LOANS - Consumer Troubled Debt Restructurings (Details) - Consumer $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($) 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	248,016	238,112
Post-modification recorded investment	$ 1,424	$ 1,832
Loans in default	$ 425	$ 524
In North America offices | Residential first mortgages
Loans receivable
Number of loans modified | loan	2,019	4,063
Post-modification recorded investment	$ 300	$ 580
Average interest rate reduction (as a percent)	0.00%	1.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 38	$ 53
Loans in default	136	253
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	$ 27	$ 36
In North America offices | Home equity loans
Loans receivable
Number of loans modified | loan	1,381	2,807
Post-modification recorded investment	$ 130	$ 247
Average interest rate reduction (as a percent)	1.00%	1.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 12	$ 21
Loans in default	23	46
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	$ 10	$ 18
In North America offices | Credit cards
Loans receivable
Number of loans modified | loan	243,253	230,042
Post-modification recorded investment	$ 978	$ 880
Average interest rate reduction (as a percent)	18.00%	17.00%
Loans in default	$ 241	$ 221
In North America offices | Installment and other
Loans receivable
Number of loans modified | loan	1,320	1,088
Post-modification recorded investment	$ 10	$ 8
Average interest rate reduction (as a percent)	5.00%	5.00%
Loans in default	$ 3	$ 2
In North America offices | Commercial banking
Loans receivable
Number of loans modified | loan	43	112
Post-modification recorded investment	$ 6	$ 117
Average interest rate reduction (as a percent)	0.00%	0.00%
Loans in default	$ 22	$ 2
In offices outside the U.S.
Loans receivable
Number of loans modified | loan	111,265	165,668
Post-modification recorded investment	$ 660	$ 826
Loans in default	$ 304	$ 293
In offices outside the U.S. | Residential first mortgages
Loans receivable
Number of loans modified | loan	2,572	4,477
Post-modification recorded investment	$ 85	$ 123
Average interest rate reduction (as a percent)	0.00%	0.00%
Loans in default	$ 9	$ 11
In offices outside the U.S. | Credit cards
Loans receivable
Number of loans modified | loan	77,823	115,941
Post-modification recorded investment	$ 323	$ 399
Average interest rate reduction (as a percent)	16.00%	11.00%
Loans in default	$ 198	$ 185
In offices outside the U.S. | Installment and other
Loans receivable
Number of loans modified | loan	30,344	44,880
Post-modification recorded investment	$ 182	$ 254
Average interest rate reduction (as a percent)	10.00%	9.00%
Loans in default	$ 80	$ 96
In offices outside the U.S. | Commercial banking
Loans receivable
Number of loans modified | loan	526	370
Post-modification recorded investment	$ 70	$ 50
Average interest rate reduction (as a percent)	1.00%	0.00%
Loans in default	$ 17	$ 1
Deferred principal | In North America offices
Loans receivable
Post-modification recorded investment	7	22
Deferred principal | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	2	6
Deferred principal | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	5	16
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	0	3
Principal forgiveness | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	2
Principal forgiveness | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	0	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	16	18
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	9	7
Principal forgiveness | In offices outside the U.S. | Installment and other
Loans receivable
Post-modification recorded investment	7	11
Principal forgiveness | In offices outside the U.S. | Commercial banking
Loans receivable
Post-modification recorded investment	$ 0	$ 0