LOANS - Consumer Loan Delinquency (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Non-Accrual Details
Loans, net of unearned income	$ 653,183	$ 624,369
Loans at fair value	4,308	3,486
Consumer
Non-Accrual Details
Loans, current	318,007	317,187
Loans, net of unearned income	325,576	325,063
Total non-accrual	2,783	3,158
90 days past due and accruing	$ 2,687	$ 2,991
Loans less than this number of days past due are considered current	30 days	30 days
Loans at fair value	$ 27	$ 29
Number of days past due, non-accrual status	60 days
Consumer | Less than or equal to 80%
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	$ 56,061	58,718
Consumer | 80% but less than or equal to 100%
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	5,055	7,120
Consumer | Greater than 100%
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	1,190	1,629
Consumer | Less than 620
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	12,676	13,088
Consumer | ≥ 620 but less than 660
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	14,796	15,431
Consumer | Equal to or greater than 660
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	166,527	172,145
Consumer | Government-guaranteed
Non-Accrual Details
Loans, past due	1,279	1,474
Consumer | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	3,406	3,275
Consumer | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	2,884	3,127
Consumer | Residential first mortgages
Non-Accrual Details
Loans at fair value	$ 27	$ 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
Purchased credit-impaired in accordance with ASC 310-30	$ 44,253	$ 45,849
Consumer | Residential first mortgages | 80% but less than or equal to 100%
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	2,658	3,467
Consumer | Residential first mortgages | Greater than 100%
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	262	324
Consumer | Residential first mortgages | Less than 620
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	2,275	2,744
Consumer | Residential first mortgages | ≥ 620 but less than 660
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	2,053	2,422
Consumer | Residential first mortgages | Equal to or greater than 660
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	42,682	44,279
Consumer | Home equity loans | Less than or equal to 80%
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	11,808	12,869
Consumer | Home equity loans | 80% but less than or equal to 100%
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	2,397	3,653
Consumer | Home equity loans | Greater than 100%
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	928	1,305
Consumer | Home equity loans | Less than 620
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	1,432	1,750
Consumer | Home equity loans | ≥ 620 but less than 660
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	1,166	1,418
Consumer | Home equity loans | Equal to or greater than 660
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	12,622	14,743
Consumer | Credit cards | Less than 620
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	8,699	8,310
Consumer | Credit cards | ≥ 620 but less than 660
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	11,325	11,320
Consumer | Credit cards | Equal to or greater than 660
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	108,809	110,522
Consumer | Installment and other revolving | Less than 620
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	270	284
Consumer | Installment and other revolving | ≥ 620 but less than 660
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	252	271
Consumer | Installment and other revolving | Equal to or greater than 660
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	$ 2,414	2,601
Consumer | Commercial banking
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	$ 318,005	317,184
Loans, net of unearned income	325,574	325,060
Total non-accrual	2,783	3,158
90 days past due and accruing	2,687	2,991
Consumer | Total GCB and Corporate/Other consumer | Government-guaranteed
Non-Accrual Details
Loans, past due	1,279	1,474
Consumer | Total GCB and Corporate/Other consumer | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	3,406	3,275
Consumer | Total GCB and Corporate/Other consumer | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	2,884	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	205,105	213,222
Loans, net of unearned income	210,946	219,491
Total non-accrual	1,721	2,160
90 days past due and accruing	2,436	2,752
Consumer | In North America offices | Government-guaranteed
Non-Accrual Details
Loans, past due	1,279	1,474
Consumer | In North America offices | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	2,407	2,365
Consumer | In North America offices | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	2,155	2,430
Consumer | In North America offices | Residential first mortgages
Non-Accrual Details
Loans, current	48,090	50,766
Loans, net of unearned income	50,218	53,133
Total non-accrual	724	848
90 days past due and accruing	985	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	1,279	1,474
Consumer | In North America offices | Residential first mortgages | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	563	522
Consumer | In North America offices | Residential first mortgages | 30 to 89 Days Past Due | Government-guaranteed
Non-Accrual Details
Loans, past due	300	200
Consumer | In North America offices | Residential first mortgages | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	286	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	1,000	1,300
Consumer | In North America offices | Home equity loans
Non-Accrual Details
Loans, current	15,004	18,767
Loans, net of unearned income	15,589	19,454
Total non-accrual	766	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	223	249
Consumer | In North America offices | Home equity loans | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	362	438
Consumer | In North America offices | Credit cards
Non-Accrual Details
Loans, current	129,261	130,327
Loans, net of unearned income	132,242	133,301
Total non-accrual	0	0
90 days past due and accruing	1,440	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	1,541	1,465
Consumer | In North America offices | Credit cards | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	1,440	1,509
Consumer | In North America offices | Installment and other revolving
Non-Accrual Details
Loans, current	3,456	4,486
Loans, net of unearned income	3,513	4,630
Total non-accrual	21	70
90 days past due and accruing	0	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	42	106
Consumer | In North America offices | Installment and other revolving | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	15	38
Consumer | In North America offices | Commercial banking
Non-Accrual Details
Loans, current	9,294	8,876
Loans, net of unearned income	9,384	8,973
Total non-accrual	210	328
90 days past due and accruing	11	14
Consumer | In North America offices | Commercial banking | Government-guaranteed
Non-Accrual Details
Loans, past due	0	0
Consumer | In North America offices | Commercial banking | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	38	23
Consumer | In North America offices | Commercial banking | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	52	74
Consumer | In offices outside North America
Non-Accrual Details
Loans, current	112,900	103,962
Loans, net of unearned income	114,628	105,569
Total non-accrual	1,062	998
90 days past due and accruing	251	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	999	910
Consumer | In offices outside North America | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	729	697
Consumer | In offices outside North America | Residential first mortgages
Non-Accrual Details
Loans, current	36,796	35,862
Loans, net of unearned income	37,174	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	225	206
Consumer | In offices outside North America | Residential first mortgages | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	153	135
Consumer | In offices outside North America | Credit cards
Non-Accrual Details
Loans, current	24,109	22,363
Loans, net of unearned income	24,908	23,055
Total non-accrual	322	258
90 days past due and accruing	251	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	433	368
Consumer | In offices outside North America | Credit cards | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	366	324
Consumer | In offices outside North America | Installment and other revolving
Non-Accrual Details
Loans, current	25,207	22,683
Loans, net of unearned income	25,614	23,073
Total non-accrual	164	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	283	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	124	126
Consumer | In offices outside North America | Commercial banking
Non-Accrual Details
Loans, current	26,788	23,054
Loans, net of unearned income	26,932	23,238
Total non-accrual	176	217
90 days past due and accruing	0	0
Consumer | In offices outside North America | Commercial banking | Government-guaranteed
Non-Accrual Details
Loans, past due	0	0
Consumer | In offices outside North America | Commercial banking | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	58	72
Consumer | In offices outside North America | Commercial banking | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	$ 86	$ 112