cm:Concept: us-gaap:DebtSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairment
| Debt Securities, Realized Gain (Loss), Excluding Other-than-temporary Impairment |
| us-gaap:DebtSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairment |
| Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in net income (trading). Excludes other-than-temporary impairment (OTTI). |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:DebtSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairment |