LOANS - Consumer Troubled Debt Restructurings (Details) - Consumer $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017 USD ($) loan	Sep. 30, 2016 USD ($) loan	Sep. 30, 2017 USD ($) loan	Sep. 30, 2016 USD ($) loan	Dec. 31, 2016
Loans receivable
Period within which default occurred post-modification			1 year
Number of days past due, non-accrual status			60 days
Residential first mortgages
Loans receivable
Number of days past due, non-accrual status			90 days		90 days
Commercial banking
Loans receivable
Number of days past due, non-accrual status			90 days
In North America offices
Loans receivable
Number of loans modified | loan	61,847	54,993	177,919	154,210
Post-modification recorded investment	$ 555	$ 473	$ 1,402	$ 1,337
TDR in payment default	$ 120	$ 113	$ 348	$ 368
In North America offices | Residential first mortgages
Loans receivable
Number of loans modified | loan	1,400	1,165	3,172	3,979
Post-modification recorded investment	$ 199	$ 165	$ 445	$ 582
Average interest rate reduction	0.00%	1.00%	1.00%	1.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 12	$ 17	$ 42	$ 58
TDR in payment default	57	49	156	188
In North America offices | Residential first mortgages | New OCC guidance
Loans receivable
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 7	$ 11	$ 28	$ 38
In North America offices | Home equity loans
Loans receivable
Number of loans modified | loan	830	1,117	2,186	2,789
Post-modification recorded investment	$ 70	$ 61	$ 185	$ 121
Average interest rate reduction	1.00%	2.00%	1.00%	2.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 5	$ 5	$ 16	$ 15
TDR in payment default	8	6	25	20
In North America offices | Home equity loans | New OCC guidance
Loans receivable
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 5	$ 5	$ 14	$ 14
In North America offices | Credit cards
Loans receivable
Number of loans modified | loan	59,285	51,260	171,702	143,161
Post-modification recorded investment	$ 225	$ 199	$ 659	$ 552
Average interest rate reduction	17.00%	18.00%	17.00%	17.00%
TDR in payment default	$ 54	$ 43	$ 163	$ 139
In North America offices | Installment and other revolving
Loans receivable
Number of loans modified | loan	299	1,421	770	4,187
Post-modification recorded investment	$ 2	$ 12	$ 6	$ 35
Average interest rate reduction	6.00%	14.00%	5.00%	14.00%
TDR in payment default	$ 1	$ 3	$ 2	$ 7
In North America offices | Commercial banking
Loans receivable
Number of loans modified | loan	33	30	89	94
Post-modification recorded investment	$ 59	$ 36	$ 107	$ 47
Average interest rate reduction	0.00%	0.00%	0.00%	0.00%
TDR in payment default	$ 0	$ 12	$ 2	$ 14
In offices outside the U.S.
Loans receivable
Number of loans modified | loan	40,779	41,830	118,949	156,612
Post-modification recorded investment	$ 209	$ 226	$ 590	$ 667
TDR in payment default	$ 76	$ 89	$ 215	$ 230
In offices outside the U.S. | Residential first mortgages
Loans receivable
Number of loans modified | loan	703	973	2,071	2,005
Post-modification recorded investment	$ 25	$ 24	$ 80	$ 62
Average interest rate reduction	0.00%	0.00%	0.00%	0.00%
TDR in payment default	$ 3	$ 3	$ 8	$ 9
In offices outside the U.S. | Credit cards
Loans receivable
Number of loans modified | loan	28,254	28,530	82,042	109,365
Post-modification recorded investment	$ 103	$ 94	$ 286	$ 307
Average interest rate reduction	11.00%	12.00%	12.00%	12.00%
TDR in payment default	$ 48	$ 41	$ 136	$ 115
In offices outside the U.S. | Installment and other revolving
Loans receivable
Number of loans modified | loan	11,725	12,283	34,654	45,125
Post-modification recorded investment	$ 70	$ 69	$ 194	$ 208
Average interest rate reduction	11.00%	8.00%	9.00%	7.00%
TDR in payment default	$ 25	$ 24	$ 71	$ 70
In offices outside the U.S. | Commercial banking
Loans receivable
Number of loans modified | loan	97	44	182	117
Post-modification recorded investment	$ 11	$ 39	$ 30	$ 90
Average interest rate reduction	0.00%	0.00%	0.00%	0.00%
TDR in payment default	$ 0	$ 21	$ 0	$ 36
Deferred principal | In North America offices
Loans receivable
Post-modification recorded investment	6	1	18	5
Deferred principal | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	1	1	5	4
Deferred principal | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	5	0	13	1
Deferred principal | In North America offices | Credit cards
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In North America offices | Installment and other revolving
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In North America offices | Commercial banking
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In offices outside the U.S.
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In offices outside the U.S. | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In offices outside the U.S. | Credit cards
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In offices outside the U.S. | Installment and other revolving
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In offices outside the U.S. | Commercial banking
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In North America offices
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In North America offices | Credit cards
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In North America offices | Installment and other revolving
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In North America offices | Commercial banking
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In offices outside the U.S.
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In offices outside the U.S. | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In offices outside the U.S. | Credit cards
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In offices outside the U.S. | Installment and other revolving
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In offices outside the U.S. | Commercial banking
Loans receivable
Post-modification recorded investment	0	0	0	0
Principal forgiveness | In North America offices
Loans receivable
Post-modification recorded investment	0	1	2	3
Principal forgiveness | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	1	2	3
Principal forgiveness | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	0	0	0	0
Principal forgiveness | In North America offices | Credit cards
Loans receivable
Post-modification recorded investment	0	0	0	0
Principal forgiveness | In North America offices | Installment and other revolving
Loans receivable
Post-modification recorded investment	0	0	0	0
Principal forgiveness | In North America offices | Commercial banking
Loans receivable
Post-modification recorded investment	0	0	0	0
Principal forgiveness | In offices outside the U.S.
Loans receivable
Post-modification recorded investment	5	4	15	13
Principal forgiveness | In offices outside the U.S. | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0	0	0
Principal forgiveness | In offices outside the U.S. | Credit cards
Loans receivable
Post-modification recorded investment	2	2	6	7
Principal forgiveness | In offices outside the U.S. | Installment and other revolving
Loans receivable
Post-modification recorded investment	3	2	9	6
Principal forgiveness | In offices outside the U.S. | Commercial banking
Loans receivable
Post-modification recorded investment	$ 0	$ 0	$ 0	$ 0