cm:Concept: us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue
| Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after 10 Years, Fair Value |
| us-gaap:AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue |
| 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 after 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:AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue |