Municipal Bond Guarantee Insurance - Schedule of Municipal Bond Guarantee Insured Obligations (Details) - BAM $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2022 USD ($) Contract	Dec. 31, 2021 USD ($) Contract	Sep. 01, 2022 USD ($)	Jan. 31, 2021 USD ($)
Guarantor Obligations [Line Items]
Contracts outstanding | Contract	13,094	12,350
Remaining weighted average contract period outstanding (in years)	10 years 9 months 18 days	10 years 9 months 18 days
Principal	$ 98,619.0	$ 89,196.5	$ 42.5	$ 805.5
Interest	47,595.0	41,486.5
Total debt service outstanding	146,214.0	130,683.0
Total gross unearned insurance premiums	$ 286.7	$ 266.3