cm:Concept: us-gaap:HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureCause
| Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Cause |
| us-gaap:HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureCause |
| 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 cause of the impairment of the held-to-maturity investments determined to be temporarily impaired. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureCause |