LOANS - Consumer Troubled Debt Restructurings (Details) - Consumer $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($) loan	Jun. 30, 2020 USD ($) loan	Jun. 30, 2021 USD ($) loan	Jun. 30, 2020 USD ($) loan
Loans receivable
Period within which default occurred post-modification			1 year
Number of days past due, non-accrual status			60 days
In North America offices
Loans receivable
Number of loans modified | loan	36,938	51,615	96,837	119,689
Post-modification recorded investment	$ 245.0	$ 282.0	$ 614.0	$ 643.0
TDR loans in payment default	$ 92.0	$ 118.0	$ 178.0	$ 226.0
In North America offices | Residential first mortgages
Loans receivable
Number of loans modified | loan	326	298	661	575
Post-modification recorded investment	$ 57.0	$ 51.0	$ 115.0	$ 95.0
Average interest rate reduction	0.00%	0.00%	0.00%	0.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 4.0	$ 3.0	$ 7.0	$ 7.0
TDR loans in payment default	15.0	21.0	33.0	35.0
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	$ 1.0	$ 2.0	$ 2.0	$ 5.0
In North America offices | Home equity loans
Loans receivable
Number of loans modified | loan	50	83	107	165
Post-modification recorded investment	$ 4.0	$ 8.0	$ 8.0	$ 16.0
Average interest rate reduction	0.00%	0.00%	0.00%	1.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 0.3	$ 1.0	$ 0.4	$ 2.0
TDR loans in payment default	3.0	4.0	7.0	6.0
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	$ 0.3	$ 1.0	$ 0.3	$ 1.0
In North America offices | Credit cards
Loans receivable
Number of loans modified | loan	36,337	50,891	95,383	118,173
Post-modification recorded investment	$ 181.0	$ 220.0	$ 481.0	$ 525.0
Average interest rate reduction	17.00%	17.00%	17.00%	17.00%
TDR loans in payment default	$ 73.0	$ 92.0	$ 136.0	$ 182.0
In North America offices | Personal, small business and other
Loans receivable
Number of loans modified | loan	225	343	686	776
Post-modification recorded investment	$ 3.0	$ 3.0	$ 10.0	$ 7.0
Average interest rate reduction	3.00%	4.00%	3.00%	3.00%
TDR loans in payment default	$ 1.0	$ 1.0	$ 2.0	$ 3.0
In offices outside North America
Loans receivable
Number of loans modified | loan	25,607	33,202	58,210	60,707
Post-modification recorded investment	$ 179.0	$ 215.0	$ 362.0	$ 353.0
TDR loans in payment default	$ 92.0	$ 61.0	$ 177.0	$ 117.0
In offices outside North America | Residential first mortgages
Loans receivable
Number of loans modified | loan	530	642	997	1,178
Post-modification recorded investment	$ 28.0	$ 44.0	$ 52.0	$ 58.0
Average interest rate reduction	1.00%	4.00%	1.00%	4.00%
TDR loans in payment default	$ 10.0	$ 5.0	$ 22.0	$ 11.0
In offices outside North America | Credit cards
Loans receivable
Number of loans modified | loan	18,297	21,276	42,896	40,591
Post-modification recorded investment	$ 94.0	$ 94.0	$ 196.0	$ 167.0
Average interest rate reduction	12.00%	16.00%	14.00%	16.00%
TDR loans in payment default	$ 45.0	$ 38.0	$ 97.0	$ 71.0
In offices outside North America | Personal, small business and other
Loans receivable
Number of loans modified | loan	6,780	11,284	14,317	18,938
Post-modification recorded investment	$ 57.0	$ 77.0	$ 114.0	$ 128.0
Average interest rate reduction	10.00%	10.00%	10.00%	10.00%
TDR loans in payment default	$ 37.0	$ 18.0	$ 58.0	$ 35.0
Deferred principal | In North America offices
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Deferred principal | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Deferred principal | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Deferred principal | In North America offices | Credit cards
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Deferred principal | In North America offices | Personal, small business and other
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Deferred principal | In offices outside North America
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Deferred principal | In offices outside North America | Residential first mortgages
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Deferred principal | In offices outside North America | Credit cards
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Deferred principal | In offices outside North America | Personal, small business and other
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Contingent principal forgiveness | In North America offices
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Contingent principal forgiveness | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Contingent principal forgiveness | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Contingent principal forgiveness | In North America offices | Credit cards
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Contingent principal forgiveness | In North America offices | Personal, small business and other
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Contingent principal forgiveness | In offices outside North America
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Contingent principal forgiveness | In offices outside North America | Residential first mortgages
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Contingent principal forgiveness | In offices outside North America | Credit cards
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Contingent principal forgiveness | In offices outside North America | Personal, small business and other
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Principal forgiveness | In North America offices
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Principal forgiveness | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Principal forgiveness | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Principal forgiveness | In North America offices | Credit cards
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Principal forgiveness | In North America offices | Personal, small business and other
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Principal forgiveness | In offices outside North America
Loans receivable
Post-modification recorded investment	3.0	5.0	13.0	9.0
Principal forgiveness | In offices outside North America | Residential first mortgages
Loans receivable
Post-modification recorded investment	0.0	0.0	0.0	0.0
Principal forgiveness | In offices outside North America | Credit cards
Loans receivable
Post-modification recorded investment	1.0	3.0	9.0	5.0
Principal forgiveness | In offices outside North America | Personal, small business and other
Loans receivable
Post-modification recorded investment	$ 2.0	$ 2.0	$ 4.0	$ 4.0