cm:Concept: us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue
| Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Fair Value |
| us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue |
| Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Debit |
| false |
| us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue |