Investments (Tables)

9 Months Ended

Sep. 30, 2026

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, 2026
						Allowance				Amortized Cost,				Gross				Gross
		Amortized				for Credit				Net of Allowance				Unrealized				Unrealized
(in millions)		Cost				Losses				for Credit Loses				Gains				Losses				Fair Value
U.S. Treasury and government agencies		$	552.2			$	—			$	552.2			$	—			$	59.3			$	492.9
Foreign governments			16.6				—				16.6				0.1				1.1				15.6
Municipals			1,100.8				—				1,100.8				0.1				112.0				988.9
Corporates			4,629.2				(0.7	)			4,628.5				4.2				216.0				4,416.7
Residential mortgage-backed			2,340.8				—				2,340.8				2.0				187.5				2,155.3
Commercial mortgage-backed			663.8				—				663.8				—				46.8				617.0
Other asset-backed			1,169.1				—				1,169.1				0.3				20.1				1,149.3
Total fixed maturities		$	10,472.5			$	(0.7	)		$	10,471.8			$	6.7			$	642.8			$	9,835.7


		December 31, 2025
						Allowance				Amortized Cost,				Gross				Gross
		Amortized				for Credit				Net of Allowance				Unrealized				Unrealized
(in millions)		Cost				Losses				for Credit Loses				Gains				Losses				Fair Value
U.S. Treasury and government agencies		$	491.3			$	—			$	491.3			$	2.4			$	38.2			$	455.5
Foreign governments			2.5				—				2.5				0.2				—				2.7
Municipals			910.8				—				910.8				4.1				67.2				847.7
Corporates			4,239.3				(0.2	)			4,239.1				71.4				57.0				4,253.5
Residential mortgage-backed			2,472.2				—				2,472.2				32.4				82.8				2,421.8
Commercial mortgage-backed			610.2				—				610.2				1.0				21.3				589.9
Other asset-backed			959.6				—				959.6				6.5				0.7				965.4
Total fixed maturities		$	9,685.9			$	(0.2	)		$	9,685.7			$	118.0			$	267.2			$	9,536.5

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, 2026
		Amortized Cost,
		Net of Allowance				Fair
(in millions)		for Credit Losses				Value
Due in one year or less		$	200.9			$	200.2
Due after one year through five years			2,590.5				2,466.1
Due after five years through ten years			2,942.0				2,743.9
Due after ten years			564.7				503.9
			6,298.1				5,914.1
Mortgage-backed and other asset-backed securities			4,173.7				3,921.6
Total fixed maturities		$	10,471.8			$	9,835.7

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, 2026 and December 31, 2025, including the length of time the securities have been in an unrealized loss position:


		September 30, 2026
		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		$	3.8			$	202.4			$	55.5			$	289.2			$	59.3			$	491.6
Foreign governments			1.1				13.8				—				—				1.1				13.8
Municipals			28.9				495.4				83.1				470.8				112.0				966.2
Corporates			138.9				3,284.1				62.7				534.2				201.6				3,818.3
Residential mortgage-backed			78.4				1,662.4				108.6				433.9				187.0				2,096.3
Commercial mortgage-backed			26.6				463.8				19.2				148.7				45.8				612.5
Other asset-backed			19.5				948.2				0.6				4.7				20.1				952.9
Total investment grade			297.2				7,070.1				329.7				1,881.5				626.9				8,951.6
Below investment grade:
Foreign governments			—				0.2				—				—				—				0.2
Corporates			9.4				251.5				5.0				33.3				14.4				284.8
Residential mortgage-backed			0.5				2.4				—				—				0.5				2.4
Commercial mortgage-backed			—				—				1.0				4.5				1.0				4.5
Other asset-backed			—				2.9				—				—				—				2.9
Total below investment grade			9.9				257.0				6.0				37.8				15.9				294.8
Total fixed maturities		$	307.1			$	7,327.1			$	335.7			$	1,919.3			$	642.8			$	9,246.4


		December 31, 2025
		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		$	—			$	11.9			$	38.2			$	319.7			$	38.2			$	331.6
Municipals			0.6				56.3				66.6				550.3				67.2				606.6
Corporates			1.0				271.3				51.2				704.2				52.2				975.5
Residential mortgage-backed			0.5				128.7				82.3				521.7				82.8				650.4
Commercial mortgage-backed			0.5				122.5				20.0				284.3				20.5				406.8
Other asset-backed			0.5				82.9				0.2				24.3				0.7				107.2
Total investment grade			3.1				673.6				258.5				2,404.5				261.6				3,078.1
Below investment grade:
Corporates			2.2				37.5				2.6				34.8				4.8				72.3
Commercial mortgage-backed			—				—				0.8				4.9				0.8				4.9
Other asset-backed			—				1.3				—				—				—				1.3
Total below investment grade			2.2				38.8				3.4				39.7				5.6				78.5
Total fixed maturities		$	5.3			$	712.4			$	261.9			$	2,444.2			$	267.2			$	3,156.6

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,
		2026				2025				2026				2025
(in millions)
Proceeds from sales		$	256.5			$	358.4			$	1,044.5			$	1,260.4
Gross gains			0.2				0.4				3.0				1.7
Gross losses			8.6				21.6				23.9				46.8

Schedule of Allowance for Credit Losses

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


	Three Months Ended September 30,								Nine Months Ended September 30,
(in millions)	2026				2025				2026				2025
Allowance for credit losses as of the beginning of the period	$	9.0			$	8.0			$	8.1			$	5.7
Additional credit losses on investments for which an allowance was previously recognized		—				0.3				2.8				2.9
Recoveries		(2.0	)			—				(2.0	)			—
Reductions for disposals		—				(0.1	)			(1.9	)			(0.4	)
Allowance for credit losses as of the end of the period	$	7.0			$	8.2			$	7.0			$	8.2

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

Pre-tax net realized and unrealized gains (losses) on equity securities recognized in income included the following:


	Three Months Ended September 30,								Nine Months Ended September 30,
(in millions)	2026				2025				2026				2025
Net realized and unrealized gains (losses) on equity securities recognized in income:
On securities sold during the period	$	3.2			$	—			$	5.5			$	0.6
On securities still held		(10.0	)			11.2				3.7				16.1
Total net realized and unrealized gains (losses) on equity securities recognized in income	$	(6.8	)		$	11.2			$	9.2			$	16.7