LOANS - Consumer Troubled Debt Restructurings (Details) - Consumer $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2017 USD ($) loan	Mar. 31, 2016 USD ($) 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	61,229	52,843
Post-modification recorded investment	$ 424	$ 447
TDR in payment default	$ 114	$ 148
In North America offices | Residential first mortgages
Loans receivable
Number of loans modified | loan	966	1,468
Post-modification recorded investment	$ 130	$ 212
Average interest rate reduction	1.00%	1.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 15	$ 20
TDR in payment default	51	87
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	$ 9	$ 14
In North America offices | Home equity loans
Loans receivable
Number of loans modified | loan	679	858
Post-modification recorded investment	$ 56	$ 30
Average interest rate reduction	1.00%	3.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 6	$ 5
TDR in payment default	9	9
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	$ 6	$ 5
In North America offices | Credit cards
Loans receivable
Number of loans modified | loan	59,337	49,109
Post-modification recorded investment	$ 231	$ 188
Average interest rate reduction	17.00%	17.00%
TDR in payment default	$ 52	$ 49
In North America offices | Installment and other revolving
Loans receivable
Number of loans modified | loan	221	1,385
Post-modification recorded investment	$ 2	$ 12
Average interest rate reduction	5.00%	14.00%
TDR in payment default	$ 0	$ 2
In North America offices | Commercial banking
Loans receivable
Number of loans modified | loan	26	23
Post-modification recorded investment	$ 5	$ 5
Average interest rate reduction	0.00%	0.00%
TDR in payment default	$ 2	$ 1
In offices outside the U.S.
Loans receivable
Number of loans modified | loan	37,189	74,298
Post-modification recorded investment	$ 185	$ 240
TDR in payment default	$ 67	$ 65
In offices outside the U.S. | Residential first mortgages
Loans receivable
Number of loans modified | loan	613	419
Post-modification recorded investment	$ 27	$ 15
Average interest rate reduction	0.00%	0.00%
TDR in payment default	$ 2	$ 3
In offices outside the U.S. | Credit cards
Loans receivable
Number of loans modified | loan	25,237	52,207
Post-modification recorded investment	$ 85	$ 123
Average interest rate reduction	14.00%	13.00%
TDR in payment default	$ 42	$ 37
In offices outside the U.S. | Installment and other revolving
Loans receivable
Number of loans modified | loan	11,307	21,644
Post-modification recorded investment	$ 60	$ 82
Average interest rate reduction	7.00%	7.00%
TDR in payment default	$ 23	$ 22
In offices outside the U.S. | Commercial banking
Loans receivable
Number of loans modified | loan	32	28
Post-modification recorded investment	$ 13	$ 20
Average interest rate reduction	2.00%	0.00%
TDR in payment default	$ 0	$ 3
Deferred principal | In North America offices
Loans receivable
Post-modification recorded investment	6	2
Deferred principal | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	3	2
Deferred principal | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	3	0
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	1	1
Principal forgiveness | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	1	1
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	6	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	2	2
Principal forgiveness | In offices outside the U.S. | Installment and other revolving
Loans receivable
Post-modification recorded investment	4	2
Principal forgiveness | In offices outside the U.S. | Commercial banking
Loans receivable
Post-modification recorded investment	$ 0	$ 0