OTHER INVESTMENTS (Tables)

12 Months Ended

Dec. 31, 2019

OTHER INVESTMENTS

Schedule of principal components of other investments, which are carried at fair value

	December 31, 2019								December 31, 2018
	Amortized		Unrealized		Unrealized				Amortized		Unrealized		Unrealized
	Cost		Gains		Losses		Fair Value		Cost		Gains		Losses		Fair Value
	(in millions)
Marketable securities	$	257.2	$	3.0	$	(0.4)	$	259.8	$	272.8	$	0.1	$	(6.5)	$	266.4
U.S. Treasury bonds		—		—		—		—		25.0		—		(0.1)		24.9
Total	$	257.2	$	3.0	$	(0.4)	$	259.8	$	297.8	$	0.1	$	(6.6)	$	291.3

Schedule of unrealized losses and fair value for investments that were in an unrealized loss position, aggregated by investment category and the length of time that individual securities have been in a continuous loss position

	December 31, 2019
	Less than 12 months				12 Months or Greater				Total
			Unrealized				Unrealized				Unrealized
	Fair Value		Losses		Fair Value		Losses		Fair Value		Losses
	(in millions)
Marketable securities	$	18.8	$	(0.2)	$	13.1	$	(0.2)	$	31.9	$	(0.4)
Total	$	18.8	$	(0.2)	$	13.1	$	(0.2)	$	31.9	$	(0.4)

	December 31, 2018
	Less than 12 months				12 Months or Greater				Total
			Unrealized				Unrealized				Unrealized
	Fair Value		Losses		Fair Value		Losses		Fair Value		Losses
	(in millions)
Marketable securities	$	57.3	$	(0.5)	$	164.0	$	(6.0)	$	221.3	$	(6.5)
U.S. Treasury bonds		—		—		24.9		(0.1)		24.9		(0.1)
Total	$	57.3	$	(0.5)	$	188.9	$	(6.1)	$	246.2	$	(6.6)

Schedule of securities by contractual maturity date

The amortized cost and estimated fair value of the marketable securities and U.S. Treasury bonds at December 31, 2019 by contractual maturity are as follows:

	Amortized		Estimated
	Cost		Fair Value
	(in millions)
Due in one year or less	$	31.3	$	31.3
Due after one year through five years		1.7		1.7
Due after five years through ten years		—		—
Due after ten years		224.2		226.8
Total	$	257.2	$	259.8