cm:Concept: us-gaap:DepositLiabilitiesEffectOfChangeInPresentValueAssumptionsResultingInAdditionsToExpectedRecoveries
| Deposit Liabilities, Effect of Change in Present Value Assumptions Resulting in Additions to Expected Recoveries |
| us-gaap:DepositLiabilitiesEffectOfChangeInPresentValueAssumptionsResultingInAdditionsToExpectedRecoveries |
| Amount of expense from increase in deposit liabilities due to change in present value assumptions used to value expected recoveries. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:DepositLiabilitiesEffectOfChangeInPresentValueAssumptionsResultingInAdditionsToExpectedRecoveries |