cm:Concept: us-gaap:AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureOtherLoanToCollateralValue
| Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Other, Loan to Collateral Value |
| us-gaap:AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureOtherLoanToCollateralValue |
| This item represents the loan to collateral ratio of the underlying assets in the security, represented as a percentage, which was considered as one of the potential factors in reaching a conclusion that the available-for-sale investments are not other-than-temporarily impaired. |
| cm:Concept |
| Percent (num:percentItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureOtherLoanToCollateralValue |