cm:Concept: us-gaap:AccretionAmortizationOfDiscountsAndPremiumsInvestments
| Accretion (Amortization) of Discounts and Premiums, Investments |
| us-gaap:AccretionAmortizationOfDiscountsAndPremiumsInvestments |
| The sum of the periodic adjustments of the differences between securities' face values and purchase prices that are charged against earnings. This is called accretion if the security was purchased at a discount and amortization if it was purchased at premium. As a noncash item, this element is an adjustment to net income when calculating cash provided by or used in operations using the indirect method. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:AccretionAmortizationOfDiscountsAndPremiumsInvestments |