Investments (Tables)

9 Months Ended

Sep. 30, 2025

Investments, Debt and Equity Securities [Abstract]

Schedule of Components of Net Investment

The components of net investment income for the following periods were as follows:

($ in millions)	Three Months Ended September 30,				Nine Months Ended September 30,
	2025		2024		2025		2024
Fixed maturity securities	$	71.5	$	69.4	$	202.5	$	211.8
Equity securities	0.9		1.3		2.9		3.9
Limited partnership interests	21.4		14.5		60.9		28.9
Short-term and other investments	5.8		6.0		16.4		15.0
Investment expenses	(3.2)		(4.0)		(9.1)		(9.8)
Net investment income - investment portfolio	96.4		87.2		273.6		249.8
Investment income - deposit asset on reinsurance	23.2		25.8		72.7		77.0
Total net investment income(1)	$	119.6	$	113.0	$	346.3	$	326.8

(1) In the second quarter of 2025, the Company recorded a reduction in net investment income due to an immaterial out-of-period correction of an error. See additional disclosure contained in Note 1 of the September 30, 2025 Form 10-Q.

Schedule of Net Investment Gains (Losses)

Net investment gains (losses) for the following periods were as follows:

($ in millions)	Three Months Ended September 30,				Nine Months Ended September 30,
	2025		2024		2025		2024
Fixed maturity securities	$	(0.6)	$	(0.3)	$	(4.5)	$	(3.6)
Equity securities	2.2		5.1		0.2		5.6
Short-term investments and other	1.7		(1.0)		(1.6)		(1.9)
Net investment gains (losses)	$	3.3	$	3.8	$	(5.9)	$	0.1

The breakdown of net investment gains (losses) by transaction type for the following periods were as follows:

($ in millions)	Three Months Ended September 30,				Nine Months Ended September 30,
	2025		2024		2025		2024
Credit loss impairments	$	1.0	$	(0.5)	$	(1.2)	$	(0.5)
Intent-to-sell impairments	(0.7)		(0.2)		(1.6)		(0.2)
Total impairments	0.3		(0.7)		(2.8)		(0.7)
Sales and other, net	0.3		0.1		4.4		(3.2)
Change in fair value - equity securities	2.2		5.2		0.3		5.7
Change in fair value and gains (losses) realized on settlements - derivatives	0.5		(0.8)		(7.8)		(1.7)
Net investment gains (losses)	$	3.3	$	3.8	$	(5.9)	$	0.1

Schedule of Allowance for Credit Loss Impairments on Fixed Maturity Securities

The following table presents changes in the allowance for credit loss impairments on fixed maturity securities classified as available for sale for the category of other asset-backed securities (no other categories of fixed maturity securities have an allowance for credit loss impairments):

($ in millions)	Three Months Ended September 30,				Nine Months Ended September 30,
	2025		2024		2025		2024
Beginning balance	$	3.1	$	1.1	$	0.9	$	1.2
Credit losses on fixed maturity securities for which credit losses were not previously reported	0.2		—		3.3		1.7
Net increase (decrease) related to credit losses previously reported	—		0.5		(0.9)		(0.4)
Reduction of credit allowances related to sales	(1.2)		—		(1.2)		(0.9)
Write-offs	—		—		—		—
Ending balance	$	2.1	$	1.6	$	2.1	$	1.6

Schedule of Available-for-sale Securities Reconciliation

Amortized cost, net, gross unrealized investment gains (losses) and fair values of all fixed maturity securities in the portfolio were as follows:

($ in millions)	Amortized Cost, net		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
September 30, 2025
Fixed maturity securities
U.S. Government and federally sponsored agency obligations:
Mortgage-backed securities	$	663.9	$	8.1	$	39.6	$	632.4
Other, including U.S. Treasury securities	415.5		1.0		56.6		359.9
Municipal bonds	1,264.0		22.2		88.0		1,198.2
Foreign government bonds	14.1		—		0.6		13.5
Corporate bonds	1,989.9		32.4		181.6		1,840.7
Other asset-backed securities	1,638.1		12.5		28.8		1,621.8
Totals	$	5,985.5	$	76.2	$	395.2	$	5,666.5
December 31, 2024
Fixed maturity securities
U.S. Government and federally sponsored agency obligations:
Mortgage-backed securities	$	827.9	$	2.7	$	74.8	$	755.8
Other, including U.S. Treasury securities	426.5		0.1		69.0		357.6
Municipal bonds	1,239.1		17.5		105.8		1,150.8
Foreign government bonds	14.1		—		1.0		13.1
Corporate bonds	1,995.2		17.3		230.1		1,782.4
Other asset-backed securities	1,339.7		10.8		22.3		1,328.2
Totals	$	5,842.5	$	48.4	$	503.0	$	5,387.9

Schedule of Fair Value and Gross Unrealized Losses of Fixed Maturity Securities and Equity Securities in an Unrealized Loss Position

In consideration of the factors, we expect to receive cash flows sufficient to recover the entire amortized cost basis of the securities in the following table.

