LOANS - Consumer Troubled Debt Restructurings (Details) - Consumer $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) 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
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
Personal, small business and other
Loans receivable
Number of days past due, non-accrual status	90 days
In North America offices
Loans receivable
Number of loans modified | loan	272,336	248,002
Post-modification recorded investment	$ 1,431	$ 1,420
Loans in default	$ 405	$ 404
In North America offices | Residential first mortgages
Loans receivable
Number of loans modified | loan	1,122	2,019
Post-modification recorded investment	$ 172	$ 300
Average interest rate reduction (as a percent)	0.00%	0.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 19	$ 38
Loans in default	85	136
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	$ 11	$ 27
In North America offices | Home equity loans
Loans receivable
Number of loans modified | loan	717	1,381
Post-modification recorded investment	$ 79	$ 130
Average interest rate reduction (as a percent)	1.00%	1.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 7	$ 12
Loans in default	15	23
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	$ 10
In North America offices | Credit cards
Loans receivable
Number of loans modified | loan	268,778	243,253
Post-modification recorded investment	$ 1,165	$ 978
Average interest rate reduction (as a percent)	17.00%	18.00%
Loans in default	$ 301	$ 241
In North America offices | Personal, small business and other
Loans receivable
Number of loans modified | loan	1,719	1,349
Post-modification recorded investment	$ 15	$ 12
Average interest rate reduction (as a percent)	5.00%	4.00%
Loans in default	$ 4	$ 4
In offices outside the U.S.
Loans receivable
Number of loans modified | loan	103,965	111,244
Post-modification recorded investment	$ 566	$ 624
Loans in default	$ 229	$ 287
In offices outside the U.S. | Residential first mortgages
Loans receivable
Number of loans modified | loan	2,448	2,572
Post-modification recorded investment	$ 74	$ 85
Average interest rate reduction (as a percent)	0.00%	0.00%
Loans in default	$ 13	$ 9
In offices outside the U.S. | Credit cards
Loans receivable
Number of loans modified | loan	72,325	77,823
Post-modification recorded investment	$ 288	$ 323
Average interest rate reduction (as a percent)	17.00%	16.00%
Loans in default	$ 142	$ 198
In offices outside the U.S. | Personal, small business and other
Loans receivable
Number of loans modified | loan	29,192	30,849
Post-modification recorded investment	$ 204	$ 216
Average interest rate reduction (as a percent)	9.00%	9.00%
Loans in default	$ 74	$ 80
Deferred principal | In North America offices
Loans receivable
Post-modification recorded investment	3	7
Deferred principal | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	2
Deferred principal | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	3	5
Deferred principal | In North America offices | Credit cards
Loans receivable
Post-modification recorded investment	0	0
Deferred principal | In North America offices | Personal, small business and other
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. | Personal, small business and other
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 | Personal, small business and other
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. | Personal, small business and other
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 | Personal, small business and other
Loans receivable
Post-modification recorded investment	0	0
Principal forgiveness | In offices outside the U.S.
Loans receivable
Post-modification recorded investment	16	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	10	9
Principal forgiveness | In offices outside the U.S. | Personal, small business and other
Loans receivable
Post-modification recorded investment	$ 6	$ 7