cm:Concept: us-gaap:AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNature
| Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Nature |
| us-gaap:AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNature |
| Disclosure regarding factors used to determine that the impairment of securities not categorized as either held-to-maturity securities or trading securities (hence equal to available for sale securities) where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the nature of the available-for-sale investments determined to be temporarily impaired. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNature |