REDEMPTION SETTLEMENT ASSETS (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
REDEMPTION SETTLEMENT ASSETS
Amortized Cost	$ 569.5	$ 600.4
Unrealized Gains	3.0	2.4
Unrealized Losses	(4.5)	(2.0)
Fair Value	568.0	600.8
Fair Value
Less than 12 months	171.8	166.6
12 Months or Greater	116.8	155.1
Total	288.6	321.7
Unrealized Losses
Less than 12 months	(3.6)	(1.3)
12 Months or Greater	(0.9)	(0.7)
Total	(4.5)	(2.0)
Amortized cost of the redemption settlement assets by contractual maturity
Due in one year or less	121.9
Due after one year through five years	384.4
Due after five year through ten years	7.3
Total	513.6
Estimated fair value of the redemption settlement assets by contractual maturity
Due in one year or less	121.6
Due after one year through five years	383.3
Due after five year through ten years	7.2
Total	512.1
Realized gains or losses from the sale of investment securities	0.0
Restricted cash
REDEMPTION SETTLEMENT ASSETS
Amortized Cost	55.9	39.3
Fair Value	55.9	39.3
Mutual funds
REDEMPTION SETTLEMENT ASSETS
Amortized Cost	22.9	25.1
Fair Value	22.9	25.1
Corporate bonds
REDEMPTION SETTLEMENT ASSETS
Amortized Cost	490.7	536.0
Unrealized Gains	3.0	2.4
Unrealized Losses	(4.5)	(2.0)
Fair Value	489.2	536.4
Fair Value
Less than 12 months	171.8	166.6
12 Months or Greater	116.8	155.1
Total	288.6	321.7
Unrealized Losses
Less than 12 months	(3.6)	(1.3)
12 Months or Greater	(0.9)	(0.7)
Total	$ (4.5)	$ (2.0)