cm:Concept: us-gaap:TaxCutsAndJobsActOf2017OtherTaxEffectDescription
| Tax Cuts and Jobs Act, Other Tax Effect, Description |
| us-gaap:TaxCutsAndJobsActOf2017OtherTaxEffectDescription |
| Description of other income tax effect related to application of Tax Cuts and Jobs Act that are reclassified from accumulated other comprehensive income to retained earnings. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:TaxCutsAndJobsActOf2017OtherTaxEffectDescription |