LOANS - Consumer Troubled Debt Restructurings (Details) - Consumer $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($) loan	Jun. 30, 2017 USD ($) loan	Jun. 30, 2018 USD ($) loan	Jun. 30, 2017 USD ($) loan	Dec. 31, 2017
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	56,643	54,843	121,241	116,072
Post-modification recorded investment	$ 337	$ 422	$ 715	$ 845
TDR in payment default	$ 107	$ 115	$ 228	$ 228
In North America offices | Residential first mortgages
Loans receivable
Number of loans modified | loan	495	806	1,083	1,772
Post-modification recorded investment	$ 77	$ 116	$ 166	$ 246
Average interest rate reduction	0.00%	1.00%	0.00%	1.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 8	$ 15	$ 19	$ 30
TDR in payment default	30	48	74	99
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	$ 5	$ 11	$ 13	$ 21
In North America offices | Home equity loans
Loans receivable
Number of loans modified | loan	380	677	836	1,356
Post-modification recorded investment	$ 37	$ 58	$ 78	$ 114
Average interest rate reduction	1.00%	2.00%	1.00%	1.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 3	$ 5	$ 7	$ 11
TDR in payment default	6	8	16	17
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	$ 3	$ 4	$ 6	$ 10
In North America offices | Credit cards
Loans receivable
Number of loans modified | loan	55,459	53,080	118,662	112,417
Post-modification recorded investment	$ 220	$ 203	$ 464	$ 433
Average interest rate reduction	17.00%	17.00%	17.00%	17.00%
TDR in payment default	$ 57	$ 57	$ 116	$ 109
In North America offices | Installment and other revolving
Loans receivable
Number of loans modified | loan	292	250	634	471
Post-modification recorded investment	$ 2	$ 2	$ 5	$ 4
Average interest rate reduction	5.00%	5.00%	5.00%	5.00%
TDR in payment default	$ 1	$ 1	$ 1	$ 1
In North America offices | Commercial banking
Loans receivable
Number of loans modified | loan	17	30	26	56
Post-modification recorded investment	$ 1	$ 43	$ 2	$ 48
Average interest rate reduction	0.00%	0.00%	0.00%	0.00%
TDR in payment default	$ 13	$ 1	$ 21	$ 2
In offices outside the U.S.
Loans receivable
Number of loans modified | loan	25,735	40,981	59,148	78,170
Post-modification recorded investment	$ 165	$ 196	$ 366	$ 380
TDR in payment default	$ 86	$ 72	$ 166	$ 139
In offices outside the U.S. | Residential first mortgages
Loans receivable
Number of loans modified | loan	624	755	1,173	1,368
Post-modification recorded investment	$ 22	$ 28	$ 41	$ 54
Average interest rate reduction	0.00%	0.00%	0.00%	0.00%
TDR in payment default	$ 2	$ 3	$ 4	$ 5
In offices outside the U.S. | Credit cards
Loans receivable
Number of loans modified | loan	17,782	28,551	41,176	53,788
Post-modification recorded investment	$ 78	$ 98	$ 173	$ 183
Average interest rate reduction	16.00%	12.00%	16.00%	13.00%
TDR in payment default	$ 55	$ 46	$ 108	$ 88
In offices outside the U.S. | Installment and other revolving
Loans receivable
Number of loans modified | loan	7,172	11,622	16,497	22,929
Post-modification recorded investment	$ 43	$ 64	$ 102	$ 124
Average interest rate reduction	11.00%	9.00%	10.00%	7.00%
TDR in payment default	$ 20	$ 23	$ 44	$ 46
In offices outside the U.S. | Commercial banking
Loans receivable
Number of loans modified | loan	157	53	302	85
Post-modification recorded investment	$ 22	$ 6	$ 50	$ 19
Average interest rate reduction	0.00%	0.00%	(1.00%)	(1.00%)
TDR in payment default	$ 9	$ 0	$ 10	$ 0
Deferred principal | In North America offices
Loans receivable
Post-modification recorded investment	2	6	4	12
Deferred principal | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	1	1	1	4
Deferred principal | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	1	5	3	8
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	0	1
Principal forgiveness | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	1	0	1
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	4	4	9	10
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	5	4
Principal forgiveness | In offices outside the U.S. | Installment and other revolving
Loans receivable
Post-modification recorded investment	2	2	4	6
Principal forgiveness | In offices outside the U.S. | Commercial banking
Loans receivable
Post-modification recorded investment	$ 0	$ 0	$ 0	$ 0