derivatives | Equity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	44,396	43,904
Recurring | Level 2 | Trading account derivatives | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	47,949	28,547
Recurring | Level 2 | Trading account derivatives | Credit derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	10,174	9,299
Recurring | Level 2 | Non-trading derivatives and other financial assets measured on a recurring basis
Assets, Fair Value Disclosure [Abstract]
Other assets, gross	6,700	8,194
Recurring | Level 3
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed and purchased under agreements to resell	202	231
Investments	2,378	2,227
Loans held at fair value	622	711
Mortgage servicing rights	520	404
Assets before netting	$ 15,090	$ 14,724
Total as a percentage of gross assets	1.10%	1.10%
Liabilities, Fair Value Disclosure [Abstract]
Interest-bearing deposits	$ 191	$ 183
Federal funds purchased and securities loaned and sold under agreements to repurchase, Gross	612	643
Securities sold, not yet purchased	38	65
Trading liabilities	38	65
Short-term borrowings	36	105
Long-term debt	27,432	25,509
Total liabilities, Gross	$ 37,372	$ 35,176
Total as a percentage of gross liabilities	4.70%	4.70%
Recurring | Level 3 | Trading account liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	$ 9,063	$ 8,670
Recurring | Level 3 | Trading account liabilities | Interest rate contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	2,226	2,172
Recurring | Level 3 | Trading account liabilities | Foreign exchange contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	1,016	726
Recurring | Level 3 | Trading account liabilities | Equity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	3,302	3,447
Recurring | Level 3 | Trading account liabilities | Commodity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	1,446	1,375
Recurring | Level 3 | Trading account liabilities | Credit derivatives
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	1,073	950
Recurring | Level 3 | Other financial liabilities measured on a recurring basis
Liabilities, Fair Value Disclosure [Abstract]
Other liabilities, gross	0	1
Recurring | Level 3 | Other trading liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	0	0
Recurring | Level 3 | Mortgage-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	668	681
Investments	90	145
Recurring | Level 3 | Mortgage securitizations - U.S. agency-sponsored
Assets, Fair Value Disclosure [Abstract]
Trading account assets	498	496
Investments	46	51
Recurring | Level 3 | Residential
Assets, Fair Value Disclosure [Abstract]
Trading account assets	118	104
Investments	44	94
Recurring | Level 3 | Commercial
Assets, Fair Value Disclosure [Abstract]
Trading account assets	52	81
Investments	0	0
Recurring | Level 3 | U.S. Treasury and federal agency securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	2	4
Investments	1	1
Recurring | Level 3 | State and municipal
Assets, Fair Value Disclosure [Abstract]
Trading account assets	6	37
Investments	705	772
Recurring | Level 3 | Foreign government
Assets, Fair Value Disclosure [Abstract]
Trading account assets	94	23
Investments	1,029	786
Recurring | Level 3 | Corporate
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,013	412
Investments	237	188
Recurring | Level 3 | Equity securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	199	174
Investments	16	16
Recurring | Level 3 | Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	466	613
Investments	2	3
Recurring | Level 3 | Other trading assets
Assets, Fair Value Disclosure [Abstract]
Trading account assets	492	576
Investments	0	0
Recurring | Level 3 | Non-marketable equity securities
Assets, Fair Value Disclosure [Abstract]
Investments	298	316
Recurring | Level 3 | Trading non-derivative assets
Assets, Fair Value Disclosure [Abstract]
Trading account assets	2,940	2,520
Recurring | Level 3 | Trading account derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	8,360	8,558
Recurring | Level 3 | Trading account derivatives | Interest rate contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	3,005	3,898
Recurring | Level 3 | Trading account derivatives | Foreign exchange contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	885	637
Recurring | Level 3 | Trading account derivatives | Equity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	1,738	1,307
Recurring | Level 3 | Trading account derivatives | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	1,663	1,797
Recurring | Level 3 | Trading account derivatives | Credit derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	1,069	919
Recurring | Level 3 | Non-trading derivatives and other financial assets measured on a recurring basis
Assets, Fair Value Disclosure [Abstract]
Other assets, gross	$ 68	$ 73