Investments (Tables)

9 Months Ended

Sep. 30, 2022

Investments, Debt and Equity Securities [Abstract]

Schedule of Available-for-sale Fixed Maturities Reconciliation

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

	September 30, 2022
						Amortized Cost,
			Allowance			Net of Allowance		Gross		Gross
	Amortized		for Credit			for Credit		Unrealized		Unrealized
(in millions)	Cost		Losses			Losses		Gains		Losses		Fair Value
U.S. Treasury and government agencies	$	441.3	$	—		$	441.3	$	0.2	$	61.6	$	379.9
Foreign government		2.2		—			2.2		—		0.1		2.1
Municipal		1,214.3		—			1,214.3		0.8		163.3		1,051.8
Corporate		4,023.5		(3.1	)		4,020.4		2.0		405.6		3,616.8
Residential mortgage-backed		1,166.3		—			1,166.3		—		148.0		1,018.3
Commercial mortgage-backed		916.8		—			916.8		—		91.0		825.8
Asset-backed		332.6		—			332.6		—		26.4		306.2
Total fixed maturities	$	8,097.0	$	(3.1	)	$	8,093.9	$	3.0	$	896.0	$	7,200.9

	December 31, 2021
						Amortized Cost,
			Allowance			Net of Allowance		Gross		Gross
	Amortized		for Credit			for Credit		Unrealized		Unrealized
(in millions)	Cost		Losses			Losses		Gains		Losses		Fair Value
U.S. Treasury and government agencies	$	394.3	$	—		$	394.3	$	9.3	$	7.4	$	396.2
Foreign government		2.2		—			2.2		0.4		—		2.6
Municipal		1,176.2		—			1,176.2		32.6		8.0		1,200.8
Corporate		3,931.5		(0.3	)		3,931.2		174.5		15.6		4,090.1
Residential mortgage-backed		1,068.2		—			1,068.2		12.4		11.0		1,069.6
Commercial mortgage-backed		802.4		—			802.4		26.6		4.6		824.4
Asset-backed		140.3		—			140.3		1.3		1.4		140.2
Total fixed maturities	$	7,515.1	$	(0.3	)	$	7,514.8	$	257.1	$	48.0	$	7,723.9

Investments Classified by Contractual Maturity Date

The amortized cost and fair value by maturity periods for fixed maturities are shown in the following table. 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, 2022
	Amortized Cost, Net
	of Allowance for		Fair
(in millions)	Credit Losses		Value
Due in one year or less	$	257.5	$	256.0
Due after one year through five years		2,263.0		2,149.2
Due after five years through ten years		2,757.6		2,319.3
Due after ten years		400.1		326.1
		5,678.2		5,050.6
Mortgage-backed and asset-backed securities		2,415.7		2,150.3
Total fixed maturities	$	8,093.9	$	7,200.9

Schedule of Unrealized Loss on Investments

The following tables provide information about the Company’s available-for-sale fixed maturity securities that were in an unrealized loss position at September 30, 2022 and December 31, 2021, including the length of time the securities have been in an unrealized loss position:

	September 30, 2022
	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
Investment grade:
U.S. Treasury and government agencies	$	21.5	$	243.2	$	40.1	$	129.7	$	61.6	$	372.9
Foreign governments		0.1		1.9		—		—		0.1		1.9
Municipal		116.6		806.3		46.7		170.9		163.3		977.2
Corporate		285.9		2,959.8		85.1		277.0		371.0		3,236.8
Residential mortgage-backed		93.6		796.7		54.4		213.7		148.0		1,010.4
Commercial mortgage-backed		62.6		716.9		28.4		105.0		91.0		821.9
Asset-backed		21.8		289.5		4.6		16.7		26.4		306.2
Total investment grade		602.1		5,814.3		259.3		913.0		861.4		6,727.3
Below investment grade:
Corporate		28.0		235.8		6.6		23.7		34.6		259.5
Total fixed maturities	$	630.1	$	6,050.1	$	265.9	$	936.7	$	896.0	$	6,986.8

	December 31, 2021
	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
Investment grade:
U.S. Treasury and government agencies	$	2.3	$	98.0	$	5.1	$	101.3	$	7.4	$	199.3
Municipal		7.9		480.8		0.1		2.5		8.0		483.3
Corporate		13.6		599.6		0.4		7.5		14.0		607.1
Residential mortgage-backed		11.0		653.5		—		—		11.0		653.5
Commercial mortgage-backed		4.6		204.0		—		—		4.6		204.0
Asset-backed		1.4		91.5		—		—		1.4		91.5
Total investment grade		40.8		2,127.4		5.6		111.3		46.4		2,238.7
Below investment grade:
Corporate		1.6		95.8		—		—		1.6		95.8
Total fixed maturities	$	42.4	$	2,223.2	$	5.6	$	111.3	$	48.0	$	2,334.5

Schedule of Realized Gain (Loss)

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2022		2021		2022		2021
(in millions)
Proceeds from sales	$	35.2	$	83.4	$	308.9	$	335.5
Gross gains		—		1.0		1.8		4.9
Gross losses		0.5		1.7		21.3		9.1

Schedule of Pre-tax Net Realized and Unrealized Gains (Losses) on Equity Securities

The following table provides pre-tax net realized and unrealized gains (losses) on equity securities:

	Three Months Ended September 30,						Nine Months Ended September 30,
(in millions)	2022			2021			2022			2021
Net gains (losses) recognized during the period	$	(29.1	)	$	0.3		$	(106.1	)	$	65.9
Less: net gains (losses) recognized on equity securities sold during      the period		(0.1	)		0.9			(8.8	)		1.4
Net unrealized gains (losses) recognized during the period on equity      securities still held	$	(29.0	)	$	(0.6	)	$	(97.3	)	$	64.5