FAIR VALUE MEASUREMENT - Items Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed and purchased under agreements to resell, Netting	$ (261,873)	$ (248,214)
Trading account assets	431,468	411,756
Netting agreements	(285,867)	(308,431)
Netting of cash collateral received	(23,492)	(21,226)
Trading derivatives	53,597	57,717
Investments	515,183	519,085
Held at fair value	8,854	7,594
Liabilities, Fair Value Disclosure [Abstract]
Federal funds purchased and securities loaned and sold under agreements to repurchase, Netting	(261,873)	(248,214)
Netting agreements	(285,867)	(308,431)
Netting of cash collateral paid	(27,720)	(26,101)
Total derivative liabilities	46,506	50,679
Non-marketable equity securities | Carried at cost
Assets, Fair Value Disclosure [Abstract]
Investments	5,318	5,497
Fair Value Measured at Net Asset Value Per Share
Liabilities, Fair Value Disclosure [Abstract]
Investments measured at net asset value excluded from Level 3	27	25
Recurring
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed and purchased under agreements to resell	454,472	453,854
Federal funds sold and securities borrowed and purchased under agreements to resell, Netting	(260,926)	(247,795)
Federal funds sold and securities borrowed and purchased under agreements to resell	193,546	206,059
Investments	255,673	257,677
Held at fair value	8,854	7,594
Mortgage servicing rights	702	691
Assets before netting	1,473,960	1,474,257
Netting, Assets, total of netting agreements and cash collateral received	(570,285)	(577,452)
Total assets	903,675	896,805
Liabilities, Fair Value Disclosure [Abstract]
Interest-bearing deposits	2,905	2,440
Federal funds purchased and securities loaned and sold under agreements to repurchase, Gross	256,984	228,438
Federal funds purchased and securities loaned and sold under agreements to repurchase, Netting	(183,203)	(165,953)
Federal funds purchased and securities loaned and sold under agreements to repurchase	73,781	62,485
Securities sold, not yet purchased	110,136	104,658
Trading liabilities	110,146	104,666
Short-term borrowings	8,131	6,545
Long-term debt	115,317	116,338
Total liabilities, Gross	857,573	848,072
Total liabilities, Netting	(496,790)	(500,485)
Total liabilities	360,783	347,587
Recurring | Trading account liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	360,093	385,211
Total trading derivatives and cash collateral, liability	360,093	385,211
Netting agreements	(285,867)	(308,431)
Netting of cash collateral paid	(27,720)	(26,101)
Netting, Liabilities, total of netting agreements and cash collateral received	(313,587)	(334,532)
Total derivative liabilities	46,506	50,679
Recurring | Trading account liabilities | Interest rate contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	141,208	153,186
Recurring | Trading account liabilities | Foreign exchange contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	124,347	157,201
Recurring | Trading account liabilities | Equity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	68,408	47,946
Recurring | Trading account liabilities | Commodity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	17,558	18,796
Recurring | Trading account liabilities | Credit derivatives
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	8,572	8,082
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	0
Non-trading derivatives and other financial liabilities measured on a recurring basis, gross	3,997	4,434
Total other assets and cash collateral, gross	3,997	4,434
Recurring | Other trading liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	10	8
Recurring | Mortgage-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	77,781	81,756
Investments	32,470	30,139
Recurring | Mortgage securitizations - U.S. agency-sponsored
Assets, Fair Value Disclosure [Abstract]
Trading account assets	76,221	80,376
Investments	31,942	29,715
Recurring | Residential
Assets, Fair Value Disclosure [Abstract]
Trading account assets	886	714
Investments	527	423
Recurring | Commercial Mortgage-Backed Securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	674	666
Investments	1	1
Recurring | U.S. Treasury and federal agency securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	109,396	115,256
Investments	75,033	80,361
Recurring | State and municipal
Assets, Fair Value Disclosure [Abstract]
Trading account assets	381	597
Investments	1,988	2,131
Recurring | Foreign government
Assets, Fair Value Disclosure [Abstract]
Trading account assets	91,923	72,495
Investments	133,698	131,198
Recurring | Corporate
Assets, Fair Value Disclosure [Abstract]
Trading account assets	21,416	19,074
Investments	5,021	5,412
Recurring | Equity securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	59,221	45,393
Investments	287	258
Recurring | Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,692	1,754
Investments	939	938
Recurring | Other debt securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	16,061	17,714
Investments	5,749	6,757
Recurring | Non-marketable equity securities
Assets, Fair Value Disclosure [Abstract]
Investments	488	483
Recurring | Trading non-derivative assets
Assets, Fair Value Disclosure [Abstract]
Trading account assets	377,871	354,039
Recurring | Trading account derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	362,956	387,374
Trading derivative, asset, gross net cash collateral paid	362,956	387,374
Netting agreements	(285,867)	(308,431)
Netting of cash collateral received	(23,492)	(21,226)
Total trading derivatives, netting	(309,359)	(329,657)
Trading derivatives	53,597	57,717
Recurring | Trading account derivatives | Interest rate contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	148,337	158,494
Recurring | Trading account derivatives | Foreign exchange contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	133,149	159,694
