cm:Concept: us-gaap:HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
| Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions |
| us-gaap:HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions |
| Disclosure regarding factors used to determine that the impairment of securities categorized as held-to-maturity where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the held-to-maturity investments determined to be temporarily impaired. |
| cm:Concept |
| Decimal (xbrli:decimalItemType) |
| As Of (instant) |
| (no balance type) |
| false |
| us-gaap:HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions |