cm:Concept: us-gaap:DemutualizationByInsuranceEntitySecuritiesIssuedAmountOfNetProceeds
| Demutualization by Insurance Entity, Securities Issued, Amount of Net Proceeds |
| us-gaap:DemutualizationByInsuranceEntitySecuritiesIssuedAmountOfNetProceeds |
| The proceeds received by an insurance entity after deducting offering and other costs of securities issued and after policy credits, in connection with its conversion from a mutual form of ownership to a stock entity. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:DemutualizationByInsuranceEntitySecuritiesIssuedAmountOfNetProceeds |