($ in millions)	12 Months or Less					More than 12 Months					Total
	Fair Value			Gross Unrealized Losses		Fair Value			Gross Unrealized Losses		Fair Value			Gross Unrealized Losses
September 30, 2025
Fixed maturity securities
U.S. Government and federally sponsored agency obligations:
Mortgage-backed securities	$	43.8		$	0.4	$	244.3		$	39.2	$	288.1		$	39.6
Other	10.7			0.2		285.6			56.4		296.3			56.6
Municipal bonds	190.3			4.9		616.2			83.1		806.5			88.0
Foreign government bonds	—			—		12.0			0.6		12.0			0.6
Corporate bonds	162.9			5.9		954.6			175.7		1,117.5			181.6
Other asset-backed securities	177.8			1.1		396.8			27.7		574.6			28.8
Total	$	585.5		$	12.5	$	2,509.5		$	382.7	$	3,095.0		$	395.2
Number of positions with a    gross unrealized loss	427					1,708					2,135
Fair value as a percentage of total fixed    maturity securities at fair value	10.3		%			44.3		%			54.6		%
December 31, 2024
Fixed maturity securities
U.S. Government and federally sponsored agency obligations:
Mortgage-backed securities	$	208.3		$	3.1	$	419.3		$	71.7	$	627.6		$	74.8
Other	77.1			1.5		274.6			67.6		351.7			69.1
Municipal bonds	193.5			3.4		632.0			102.4		825.5			105.8
Foreign government bonds	1.5			—		11.7			0.9		13.2			0.9
Corporate bonds	235.4			10.3		1,075.8			219.8		1,311.2			230.1
Other asset-backed securities	133.3			0.9		338.3			21.4		471.6			22.3
Total	$	849.1		$	19.2	$	2,751.7		$	483.8	$	3,600.8		$	503.0
Number of positions with a    gross unrealized loss	665					1,862					2,527
Fair value as a percentage of total fixed    maturity securities at fair value	15.8		%			51.1		%			66.9		%

Schedule of Distribution of the Company's Fixed Maturity Portfolio by Estimated Expected Maturity

With regards to fixed maturity securities that had gross unrealized losses more than 12 months, the number of positions by their respective credit ratings were as follows:

	Number of Positions
	September 30, 2025	December 31, 2024
Credit Rating
AAA	140	155
AA	882	899
A	286	320
BBB	317	370
Total investment grade	1,625	1,744
BB	29	40
B	8	18
CCC or lower	2	4
Total below investment grade	39	62
Not rated	44	56
Totals:	1,708	1,862

The following table presents the distribution of the Company’s fixed maturity securities portfolio by estimated expected maturity. Estimated expected maturities differ from contractual maturities, reflecting assumptions regarding borrowers' utilization of the right to call or prepay obligations with or without call or prepayment penalties. For structured securities, estimated expected maturities consider broker-dealer survey prepayment assumptions and are verified for consistency with the interest rate and economic environments.

($ in millions)	September 30, 2025
	Amortized Cost, net		Fair Value		Percent of Total Fair Value
Estimated expected maturity:
Due in 1 year or less	$	333.4	$	333.1	5.9	%
Due after 1 year through 5 years	1,340.3		1,323.0		23.3	%
Due after 5 years through 10 years	1,573.5		1,547.9		27.3	%
Due after 10 years through 20 years	1,634.5		1,509.8		26.6	%
Due after 20 years	1,103.8		952.7		16.8	%
Total	$	5,985.5	$	5,666.5	100.0	%
Average option-adjusted duration, in years	5.9

Schedule of Proceeds Received From Sales of Fixed Maturities and Equity Securities

Proceeds received from sales of fixed maturity and equity securities, each determined using the specific identification method, and gross gains and gross losses realized as a result of those sales for each period were as follows:

($ in millions)	Three Months Ended September 30,				Nine Months Ended September 30,
	2025		2024		2025		2024
Fixed maturity securities
Proceeds received	$	153.1	$	9.3	$	283.0	$	202.3
Gross gains realized	0.8		0.1		2.5		2.1
Gross losses realized	(1.2)		—		(3.7)		(5.3)
Equity securities
Proceeds received	$	10.1	$	—	$	16.4	$	—
Gross gains realized	—		—		—		—
Gross losses realized	(0.1)		—		(0.1)		—

Schedule of Reconciliation of Net Unrealized Investment Gains (Losses) on Fixed Maturity Securities and Equity Securities

The following table reconciles net unrealized investment gains (losses) on fixed maturity securities, net of tax, included in AOCI:

($ in millions)	Three Months Ended September 30,				Nine Months Ended September 30,
	2025		2024		2025		2024
Net unrealized investment gains (losses)    on fixed maturity securities, net of tax
Beginning of period	$	(309.9)	$	(370.4)	$	(357.4)	$	(328.3)
Change in net unrealized investment gains    (losses) on fixed maturity securities	58.7		132.8		103.1		88.2
Reclassification of net investment losses    on fixed maturity securities to net income	0.4		0.4		3.5		2.9
End of period	$	(250.8)	$	(237.2)	$	(250.8)	$	(237.2)

Schedule of Carrying Amounts of Equity Method Limited Partnership Interests

The carrying amounts of EMA limited partnership interests were as follows:

($ in millions)
	September 30, 2025		December 31, 2024
Commercial mortgage loan funds	$	593.2	$	596.0
Real estate equity funds	146.5		144.7
Private equity funds	112.5		102.2
Infrastructure equity funds	83.6		81.7
Infrastructure debt funds	66.5		69.0
Other funds(1)	135.5		127.7
Total	$	1,137.8	$	1,121.3

(1)Other funds consist primarily of limited partnership interests in corporate mezzanine, venture capital and private credit funds.

Schedule of Offsetting Assets and Liability

The following table presents instruments that were subject to a master netting arrangement for the Company.

($ in millions)			Gross Amounts Offset in the Consolidated Balance Sheets		Net Amounts of Assets/ Liabilities Presented in the Consolidated Balance Sheets		Gross Amounts Not Offset in the Consolidated Balance Sheets
	Gross Amounts						Financial Instruments		Cash Collateral Received		Net Amount
September 30, 2025
Asset derivatives:
Free-standing derivatives	$	19.5	$	—	$	19.5	$	—	$	18.2	$	1.3
December 31, 2024
Asset derivatives:
Free-standing derivatives	$	18.5	$	—	$	18.5	$	—	$	20.4	$	(1.9)