Investments (Tables)

9 Months Ended

Sep. 30, 2017

Investments Debt And Equity Securities [Abstract]

Schedule of Available-for-sale Securities Reconciliation

The amortized cost and fair value of available-for-sale fixed maturities and the cost and fair value of equity securities were as follows:

	September 30, 2017
	Amortized		Gross		Gross				OTTI
	Cost or		Unrealized		Unrealized				Unrealized
(in millions)	Cost		Gains		Losses		Fair Value		Losses
Fixed maturities:
U.S. Treasury and government agencies	$	434.3	$	4.1	$	4.3	$	434.1	$	—
Foreign government		241.7		4.5		1.2		245.0		—
Municipal		1,061.1		36.9		4.8		1,093.2		—
Corporate		4,330.2		125.5		29.2		4,426.5		12.4
Residential mortgage-backed		1,032.8		9.7		9.4		1,033.1		—
Commercial mortgage-backed		592.0		8.8		2.6		598.2		—
Asset-backed		60.3		0.2		0.1		60.4		—
Total fixed maturities	$	7,752.4	$	189.7	$	51.6	$	7,890.5	$	12.4
Equity securities	$	443.1	$	123.7	$	0.3	$	566.5	$	—

	December 31, 2016
	Amortized		Gross		Gross				OTTI
	Cost or		Unrealized		Unrealized				Unrealized
(in millions)	Cost		Gains		Losses		Fair Value		Losses
Fixed maturities:
U.S. Treasury and government agencies	$	342.5	$	3.7	$	5.1	$	341.1		—
Foreign government		235.8		5.4		0.5		240.7		—
Municipal		1,065.8		38.8		9.2		1,095.4		—
Corporate		3,989.8		113.0		49.0		4,053.8		15.8
Residential mortgage-backed		978.2		9.6		13.6		974.2		0.4
Commercial mortgage-backed		550.6		7.8		4.1		554.3		—
Asset-backed		72.4		0.2		0.8		71.8		—
Total fixed maturities	$	7,235.1	$	178.5	$	82.3	$	7,331.3		16.2
Equity securities	$	498.4	$	86.7	$	0.7	$	584.4		—

Investments Classified by Contractual Maturity Date

The amortized cost and fair value by maturity periods for fixed maturities are shown below. Actual maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties, or the Company may have the right to put or sell the obligations back to the issuers.

	September 30, 2017
	Amortized		Fair
(in millions)	Cost		Value
Due in one year or less	$	401.2	$	404.8
Due after one year through five years		2,763.4		2,841.9
Due after five years through ten years		2,515.0		2,548.9
Due after ten years		387.7		403.2
		6,067.3		6,198.8
Mortgage-backed and asset-backed securities		1,685.1		1,691.7
Total fixed maturities	$	7,752.4	$	7,890.5

Schedule of Unrealized Loss on Investments

The following tables provide information about the Company’s fixed maturities and equity securities that were in an unrealized loss position at September 30, 2017 and December 31, 2016 including the length of time the securities have been in an unrealized loss position:

	September 30, 2017
	12 months or less				Greater than 12 months				Total
	Gross				Gross				Gross
	Unrealized		Fair		Unrealized		Fair		Unrealized		Fair
(in millions)	Losses		Value		Losses		Value		Losses		Value
Fixed maturities:
Investment grade:
U.S. Treasury and government    agencies	$	3.1	$	213.1	$	1.2	$	40.8	$	4.3	$	253.9
Foreign governments		1.1		112.0		0.1		7.3		1.2		119.3
Municipal		2.3		187.3		2.5		57.9		4.8		245.2
Corporate		10.1		792.5		10.2		229.9		20.3		1,022.4
Residential mortgage-backed		6.0		440.5		3.4		95.1		9.4		535.6
Commercial mortgage-backed		1.3		118.5		1.3		50.1		2.6		168.6
Asset-backed		0.1		32.5		—		—		0.1		32.5
Total investment grade		24.0		1,896.4		18.7		481.1		42.7		2,377.5
Below investment grade:
Corporate		1.3		33.7		7.6		52.4		8.9		86.1
Total fixed maturities		25.3		1,930.1		26.3		533.5		51.6		2,463.6
Equity securities		0.3		11.0		—		—		0.3		11.0
Total	$	25.6	$	1,941.1	$	26.3	$	533.5	$	51.9	$	2,474.6

