GUARANTEES, LEASES AND COMMITMENTS - Performance Risk (Details) - USD ($) $ in Billions	Sep. 30, 2021	Dec. 31, 2020
Guarantor Obligations
Maximum potential amount of future payments	$ 450.3	$ 441.5
Investment grade
Guarantor Obligations
Maximum potential amount of future payments	101.9	113.2
Non-investment grade
Guarantor Obligations
Maximum potential amount of future payments	27.5	30.0
Not rated
Guarantor Obligations
Maximum potential amount of future payments	320.9	298.3
Financial standby letters of credit
Guarantor Obligations
Maximum potential amount of future payments	92.5	93.7
Financial standby letters of credit | Investment grade
Guarantor Obligations
Maximum potential amount of future payments	80.1	78.5
Financial standby letters of credit | Non-investment grade
Guarantor Obligations
Maximum potential amount of future payments	12.2	14.6
Financial standby letters of credit | Not rated
Guarantor Obligations
Maximum potential amount of future payments	0.2	0.6
Performance guarantees
Guarantor Obligations
Maximum potential amount of future payments	12.6	13.3
Performance guarantees | Investment grade
Guarantor Obligations
Maximum potential amount of future payments	10.0	9.8
Performance guarantees | Non-investment grade
Guarantor Obligations
Maximum potential amount of future payments	2.6	3.0
Performance guarantees | Not rated
Guarantor Obligations
Maximum potential amount of future payments	0.0	0.5
Derivative instruments deemed to be guarantees
Guarantor Obligations
Maximum potential amount of future payments	71.9	80.9
Derivative instruments deemed to be guarantees | Investment grade
Guarantor Obligations
Maximum potential amount of future payments	0.0	0.0
Derivative instruments deemed to be guarantees | Non-investment grade
Guarantor Obligations
Maximum potential amount of future payments	0.0	0.0
Derivative instruments deemed to be guarantees | Not rated
Guarantor Obligations
Maximum potential amount of future payments	71.9	80.9
Loans sold with recourse
Guarantor Obligations
Maximum potential amount of future payments	1.7	1.2
Loans sold with recourse | Investment grade
Guarantor Obligations
Maximum potential amount of future payments	0.0	0.0
Loans sold with recourse | Non-investment grade
Guarantor Obligations
Maximum potential amount of future payments	0.0	0.0
Loans sold with recourse | Not rated
Guarantor Obligations
Maximum potential amount of future payments	1.7	1.2
Securities lending indemnifications
Guarantor Obligations
Maximum potential amount of future payments	131.7	112.2
Securities lending indemnifications | Investment grade
Guarantor Obligations
Maximum potential amount of future payments	0.0	0.0
Securities lending indemnifications | Non-investment grade
Guarantor Obligations
Maximum potential amount of future payments	0.0	0.0
Securities lending indemnifications | Not rated
Guarantor Obligations
Maximum potential amount of future payments	131.7	112.2
Credit card merchant processing
Guarantor Obligations
Maximum potential amount of future payments	114.6	101.9
Credit card merchant processing | Investment grade
Guarantor Obligations
Maximum potential amount of future payments	0.0	0.0
Credit card merchant processing | Non-investment grade
Guarantor Obligations
Maximum potential amount of future payments	0.0	0.0
Credit card merchant processing | Not rated
Guarantor Obligations
Maximum potential amount of future payments	114.6	101.9
Credit card arrangements with partners
Guarantor Obligations
Maximum potential amount of future payments	0.8	1.0
Credit card arrangements with partners | Investment grade
Guarantor Obligations
Maximum potential amount of future payments	0.0	0.0
Credit card arrangements with partners | Non-investment grade
Guarantor Obligations
Maximum potential amount of future payments	0.0	0.0
Credit card arrangements with partners | Not rated
Guarantor Obligations
Maximum potential amount of future payments	0.8	1.0
Custody indemnifications and other
Guarantor Obligations
Maximum potential amount of future payments	24.5	37.3
Custody indemnifications and other | Investment grade
Guarantor Obligations
Maximum potential amount of future payments	11.8	24.9
Custody indemnifications and other | Non-investment grade
Guarantor Obligations
Maximum potential amount of future payments	12.7	12.4
Custody indemnifications and other | Not rated
Guarantor Obligations
Maximum potential amount of future payments	$ 0.0	$ 0.0