cm:Concept: us-gaap:ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill
| Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill) |
| us-gaap:ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill |
| Amount of impairment loss resulting from write-down of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit to fair value. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill |