cm:Concept: us-gaap:PrepayableFinancialAssetClosedPortfolioLastOfLayerAmortizedCost
| Prepayable Financial Asset Closed Portfolio, Last-of-Layer, Amortized Cost |
| us-gaap:PrepayableFinancialAssetClosedPortfolioLastOfLayerAmortizedCost |
| Amortized cost of closed portfolio of prepayable financial asset, used to designate hedging relationship in which hedged item is last layer expected to be remaining at end of hedging relationship. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Debit |
| false |
| us-gaap:PrepayableFinancialAssetClosedPortfolioLastOfLayerAmortizedCost |