OTHER INVESTMENTS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Marketable securities
Amortized Cost	$ 257.2	$ 272.8
Unrealized Gains	3.0	0.1
Unrealized Losses	(0.4)	(6.5)
Fair Value	259.8	266.4
U.S. Treasury bonds
Amortized Cost		25.0
Unrealized Losses		(0.1)
Fair Value		24.9
Other Investments, Total
Amortized Cost	257.2	297.8
Unrealized Gains	3.0	0.1
Unrealized Losses	(0.4)	(6.6)
Fair Value	259.8	291.3
Fair Value, Marketable securities
Less than 12 months	18.8	57.3
12 Months or Greater	13.1	164.0
Total	31.9	221.3
Unrealized Losses, Marketable securities
Less than 12 months	(0.2)	(0.5)
12 Months or Greater	(0.2)	(6.0)
Total	(0.4)	(6.5)
Fair Value, U.S. Treasury bonds
12 Months or Greater		24.9
Total		24.9
Unrealized Losses, U.S. Treasury bonds
12 Months or Greater		(0.1)
Total		(0.1)
Fair Value, Total
Less than 12 months	18.8	57.3
12 Months or Greater	13.1	188.9
Total	31.9	246.2
Unrealized Losses, Total
Less than 12 months	(0.2)	(0.5)
12 Months or Greater	(0.2)	(6.1)
Total	(0.4)	(6.6)
Amortized Cost
Due in one year or less	31.3
Due after one year through five years	1.7
Due after ten years	224.2
Total	257.2
Fair Value
Due in one year or less	31.3
Due after one year through five years	1.7
Due after ten years	226.8
Fair Value	259.8
Realized gains or losses
Realized gains or losses from the sale of investment securities	$ 0.0	$ 0.0	$ 0.0