cm:Concept: us-gaap:DeferredGainLossOnDiscontinuationOfFairValueHedge
| Deferred (Gain) Loss on Discontinuation of Fair Value Hedge |
| us-gaap:DeferredGainLossOnDiscontinuationOfFairValueHedge |
| Amount as of the balance sheet date of the unamortized adjustment to the carrying value of an interest-bearing hedged item made under an effective fair value hedge that is amortized upon discontinuation of the fair value hedge. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Debit |
| false |
| us-gaap:DeferredGainLossOnDiscontinuationOfFairValueHedge |