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