LOANS - Consumer Troubled Debt Restructurings (Details) - Consumer $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($) loan	Jun. 30, 2018 USD ($) loan	Jun. 30, 2019 USD ($) loan	Jun. 30, 2018 USD ($) loan	Dec. 31, 2018
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	63,958	56,643	137,270	121,241
Post-modification recorded investment	$ 329	$ 337	$ 769	$ 715
TDR loans in payment default	$ 105	$ 107	$ 204	$ 228
In North America offices | Residential first mortgages
Loans receivable
Number of loans modified | loan	137	495	630	1,083
Post-modification recorded investment	$ 21	$ 77	$ 95	$ 166
Average interest rate reduction	0.00%	0.00%	0.00%	0.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 5	$ 8	$ 12	$ 19
TDR loans in payment default	26	30	50	74
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	$ 3	$ 5	$ 7	$ 13
In North America offices | Home equity loans
Loans receivable
Number of loans modified | loan	188	380	394	836
Post-modification recorded investment	$ 22	$ 37	$ 42	$ 78
Average interest rate reduction	1.00%	1.00%	1.00%	1.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 2	$ 3	$ 4	$ 7
TDR loans in payment default	4	6	7	16
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	$ 1	$ 3	$ 3	$ 6
In North America offices | Credit cards
Loans receivable
Number of loans modified | loan	63,281	55,459	135,528	118,662
Post-modification recorded investment	$ 273	$ 220	$ 578	$ 464
Average interest rate reduction	17.00%	17.00%	17.00%	17.00%
TDR loans in payment default	$ 73	$ 57	$ 144	$ 116
In North America offices | Installment and other revolving
Loans receivable
Number of loans modified | loan	340	292	691	634
Post-modification recorded investment	$ 3	$ 2	$ 6	$ 5
Average interest rate reduction	6.00%	5.00%	6.00%	5.00%
TDR loans in payment default	$ 1	$ 1	$ 2	$ 1
In North America offices | Commercial banking
Loans receivable
Number of loans modified | loan	12	17	27	26
Post-modification recorded investment	$ 10	$ 1	$ 48	$ 2
Average interest rate reduction	0.00%	0.00%	0.00%	0.00%
TDR loans in payment default	$ 1	$ 13	$ 1	$ 21
In offices outside North America(1)
Loans receivable
Number of loans modified | loan	26,253	25,735	53,122	59,148
Post-modification recorded investment	$ 143	$ 165	$ 314	$ 366
TDR loans in payment default	$ 61	$ 86	$ 121	$ 166
In offices outside North America(1) | Residential first mortgages
Loans receivable
Number of loans modified | loan	638	624	1,363	1,173
Post-modification recorded investment	$ 17	$ 22	$ 37	$ 41
Average interest rate reduction	0.00%	0.00%	0.00%	0.00%
TDR loans in payment default	$ 4	$ 2	$ 7	$ 4
In offices outside North America(1) | Credit cards
Loans receivable
Number of loans modified | loan	18,453	17,782	36,946	41,176
Post-modification recorded investment	$ 73	$ 78	$ 148	$ 173
Average interest rate reduction	16.00%	16.00%	16.00%	16.00%
TDR loans in payment default	$ 36	$ 55	$ 75	$ 108
In offices outside North America(1) | Installment and other revolving
Loans receivable
Number of loans modified | loan	7,073	7,172	14,625	16,497
Post-modification recorded investment	$ 44	$ 43	$ 88	$ 102
Average interest rate reduction	10.00%	11.00%	10.00%	10.00%
TDR loans in payment default	$ 19	$ 20	$ 37	$ 44
In offices outside North America(1) | Commercial banking
Loans receivable
Number of loans modified | loan	89	157	188	302
Post-modification recorded investment	$ 9	$ 22	$ 41	$ 50
Average interest rate reduction	0.00%	0.00%	0.00%	1.00%
TDR loans in payment default	$ 2	$ 9	$ 2	$ 10
Deferred principal | In North America offices
Loans receivable
Post-modification recorded investment	1	2	2	4
Deferred principal | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	1	0	1
Deferred principal | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	1	1	2	3
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 North America(1)
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In offices outside North America(1) | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In offices outside North America(1) | Credit cards
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In offices outside North America(1) | Installment and other revolving
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In offices outside North America(1) | 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 North America(1)
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In offices outside North America(1) | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In offices outside North America(1) | Credit cards
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In offices outside North America(1) | Installment and other revolving
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In offices outside North America(1) | 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	0	0	0
Principal forgiveness | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0	0	0
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 North America(1)
Loans receivable
Post-modification recorded investment	5	4	9	9
Principal forgiveness | In offices outside North America(1) | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0	0	0
Principal forgiveness | In offices outside North America(1) | Credit cards
Loans receivable
Post-modification recorded investment	3	2	6	5
Principal forgiveness | In offices outside North America(1) | Installment and other revolving
Loans receivable
Post-modification recorded investment	2	2	3	4
Principal forgiveness | In offices outside North America(1) | Commercial banking
Loans receivable
Post-modification recorded investment	$ 0	$ 0	$ 0	$ 0