cm:Level3TextBlock: us-gaap:FinancialGuaranteeInsuranceContractsClaimLiabilityTableTextBlock
| Financial Guarantee Insurance Contracts, Claim Liability [Table Text Block] |
| us-gaap:FinancialGuaranteeInsuranceContractsClaimLiabilityTableTextBlock |
| Tabular disclosure of the claim liability for financial guarantee insurance contracts. |
| cm:Level3TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:FinancialGuaranteeInsuranceContractsClaimLiabilityTableTextBlock |