cm:Concept: us-gaap:OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet
| Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net |
| us-gaap:OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet |
| The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet |