cm:Concept: us-gaap:IncreaseDecreaseInFairValueOfHedgedItemInInterestRateFairValueHedge1
| Increase (Decrease) in Fair Value of Hedged Item in Interest Rate Fair Value Hedge |
| us-gaap:IncreaseDecreaseInFairValueOfHedgedItemInInterestRateFairValueHedge1 |
| Amount of unrealized gain (loss) included in earnings related to the fair value of the hedged item in an interest rate fair value hedge, offset by the gain (loss) on the hedging instrument to the extent that the fair value hedge is determined to be effective. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:IncreaseDecreaseInFairValueOfHedgedItemInInterestRateFairValueHedge1 |