LOANS - Consumer Troubled Debt Restructurings (Details) - Consumer $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) loan	Dec. 31, 2016 USD ($) loan
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
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
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	238,112	210,908
Post-modification recorded investment	$ 1,832	$ 1,826
Loans in default	$ 524	$ 466
In North America offices | Residential first mortgages
Loans receivable
Number of loans modified | loan	4,063	5,023
Post-modification recorded investment	$ 580	$ 726
Average interest rate reduction (as a percent)	1.00%	1.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 53	$ 74
Loans in default	253	229
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	$ 36	$ 48
In North America offices | Home equity loans
Loans receivable
Number of loans modified | loan	2,807	4,100
Post-modification recorded investment	$ 247	$ 200
Average interest rate reduction (as a percent)	1.00%	2.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 21	$ 22
Loans in default	46	25
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	$ 18	$ 20
In North America offices | Credit cards
Loans receivable
Number of loans modified | loan	230,042	196,004
Post-modification recorded investment	$ 880	$ 762
Average interest rate reduction (as a percent)	17.00%	17.00%
Loans in default	$ 221	$ 188
In North America offices | Installment and other
Loans receivable
Number of loans modified | loan	1,088	5,649
Post-modification recorded investment	$ 8	$ 47
Average interest rate reduction (as a percent)	5.00%	14.00%
Loans in default	$ 2	$ 9
In North America offices | Commercial banking
Loans receivable
Number of loans modified | loan	112	132
Post-modification recorded investment	$ 117	$ 91
Average interest rate reduction (as a percent)	0.00%	0.00%
Loans in default	$ 2	$ 15
In offices outside the U.S.
Loans receivable
Number of loans modified | loan	165,668	200,444
Post-modification recorded investment	$ 826	$ 850
Loans in default	$ 293	$ 286
In offices outside the U.S. | Residential first mortgages
Loans receivable
Number of loans modified | loan	4,477	2,722
Post-modification recorded investment	$ 123	$ 80
Average interest rate reduction (as a percent)	0.00%	0.00%
Loans in default	$ 11	$ 11
In offices outside the U.S. | Credit cards
Loans receivable
Number of loans modified | loan	115,941	137,466
Post-modification recorded investment	$ 399	$ 385
Average interest rate reduction (as a percent)	11.00%	12.00%
Loans in default	$ 185	$ 148
In offices outside the U.S. | Installment and other
Loans receivable
Number of loans modified | loan	44,880	60,094
Post-modification recorded investment	$ 254	$ 276
Average interest rate reduction (as a percent)	9.00%	7.00%
Loans in default	$ 96	$ 90
In offices outside the U.S. | Commercial banking
Loans receivable
Number of loans modified | loan	370	162
Post-modification recorded investment	$ 50	$ 109
Average interest rate reduction (as a percent)	0.00%	0.00%
Loans in default	$ 1	$ 37
Deferred principal | In North America offices
Loans receivable
Post-modification recorded investment	22	12
Deferred principal | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	6	6
Deferred principal | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	16	6
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
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
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
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
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	3	4
Principal forgiveness | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	2	3
Principal forgiveness | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	1	1
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
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	18	16
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	7	9
Principal forgiveness | In offices outside the U.S. | Installment and other
Loans receivable
Post-modification recorded investment	11	7
Principal forgiveness | In offices outside the U.S. | Commercial banking
Loans receivable
Post-modification recorded investment	$ 0	$ 0