FAIR VALUE MEASUREMENT - Items Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed or purchased under agreements to resell, selected portfolios of securities purchased under agreements to resell, Netting	$ (50,920)	$ (44,811)
Trading account assets	244,903	243,925
Netting of cash collateral received	(36,198)	(45,912)
Investments	345,833	353,304
Loans	4,035	3,486
Mortgage servicing rights	567	1,564
Liabilities, Fair Value Disclosure [Abstract]
Federal funds purchased and securities loaned or sold under agreements to repurchase, selected portfolios of securities sold under agreements to repurchase, Netting	(50,920)	(44,811)
Netting of cash collateral paid	(40,577)	(49,811)
Assets transferred from Level 1 to Level 2	900	2,600
Assets transferred from Level 2 to Level 1	1,400	4,000
Liabilities transferred from Level 2 to Level 1	100	400
Liabilities transferred from Level 1 to Level 2	100	300
Investments measured at net asset value excluded from Level 3	416	408
Accounting Standards Update 2015-07
Liabilities, Fair Value Disclosure [Abstract]
Investments measured at net asset value excluded from Level 3	400	400
Recurring
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed or purchased under agreements to resell	176,149	173,890
Federal funds sold and securities borrowed or purchased under agreements to resell, selected portfolios of securities purchased under agreements to resell, Netting	(38,789)	(40,686)
Federal funds sold and securities borrowed or purchased under agreements to resell, selected portfolios of securities purchased under agreements to resell	137,360	133,204
Investments	291,395	300,790
Loans	4,035	3,486
Mortgage servicing rights	567	1,564
Assets before netting	1,187,697	1,305,641
Netting, Assets, total of netting agreements and cash collateral received	(492,156)	(606,943)
Total assets	695,541	698,698
Liabilities, Fair Value Disclosure [Abstract]
Interest-bearing deposits	1,307	1,212
Federal funds purchased and securities loaned or sold under agreements to repurchase, selected portfolios of securities sold under agreements to repurchase, Gross	79,728	74,349
Federal funds purchased and securities loaned or sold under agreements to repurchase, selected portfolios of securities sold under agreements to repurchase, Netting	(38,789)	(40,686)
Federal funds purchased and securities loaned or sold under agreements to repurchase, selected portfolios of securities sold under agreements to repurchase	40,939	33,663
Securities sold, not yet purchased	88,607	80,790
Trading liabilities	91,212	82,618
Short-term borrowings	3,473	2,700
Long-term debt, at fair value	27,526	26,254
Total liabilities, Gross	725,643	823,220
Total liabilities, Netting	(495,646)	(609,550)
Total liabilities	229,997	213,670
Recurring | Trading derivatives liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	495,704	609,507
Cash collateral received	13,961	15,731
Total trading derivatives and cash collateral, liability	509,665	625,238
Netting agreements	(416,229)	(519,000)
Netting of cash collateral paid	(40,577)	(49,811)
Netting, Liabilities, total of netting agreements and cash collateral received	(456,806)	(568,811)
Total derivative liabilities	52,859	56,427
Cash collateral received, gross	50,159	61,643
Recurring | Trading derivatives liabilities | Interest rate contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	300,349	354,761
Recurring | Trading derivatives liabilities | Foreign exchange contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	128,667	187,761
Recurring | Trading derivatives liabilities | Equity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	28,690	26,516
Recurring | Trading derivatives liabilities | Commodity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	13,312	15,032
Recurring | Trading derivatives liabilities | Credit derivatives
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	24,686	25,437
Recurring | Non-trading derivatives and other financial liabilities
Assets, Fair Value Disclosure [Abstract]
Netting of cash collateral received		(1,345)
Cash collateral paid, gross	56	61
Liabilities, Fair Value Disclosure [Abstract]
Cash collateral received	15	1
Netting of cash collateral paid	(51)	(53)
Netting, Liabilities, total of netting agreements and cash collateral received	(51)
Other liabilities, gross	12,717	10,848
Non-trading derivatives and other financial liabilities measured on a recurring basis, gross	12,732	10,849
Total other assets and cash collateral, gross	12,681	10,796
Cash collateral received, gross	955	1,346
Recurring | Trading account liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	2,605	1,828
Recurring | Mortgage-backed securities - U.S. agency-sponsored
Assets, Fair Value Disclosure [Abstract]
Trading account assets	21,681	22,894
Investments	35,703	38,405
Recurring | Mortgage-backed securities - Residential
Assets, Fair Value Disclosure [Abstract]
Trading account assets	657	690
Investments	3,474	3,910
Recurring | Mortgage-backed securities - Commercial
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,318	1,206
Investments	360	358
Recurring | Mortgage-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	23,656	24,790
Investments	39,537	42,673
