cm:Concept: us-gaap:GainLossOnComponentsExcludedFromAssessmentOfCreditRiskHedgeEffectiveness
| Gain (Loss) on Components Excluded from Assessment of Credit Risk Hedge Effectiveness |
| us-gaap:GainLossOnComponentsExcludedFromAssessmentOfCreditRiskHedgeEffectiveness |
| Amount of gain (loss) excluded from the assessment of hedge effectiveness for credit risk hedging instruments. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:GainLossOnComponentsExcludedFromAssessmentOfCreditRiskHedgeEffectiveness |