REVENUE RECOGNITION - Rollforward of contract liabilities (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020 USD ($)
Revenue recognized from contract liabilities and remaining balance
Beginning Balance	$ 4.5
Cash Additions	33.6
Revenue Recognition	(20.6)
Ending Balance	17.5
Liquidity provider sliding scale
Revenue recognized from contract liabilities and remaining balance
Cash Additions	9.6
Revenue Recognition	(4.8)
Ending Balance	4.8
Other, net
Revenue recognized from contract liabilities and remaining balance
Beginning Balance	4.5
Cash Additions	24.0
Revenue Recognition	(15.8)
Ending Balance	$ 12.7