cm:Concept: us-gaap:IncreaseDecreaseInFuturePolicyBenefitReservesAndOtherInsuranceLiabilities
| Increase (Decrease) in Future Policy Benefit Reserves and Other Insurance Liabilities |
| us-gaap:IncreaseDecreaseInFuturePolicyBenefitReservesAndOtherInsuranceLiabilities |
| Amount of increase (decrease) in estimated future policy benefit obligations under insurance contracts, and obligations under insurance contracts classified as other. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:IncreaseDecreaseInFuturePolicyBenefitReservesAndOtherInsuranceLiabilities |