LOANS - Consumer Troubled Debt Restructurings (Details) - Consumer $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016 USD ($) loan	Mar. 31, 2015 USD ($) loan	Dec. 31, 2015
Loans receivable
Period within which default occurred post-modification (in years)	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
Home equity loans
Loans receivable
Number of days past due, non-accrual status	90 days
Credit cards
Loans receivable
Number of days past due, non-accrual status	180 days
Installment and other revolving
Loans receivable
Number of days past due, non-accrual status	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	52,843	55,702
Post-modification recorded investment	$ 447	$ 684
Deferred principal	2	4
Contingent principal forgiveness	0	2
Principal forgiveness	1	9
Loans in default	$ 148	$ 168
In North America offices | Residential first mortgages
Loans receivable
Number of loans modified | loan	1,468	3,093
Post-modification recorded investment	$ 212	$ 407
Deferred principal	2	4
Contingent principal forgiveness	0	2
Principal forgiveness	$ 1	$ 8
Average interest rate reduction (as a percent)	1.00%	1.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 20	$ 66
Loans in default	87	110
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	$ 14	$ 38
In North America offices | Home equity loans
Loans receivable
Number of loans modified | loan	858	1,258
Post-modification recorded investment	$ 30	$ 46
Deferred principal	0	0
Contingent principal forgiveness	0	0
Principal forgiveness	$ 0	$ 1
Average interest rate reduction (as a percent)	3.00%	2.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 5	$ 15
Loans in default	9	11
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	$ 12
In North America offices | Credit cards
Loans receivable
Number of loans modified | loan	49,109	50,310
Post-modification recorded investment	$ 188	$ 211
Deferred principal	0	0
Contingent principal forgiveness	0	0
Principal forgiveness	$ 0	$ 0
Average interest rate reduction (as a percent)	17.00%	16.00%
Loans in default	$ 49	$ 43
In North America offices | Installment and other revolving
Loans receivable
Number of loans modified | loan	1,385	984
Post-modification recorded investment	$ 12	$ 9
Deferred principal	0	0
Contingent principal forgiveness	0	0
Principal forgiveness	$ 0	$ 0
Average interest rate reduction (as a percent)	14.00%	12.00%
Loans in default	$ 2	$ 2
In North America offices | Commercial banking
Loans receivable
Number of loans modified | loan	23	57
Post-modification recorded investment	$ 5	$ 11
Deferred principal	0	0
Contingent principal forgiveness	0	0
Principal forgiveness	$ 0	$ 0
Average interest rate reduction (as a percent)	0.00%	0.00%
Loans in default	$ 1	$ 2
In offices outside the U.S.
Loans receivable
Number of loans modified | loan	74,298	57,338
Post-modification recorded investment	$ 240	$ 218
Deferred principal	0	0
Contingent principal forgiveness	0	0
Principal forgiveness	4	4
Loans in default	$ 65	$ 72
In offices outside the U.S. | Residential first mortgages
Loans receivable
Number of loans modified | loan	419	883
Post-modification recorded investment	$ 15	$ 24
Deferred principal	0	0
Contingent principal forgiveness	0	0
Principal forgiveness	$ 0	$ 0
Average interest rate reduction (as a percent)	0.00%	0.00%
Loans in default	$ 3	$ 6
In offices outside the U.S. | Credit cards
Loans receivable
Number of loans modified | loan	52,207	40,431
Post-modification recorded investment	$ 123	$ 98
Deferred principal	0	0
Contingent principal forgiveness	0	0
Principal forgiveness	$ 2	$ 2
Average interest rate reduction (as a percent)	13.00%	13.00%
Loans in default	$ 37	$ 35
In offices outside the U.S. | Installment and other revolving
Loans receivable
Number of loans modified | loan	21,644	15,947
Post-modification recorded investment	$ 82	$ 69
Deferred principal	0	0
Contingent principal forgiveness	0	0
Principal forgiveness	$ 2	$ 2
Average interest rate reduction (as a percent)	7.00%	5.00%
Loans in default	$ 22	$ 23
In offices outside the U.S. | Commercial banking
Loans receivable
Number of loans modified | loan	28	77
Post-modification recorded investment	$ 20	$ 27
Deferred principal	0	0
Contingent principal forgiveness	0	0
Principal forgiveness	$ 0	$ 0
Average interest rate reduction (as a percent)	0.00%	3.00%
Loans in default	$ 3	$ 8