cm:Concept: us-gaap:AdditionalLiabilityLongDurationInsuranceDerecognition
| Additional Liability, Long-Duration Insurance, Derecognition |
| us-gaap:AdditionalLiabilityLongDurationInsuranceDerecognition |
| Amount of decrease in present value of total expected payment to policyholder in excess of present value of total expected assessment from derecognition of contract. Excludes benefit classified as market risk benefit or under provisions of Topic 815 on derivative and hedging. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:AdditionalLiabilityLongDurationInsuranceDerecognition |