LOANS - Consumer Troubled Debt Restructurings (Details) - Consumer $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($) 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	219,439	272,336
Post-modification recorded investment	$ 1,302	$ 1,431
Loans in default	$ 406	$ 405
In North America offices | Residential first mortgages
Loans receivable
Number of loans modified | loan	1,225	1,122
Post-modification recorded investment	$ 209	$ 172
Average interest rate reduction (as a percent)	0.00%	0.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 13	$ 19
Loans in default	71	85
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	$ 11
In North America offices | Home equity loans
Loans receivable
Number of loans modified | loan	296	717
Post-modification recorded investment	$ 27	$ 79
Average interest rate reduction (as a percent)	1.00%	1.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 2	$ 7
Loans in default	14	15
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	$ 2	$ 6
In North America offices | Credit cards
Loans receivable
Number of loans modified | loan	215,466	268,778
Post-modification recorded investment	$ 1,038	$ 1,165
Average interest rate reduction (as a percent)	17.00%	17.00%
Loans in default	$ 317	$ 301
In North America offices | Personal, small business and other
Loans receivable
Number of loans modified | loan	2,452	1,719
Post-modification recorded investment	$ 28	$ 15
Average interest rate reduction (as a percent)	5.00%	5.00%
Loans in default	$ 4	$ 4
In offices outside the U.S.
Loans receivable
Number of loans modified | loan	134,315	103,965
Post-modification recorded investment	$ 843	$ 566
Loans in default	$ 282	$ 229
In offices outside the U.S. | Residential first mortgages
Loans receivable
Number of loans modified | loan	2,542	2,448
Post-modification recorded investment	$ 141	$ 74
Average interest rate reduction (as a percent)	2.00%	0.00%
Loans in default	$ 26	$ 13
In offices outside the U.S. | Credit cards
Loans receivable
Number of loans modified | loan	90,694	72,325
Post-modification recorded investment	$ 401	$ 288
Average interest rate reduction (as a percent)	15.00%	17.00%
Loans in default	$ 178	$ 142
In offices outside the U.S. | Personal, small business and other
Loans receivable
Number of loans modified | loan	41,079	29,192
Post-modification recorded investment	$ 301	$ 204
Average interest rate reduction (as a percent)	10.00%	9.00%
Loans in default	$ 78	$ 74
Deferred principal | In North America offices
Loans receivable
Post-modification recorded investment	0	3
Deferred principal | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0
Deferred principal | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	0	3
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	3	0
Deferred principal | In offices outside the U.S. | Residential first mortgages
Loans receivable
Post-modification recorded investment	3	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	20	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	12	10
Principal forgiveness | In offices outside the U.S. | Personal, small business and other
Loans receivable
Post-modification recorded investment	$ 8	$ 6