LOANS - Consumer Troubled Debt Restructurings (Details) - Consumer $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($) loan	Mar. 31, 2018 USD ($) 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	73,312	64,598
Post-modification recorded investment	$ 441	$ 378
TDR loans in payment default	$ 97	$ 122
In North America offices | Residential first mortgages
Loans receivable
Number of loans modified | loan	493	588
Post-modification recorded investment	$ 74	$ 89
Average interest rate reduction	0.00%	0.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 7	$ 11
TDR loans in payment default	23	44
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	$ 4	$ 8
In North America offices | Home equity loans
Loans receivable
Number of loans modified | loan	206	456
Post-modification recorded investment	$ 21	$ 41
Average interest rate reduction	2.00%	1.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 2	$ 4
TDR loans in payment default	3	10
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	$ 2	$ 3
In North America offices | Credit cards
Loans receivable
Number of loans modified | loan	72,247	63,203
Post-modification recorded investment	$ 305	$ 244
Average interest rate reduction	18.00%	18.00%
TDR loans in payment default	$ 70	$ 59
In North America offices | Installment and other revolving
Loans receivable
Number of loans modified | loan	351	342
Post-modification recorded investment	$ 3	$ 3
Average interest rate reduction	6.00%	5.00%
TDR loans in payment default	$ 1	$ 1
In North America offices | Commercial banking
Loans receivable
Number of loans modified | loan	15	9
Post-modification recorded investment	$ 38	$ 1
Average interest rate reduction	0.00%	0.00%
TDR loans in payment default	$ 0	$ 8
In offices outside the U.S.
Loans receivable
Number of loans modified | loan	26,869	33,413
Post-modification recorded investment	$ 172	$ 199
TDR loans in payment default	$ 59	$ 79
In offices outside the U.S. | Residential first mortgages
Loans receivable
Number of loans modified | loan	725	549
Post-modification recorded investment	$ 20	$ 18
Average interest rate reduction	0.00%	0.00%
TDR loans in payment default	$ 3	$ 2
In offices outside the U.S. | Credit cards
Loans receivable
Number of loans modified | loan	18,493	23,394
Post-modification recorded investment	$ 75	$ 94
Average interest rate reduction	16.00%	15.00%
TDR loans in payment default	$ 38	$ 53
In offices outside the U.S. | Installment and other revolving
Loans receivable
Number of loans modified | loan	7,552	9,325
Post-modification recorded investment	$ 45	$ 59
Average interest rate reduction	10.00%	10.00%
TDR loans in payment default	$ 18	$ 24
In offices outside the U.S. | Commercial banking
Loans receivable
Number of loans modified | loan	99	145
Post-modification recorded investment	$ 32	$ 28
Average interest rate reduction	0.00%	2.00%
TDR loans in payment default	$ 0	$ 0
Deferred principal | In North America offices
Loans receivable
Post-modification recorded investment	1	3
Deferred principal | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	1
Deferred principal | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	1	2
Deferred principal | In North America offices | Credit cards
Loans receivable
Post-modification recorded investment	0	0
Deferred principal | In North America offices | Installment and other revolving
Loans receivable
Post-modification recorded investment	0	0
Deferred principal | In North America offices | Commercial banking
Loans receivable
Post-modification recorded investment	0	0
Deferred principal | In offices outside the U.S.
Loans receivable
Post-modification recorded investment	0	0
Deferred principal | In offices outside the U.S. | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0
Deferred principal | In offices outside the U.S. | Credit cards
Loans receivable
Post-modification recorded investment	0	0
Deferred principal | In offices outside the U.S. | Installment and other revolving
Loans receivable
Post-modification recorded investment	0	0
Deferred principal | In offices outside the U.S. | Commercial banking
Loans receivable
Post-modification recorded investment	0	0
Contingent principal forgiveness | In North America offices
Loans receivable
Post-modification recorded investment	0	0
Contingent principal forgiveness | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0
Contingent principal forgiveness | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	0	0
Contingent principal forgiveness | In North America offices | Credit cards
Loans receivable
Post-modification recorded investment	0	0
Contingent principal forgiveness | In North America offices | Installment and other revolving
Loans receivable
Post-modification recorded investment	0	0
Contingent principal forgiveness | In North America offices | Commercial banking
Loans receivable
Post-modification recorded investment	0	0
Contingent principal forgiveness | In offices outside the U.S.
Loans receivable
Post-modification recorded investment	0	0
Contingent principal forgiveness | In offices outside the U.S. | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0
Contingent principal forgiveness | In offices outside the U.S. | Credit cards
Loans receivable
Post-modification recorded investment	0	0
Contingent principal forgiveness | In offices outside the U.S. | Installment and other revolving
Loans receivable
Post-modification recorded investment	0	0
Contingent principal forgiveness | In offices outside the U.S. | Commercial banking
Loans receivable
Post-modification recorded investment	0	0
Principal forgiveness | In North America offices
Loans receivable
Post-modification recorded investment	0	0
Principal forgiveness | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0
Principal forgiveness | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	0	0
Principal forgiveness | In North America offices | Credit cards
Loans receivable
Post-modification recorded investment	0	0
Principal forgiveness | In North America offices | Installment and other revolving
Loans receivable
Post-modification recorded investment	0	0
Principal forgiveness | In North America offices | Commercial banking
Loans receivable
Post-modification recorded investment	0	0
Principal forgiveness | In offices outside the U.S.
Loans receivable
Post-modification recorded investment	5	4
Principal forgiveness | In offices outside the U.S. | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0
Principal forgiveness | In offices outside the U.S. | Credit cards
Loans receivable
Post-modification recorded investment	3	2
Principal forgiveness | In offices outside the U.S. | Installment and other revolving
Loans receivable
Post-modification recorded investment	2	2
Principal forgiveness | In offices outside the U.S. | Commercial banking
Loans receivable
Post-modification recorded investment	$ 0	$ 0