cm:Level3TextBlock: us-gaap:InvestmentsClassifiedByContractualMaturityDateTableTextBlock
| Investments Classified by Contractual Maturity Date [Table Text Block] |
| us-gaap:InvestmentsClassifiedByContractualMaturityDateTableTextBlock |
| Tabular disclosure of maturities of an entity's investments as well as any other information pertinent to the investments. |
| cm:Level3TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:InvestmentsClassifiedByContractualMaturityDateTableTextBlock |
| InvestmentsClassifiedByContractualMaturityDate |