Investments (Tables)

3 Months Ended

Mar. 31, 2024

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:

	March 31, 2024
						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	$	520.0	$	—		$	520.0	$	0.5	$	58.8	$	461.7
Foreign governments		3.5		—			3.5		—		—		3.5
Municipals		1,300.7		—			1,300.7		3.8		131.5		1,173.0
Corporate		4,109.2		(1.6	)		4,107.6		16.6		235.8		3,888.4
Residential mortgage-backed		1,469.1		—			1,469.1		2.7		145.7		1,326.1
Commercial mortgage-backed		873.0		—			873.0		0.1		67.5		805.6
Other asset-backed		371.5		—			371.5		0.5		14.9		357.1
Total fixed maturities	$	8,647.0	$	(1.6	)	$	8,645.4	$	24.2	$	654.2	$	8,015.4

	December 31, 2023
						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	$	512.9	$	—		$	512.9	$	1.4	$	51.7	$	462.6
Foreign governments		2.2		—			2.2		—		—		2.2
Municipals		1,309.3		—			1,309.3		5.5		129.6		1,185.2
Corporate		4,053.8		(1.9	)		4,051.9		22.9		225.1		3,849.7
Residential mortgage-backed		1,435.6		—			1,435.6		5.5		130.2		1,310.9
Commercial mortgage-backed		890.3		—			890.3		0.1		72.2		818.2
Other asset-backed		371.7		—			371.7		0.7		15.9		356.5
Total fixed maturities	$	8,575.8	$	(1.9	)	$	8,573.9	$	36.1	$	624.7	$	7,985.3

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.

	March 31, 2024
	Amortized Cost, Net
	of Allowance for		Fair
(in millions)	Credit Losses		Value
Due in one year or less	$	481.3	$	476.7
Due after one year through five years		2,744.1		2,641.8
Due after five years through ten years		2,403.5		2,136.9
Due after ten years		302.9		271.2
		5,931.8		5,526.6
Mortgage-backed and other asset-backed securities		2,713.6		2,488.8
Total fixed maturities	$	8,645.4	$	8,015.4

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 March 31, 2024 and December 31, 2023, including the length of time the securities have been in an unrealized loss position:

	March 31, 2024
	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	$	1.6	$	98.3	$	57.2	$	323.1	$	58.8	$	421.4
Foreign governments		—		—		—		1.9		—		1.9
Municipals		1.1		85.3		130.4		943.8		131.5		1,029.1
Corporate		2.3		260.7		223.9		2,779.6		226.2		3,040.3
Residential mortgage-backed		3.5		286.9		142.2		859.1		145.7		1,146.0
Commercial mortgage-backed		0.1		8.4		67.4		763.8		67.5		772.2
Other asset-backed		0.2		41.4		14.7		252.4		14.9		293.8
Total investment grade		8.8		781.0		635.8		5,923.7		644.6		6,704.7
Below investment grade:
Corporate		1.2		34.0		8.4		67.9		9.6		101.9
Total fixed maturities	$	10.0	$	815.0	$	644.2	$	5,991.6	$	654.2	$	6,806.6

	December 31, 2023
	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	$	0.6	$	62.2	$	51.1	$	331.0	$	51.7	$	393.2
Foreign governments		—		—		—		2.0		—		2.0
Municipals		2.5		72.5		127.1		935.2		129.6		1,007.7
Corporate		1.3		159.9		214.9		2,870.2		216.2		3,030.1
Residential mortgage-backed		1.2		139.3		129.0		865.4		130.2		1,004.7
Commercial mortgage-backed		0.2		14.0		72.0		770.0		72.2		784.0
Other asset-backed		0.1		28.1		15.8		260.2		15.9		288.3
Total investment grade		5.9		476.0		609.9		6,034.0		615.8		6,510.0
Below investment grade:
Corporate		2.5		33.8		6.4		66.2		8.9		100.0
Commercial mortgage-backed		—		—		—		0.9		—		0.9
Total below investment grade		2.5		33.8		6.4		67.1		8.9		100.9
Total fixed maturities	$	8.4	$	509.8	$	616.3	$	6,101.1	$	624.7	$	6,610.9

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 March 31,
	2024		2023
(in millions)
Proceeds from sales	$	27.8	$	27.6
Gross gains		0.1		0.1
Gross losses		1.5		1.4

Schedule of Allowance for Credit Losses

The following table provides a rollforward of the allowance for credit losses on mortgage loans:

	Three Months Ended March 31,
(in millions)	2024			2023
Allowance for credit losses as of the beginning of the period	$	10.0		$	3.2
Reductions for disposals		(0.3	)		—
Additional credit losses on investments for which an allowance was    previously recognized		—			4.1
Recoveries		—			(0.1	)
Allowance for credit losses as of the end of the period	$	9.7		$	7.2

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

The following table provides pre-tax net unrealized gains (losses) on equity securities. There were no realized gains or losses from sales of equities for the three months ended March 31, 2024 and 2023.

	Three Months Ended March 31,
(in millions)	2024		2023
Net unrealized gains (losses) recognized during the period on equity securities still held	$	6.5	$	(7.1	)