LOANS - Consumer Loan Delinquency (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Non-Accrual Details
Loans, net of unearned income	$ 628,595	$ 624,369
Loans at fair value	4,035	3,486
Consumer
Non-Accrual Details
Loans, current	313,132	317,187
Loans, net of unearned income	320,556	325,063
Total non-accrual	2,955	3,158
90 days past due and accruing	$ 2,805	$ 2,991
Loans less than this number of days past due are considered current	30 days	30 days
Number of days past due, non-accrual status	60 days
Consumer | Less than or equal to 80%
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	$ 57,679	$ 58,718
Consumer | 80% but less than or equal to 100%
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	6,663	7,120
Consumer | Greater than 100%
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	1,495	1,629
Consumer | Less than 620
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	13,205	13,088
Consumer | ≥ 620 but less than 660
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	15,197	15,431
Consumer | Equal to or greater than 660
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	163,418	172,145
Consumer | Government-guaranteed
Non-Accrual Details
Loans, past due	1,368	1,474
Consumer | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	3,131	3,275
Consumer | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	2,925	3,127
Consumer | Residential first mortgages
Non-Accrual Details
Loans at fair value	$ 28	$ 29
Number of days past due, non-accrual status	90 days	90 days
Consumer | Residential first mortgages | Less than or equal to 80%
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	$ 45,335	$ 45,849
Consumer | Residential first mortgages | 80% but less than or equal to 100%
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	3,358	3,467
Consumer | Residential first mortgages | Greater than 100%
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	312	324
Consumer | Residential first mortgages | Less than 620
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	2,643	2,744
Consumer | Residential first mortgages | ≥ 620 but less than 660
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	2,323	2,422
Consumer | Residential first mortgages | Equal to or greater than 660
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	43,848	44,279
Consumer | Home equity loans | Less than or equal to 80%
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	12,344	12,869
Consumer | Home equity loans | 80% but less than or equal to 100%
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	3,305	3,653
Consumer | Home equity loans | Greater than 100%
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	1,183	1,305
Consumer | Home equity loans | Less than 620
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	1,650	1,750
Consumer | Home equity loans | ≥ 620 but less than 660
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	1,330	1,418
Consumer | Home equity loans | Equal to or greater than 660
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	13,935	14,743
Consumer | Credit cards | Less than 620
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	8,631	8,310
Consumer | Credit cards | ≥ 620 but less than 660
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	11,270	11,320
Consumer | Credit cards | Equal to or greater than 660
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	103,156	110,522
Consumer | Installment and other revolving | Less than 620
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	281	284
Consumer | Installment and other revolving | ≥ 620 but less than 660
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	274	271
Consumer | Installment and other revolving | Equal to or greater than 660
Financing Receivable
Loans acquired with deteriorated credit quality in accordance with ASC 310-30	$ 2,479	2,601
Consumer | Commercial banking loans
Non-Accrual Details
Number of days past due, non-accrual status	90 days
Consumer | Total GCB and Corporate/Other consumer
Non-Accrual Details
Loans, current	$ 313,130	317,184
Loans, net of unearned income	320,554	325,060
Total non-accrual	2,955	3,158
90 days past due and accruing	2,805	2,991
Consumer | Total GCB and Corporate/Other consumer | Government-guaranteed
Non-Accrual Details
Loans, past due	1,368	1,474
Consumer | Total GCB and Corporate/Other consumer | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	3,131	3,275
Consumer | Total GCB and Corporate/Other consumer | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	2,925	3,127
Consumer | Other
Non-Accrual Details
Loans, current	2	3
Loans, net of unearned income	2	3
Total non-accrual	0	0
90 days past due and accruing	0	0
Consumer | Other | Government-guaranteed
Non-Accrual Details
Loans, past due	0	0
Consumer | Other | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	0	0
Consumer | Other | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	0	0
Consumer | In North America offices
Non-Accrual Details
Loans, current	203,420	213,222
Loans, net of unearned income	209,116	219,491
Total non-accrual	1,926	2,160
90 days past due and accruing	2,563	2,752
Consumer | In North America offices | Government-guaranteed
Non-Accrual Details
Loans, past due	1,368	1,474
Consumer | In North America offices | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	2,106	2,365
Consumer | In North America offices | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	2,222	2,430
Consumer | In North America offices | Residential first mortgages
Non-Accrual Details
Loans, current	50,423	50,766
Loans, net of unearned income	52,537	53,133
Total non-accrual	763	848
90 days past due and accruing	1,117	1,227
Mortgage loans in process of foreclosure	100	100
Consumer | In North America offices | Residential first mortgages | Government-guaranteed
Non-Accrual Details
Loans, past due	1,368	1,474
Consumer | In North America offices | Residential first mortgages | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	447	522
