cm:Concept: us-gaap:ResellAgreementsPeriodEndAmountsExcludingEffectsOfAgreementsReportedNetByCounterparty
| Resell Agreements, Period End Amounts Excluding Effects of Agreements Reported Net by Counterparty |
| us-gaap:ResellAgreementsPeriodEndAmountsExcludingEffectsOfAgreementsReportedNetByCounterparty |
| This is the total amount of resale agreements as of the reporting date. This is a gross amount (does not net agreement amounts by counterparty). |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Debit |
| false |
| us-gaap:ResellAgreementsPeriodEndAmountsExcludingEffectsOfAgreementsReportedNetByCounterparty |