cm:Concept: us-gaap:FinancialGuaranteeInsuranceContractsPremiumExpectedToBeCollectedMoreThan25AndWithin30YearsFromBalanceSheetDate
| Financial Guarantee Insurance Contracts, Premium Receivable, Premium Expected to be Collected, Year 26 Through 30 |
| us-gaap:FinancialGuaranteeInsuranceContractsPremiumExpectedToBeCollectedMoreThan25AndWithin30YearsFromBalanceSheetDate |
| Amount of premium receivables under financial guarantee insurance contracts expected to be collected in the twenty-sixth through the thirtieth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Debit |
| false |
| us-gaap:FinancialGuaranteeInsuranceContractsPremiumExpectedToBeCollectedMoreThan25AndWithin30YearsFromBalanceSheetDate |