Recurring | U.S. Treasury and federal agency securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	22,269	21,180
Investments	117,647	123,671
Recurring | State and municipal securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	3,356	4,076
Investments	9,625	10,120
Recurring | Foreign government
Assets, Fair Value Disclosure [Abstract]
Trading account assets	58,866	49,696
Investments	100,130	98,148
Recurring | Corporate
Assets, Fair Value Disclosure [Abstract]
Trading account assets	16,547	14,947
Investments	15,879	17,124
Recurring | Equity securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	48,686	50,443
Investments	391	391
Recurring | Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	3,477	2,760
Investments	6,523	6,794
Recurring | Other
Assets, Fair Value Disclosure [Abstract]
Trading account assets	11,667	12,280
Investments	550	503
Recurring | Non-marketable equity securities
Assets, Fair Value Disclosure [Abstract]
Investments	1,113	1,366
Recurring | Trading securities (excluding trading account derivatives)
Assets, Fair Value Disclosure [Abstract]
Trading account assets	188,524	180,172
Recurring | Trading account assets
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	498,370	617,477
Cash collateral paid	10,436	11,188
Trading derivative, asset, gross net cash collateral paid	508,806	628,665
Netting agreements	(416,229)	(519,000)
Netting of cash collateral received	(36,198)	(45,912)
Total trading derivatives, netting	(452,427)	(564,912)
Trading derivatives	56,379	63,753
Cash collateral paid, gross	51,013	60,999
Recurring | Trading account assets | Interest rate contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	313,727	369,325
Recurring | Trading account assets | Foreign exchange contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	125,236	185,662
Recurring | Trading account assets | Equity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	24,636	24,110
Recurring | Trading account assets | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	11,449	13,765
Recurring | Trading account assets | Credit derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	23,322	24,615
Recurring | Non-trading derivatives and other financial assets
Assets, Fair Value Disclosure [Abstract]
Netting of cash collateral received	(940)	(1,345)
Total trading derivatives, netting	(940)	(1,345)
Other assets, gross	18,216	17,066
Cash collateral paid, gross	5	8
Total other assets and cash collateral, gross	18,221	17,074
Other assets	17,281	15,729
Recurring | Level 1
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed or purchased under agreements to resell	0	0
Investments	165,437	170,495
Loans	0	0
Mortgage servicing rights	0	0
Assets before netting	$ 278,988	$ 282,885
Total as a percentage of gross assets	23.70%	21.90%
Liabilities, Fair Value Disclosure [Abstract]
Interest-bearing deposits	$ 0	$ 0
Federal funds purchased and securities loaned or sold under agreements to repurchase, selected portfolios of securities sold under agreements to repurchase, Gross	0	0
Securities sold, not yet purchased	80,154	73,782
Trading liabilities	80,154	73,782
Short-term borrowings	0	0
Long-term debt, at fair value	0	0
Total liabilities, Gross	$ 93,747	$ 85,643
Total as a percentage of gross liabilities	13.20%	10.60%
Recurring | Level 1 | Trading derivatives liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	$ 1,843	$ 2,561
Recurring | Level 1 | Trading derivatives liabilities | Interest rate contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	5	107
Recurring | Level 1 | Trading derivatives liabilities | Foreign exchange contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	8	13
Recurring | Level 1 | Trading derivatives liabilities | Equity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	1,675	2,245
Recurring | Level 1 | Trading derivatives liabilities | Commodity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	155	196
Recurring | Level 1 | Trading derivatives liabilities | Credit derivatives
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	0	0
Recurring | Level 1 | Non-trading derivatives and other financial liabilities
Liabilities, Fair Value Disclosure [Abstract]
Other liabilities, gross	11,750	9,300
Recurring | Level 1 | Trading account liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	0	0
Recurring | Level 1 | Mortgage-backed securities - U.S. agency-sponsored
Assets, Fair Value Disclosure [Abstract]
Trading account assets	0	0
Investments	0	0
Recurring | Level 1 | Mortgage-backed securities - Residential
Assets, Fair Value Disclosure [Abstract]
Trading account assets	0	0
Investments	0	0
Recurring | Level 1 | Mortgage-backed securities - Commercial
Assets, Fair Value Disclosure [Abstract]
Trading account assets	0	0
Investments	0	0
Recurring | Level 1 | 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	18,757	17,756
Investments	106,915	112,916
Recurring | Level 1 | State and municipal securities
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	37,588	36,852
Investments	56,398	54,028
Recurring | Level 1 | Corporate
Assets, Fair Value Disclosure [Abstract]
Trading account assets	240	424
Investments	1,807	3,215
Recurring | Level 1 | Equity securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	43,108	45,331
Investments	317	336