Recurring | Trading account derivatives | Equity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	56,602	43,278
Recurring | Trading account derivatives | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	16,076	17,569
Recurring | Trading account derivatives | Credit derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	8,792	8,339
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	13,432	13,028
Other assets	13,432	13,028
Recurring | Level 1
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed and purchased under agreements to resell	0	0
Investments	142,573	143,034
Held at fair value	0	0
Mortgage servicing rights	0	0
Assets before netting	$ 354,664	$ 339,746
Total as a percentage of gross assets	24.10%	23.00%
Liabilities, Fair Value Disclosure [Abstract]
Interest-bearing deposits	$ 13	$ 0
Federal funds purchased and securities loaned and sold under agreements to repurchase, Gross	0	0
Securities sold, not yet purchased	96,215	91,163
Trading liabilities	96,215	91,163
Short-term borrowings	0	0
Long-term debt	0	0
Total liabilities, Gross	$ 99,995	$ 95,528
Total as a percentage of gross liabilities	11.60%	11.30%
Recurring | Level 1 | Trading account liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	$ 70	$ 67
Recurring | Level 1 | Trading account liabilities | Interest rate contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	39	49
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	31	18
Recurring | Level 1 | Trading account liabilities | Commodity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	0	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	3,697	4,298
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 Mortgage-Backed Securities
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	106,157	112,851
Investments	75,033	80,062
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	54,414	44,203
Investments	64,280	60,133
Recurring | Level 1 | Corporate
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,284	1,858
Investments	2,989	2,680
Recurring | Level 1 | Equity securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	45,761	32,966
Investments	271	159
Recurring | Level 1 | Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	0	0
Investments	0	0
Recurring | Level 1 | Other debt securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	218	97
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	207,834	191,976
Recurring | Level 1 | Trading account derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	59	59
Recurring | Level 1 | Trading account derivatives | Interest rate contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	46	49
Recurring | Level 1 | Trading account derivatives | Foreign exchange contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	1	0
Recurring | Level 1 | Trading account derivatives | Equity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	12	8
Recurring | Level 1 | Trading account derivatives | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	0	2
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	4,198	4,677
Recurring | Level 2
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed and purchased under agreements to resell	454,340	453,715
Investments	111,661	112,844
Held at fair value	7,797	7,167
Mortgage servicing rights	0	0
Assets before netting	$ 1,107,116	$ 1,121,860
Total as a percentage of gross assets	75.10%	76.10%
Liabilities, Fair Value Disclosure [Abstract]
Interest-bearing deposits	$ 2,820	$ 2,411
Federal funds purchased and securities loaned and sold under agreements to repurchase, Gross	256,658	228,048
Securities sold, not yet purchased	13,816	13,460
Trading liabilities	13,826	13,468
Short-term borrowings	7,548	6,064
Long-term debt	74,953	77,958
Total liabilities, Gross	$ 707,154	$ 704,559
Total as a percentage of gross liabilities	82.50%	83.00%
Recurring | Level 2 | Trading account liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	$ 351,052	$ 376,480
Recurring | Level 2 | Trading account liabilities | Interest rate contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	137,720	149,914
Recurring | Level 2 | Trading account liabilities | Foreign exchange contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	123,578	156,474
Recurring | Level 2 | Trading account liabilities | Equity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	65,221	44,894
Recurring | Level 2 | Trading account liabilities | Commodity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	16,726	17,964
Recurring | Level 2 | Trading account liabilities | Credit derivatives
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	7,807	7,234
Recurring | Level 2 | Other financial liabilities measured on a recurring basis
Liabilities, Fair Value Disclosure [Abstract]
Other liabilities, gross	297	130
Recurring | Level 2 | Other trading liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	10	8
Recurring | Level 2 | Mortgage-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	76,921	80,856
Investments	32,418	29,948
Recurring | Level 2 | Mortgage securitizations - U.S. agency-sponsored
Assets, Fair Value Disclosure [Abstract]
Trading account assets	75,690	79,795
Investments	31,915	29,640
Recurring | Level 2 | Residential
Assets, Fair Value Disclosure [Abstract]
Trading account assets	716	597
Investments	502	307
Recurring | Level 2 | Commercial Mortgage-Backed Securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	515	464
Investments	1	1
Recurring | Level 2 | U.S. Treasury and federal agency securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	3,239	2,398
Investments	0	299
Recurring | Level 2 | State and municipal
Assets, Fair Value Disclosure [Abstract]
Trading account assets	380	594
Investments	1,509	1,589
Recurring | Level 2 | Foreign government
Assets, Fair Value Disclosure [Abstract]
Trading account assets	37,396	28,238
Investments	69,394	70,871
Recurring | Level 2 | Corporate
Assets, Fair Value Disclosure [Abstract]
Trading account assets	19,668	16,716
Investments	1,644	2,370
Recurring | Level 2 | Equity securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	13,228	12,135
Investments	8	72
Recurring | Level 2 | Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,322	1,223
Investments	939	938
Recurring | Level 2 | Other debt securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	15,091	16,784
Investments	5,749	6,757
Recurring | Level 2 | Non-marketable equity securities
Assets, Fair Value Disclosure [Abstract]
Investments	0	0
Recurring | Level 2 | Trading non-derivative assets
Assets, Fair Value Disclosure [Abstract]
Trading account assets	167,245	158,944
Recurring | Level 2 | Trading account derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	356,870	380,869
Recurring | Level 2 | Trading account derivatives | Interest rate contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	146,204	156,307
Recurring | Level 2 | Trading account derivatives | Foreign exchange contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	132,044	158,672
Recurring | Level 2 | Trading account derivatives | Equity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	55,656	41,870
Recurring | Level 2 | Trading account derivatives | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	14,902	16,456
Recurring | Level 2 | Trading account derivatives | Credit derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	8,064	7,564
Recurring | Level 2 | Non-trading derivatives and other financial assets measured on a recurring basis
Assets, Fair Value Disclosure [Abstract]
Other assets, gross	9,203	8,321
Recurring | Level 3
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed and purchased under agreements to resell	132	139
Investments	1,439	1,799
Held at fair value	1,057	427
Mortgage servicing rights	702	691
Assets before netting	$ 12,180	$ 12,651
Total as a percentage of gross assets	0.80%	0.90%
Liabilities, Fair Value Disclosure [Abstract]
Interest-bearing deposits	$ 72	$ 29
Federal funds purchased and securities loaned and sold under agreements to repurchase, Gross	326	390
Securities sold, not yet purchased	105	35
Trading liabilities	105	35
Short-term borrowings	583	481
Long-term debt	40,364	38,380
Total liabilities, Gross	$ 50,424	$ 47,985
Total as a percentage of gross liabilities	5.90%	5.70%
Recurring | Level 3 | Trading account liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	$ 8,971	$ 8,664
Recurring | Level 3 | Trading account liabilities | Interest rate contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	3,449	3,223
Recurring | Level 3 | Trading account liabilities | Foreign exchange contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	769	727
Recurring | Level 3 | Trading account liabilities | Equity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	3,156	3,034
Recurring | Level 3 | Trading account liabilities | Commodity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	832	832
Recurring | Level 3 | Trading account liabilities | Credit derivatives
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	765	848
Recurring | Level 3 | Other financial liabilities measured on a recurring basis
Liabilities, Fair Value Disclosure [Abstract]
Other liabilities, gross	3	6
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	860	899
Investments	52	191
Recurring | Level 3 | Mortgage securitizations - U.S. agency-sponsored
Assets, Fair Value Disclosure [Abstract]
Trading account assets	531	581
Investments	27	75
Recurring | Level 3 | Residential
Assets, Fair Value Disclosure [Abstract]
Trading account assets	170	116
Investments	25	116
Recurring | Level 3 | Commercial Mortgage-Backed Securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	159	202
Investments	0	0
Recurring | Level 3 | U.S. Treasury and federal agency securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	0	7
Investments	0	0
Recurring | Level 3 | State and municipal
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1	3
Investments	479	542
Recurring | Level 3 | Foreign government
Assets, Fair Value Disclosure [Abstract]
Trading account assets	113	54
Investments	24	194
Recurring | Level 3 | Corporate
Assets, Fair Value Disclosure [Abstract]
Trading account assets	464	500
Investments	388	362
Recurring | Level 3 | Equity securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	232	292
Investments	8	27
Recurring | Level 3 | Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	370	531
Investments	0	0
Recurring | Level 3 | Other debt securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	752	833
Investments	0	0
Recurring | Level 3 | Non-marketable equity securities
Assets, Fair Value Disclosure [Abstract]
Investments	488	483
Recurring | Level 3 | Trading non-derivative assets
Assets, Fair Value Disclosure [Abstract]
Trading account assets	2,792	3,119
Recurring | Level 3 | Trading account derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	6,027	6,446
Recurring | Level 3 | Trading account derivatives | Interest rate contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	2,087	2,138
Recurring | Level 3 | Trading account derivatives | Foreign exchange contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	1,104	1,022
Recurring | Level 3 | Trading account derivatives | Equity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	934	1,400
Recurring | Level 3 | Trading account derivatives | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	1,174	1,111
Recurring | Level 3 | Trading account derivatives | Credit derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	728	775
Recurring | Level 3 | Non-trading derivatives and other financial assets measured on a recurring basis
Assets, Fair Value Disclosure [Abstract]
Other assets, gross	$ 31	$ 30