cm:Concept: us-gaap:ClosedBlockDividendObligationChangeInUnrealizedInvestmentGainsLosses
| Closed Block Dividend Obligation, Change in Unrealized Investment Gain (Loss) |
| us-gaap:ClosedBlockDividendObligationChangeInUnrealizedInvestmentGainsLosses |
| Amount of increase (decrease) in the closed block dividend obligation from the unrealized gain (loss) on investments allocated to the closed block. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:ClosedBlockDividendObligationChangeInUnrealizedInvestmentGainsLosses |