CREDIT CARD AND LOAN RECEIVABLES - Amortized Cost Basis Credit Card and Loan Receivables (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Total delinquent	$ 1,288.5	$ 1,391.4
Current	16,072.5	17,656.4
Amortized cost of credit card and loan receivables	17,361.0	19,047.8
31 to 60 days delinquent
Financing Receivable, Past Due [Line Items]
Total delinquent	347.6	399.1
61 to 90 days delinquent
Financing Receivable, Past Due [Line Items]
Total delinquent	273.8	293.9
91 or more days delinquent
Financing Receivable, Past Due [Line Items]
Total delinquent	$ 667.1	$ 698.4

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5074-111524

Name:	us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant