GUARANTEES, LEASES AND COMMITMENTS - Performance Risk (Details) - USD ($) $ in Billions	Mar. 31, 2020	Dec. 31, 2019
Guarantor Obligations
Maximum potential amount of future payments	$ 395.1	$ 417.6
Investment grade
Guarantor Obligations
Maximum potential amount of future payments	85.4	97.4
Non-investment grade
Guarantor Obligations
Maximum potential amount of future payments	28.4	27.2
Not rated
Guarantor Obligations
Maximum potential amount of future payments	281.3	293.0
Financial standby letters of credit
Guarantor Obligations
Maximum potential amount of future payments	86.6	94.3
Financial standby letters of credit | Investment grade
Guarantor Obligations
Maximum potential amount of future payments	59.8	66.4
Financial standby letters of credit | Non-investment grade
Guarantor Obligations
Maximum potential amount of future payments	13.8	12.5
Financial standby letters of credit | Not rated
Guarantor Obligations
Maximum potential amount of future payments	13.0	15.4
Performance guarantees
Guarantor Obligations
Maximum potential amount of future payments	12.1	12.4
Performance guarantees | Investment grade
Guarantor Obligations
Maximum potential amount of future payments	9.3	9.7
Performance guarantees | Non-investment grade
Guarantor Obligations
Maximum potential amount of future payments	2.3	2.3
Performance guarantees | Not rated
Guarantor Obligations
Maximum potential amount of future payments	0.5	0.4
Derivative instruments deemed to be guarantees
Guarantor Obligations
Maximum potential amount of future payments	74.0	96.0
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	74.0	96.0
Loans sold with recourse
Guarantor Obligations
Maximum potential amount of future payments	1.2	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	1.2	1.2
Securities lending indemnifications
Guarantor Obligations
Maximum potential amount of future payments	107.8	87.8
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	107.8	87.8
Credit card merchant processing
Guarantor Obligations
Maximum potential amount of future payments	84.2	91.6
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	84.2	91.6
Credit card arrangements with partners
Guarantor Obligations
Maximum potential amount of future payments	0.6	0.6
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	0.6	0.6
Custody indemnifications and other
Guarantor Obligations
Maximum potential amount of future payments	28.6	33.7
Custody indemnifications and other | Investment grade
Guarantor Obligations
Maximum potential amount of future payments	16.3	21.3
Custody indemnifications and other | Non-investment grade
Guarantor Obligations
Maximum potential amount of future payments	12.3	12.4
Custody indemnifications and other | Not rated
Guarantor Obligations
Maximum potential amount of future payments	$ 0.0	$ 0.0