Municipal Bond Guarantee Insurance - Schedule of Municipal Bond Guarantee Insured Obligations (Details) - BAM $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2024 USD ($) contract	Dec. 31, 2023 USD ($) contract
Guarantor Obligations [Line Items]
Contracts outstanding | contract	15,041	14,485
Remaining weighted average contract period (in years)	11 years 1 month 6 days	11 years 1 month 6 days
Principal	$ 115,852.9	$ 109,673.8
Interest	60,067.0	56,012.2
Total debt service outstanding	175,919.9	165,686.0
Total gross unearned insurance premiums	$ 333.2	$ 325.8