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