LOANS - Consumer Troubled Debt Restructurings (Details) - Consumer $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($) loan	Mar. 31, 2020 USD ($) 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	59,888	68,074
Post-modification recorded investment	$ 368.0	$ 361.0
TDR loans in payment default	$ 86.0	$ 107.0
In North America offices | Residential first mortgages
Loans receivable
Number of loans modified | loan	331	277
Post-modification recorded investment	$ 57.0	$ 44.0
Average interest rate reduction	0.00%	0.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 3.0	$ 4.0
TDR loans in payment default	18.0	14.0
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	$ 3.0
In North America offices | Home equity loans
Loans receivable
Number of loans modified | loan	50	82
Post-modification recorded investment	$ 4.0	$ 8.0
Average interest rate reduction	0.00%	2.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 0.1	$ 1.0
TDR loans in payment default	4.0	2.0
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	$ 0.1	$ 1.0
In North America offices | Credit cards
Loans receivable
Number of loans modified | loan	59,046	67,282
Post-modification recorded investment	$ 300.0	$ 305.0
Average interest rate reduction	17.00%	17.00%
TDR loans in payment default	$ 63.0	$ 90.0
In North America offices | Personal, small business and other
Loans receivable
Number of loans modified | loan	461	433
Post-modification recorded investment	$ 7.0	$ 4.0
Average interest rate reduction	4.00%	6.00%
TDR loans in payment default	$ 1.0	$ 1.0
In offices outside North America
Loans receivable
Number of loans modified | loan	32,603	27,505
Post-modification recorded investment	$ 183.0	$ 139.0
TDR loans in payment default	$ 87.0	$ 56.0
In offices outside North America | Residential first mortgages
Loans receivable
Number of loans modified | loan	467	536
Post-modification recorded investment	$ 24.0	$ 14.0
Average interest rate reduction	1.00%	5.00%
TDR loans in payment default	$ 12.0	$ 6.0
In offices outside North America | Credit cards
Loans receivable
Number of loans modified | loan	24,599	19,315
Post-modification recorded investment	$ 102.0	$ 73.0
Average interest rate reduction	15.00%	16.00%
TDR loans in payment default	$ 52.0	$ 33.0
In offices outside North America | Personal, small business and other
Loans receivable
Number of loans modified | loan	7,537	7,654
Post-modification recorded investment	$ 57.0	$ 52.0
Average interest rate reduction	11.00%	11.00%
TDR loans in payment default	$ 23.0	$ 17.0
Deferred principal | In North America offices
Loans receivable
Post-modification recorded investment	0.0	0.0
Deferred principal | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0.0	0.0
Deferred principal | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	0.0	0.0
Deferred principal | In North America offices | Credit cards
Loans receivable
Post-modification recorded investment	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
Deferred principal | In offices outside North America
Loans receivable
Post-modification recorded investment	0.0	0.0
Deferred principal | In offices outside North America | Residential first mortgages
Loans receivable
Post-modification recorded investment	0.0	0.0
Deferred principal | In offices outside North America | Credit cards
Loans receivable
Post-modification recorded investment	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
Contingent principal forgiveness | In North America offices
Loans receivable
Post-modification recorded investment	0.0	0.0
Contingent principal forgiveness | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0.0	0.0
Contingent principal forgiveness | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	0.0	0.0
Contingent principal forgiveness | In North America offices | Credit cards
Loans receivable
Post-modification recorded investment	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
Contingent principal forgiveness | In offices outside North America
Loans receivable
Post-modification recorded investment	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
Contingent principal forgiveness | In offices outside North America | Credit cards
Loans receivable
Post-modification recorded investment	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
Principal forgiveness | In North America offices
Loans receivable
Post-modification recorded investment	0.0	0.0
Principal forgiveness | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0.0	0.0
Principal forgiveness | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	0.0	0.0
Principal forgiveness | In North America offices | Credit cards
Loans receivable
Post-modification recorded investment	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
Principal forgiveness | In offices outside North America
Loans receivable
Post-modification recorded investment	9.0	5.0
Principal forgiveness | In offices outside North America | Residential first mortgages
Loans receivable
Post-modification recorded investment	0.0	0.0
Principal forgiveness | In offices outside North America | Credit cards
Loans receivable
Post-modification recorded investment	7.0	3.0
Principal forgiveness | In offices outside North America | Personal, small business and other
Loans receivable
Post-modification recorded investment	$ 2.0	$ 2.0