cm:Level2TextBlock: us-gaap:AvailableForSaleSecuritiesPurchasedOptionsPricePolicy
| Debt Securities, Available-for-sale, Premium on Purchased Options [Policy Text Block] |
| us-gaap:AvailableForSaleSecuritiesPurchasedOptionsPricePolicy |
| Disclosure of accounting policy for premium paid to acquire option for investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). |
| cm:Level2TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:AvailableForSaleSecuritiesPurchasedOptionsPricePolicy |