cm:Table: us-gaap:FinancialGuaranteeInsuranceContractsPremiumReceivedOverContractPeriodTable
| Financial Guarantee Insurance Contracts, Premium Received over Contract Period [Table] |
| us-gaap:FinancialGuaranteeInsuranceContractsPremiumReceivedOverContractPeriodTable |
| Disclosure of information about financial guarantee insurance contracts in which premiums are received over the contract period. |
| cm:Table |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| true |
| us-gaap:FinancialGuaranteeInsuranceContractsPremiumReceivedOverContractPeriodTable |