Business and Basis of Presentation (Details) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2022 USD ($) Company	Sep. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2022 USD ($) Company	Sep. 30, 2021 USD ($)
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Fair value gains (losses) on financial guaranty variable interest entities	$ 11.0	$ 5.0		$ 27.0	$ 18.0
Number of holding companies with outstanding public debt | Company	2			2
Revision of Prior Period, Error Correction, Adjustment
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Fair value gains (losses) on financial guaranty variable interest entities				$ 6.9
Municipal Assurance Corp
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Write off of licenses			$ 16.0