cm:Level3TextBlock: us-gaap:FinancialGuaranteeInsuranceContractsPremiumReceivedOverContractPeriodTableTextBlock
| Financial Guarantee Insurance Contracts, Premium Received over Contract Period [Table Text Block] |
| us-gaap:FinancialGuaranteeInsuranceContractsPremiumReceivedOverContractPeriodTableTextBlock |
| Tabular disclosure of financial guarantee insurance contracts in which premiums are received over the contract period. |
| cm:Level3TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:FinancialGuaranteeInsuranceContractsPremiumReceivedOverContractPeriodTableTextBlock |