cm:Member: us-gaap:DefinedBenefitPlanEquitySecuritiesClassACommonStockEmployerRelatedPartyMember
| Defined Benefit Plan, Equity Securities, Class A Common Stock, Employer, Related Party [Member] |
| us-gaap:DefinedBenefitPlanEquitySecuritiesClassACommonStockEmployerRelatedPartyMember |
| Class A stock subordinate to all other stock of employer, in which defined benefit plan asset is invested. Includes, but is not limited to, common stock issued or managed by related party of employer. |
| cm:Member |
| [Member] (nonnum:domainItemType) |
| For Period (duration) |
| (no balance type) |
| true |
| us-gaap:DefinedBenefitPlanEquitySecuritiesClassACommonStockEmployerRelatedPartyMember |