cm:Concept: us-gaap:InterestAndDividendIncomeSecuritiesTradingOrMeasuredAtFairValue
| Interest and Dividend Income, Securities, Operating, Trading or Measured at Fair Value |
| us-gaap:InterestAndDividendIncomeSecuritiesTradingOrMeasuredAtFairValue |
| Amount of operating dividend and interest income, including amortization and accretion of premiums and discounts, on trading securities and other forms of securities that provide ownership interests. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:InterestAndDividendIncomeSecuritiesTradingOrMeasuredAtFairValue |