	December 31, 2016
	12 months or less				Greater than 12 months				Total
	Gross				Gross				Gross
	Unrealized		Fair		Unrealized		Fair		Unrealized		Fair
(in millions)	Losses		Value		Losses		Value		Losses		Value
Fixed maturities:
Investment grade:
U.S. Treasury and government    agencies	$	5.1	$	165.9	$	—	$	—	$	5.1	$	165.9
Foreign governments		0.5		55.0		—		1.8		0.5		56.8
Municipal		7.2		268.4		2.0		29.3		9.2		297.7
Corporate		30.6		1,081.0		5.0		64.2		35.6		1,145.2
Residential mortgage-backed		12.1		570.0		1.5		29.0		13.6		599.0
Commercial mortgage-backed		4.1		187.5		—		6.3		4.1		193.8
Asset-backed		0.6		29.1		0.2		3.5		0.8		32.6
Total investment grade		60.2		2,356.9		8.7		134.1		68.9		2,491.0
Below investment grade:
Corporate		1.2		45.9		12.2		81.8		13.4		127.7
Residential mortgage-backed		—		0.1		—		—		—		0.1
Total below investment grade		1.2		46.0		12.2		81.8		13.4		127.8
Total fixed maturities		61.4		2,402.9		20.9		215.9		82.3		2,618.8
Equity securities		0.7		16.3		—		—		0.7		16.3
Total	$	62.1	$	2,419.2	$	20.9	$	215.9	$	83.0	$	2,635.1

Schedule of Realized Gain (Loss)

The proceeds from sales of available-for-sale securities and gross realized gains and losses on those sales, were as follows:

	Three Months Ended September 30,
	2017						2016
	Proceeds from		Gross		Gross		Proceeds from		Gross		Gross
(in millions)	Sales		Gains		Losses		Sales		Gains		Losses
Fixed maturities	$	92.6	$	3.0	$	0.5	$	94.2	$	3.6	$	0.3
Equity securities	$	68.2	$	12.0	$	0.2	$	20.7	$	-	$	1.2

	Nine Months Ended September 30,
	2017						2016
	Proceeds from		Gross		Gross		Proceeds from		Gross		Gross
(in millions)	Sales		Gains		Losses		Sales		Gains		Losses
Fixed maturities	$	322.7	$	8.2	$	1.9	$	402.1	$	9.5	$	4.5
Equity securities	$	114.5	$	17.9	$	0.3	$	194.1	$	26.4	$	2.9

Rollforward of Cumulative Amounts Related to Credit Loss Portion of OTTI Losses

The following table provides rollforwards of the cumulative amounts related to the Company’s credit loss portion of the OTTI losses on fixed maturity securities for which the non-credit portion of the loss is included in other comprehensive income.

	Three Months Ended September 30,						Nine Months Ended September 30,
(in millions)	2017			2016			2017			2016
Credit losses at beginning of period	$	9.6		$	11.7		$	10.0		$	18.0
Credit losses on securities for which an OTTI was not    previously recognized		0.2			—			0.4			5.2
Additional credit losses on securities for which an OTTI was    previously recognized		—			0.1			0.1			2.2
Reductions for securities sold, matured or called		(1.9	)		(2.3	)		(2.6	)		(3.9	)
Reductions for securities reclassified as intend to sell		(0.4	)		—			(0.4	)		(12.0	)
Credit losses at end of period	$	7.5		$	9.5		$	7.5		$	9.5