cm:Concept: us-gaap:AssetsSoldUnderAgreementsToRepurchaseCarryingAmounts
| Assets Sold under Agreements to Repurchase, Carrying Amount |
| us-gaap:AssetsSoldUnderAgreementsToRepurchaseCarryingAmounts |
| Carrying amount of assets sold under agreements to repurchase when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under repurchase agreements exceeds 10 percent of total assets. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Credit |
| false |
| us-gaap:AssetsSoldUnderAgreementsToRepurchaseCarryingAmounts |