cm:Concept: us-gaap:DepositAssetsOrLiabilitiesChangeInAmountsBasedOnChangeInAssumptionsSupportingExpectedRecoveryAmounts
| Deposit Assets or Liabilities, Change in Amounts Based on Change in Assumptions Supporting Expected Recovery Amounts |
| us-gaap:DepositAssetsOrLiabilitiesChangeInAmountsBasedOnChangeInAssumptionsSupportingExpectedRecoveryAmounts |
| On contracts that transfer only significant underwriting risk, description of an adjustment in the carrying amount of recorded deposit assets or liabilities resulting from a change in the underlying assumptions on which calculation of the initial amount of expected recoveries (in other words, the initial amount of the deposit asset or liability) had been based. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:DepositAssetsOrLiabilitiesChangeInAmountsBasedOnChangeInAssumptionsSupportingExpectedRecoveryAmounts |