cm:Concept: us-gaap:DebtSecuritiesHeldToMaturityOriginatedFiveOrMoreYearsBeforeLatestFiscalYear
| Debt Securities, Held-to-maturity, Originated Five or More Years before Latest Fiscal Year |
| us-gaap:DebtSecuritiesHeldToMaturityOriginatedFiveOrMoreYearsBeforeLatestFiscalYear |
| Amount of investment in debt security measured at amortized cost (held-to-maturity), originated five or more years prior to latest fiscal year. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Debit |
| false |
| us-gaap:DebtSecuritiesHeldToMaturityOriginatedFiveOrMoreYearsBeforeLatestFiscalYear |