Investments (Tables)

3 Months Ended

Mar. 31, 2015

Fair Value of Investments Available-for-Sale

As of March 31, 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:



	March 31, 2015
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Carrying Value
	(Dollars in millions)
Current:
Asset-backed securities	$	692.4	$	5.1	$	(1.0	)	$	696.5
U.S. government and agencies	29.7		—		—			29.7
Obligations of states and other political subdivisions	965.3		20.8		(2.3		)	983.8
Corporate debt securities	803.4		8.5		(1.5		)	810.4
	$	2,490.8	$	34.4	$	(4.8	)	$	2,520.4
Noncurrent:
Asset-backed securities	$	0.8	$	—	$	(0.2	)	$	0.6
Corporate debt securities	6.6		—		(0.9		)	5.7
	$	7.4	$	—	$	(1.1	)	$	6.3



	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 March 31, 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	$	56.6	$	56.7
Due after one year through five years	599.9		603.8
Due after five years through ten years	628.7		639.7
Due after ten years	513.2		523.7
Asset-backed securities	692.4		696.5
Total current investments available-for-sale	$	2,490.8	$	2,520.4

	Amortized Cost		Estimated Fair Value
Noncurrent:	(Dollars in millions)
Due after one year through five years	$	0.2	$	0.2
Due after five years through ten years	6.4		5.5
Asset-backed securities	0.8		0.6
Total noncurrent investments available-for-sale	$	7.4	$	6.3

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 March 31, 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	$	205.4	$	(0.6	)	$	45.5	$	(0.4	)	$	250.9	$	(1.0	)
U.S. government and agencies	23.7		—			—		—			23.7		—
Obligations of states and other political subdivisions	203.6		(1.4		)	28.9		(0.9		)	232.5		(2.3		)
Corporate debt securities	108.8		(1.1		)	26.7		(0.4		)	135.5		(1.5		)
	$	541.5	$	(3.1	)	$	101.1	$	(1.7	)	$	642.6	$	(4.8	)

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 March 31, 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	$	—	$	—		$	0.6	$	(0.2	)	$	0.6	$	(0.2	)
Corporate debt securities	5.7		(0.9		)	—		—			5.7		(0.9		)
	$	5.7	$	(0.9	)	$	0.6	$	(0.2	)	$	6.3	$	(1.1	)

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 March 31, 2015:



	Less than 12 Months	12 Months or More	Total
Asset-backed securities	118	21	139
U.S. government and agencies	3	—	3
Obligations of states and other political subdivisions	129	16	145
Corporate debt securities	102	30	132
	352	67	419

The following table shows the number of our individual securities-noncurrent that have been in a continuous loss position through March 31, 2015:



	Less than 12 Months	12 Months or More	Total
Asset-backed securities	—	1	1
Corporate debt securities	10	—	10
	10	1	11