Consumer | In North America offices | Residential first mortgages | 30 to 89 Days Past Due | Government-guaranteed
Non-Accrual Details
Loans, past due	200	200
Consumer | In North America offices | Residential first mortgages | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	299	371
Consumer | In North America offices | Residential first mortgages | Equal to greater than 90 days past due | Government-guaranteed
Non-Accrual Details
Loans, past due	1,200	1,300
Consumer | In North America offices | Home equity loans
Non-Accrual Details
Loans, current	16,694	18,767
Loans, net of unearned income	17,331	19,454
Total non-accrual	848	914
90 days past due and accruing	0	0
Home equity loans in process of foreclosure	100	100
Consumer | In North America offices | Home equity loans | Government-guaranteed
Non-Accrual Details
Loans, past due	0	0
Consumer | In North America offices | Home equity loans | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	233	249
Consumer | In North America offices | Home equity loans | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	404	438
Consumer | In North America offices | Credit cards
Non-Accrual Details
Loans, current	123,638	130,327
Loans, net of unearned income	126,433	133,301
Total non-accrual	0	0
90 days past due and accruing	1,433	1,509
Consumer | In North America offices | Credit cards | Government-guaranteed
Non-Accrual Details
Loans, past due	0	0
Consumer | In North America offices | Credit cards | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	1,362	1,465
Consumer | In North America offices | Credit cards | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	1,433	1,509
Consumer | In North America offices | Installment and other revolving
Non-Accrual Details
Loans, current	3,537	4,486
Loans, net of unearned income	3,601	4,630
Total non-accrual	24	70
90 days past due and accruing	1	2
Consumer | In North America offices | Installment and other revolving | Government-guaranteed
Non-Accrual Details
Loans, past due	0	0
Consumer | In North America offices | Installment and other revolving | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	46	106
Consumer | In North America offices | Installment and other revolving | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	18	38
Consumer | In North America offices | Commercial banking loans
Non-Accrual Details
Loans, current	9,128	8,876
Loans, net of unearned income	9,214	8,973
Total non-accrual	291	328
90 days past due and accruing	12	14
Consumer | In North America offices | Commercial banking loans | Government-guaranteed
Non-Accrual Details
Loans, past due	0	0
Consumer | In North America offices | Commercial banking loans | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	18	23
Consumer | In North America offices | Commercial banking loans | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	68	74
Consumer | In offices outside North America
Non-Accrual Details
Loans, current	109,710	103,962
Loans, net of unearned income	111,438	105,569
Total non-accrual	1,029	998
90 days past due and accruing	242	239
Consumer | In offices outside North America | Government-guaranteed
Non-Accrual Details
Loans, past due	0	0
Consumer | In offices outside North America | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	1,025	910
Consumer | In offices outside North America | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	703	697
Consumer | In offices outside North America | Residential first mortgages
Non-Accrual Details
Loans, current	36,624	35,862
Loans, net of unearned income	37,025	36,203
Total non-accrual	400	360
90 days past due and accruing	0	0
Consumer | In offices outside North America | Residential first mortgages | Government-guaranteed
Non-Accrual Details
Loans, past due	0	0
Consumer | In offices outside North America | Residential first mortgages | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	245	206
Consumer | In offices outside North America | Residential first mortgages | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	156	135
Consumer | In offices outside North America | Credit cards
Non-Accrual Details
Loans, current	23,272	22,363
Loans, net of unearned income	23,997	23,055
Total non-accrual	272	258
90 days past due and accruing	242	239
Consumer | In offices outside North America | Credit cards | Government-guaranteed
Non-Accrual Details
Loans, past due	0	0
Consumer | In offices outside North America | Credit cards | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	394	368
Consumer | In offices outside North America | Credit cards | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	331	324
Consumer | In offices outside North America | Installment and other revolving
Non-Accrual Details
Loans, current	24,088	22,683
Loans, net of unearned income	24,506	23,073
Total non-accrual	149	163
90 days past due and accruing	0	0
Consumer | In offices outside North America | Installment and other revolving | Government-guaranteed
Non-Accrual Details
Loans, past due	0	0
Consumer | In offices outside North America | Installment and other revolving | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	295	264
Consumer | In offices outside North America | Installment and other revolving | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	123	126
Consumer | In offices outside North America | Commercial banking loans
Non-Accrual Details
Loans, current	25,726	23,054
Loans, net of unearned income	25,910	23,238
Total non-accrual	208	217
90 days past due and accruing	0	0
Consumer | In offices outside North America | Commercial banking loans | Government-guaranteed
Non-Accrual Details
Loans, past due	0	0
Consumer | In offices outside North America | Commercial banking loans | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	91	72
Consumer | In offices outside North America | Commercial banking loans | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	$ 93	$ 112