cm:Concept: us-gaap:ShortDurationContractsDiscountedLiabilitiesBasisForDiscountRate
| Short-Duration Contracts, Discounted Liabilities, Basis for Discount Rate |
| us-gaap:ShortDurationContractsDiscountedLiabilitiesBasisForDiscountRate |
| Describes the facts and circumstances pertaining to the selection of the discount rate used to reduce the estimated amount of loss reserves on short-duration contracts to present value. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:ShortDurationContractsDiscountedLiabilitiesBasisForDiscountRate |