cm:Concept: us-gaap:DemutualizationByInsuranceEntitySecuritiesIssuedGrossCashProceeds
| Demutualization by Insurance Entity, Securities Issued, Gross Cash Proceeds |
| us-gaap:DemutualizationByInsuranceEntitySecuritiesIssuedGrossCashProceeds |
| The price per share or unit times the number of shares or units issued in an insurance entity stock offering in connection with its conversion from a mutual form of ownership to a stock entity. Amount is gross, before offering costs. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:DemutualizationByInsuranceEntitySecuritiesIssuedGrossCashProceeds |