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