LOANS - Consumer Loan Delinquency (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Non-Accrual Details
Loans, net of unearned income	$ 682,346	$ 684,196
Loans at fair value	3,874	3,223
Consumer
Non-Accrual Details
Loans, current	313,147	323,436
Loans, net of unearned income	319,887	330,487
Total non-accrual	2,205	2,226
90 days past due and accruing	$ 2,436	$ 2,548
Loans less than this number of days past due are considered current	30 days	30 days
Loans at fair value	$ 20	$ 20
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	$ 49,067	51,844
Consumer | 80% but less than or equal to 100%
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	3,969	3,761
Consumer | Greater than 100%
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	614	587
Consumer | Less than 680
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	39,157	40,279
Consumer | 680 to 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	73,999	77,963
Consumer | Greater than 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	77,101	83,437
Consumer | Government-guaranteed
Non-Accrual Details
Loans, past due	677	786
Consumer | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	3,124	3,264
Consumer | 90 days past due
Non-Accrual Details
Loans, past due	2,939	3,001
Consumer | Residential first mortgages
Non-Accrual Details
Loans at fair value	$ 20	$ 20
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	$ 40,112	$ 42,379
Consumer | Residential first mortgages | 80% but less than or equal to 100%
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	2,745	2,474
Consumer | Residential first mortgages | Greater than 100%
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	234	197
Consumer | Residential first mortgages | Less than 680
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	4,169	4,530
Consumer | Residential first mortgages | 680 to 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	12,922	13,848
Consumer | Residential first mortgages | Greater than 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	25,874	26,546
Consumer | Home equity loans | Less than or equal to 80%
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	8,955	9,465
Consumer | Home equity loans | 80% but less than or equal to 100%
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	1,224	1,287
Consumer | Home equity loans | Greater than 100%
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	380	390
Consumer | Home equity loans | Less than 680
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	2,321	2,438
Consumer | Home equity loans | 680 to 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	4,093	4,296
Consumer | Home equity loans | Greater than 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	4,188	4,471
Consumer | Credit cards | Less than 680
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	32,056	32,686
Consumer | Credit cards | 680 to 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	55,975	58,722
Consumer | Credit cards | Greater than 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	45,934	51,299
Consumer | Installment and other revolving | Less than 680
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	611	625
Consumer | Installment and other revolving | 680 to 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	1,009	1,097
Consumer | Installment and other revolving | Greater than 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	$ 1,105	1,121
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	$ 313,146	323,435
Loans, net of unearned income	319,886	330,486
Total non-accrual	2,205	2,226
90 days past due and accruing	2,436	2,548
Consumer | Total GCB and Corporate/Other— Consumer | Government-guaranteed
Non-Accrual Details
Loans, past due	677	786
Consumer | Total GCB and Corporate/Other— Consumer | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	3,124	3,264
Consumer | Total GCB and Corporate/Other— Consumer | 90 days past due
Non-Accrual Details
Loans, past due	2,939	3,001
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 | 90 days past due
Non-Accrual Details
Loans, past due	0	0
Consumer | In North America offices
Non-Accrual Details
Loans, current	200,706	211,250
Loans, net of unearned income	205,869	216,693
Total non-accrual	1,230	1,241
90 days past due and accruing	2,202	2,313
Consumer | In North America offices | Government-guaranteed
Non-Accrual Details
Loans, past due	677	786
Consumer | In North America offices | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	2,207	2,331
Consumer | In North America offices | 90 days past due
Non-Accrual Details
Loans, past due	2,279	2,326
Consumer | In North America offices | Residential first mortgages
Non-Accrual Details
Loans, current	44,047	45,953
Loans, net of unearned income	45,351	47,412
Total non-accrual	564	583
90 days past due and accruing	456	549
Mortgage loans in process of foreclosure	100	100
Consumer | In North America offices | Residential first mortgages | Government-guaranteed
Non-Accrual Details
Loans, past due	677	786
Consumer | In North America offices | Residential first mortgages | 30 to 89 Days Past Due
Non-Accrual Details
Loans, past due	393	420
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 | 90 days past due
Non-Accrual Details
Loans, past due	234	253
Consumer | In North America offices | Residential first mortgages | 90 days past due | Government-guaranteed
Non-Accrual Details
Loans, past due	500	600
Consumer | In North America offices | Home equity loans
Non-Accrual Details
Loans, current	10,527	11,135
Loans, net of unearned income	10,937	11,543
Total non-accrual	500	527
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	174	161
Consumer | In North America offices | Home equity loans | 90 days past due
Non-Accrual Details
Loans, past due	236	247
Consumer | In North America offices | Credit cards
Non-Accrual Details
Loans, current	132,572	141,106
Loans, net of unearned income	135,908	144,557
Total non-accrual	0	0
90 days past due and accruing	1,746	1,764
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	1,590	1,687
Consumer | In North America offices | Credit cards | 90 days past due
Non-Accrual Details
Loans, past due	1,746	1,764
Consumer | In North America offices | Installment and other revolving
Non-Accrual Details
Loans, current	3,257	3,394
Loans, net of unearned income	3,313	3,453
Total non-accrual	21	22
90 days past due and accruing	0	0
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	41	43
Consumer | In North America offices | Installment and other revolving | 90 days past due
Non-Accrual Details
Loans, past due	15	16
Consumer | In North America offices | Commercial banking loans
Non-Accrual Details
Loans, current	10,303	9,662
Loans, net of unearned income	10,360	9,728
Total non-accrual	145	109
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	9	20
Consumer | In North America offices | Commercial banking loans | 90 days past due
Non-Accrual Details
Loans, past due	48	46
Consumer | In offices outside North America
Non-Accrual Details
Loans, current	112,440	112,185
Loans, net of unearned income	114,017	113,793
Total non-accrual	975	985
90 days past due and accruing	234	235
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	917	933
Consumer | In offices outside North America | 90 days past due
Non-Accrual Details
Loans, past due	660	675
Consumer | In offices outside North America | Residential first mortgages
Non-Accrual Details
Loans, current	35,777	35,624
Loans, net of unearned income	36,114	35,972
Total non-accrual	397	383
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	203	203
Consumer | In offices outside North America | Residential first mortgages | 90 days past due
Non-Accrual Details
Loans, past due	134	145
Consumer | In offices outside North America | Credit cards
Non-Accrual Details
Loans, current	23,561	24,131
Loans, net of unearned income	24,343	24,926
Total non-accrual	297	312
90 days past due and accruing	234	235
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	417	425
Consumer | In offices outside North America | Credit cards | 90 days past due
Non-Accrual Details
Loans, past due	365	370
Consumer | In offices outside North America | Installment and other revolving
Non-Accrual Details
Loans, current	25,687	25,085
Loans, net of unearned income	26,028	25,446
Total non-accrual	130	152
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	244	254
Consumer | In offices outside North America | Installment and other revolving | 90 days past due
Non-Accrual Details
Loans, past due	97	107
Consumer | In offices outside North America | Commercial banking loans
Non-Accrual Details
Loans, current	27,415	27,345
Loans, net of unearned income	27,532	27,449
Total non-accrual	151	138
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	53	51
Consumer | In offices outside North America | Commercial banking loans | 90 days past due
Non-Accrual Details
Loans, past due	$ 64	$ 53