INVESTMENTS IN VARIABLE INTEREST ENTITIES - SCHEDULE OF VIEs (Details) $ in Millions	Jun. 30, 2018 USD ($)
Investment Holdings [Line Items]
Total amortized cost	$ 1,550.6
Total fair value	1,543.3
Amortized cost
Investment Holdings [Line Items]
Due in one year or less	5.1
Due after one year through five years	511.6
Due after five years through ten years	1,033.9
Total amortized cost	1,550.6
Estimated fair value
Investment Holdings [Line Items]
Due in one year or less	5.0
Due after one year through five years	509.0
Due after five years through ten years	1,029.3
Total fair value	$ 1,543.3