DEBT AND OTHER OBLIGATIONS - Schedule of Interest Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
Subordinated funding obligations	$ 2.6	$ 0.0	$ 0.0
Non-recourse funding obligations, other obligations, and repurchase agreements	181.9	177.7	170.8
Total interest expense	$ 184.5	$ 177.7	$ 170.8