Municipal Bond Guarantee Insurance - Schedule of Change in the Fair Value of BAM Surplus Notes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024	Jul. 01, 2024
Changes In Nominal Value Of Surplus Notes [Roll Forward]
Interest income from BAM Surplus Notes	$ 7.5	$ 7.9	$ 22.5	$ 7.9
Changes In Fair Value Discount Of Surplus Notes [Roll Forward]
Change in fair value of BAM Surplus Notes			0.0	15.8
Operating Segments | Financial Guarantee (HG Global)
Changes In Nominal Value Of Surplus Notes [Roll Forward]
Beginning nominal value	510.7		495.7
Interest income from BAM Surplus Notes	7.5	7.9	22.5	7.9
Payments of principal and interest	(8.0)		(8.0)
Ending nominal value	510.2		510.2
Changes In Fair Value Discount Of Surplus Notes [Roll Forward]
Beginning fair value discount	(114.0)		(114.0)
Change in fair value of BAM Surplus Notes	0.0	$ 15.8	0.0	$ 15.8
Ending fair value discount	(114.0)		(114.0)
BAM Surplus Notes, at fair value	$ 396.2		$ 396.2		$ 381.7	$ 387.4