LOANS - Consumer Loan Delinquency (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Non-Accrual Details
Loans, net of unearned income	$ 671,180	$ 667,034
Loans at fair value	3,000	4,374
Consumer
Non-Accrual Details
Loans, current	317,028	326,092
Loans, net of unearned income	323,632	333,656
Total non-accrual	2,383	2,690
90 days past due and accruing	$ 2,393	$ 2,797
Loans less than this number of days past due are considered current	30 days	30 days
Loans at fair value	$ 22	$ 25
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	$ 52,750	55,029
Consumer | 80% but less than or equal to 100%
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	3,992	4,725
Consumer | Greater than 100%
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	742	1,047
Consumer | Less than 620
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	11,621	12,834
Consumer | ≥ 620 but less than 660
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	13,903	14,914
Consumer | ≥ 660 but less than 720
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	48,619	48,960
Consumer | Equal to or greater than 720
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	119,335	123,343
Consumer | Government-guaranteed
Non-Accrual Details
Loans, past due	931	1,225
Consumer | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	2,913	3,304
Consumer | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	2,760	3,035
Consumer | Residential first mortgages
Non-Accrual Details
Loans at fair value	$ 22	$ 25
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	$ 42,778	$ 43,626
Consumer | Residential first mortgages | 80% but less than or equal to 100%
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	2,382	2,578
Consumer | Residential first mortgages | Greater than 100%
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	189	247
Consumer | Residential first mortgages | Less than 620
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	1,707	2,100
Consumer | Residential first mortgages | ≥ 620 but less than 660
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	1,626	1,932
Consumer | Residential first mortgages | ≥ 660 but less than 720
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	6,421	6,931
Consumer | Residential first mortgages | Equal to or greater than 720
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	35,465	35,334
Consumer | Home equity loans | Less than or equal to 80%
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	9,972	11,403
Consumer | Home equity loans | 80% but less than or equal to 100%
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	1,610	2,147
Consumer | Home equity loans | Greater than 100%
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	553	800
Consumer | Home equity loans | Less than 620
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	1,085	1,379
Consumer | Home equity loans | ≥ 620 but less than 660
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	906	1,081
Consumer | Home equity loans | ≥ 660 but less than 720
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	2,946	3,446
Consumer | Home equity loans | Equal to or greater than 720
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	7,274	8,530
Consumer | Credit cards | Less than 620
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	8,682	9,079
Consumer | Credit cards | ≥ 620 but less than 660
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	11,129	11,651
Consumer | Credit cards | ≥ 660 but less than 720
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	38,544	37,916
Consumer | Credit cards | Equal to or greater than 720
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	74,911	77,661
Consumer | Installment and other revolving | Less than 620
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	147	276
Consumer | Installment and other revolving | ≥ 620 but less than 660
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	242	250
Consumer | Installment and other revolving | ≥ 660 but less than 720
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	708	667
Consumer | Installment and other revolving | Equal to or greater than 720
Financing Receivable
Purchased credit-impaired in accordance with ASC 310-30	$ 1,685	1,818
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	$ 317,027	326,091
Loans, net of unearned income	323,631	333,655
Total non-accrual	2,383	2,690
90 days past due and accruing	2,393	2,797
Consumer | Total GCB and Corporate/Other— Consumer | Government-guaranteed
Non-Accrual Details
Loans, past due	931	1,225
Consumer | Total GCB and Corporate/Other— Consumer | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	2,913	3,304
Consumer | Total GCB and Corporate/Other— Consumer | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	2,760	3,035
Consumer | Other
Non-Accrual Details
Loans, current	1	1
Loans, net of unearned income	1	1
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	205,050	211,012
Loans, net of unearned income	210,063	216,899
Total non-accrual	1,373	1,650
90 days past due and accruing	2,166	2,538
Consumer | In North America offices | Government-guaranteed
Non-Accrual Details
Loans, past due	931	1,225
Consumer | In North America offices | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	1,995	2,336
Consumer | In North America offices | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	2,087	2,326
Consumer | In North America offices | Residential first mortgages
Non-Accrual Details
Loans, current	46,314	47,366
Loans, net of unearned income	47,904	49,376
Total non-accrual	619	665
90 days past due and accruing	673	941
Mortgage loans in process of foreclosure	100	100
Consumer | In North America offices | Residential first mortgages | Government-guaranteed
Non-Accrual Details
Loans, past due	931	1,225
Consumer | In North America offices | Residential first mortgages | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	404	505
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	255	280
Consumer | In North America offices | Residential first mortgages | Equal to greater than 90 days past due | Government-guaranteed
Non-Accrual Details
Loans, past due	700	1,000
Consumer | In North America offices | Home equity loans
Non-Accrual Details
Loans, current	12,420	14,268
Loans, net of unearned income	12,861	14,827
Total non-accrual	606	750
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	155	207
Consumer | In North America offices | Home equity loans | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	286	352
Consumer | In North America offices | Credit cards
Non-Accrual Details
Loans, current	133,860	136,588
Loans, net of unearned income	136,741	139,729
Total non-accrual	0	0
90 days past due and accruing	1,493	1,596
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	1,388	1,528
Consumer | In North America offices | Credit cards | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	1,493	1,613
Consumer | In North America offices | Installment and other revolving
Non-Accrual Details
Loans, current	3,402	3,395
Loans, net of unearned income	3,453	3,456
Total non-accrual	20	22
90 days past due and accruing	0	1
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	38	45
Consumer | In North America offices | Installment and other revolving | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	13	16
Consumer | In North America offices | Commercial banking loans
Non-Accrual Details
Loans, current	9,054	9,395
Loans, net of unearned income	9,104	9,511
Total non-accrual	128	213
90 days past due and accruing	0	0
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	10	51
Consumer | In North America offices | Commercial banking loans | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	40	65
Consumer | In offices outside North America
Non-Accrual Details
Loans, current	111,977	115,079
Loans, net of unearned income	113,568	116,756
Total non-accrual	1,010	1,040
90 days past due and accruing	227	259
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	918	968
Consumer | In offices outside North America | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	673	709
Consumer | In offices outside North America | Residential first mortgages
Non-Accrual Details
Loans, current	35,789	37,062
Loans, net of unearned income	36,134	37,419
Total non-accrual	382	400
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	205	209
Consumer | In offices outside North America | Residential first mortgages | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	140	148
Consumer | In offices outside North America | Credit cards
Non-Accrual Details
Loans, current	23,389	24,934
Loans, net of unearned income	24,157	25,727
Total non-accrual	312	323
90 days past due and accruing	227	259
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	416	427
Consumer | In offices outside North America | Credit cards | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	352	366
Consumer | In offices outside North America | Installment and other revolving
Non-Accrual Details
Loans, current	24,772	25,634
Loans, net of unearned income	25,124	26,032
Total non-accrual	144	157
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	243	275
Consumer | In offices outside North America | Installment and other revolving | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	109	123
Consumer | In offices outside North America | Commercial banking loans
Non-Accrual Details
Loans, current	28,027	27,449
Loans, net of unearned income	28,153	27,578
Total non-accrual	172	160
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	54	57
Consumer | In offices outside North America | Commercial banking loans | Equal to greater than 90 days past due
Non-Accrual Details
Loans, past due	$ 72	$ 72