cm:Concept: us-gaap:ThresholdPercentageOfValueDeclineInEquitySecuritiesToBeConsideredOtherThanTemporaryImpairment
| Threshold Percentage of Value Decline in Equity Securities to be considered Other than Temporary Impairment |
| us-gaap:ThresholdPercentageOfValueDeclineInEquitySecuritiesToBeConsideredOtherThanTemporaryImpairment |
| Threshold percentage by which investments in equity securities have declined in value to be considered other than temporary impairment (OTTI). |
| cm:Concept |
| Percent (num:percentItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:ThresholdPercentageOfValueDeclineInEquitySecuritiesToBeConsideredOtherThanTemporaryImpairment |