cm:Concept: us-gaap:OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsAdditionsAdditionalCreditLosses
| Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses |
| us-gaap:OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsAdditionsAdditionalCreditLosses |
| This item represents an increase to the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held for which a previous OTTI was recognized and the investor does not intend to sell the debt security and it is not more likely than not that the investor will be required to sell the debt security before recovery of its amortized cost basis. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsAdditionsAdditionalCreditLosses |