cm:Concept: us-gaap:ImpairmentOfInvestments
| Other than Temporary Impairment Losses, Investments |
| us-gaap:ImpairmentOfInvestments |
| The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:ImpairmentOfInvestments |