Recurring | Level 1 | Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	0	0
Investments	0	0
Recurring | Level 1 | Other
Assets, Fair Value Disclosure [Abstract]
Trading account assets	8	2
Investments	0	0
Recurring | Level 1 | Non-marketable equity securities
Assets, Fair Value Disclosure [Abstract]
Investments	0	0
Recurring | Level 1 | Trading securities (excluding trading account derivatives)
Assets, Fair Value Disclosure [Abstract]
Trading account assets	99,701	100,365
Recurring | Level 1 | Trading account assets
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	2,100	2,725
Recurring | Level 1 | Trading account assets | Interest rate contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	17	105
Recurring | Level 1 | Trading account assets | Foreign exchange contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	18	53
Recurring | Level 1 | Trading account assets | Equity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	1,815	2,306
Recurring | Level 1 | Trading account assets | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	250	261
Recurring | Level 1 | Trading account assets | Credit derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	0	0
Recurring | Level 1 | Non-trading derivatives and other financial assets
Assets, Fair Value Disclosure [Abstract]
Other assets, gross	11,750	9,300
Recurring | Level 2
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed or purchased under agreements to resell	174,962	172,394
Investments	122,292	126,434
Loans	3,455	2,918
Mortgage servicing rights	0	0
Assets before netting	$ 881,352	$ 992,034
Total as a percentage of gross assets	74.90%	76.60%
Liabilities, Fair Value Disclosure [Abstract]
Interest-bearing deposits	$ 1,005	$ 919
Federal funds purchased and securities loaned or sold under agreements to repurchase, selected portfolios of securities sold under agreements to repurchase, Gross	78,919	73,500
Securities sold, not yet purchased	7,302	5,831
Trading liabilities	9,907	7,658
Short-term borrowings	3,413	2,658
Long-term debt, at fair value	17,350	16,510
Total liabilities, Gross	$ 594,620	$ 699,226
Total as a percentage of gross liabilities	83.60%	86.60%
Recurring | Level 2 | Trading derivatives liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	$ 483,063	$ 596,441
Recurring | Level 2 | Trading derivatives liabilities | Interest rate contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	297,445	351,766
Recurring | Level 2 | Trading derivatives liabilities | Foreign exchange contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	128,229	187,328
Recurring | Level 2 | Trading derivatives liabilities | Equity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	24,866	22,119
Recurring | Level 2 | Trading derivatives liabilities | Commodity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	10,531	12,386
Recurring | Level 2 | Trading derivatives liabilities | Credit derivatives
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	21,992	22,842
Recurring | Level 2 | Non-trading derivatives and other financial liabilities
Liabilities, Fair Value Disclosure [Abstract]
Other liabilities, gross	963	1,540
Recurring | Level 2 | Trading account liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	2,605	1,827
Recurring | Level 2 | Mortgage-backed securities - U.S. agency-sponsored
Assets, Fair Value Disclosure [Abstract]
Trading account assets	21,410	22,718
Investments	35,648	38,304
Recurring | Level 2 | Mortgage-backed securities - Residential
Assets, Fair Value Disclosure [Abstract]
Trading account assets	289	291
Investments	3,474	3,860
Recurring | Level 2 | Mortgage-backed securities - Commercial
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,052	1,000
Investments	360	358
Recurring | Level 2 | Mortgage-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	22,751	24,009
Investments	39,482	42,522
Recurring | Level 2 | U.S. Treasury and federal agency securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	3,511	3,423
Investments	10,731	10,753
Recurring | Level 2 | State and municipal securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	3,086	3,780
Investments	8,392	8,909
Recurring | Level 2 | Foreign government
Assets, Fair Value Disclosure [Abstract]
Trading account assets	21,152	12,804
Investments	43,497	43,934
Recurring | Level 2 | Corporate
Assets, Fair Value Disclosure [Abstract]
Trading account assets	16,011	14,199
Investments	13,733	13,598
Recurring | Level 2 | Equity securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	5,468	4,985
Investments	65	46
Recurring | Level 2 | Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,536	892
Investments	5,811	6,134
Recurring | Level 2 | Other
Assets, Fair Value Disclosure [Abstract]
Trading account assets	9,771	9,464
Investments	550	503
Recurring | Level 2 | Non-marketable equity securities
Assets, Fair Value Disclosure [Abstract]
Investments	31	35
Recurring | Level 2 | Trading securities (excluding trading account derivatives)
Assets, Fair Value Disclosure [Abstract]
Trading account assets	83,286	73,556
Recurring | Level 2 | Trading account assets
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	490,918	609,000
Recurring | Level 2 | Trading account assets | Interest rate contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	311,584	366,995
Recurring | Level 2 | Trading account assets | Foreign exchange contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	124,740	184,776
Recurring | Level 2 | Trading account assets | Equity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	22,196	21,209
Recurring | Level 2 | Trading account assets | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	10,647	12,999
Recurring | Level 2 | Trading account assets | Credit derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	21,751	23,021
Recurring | Level 2 | Non-trading derivatives and other financial assets
Assets, Fair Value Disclosure [Abstract]
Other assets, gross	6,439	7,732
Recurring | Level 3
Assets, Fair Value Disclosure [Abstract]
Federal funds sold and securities borrowed or purchased under agreements to resell	1,187	1,496
Investments	3,666	3,861
Loans	580	568
Mortgage servicing rights	567	1,564
Assets before netting	$ 16,916	$ 19,526
Total as a percentage of gross assets	1.40%	1.50%
Liabilities, Fair Value Disclosure [Abstract]
Interest-bearing deposits	$ 302	$ 293
Federal funds purchased and securities loaned or sold under agreements to repurchase, selected portfolios of securities sold under agreements to repurchase, Gross	809	849
Securities sold, not yet purchased	1,151	1,177
Trading liabilities	1,151	1,178
Short-term borrowings	60	42
Long-term debt, at fair value	10,176	9,744
Total liabilities, Gross	$ 23,300	$ 22,619
Total as a percentage of gross liabilities	3.30%	2.80%
Recurring | Level 3 | Trading derivatives liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	$ 10,798	$ 10,505
Recurring | Level 3 | Trading derivatives liabilities | Interest rate contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	2,899	2,888
Recurring | Level 3 | Trading derivatives liabilities | Foreign exchange contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	430	420
Recurring | Level 3 | Trading derivatives liabilities | Equity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	2,149	2,152
Recurring | Level 3 | Trading derivatives liabilities | Commodity contracts
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	2,626	2,450
Recurring | Level 3 | Trading derivatives liabilities | Credit derivatives
Liabilities, Fair Value Disclosure [Abstract]
Trading derivatives, liability	2,694	2,595
Recurring | Level 3 | Non-trading derivatives and other financial liabilities
Liabilities, Fair Value Disclosure [Abstract]
Other liabilities, gross	4	8
Recurring | Level 3 | Trading account liabilities
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	0	1
Recurring | Level 3 | Mortgage-backed securities - U.S. agency-sponsored
Assets, Fair Value Disclosure [Abstract]
Trading account assets	271	176
Investments	55	101
Recurring | Level 3 | Mortgage-backed securities - Residential
Assets, Fair Value Disclosure [Abstract]
Trading account assets	368	399
Investments	0	50
Recurring | Level 3 | Mortgage-backed securities - Commercial
Assets, Fair Value Disclosure [Abstract]
Trading account assets	266	206
Investments	0	0
Recurring | Level 3 | Mortgage-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	905	781
Investments	55	151
Recurring | Level 3 | U.S. Treasury and federal agency securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1	1
Investments	1	2
Recurring | Level 3 | State and municipal securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	270	296
Investments	1,233	1,211
Recurring | Level 3 | Foreign government
Assets, Fair Value Disclosure [Abstract]
Trading account assets	126	40
Investments	235	186
Recurring | Level 3 | Corporate
Assets, Fair Value Disclosure [Abstract]
Trading account assets	296	324
Investments	339	311
Recurring | Level 3 | Equity securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	110	127
Investments	9	9
Recurring | Level 3 | Asset-backed securities
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,941	1,868
Investments	712	660
Recurring | Level 3 | Other
Assets, Fair Value Disclosure [Abstract]
Trading account assets	1,888	2,814
Investments	0	0
Recurring | Level 3 | Non-marketable equity securities
Assets, Fair Value Disclosure [Abstract]
Investments	1,082	1,331
Recurring | Level 3 | Trading securities (excluding trading account derivatives)
Assets, Fair Value Disclosure [Abstract]
Trading account assets	5,537	6,251
Recurring | Level 3 | Trading account assets
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	5,352	5,752
Recurring | Level 3 | Trading account assets | Interest rate contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	2,126	2,225
Recurring | Level 3 | Trading account assets | Foreign exchange contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	478	833
Recurring | Level 3 | Trading account assets | Equity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	625	595
Recurring | Level 3 | Trading account assets | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	552	505
Recurring | Level 3 | Trading account assets | Credit derivatives
Assets, Fair Value Disclosure [Abstract]
Trading derivatives, asset, Gross	1,571	1,594
Recurring | Level 3 | Non-trading derivatives and other financial assets
Assets, Fair Value Disclosure [Abstract]
Other assets, gross	$ 27	$ 34