cm:Concept: us-gaap:CostmethodInvestmentsRealizedLossesExcludingOtherThanTemporaryImpairments
| Cost-method Investments, Realized Losses, Excluding Other than Temporary Impairments |
| us-gaap:CostmethodInvestmentsRealizedLossesExcludingOtherThanTemporaryImpairments |
| For investments in debt and equity securities accounted for at cost, the excess of the carrying amount over net sale proceeds of investments disposed of during the period. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:CostmethodInvestmentsRealizedLossesExcludingOtherThanTemporaryImpairments |