cm:Concept: us-gaap:DebtSecuritiesAvailableForSaleTransferToTradingGain
| Debt Securities, Available-for-sale, Transfer to Trading, Gain |
| us-gaap:DebtSecuritiesAvailableForSaleTransferToTradingGain |
| Amount of unrealized gain recognized in earnings from transfer of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) to investment in debt security measured at fair value with change in fair value recognized in net income (trading). |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:DebtSecuritiesAvailableForSaleTransferToTradingGain |