Municipal Bond Guarantee Insurance - Schedule of Municipal Bond Guarantee Insured Obligations (Details) - BAM $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2023 USD ($) Contract	Dec. 31, 2022 USD ($) Contract
Guarantor Obligations [Line Items]
Contracts outstanding \| Contract	13,607	13,382
Remaining weighted average contract period (in years)	10 years 9 months 18 days	10 years 9 months 18 days
Principal	$ 101,785.7	$ 99,996.9
Interest	49,801.9	48,880.6
Total debt service outstanding	151,587.6	148,877.5
Total gross unearned insurance premiums	$ 299.8	$ 298.3

Remaining weighted average contract period of financial guarantee insurance contracts, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 55
-Paragraph 32
-URI https://asc.fasb.org/extlink&oid=99379334&loc=SL5751133-161288

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 9
-Subparagraph (a)(5)(ii)
-URI https://asc.fasb.org/extlink&oid=99382878&loc=SL5749324-161292

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