cm:Concept: us-gaap:TranslationAdjustmentForNetInvestmentHedgeIncreaseDecreaseNetOfTax
| Gain (Loss) on Derivative Used in Net Investment Hedge, after Tax |
| us-gaap:TranslationAdjustmentForNetInvestmentHedgeIncreaseDecreaseNetOfTax |
| Amount, after tax, of reclassification from accumulated other comprehensive income (AOCI) of gain (loss) from increase (decrease) in fair value of net investment hedge. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:TranslationAdjustmentForNetInvestmentHedgeIncreaseDecreaseNetOfTax |