FAIR VALUE MEASUREMENT - Items Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed and purchased under agreements to resell, Netting	$ (204,793)	$ (323,772)
Trading account assets	518,577	442,747
Netting agreements	(304,560)	(334,900)
Netting of cash collateral received	(25,022)	(27,303)
Trading derivatives	55,009	60,599
Investments	452,888	476,657
Held at fair value	8,165	8,040
Liabilities, Fair Value Disclosure [Abstract]
Federal funds purchased and securities loaned and sold under agreements to repurchase, Netting	(204,793)	(323,772)
Netting agreements	(304,560)	(334,900)
Netting of cash collateral paid	(19,204)	(28,570)
Total derivative liabilities	49,498	48,298
Marketable equity securities carried at fair value	133	151
Allowance for credit losses	18,726	18,574	$ 18,296	$ 18,145
Non-marketable equity securities | Carried at cost
Assets, Fair Value Disclosure [Abstract]
Investments	5,200	5,200
Fair Value Measured at Net Asset Value Per Share
Liabilities, Fair Value Disclosure [Abstract]
Investments measured at net asset value excluded from Level 3	29	23
Recurring
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed and purchased under agreements to resell	460,014	462,670
Federal funds sold and securities borrowed and purchased under agreements to resell, Netting	(195,140)	(321,815)
Federal funds sold and securities borrowed and purchased under agreements to resell	264,874	140,855
Investments	225,727	227,431
Held at fair value	8,165	8,040
Mortgage servicing rights	751	760
Assets before netting	1,559,974	1,518,663
Netting, Assets, total of netting agreements and cash collateral received	(524,722)	(684,018)
Total assets	1,035,252	834,645
Liabilities, Fair Value Disclosure [Abstract]
Interest-bearing deposits	4,226	3,608
Federal funds purchased and securities loaned and sold under agreements to repurchase, Gross	301,601	260,676
Federal funds purchased and securities loaned and sold under agreements to repurchase, Netting	(141,778)	(211,522)
Federal funds purchased and securities loaned and sold under agreements to repurchase	159,823	49,154
Securities sold, not yet purchased	99,175	85,536
Trading liabilities	99,190	85,548
Short-term borrowings	18,621	12,484
Long-term debt	117,248	112,719
Total liabilities, Gross	921,118	892,025
Total liabilities, Netting	(465,542)	(574,992)
Total liabilities	455,576	317,033
Recurring | Securities sold, not yet purchased
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	373,262	411,768
Total trading derivatives and cash collateral, liability	373,262	411,768
Netting agreements	(304,560)	(334,900)
Netting of cash collateral paid	(19,204)	(28,570)
Netting, Liabilities, total of netting agreements and cash collateral received	(323,764)	(363,470)
Total derivative liabilities	49,498	48,298
Recurring | Securities sold, not yet purchased | Interest rate contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	151,076	122,132
Recurring | Securities sold, not yet purchased | Foreign exchange contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	129,176	206,017
Recurring | Securities sold, not yet purchased | Equity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	66,145	61,736
Recurring | Securities sold, not yet purchased | Commodity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	18,646	14,630
Recurring | Securities sold, not yet purchased | Credit derivatives
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	8,219	7,253
Recurring | Other financial liabilities
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	6,970	5,222
Total other assets and cash collateral, gross	6,970	5,222
Recurring | Other trading liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	15	12
Recurring | Mortgage-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	81,255	64,928
Investments	35,632	29,931
Recurring | Mortgage securitizations - U.S. agency-sponsored
Assets, Fair Value Disclosure [Abstract]
Trading account assets	79,484	63,666
Investments	34,883	29,306
Recurring | Residential
Assets, Fair Value Disclosure [Abstract]
Trading account assets	785	595
Investments	748	624
Recurring | Commercial
Assets, Fair Value Disclosure [Abstract]
Trading account assets	986	667
Investments	1	1
Recurring | U.S. Treasury and federal agency securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	132,927	149,355
Investments	33,952	52,379
Recurring | State and municipal
Assets, Fair Value Disclosure [Abstract]
Trading account assets	172	179
Investments	1,671	1,658
Recurring | Foreign government
Assets, Fair Value Disclosure [Abstract]
Trading account assets	116,272	74,855
Investments	142,723	133,359
Recurring | Corporate
Assets, Fair Value Disclosure [Abstract]
Trading account assets	22,057	14,940
Investments	5,522	4,814
Recurring | Equity securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	75,332	48,808
Investments	133	151
Recurring | Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,983	2,309
Investments	933	848
Recurring | Other debt securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	33,570	26,774
Investments	4,747	3,887
Recurring | Non-marketable equity securities
Assets, Fair Value Disclosure [Abstract]
Investments	414	404
Recurring | Trading mortgage-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	463,568	382,148
Recurring | Trading account derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	384,591	422,802
Trading derivative, asset, gross net cash collateral paid	384,591	422,802
Netting agreements	(304,560)	(334,900)
Netting of cash collateral received	(25,022)	(27,303)
Total trading derivatives, netting	(329,582)	(362,203)
Trading derivatives	55,009	60,599
Recurring | Trading account derivatives | Interest rate contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	159,424	130,278
Recurring | Trading account derivatives | Foreign exchange contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	138,469	216,045
Recurring | Trading account derivatives | Equity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	61,092	55,144
Recurring | Trading account derivatives | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	16,554	12,620
Recurring | Trading account derivatives | Credit derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	9,052	8,715
Recurring | Other financial assets
Assets, Fair Value Disclosure [Abstract]
Total trading derivatives, netting	0	0
Total other assets and cash collateral, gross	17,158	14,812
Other assets	17,158	14,812
Recurring | Level 1
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed and purchased under agreements to resell	0	0
Investments	107,693	116,900
Held at fair value	0	0
Mortgage servicing rights	0	0
Assets before netting	$ 384,234	$ 343,336
Total as a percentage of gross assets	24.60%	22.60%
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	84,876	72,324
Trading liabilities	84,876	72,324
Short-term borrowings	0	0
Long-term debt	0	0
Total liabilities, Gross	$ 91,777	$ 76,848
Total as a percentage of gross liabilities	10.00%	8.60%
Recurring | Level 1 | Securities sold, not yet purchased
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	$ 84	$ 46
Recurring | Level 1 | Securities sold, not yet purchased | Interest rate contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	42	6
Recurring | Level 1 | Securities sold, not yet purchased | Foreign exchange contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	0	0
Recurring | Level 1 | Securities sold, not yet purchased | Equity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	42	40
Recurring | Level 1 | Securities sold, not yet purchased | Commodity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	0	0
Recurring | Level 1 | Securities sold, not yet purchased | Credit derivatives
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	0	0
Recurring | Level 1 | Other financial liabilities
Liabilities, Fair Value Disclosure [Abstract]
Other liabilities, gross	6,817	4,478
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	0
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	0
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	131,572	142,837
Investments	33,952	51,501
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	67,902	35,805
Investments	69,937	62,106
Recurring | Level 1 | Corporate
Assets, Fair Value Disclosure [Abstract]
Trading account assets	2,151	1,197
Investments	3,686	3,163
Recurring | Level 1 | Equity securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	66,974	41,163
Investments	118	130
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	0	0
Investments	0	0
Recurring | Level 1 | Non-marketable equity securities
Assets, Fair Value Disclosure [Abstract]
Investments	0	0
Recurring | Level 1 | Trading mortgage-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	268,599	221,002
Recurring | Level 1 | Trading account derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	162	61
Recurring | Level 1 | Trading account derivatives | Interest rate contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	55	17
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	107	44
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 | Other financial assets
Assets, Fair Value Disclosure [Abstract]
Other assets, gross	7,780	5,373
Recurring | Level 2
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed and purchased under agreements to resell	459,861	462,542
Investments	116,933	109,455
Held at fair value	7,847	7,778
Mortgage servicing rights	0	0
Assets before netting	$ 1,166,658	$ 1,166,133
Total as a percentage of gross assets	74.80%	76.80%
Liabilities, Fair Value Disclosure [Abstract]
Interest-bearing deposits	$ 4,179	$ 3,569
Federal funds purchased and securities loaned and sold under agreements to repurchase, Gross	300,803	260,286
Securities sold, not yet purchased	14,270	13,184
Trading liabilities	14,285	13,196
Short-term borrowings	17,900	12,187
Long-term debt	95,807	91,619
Total liabilities, Gross	$ 799,238	$ 786,422
Total as a percentage of gross liabilities	86.80%	88.20%
Recurring | Level 2 | Securities sold, not yet purchased
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	$ 366,112	$ 404,821
Recurring | Level 2 | Securities sold, not yet purchased | Interest rate contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	149,026	120,097
Recurring | Level 2 | Securities sold, not yet purchased | Foreign exchange contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	128,665	205,487
Recurring | Level 2 | Securities sold, not yet purchased | Equity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	62,777	58,642
Recurring | Level 2 | Securities sold, not yet purchased | Commodity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	18,034	13,960
Recurring | Level 2 | Securities sold, not yet purchased | Credit derivatives
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	7,610	6,635
Recurring | Level 2 | Other financial liabilities
Liabilities, Fair Value Disclosure [Abstract]
Other liabilities, gross	152	744
Recurring | Level 2 | Other trading liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	15	12
Recurring | Level 2 | Mortgage-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	80,436	64,524
Investments	35,590	29,867
Recurring | Level 2 | Mortgage securitizations - U.S. agency-sponsored
Assets, Fair Value Disclosure [Abstract]
Trading account assets	78,870	63,365
Investments	34,851	29,270
Recurring | Level 2 | Residential
Assets, Fair Value Disclosure [Abstract]
Trading account assets	667	528
Investments	738	596
Recurring | Level 2 | Commercial
Assets, Fair Value Disclosure [Abstract]
Trading account assets	899	631
Investments	1	1
Recurring | Level 2 | U.S. Treasury and federal agency securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,355	6,517
Investments	0	878
Recurring | Level 2 | State and municipal
Assets, Fair Value Disclosure [Abstract]
Trading account assets	171	168
Investments	1,236	1,230
Recurring | Level 2 | Foreign government
Assets, Fair Value Disclosure [Abstract]
Trading account assets	48,367	39,035
Investments	72,777	71,241
Recurring | Level 2 | Corporate
Assets, Fair Value Disclosure [Abstract]
Trading account assets	19,656	13,474
Investments	1,642	1,505
Recurring | Level 2 | Equity securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	8,131	7,479
Investments	9	7
Recurring | Level 2 | Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,763	2,131
Investments	933	846
Recurring | Level 2 | Other debt securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	33,102	26,441
Investments	4,746	3,881
Recurring | Level 2 | Non-marketable equity securities
Assets, Fair Value Disclosure [Abstract]
Investments	0	0
Recurring | Level 2 | Trading mortgage-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	192,981	159,769
Recurring | Level 2 | Trading account derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	379,671	417,165
Recurring | Level 2 | Trading account derivatives | Interest rate contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	157,998	128,562
Recurring | Level 2 | Trading account derivatives | Foreign exchange contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	137,777	215,330
Recurring | Level 2 | Trading account derivatives | Equity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	59,864	53,734
Recurring | Level 2 | Trading account derivatives | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	15,617	11,546
Recurring | Level 2 | Trading account derivatives | Credit derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	8,415	7,993
Recurring | Level 2 | Other financial assets
Assets, Fair Value Disclosure [Abstract]
Other assets, gross	9,365	9,424
Recurring | Level 3
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed and purchased under agreements to resell	153	128
Investments	1,101	1,076
Held at fair value	318	262
Mortgage servicing rights	751	760
Assets before netting	$ 9,082	$ 9,194
Total as a percentage of gross assets	0.60%	0.60%
Liabilities, Fair Value Disclosure [Abstract]
Interest-bearing deposits	$ 47	$ 39
Federal funds purchased and securities loaned and sold under agreements to repurchase, Gross	798	390
Securities sold, not yet purchased	29	28
Trading liabilities	29	28
Short-term borrowings	721	297
Long-term debt	21,441	21,100
Total liabilities, Gross	$ 30,103	$ 28,755
Total as a percentage of gross liabilities	3.20%	3.20%
Recurring | Level 3 | Securities sold, not yet purchased
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	$ 7,066	$ 6,901
Recurring | Level 3 | Securities sold, not yet purchased | Interest rate contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	2,008	2,029
Recurring | Level 3 | Securities sold, not yet purchased | Foreign exchange contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	511	530
Recurring | Level 3 | Securities sold, not yet purchased | Equity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	3,326	3,054
Recurring | Level 3 | Securities sold, not yet purchased | Commodity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	612	670
Recurring | Level 3 | Securities sold, not yet purchased | Credit derivatives
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	609	618
Recurring | Level 3 | Other financial liabilities
Liabilities, Fair Value Disclosure [Abstract]
Other liabilities, gross	1	0
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	819	404
Investments	42	64
Recurring | Level 3 | Mortgage securitizations - U.S. agency-sponsored
Assets, Fair Value Disclosure [Abstract]
Trading account assets	614	301
Investments	32	36
Recurring | Level 3 | Residential
Assets, Fair Value Disclosure [Abstract]
Trading account assets	118	67
Investments	10	28
Recurring | Level 3 | Commercial
Assets, Fair Value Disclosure [Abstract]
Trading account assets	87	36
Investments	0	0
Recurring | Level 3 | U.S. Treasury and federal agency securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	0	1
Investments	0	0
Recurring | Level 3 | State and municipal
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1	11
Investments	435	428
Recurring | Level 3 | Foreign government
Assets, Fair Value Disclosure [Abstract]
Trading account assets	3	15
Investments	9	12
Recurring | Level 3 | Corporate
Assets, Fair Value Disclosure [Abstract]
Trading account assets	250	269
Investments	194	146
Recurring | Level 3 | Equity securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	227	166
Investments	6	14
Recurring | Level 3 | Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	220	178
Investments	0	2
Recurring | Level 3 | Other debt securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	468	333
Investments	1	6
Recurring | Level 3 | Non-marketable equity securities
Assets, Fair Value Disclosure [Abstract]
Investments	414	404
Recurring | Level 3 | Trading mortgage-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,988	1,377
Recurring | Level 3 | Trading account derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	4,758	5,576
Recurring | Level 3 | Trading account derivatives | Interest rate contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	1,371	1,699
Recurring | Level 3 | Trading account derivatives | Foreign exchange contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	692	715
Recurring | Level 3 | Trading account derivatives | Equity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	1,121	1,366
Recurring | Level 3 | Trading account derivatives | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	937	1,074
Recurring | Level 3 | Trading account derivatives | Credit derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	637	722
Recurring | Level 3 | Other financial assets
Assets, Fair Value Disclosure [Abstract]
Other assets, gross	$ 13	$ 15