Investments (Tables)

9 Months Ended

Sep. 30, 2015

Fair Value of Investments Available-for-Sale

As of September 30, 2015 and December 31, 2014, the amortized cost, gross unrealized holding gains and losses, and fair value of our current investments available-for-sale and our investments available-for-sale-noncurrent, after giving effect to other-than-temporary impairments, were as follows:



	September 30, 2015
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Carrying Value
	(Dollars in millions)
Current:
Asset-backed securities	$	556.2	$	3.1	$	(1.8	)	$	557.5
U.S. government and agencies	28.1		—		—			28.1
Obligations of states and other political subdivisions	925.1		16.5		(3.0		)	938.6
Corporate debt securities	701.0		2.2		(6.1		)	697.1
	$	2,210.4	$	21.8	$	(10.9	)	$	2,221.3
Noncurrent:
Asset-backed securities	$	0.5	$	—	$	(0.1	)	$	0.4
Obligations of states and other political subdivisions	1.6		—		(0.1		)	1.5
Corporate debt securities	21.7		—		(3.5		)	18.2
	$	23.8	$	—	$	(3.7	)	$	20.1



	December 31, 2014
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Carrying Value
	(Dollars in millions)
Current:
Asset-backed securities	$	437.2	$	2.6	$	(1.9	)	$	437.9
U.S. government and agencies	36.5		—		—			36.5
Obligations of states and other political subdivisions	716.7		17.2		(1.7		)	732.2
Corporate debt securities	587.0		2.7		(5.3		)	584.4
	$	1,777.4	$	22.5	$	(8.9	)	$	1,791.0
Noncurrent:
Asset-backed securities	$	0.8	$	—	$	(0.2	)	$	0.6
Corporate debt securities	4.7		—		(0.7		)	4.0
	$	5.5	$	—	$	(0.9	)	$	4.6

Available-for-Sale Current Investments Classified by Contractual Maturity Date

As of September 30, 2015, the contractual maturities of our current investments available-for-sale and our investments available-for-sale-noncurrent were as follows:



	Amortized Cost		Estimated Fair Value
Current:	(Dollars in millions)
Due in one year or less	$	42.3	$	42.4
Due after one year through five years	492.1		492.3
Due after five years through ten years	610.5		612.4
Due after ten years	509.3		516.7
Asset-backed securities	556.2		557.5
Total current investments available-for-sale	$	2,210.4	$	2,221.3

	Amortized Cost		Estimated Fair Value
Noncurrent:	(Dollars in millions)
Due after one year through five years	$	10.8	$	9.0
Due after five years through ten years	12.5		10.7
Asset-backed securities	0.5		0.4
Total noncurrent investments available-for-sale	$	23.8	$	20.1

Schedule of Unrealized Loss on Investments

The following table shows our current investments' fair values and gross unrealized losses for individual securities that have been in a continuous loss position through September 30, 2015:



	Less than 12 Months					12 Months or More					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	(Dollars in millions)
Asset-backed securities	$	262.2	$	(1.6	)	$	23.9	$	(0.2	)	$	286.1	$	(1.8	)
U.S. government and agencies	12.3		—			—		—			12.3		—
Obligations of states and other political subdivisions	211.2		(2.3		)	17.2		(0.7		)	228.4		(3.0		)
Corporate debt securities	379.4		(5.1		)	27.3		(1.0		)	406.7		(6.1		)
	$	865.1	$	(9.0	)	$	68.4	$	(1.9	)	$	933.5	$	(10.9	)

The following table shows our noncurrent investments' fair values and gross unrealized losses for individual securities that have been in a continuous loss position through September 30, 2015:



	Less than 12 Months					12 Months or More					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	(Dollars in millions)
Asset-backed securities	$	—	$	—		$	0.4	$	(0.1	)	$	0.4	$	(0.1	)
Obligations of states and other political subdivisions	—		—			1.5		(0.1		)	1.5		(0.1		)
Corporate debt securities	11.1		(1.9		)	7.1		(1.6		)	18.2		(3.5		)
	$	11.1	$	(1.9	)	$	9.0	$	(1.8	)	$	20.1	$	(3.7	)

The following table shows our current investments’ fair values and gross unrealized losses for individual securities that have been in a continuous loss position through December 31, 2014:



	Less than 12 Months					12 Months or More					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	(Dollars in millions)
Asset-backed securities	$	149.3	$	(0.5	)	$	112.5	$	(1.4	)	$	261.8	$	(1.9	)
U.S. government and agencies	20.7		—			—		—			20.7		—
Obligations of states and other political subdivisions	37.3		(0.1		)	104.8		(1.6		)	142.1		(1.7		)
Corporate debt securities	299.1		(3.9		)	56.0		(1.4		)	355.1		(5.3		)
	$	506.4	$	(4.5	)	$	273.3	$	(4.4	)	$	779.7	$	(8.9	)

The following table shows our noncurrent investments' fair value and gross unrealized losses for our individual securities that have been in a continuous loss position through December 31, 2014:



	Less than 12 Months					12 Months or More					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	(Dollars in millions)
Asset-backed securities	$	—	$	—		$	0.6	$	(0.2	)	$	0.6	$	(0.2	)
Corporate debt securities	4.0		(0.7		)	—		—			4.0		(0.7		)
	$	4.0	$	(0.7	)	$	0.6	$	(0.2	)	$	4.6	$	(0.9	)

Number of Securities Included in Loss Position of Current Investments

The following table shows the number of our individual securities-current that have been in a continuous loss position through September 30, 2015:



	Less than 12 Months	12 Months or More	Total
Asset-backed securities	153	29	182
U.S. government and agencies	1	—	1
Obligations of states and other political subdivisions	149	11	160
Corporate debt securities	343	30	373
	646	70	716

The following table shows the number of our individual securities-noncurrent that have been in a continuous loss position through September 30, 2015:



	Less than 12 Months	12 Months or More	Total
Asset-backed securities	—	1	1
Obligations of states and other political subdivisions	—	1	1
Corporate debt securities	13	11	24
	13	13	26