Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2025

Fair Value Disclosures [Abstract]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis

The following tables present the financial instruments measured at fair value on a basis at December 31, 2025 and 2024:

	December 31, 2025
Assets	Level 1		Level 2		Level 3		Total
Fixed maturity securities
U.S. Treasuries	$	484.2	$	—	$	—	$	484.2
Agencies	—		6.9		—		6.9
Non-U.S. government	—		47.2		—		47.2
Corporate bonds	—		1,652.2		—		1,652.2
Residential mortgage-backed	—		249.9		—		249.9
Commercial mortgage-backed	—		1.0		—		1.0
Other asset-backed securities	—		199.0		—		199.0
Total fixed maturity securities	484.2		2,156.2		—		2,640.4
Short-term investments
Corporate bonds	—		1.0		—		1.0
U.S. Treasuries	109.9		—		—		109.9
Other asset-backed securities	—		0.4		—		0.4
Total short-term investments	109.9		1.4		—		111.3
Other assets
Investments pending settlement	4.8		—		—		4.8
Derivative assets	—		2.4		—		2.4
Total other assets	4.8		2.4		—		7.2
Total assets measured at fair value	$	598.9	$	2,160.0	$	—	$	2,758.9
Liabilities
Other liabilities
Derivative liabilities	$	—	$	(1.7)	$	—	$	(1.7)
Investments pending settlement	(6.6)		—		—		(6.6)
Total other liabilities	(6.6)		(1.7)		—		(8.3)
Total liabilities measured at fair value	$	(6.6)	$	(1.7)	$	—	$	(8.3)

	December 31, 2024
Assets	Level 1		Level 2		Level 3		Total
Fixed maturity securities
U.S. Treasuries	$	746.6	$	—	$	—	$	746.6
Agencies	—		11.5		—		11.5
Non-U.S. government	—		46.4		—		46.4
Corporate bonds	—		1,913.2		—		1,913.2
Residential mortgage-backed	—		279.1		—		279.1
Commercial mortgage-backed	—		0.4		—		0.4
Other asset-backed securities	—		414.4		—		414.4
Total fixed maturity securities	746.6		2,665.0		—		3,411.6
Short-term investments
Corporate bonds	—		1.1		—		1.1
U.S. Treasuries	220.7		—		—		220.7
Other asset-backed securities	—		0.3		—		0.3
Total short-term investments	220.7		1.4		—		222.1
Other assets
Investments pending settlement	0.5		—		—		0.5
Total other assets	0.5		—		—		0.5
Total assets measured at fair value	$	967.8	$	2,666.4	$	—	$	3,634.2
Liabilities
Other liabilities
Derivative liabilities	$	—	$	(0.5)	$	—	$	(0.5)
Investments pending settlement	(21.1)		—		—		(21.1)
Total other liabilities	(21.1)		(0.5)		—		(21.6)
Total liabilities measured at fair value	$	(21.1)	$	(0.5)	$	—	$	(21.6)

Schedule of Fair Value by Balance Sheet Grouping

The fair values of the below financial instruments are based on observable inputs and are considered Level 2 measurements.

	December 31, 2025				December 31, 2024
	Fair Value		Carrying Value		Fair Value		Carrying Value
7.750% Subordinated notes due 2055	$	431.0	$	393.5	$	—	$	—
4.875% Senior notes due 2030	327.7		326.4		319.7		325.6
6.625% Fixed Rate Reset Junior Subordinated notes due 2041	124.4		123.3		123.2		123.3
Preference securities	$	—	$	—	$	57.2	$	58.4