cm:Concept: us-gaap:OtherComprehensiveIncomeReclassificationAdjustmentForHeldToMaturityTransferredToAvailableForSaleSecuritiesTax
| Other Comprehensive Income (Loss), Transfers from Held-to-maturity to Available-for-Sale Securities, Tax |
| us-gaap:OtherComprehensiveIncomeReclassificationAdjustmentForHeldToMaturityTransferredToAvailableForSaleSecuritiesTax |
| Amount of tax expense (benefit) before reclassification adjustments of unrealized holding gain (loss) related to transfers of securities into the available-for-sale category and out of the held-to-maturity category. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:OtherComprehensiveIncomeReclassificationAdjustmentForHeldToMaturityTransferredToAvailableForSaleSecuritiesTax |