cm:Concept: us-gaap:ClosedBlockOperationsRealizedInvestmentGainsLosses
| Closed Block Operations, Realized Investment Gains (Losses) |
| us-gaap:ClosedBlockOperationsRealizedInvestmentGainsLosses |
| Gains and losses realized for the period from the investments allocated to an insurance entity's segregated group of participating or dividend-paying policies and contracts (known as a closed block). |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:ClosedBlockOperationsRealizedInvestmentGainsLosses |