cm:Concept: us-gaap:GainLossFromHedgedFirmCommitmentNotQualifyingAsPriceRiskFairValueHedgeNet
| Gain (Loss) from Hedged Firm Commitment Not Qualifying as Price Risk Fair Value Hedge, Net |
| us-gaap:GainLossFromHedgedFirmCommitmentNotQualifyingAsPriceRiskFairValueHedgeNet |
| Amount of gain (loss) recognized in earnings when a hedged firm commitment no longer qualifies as an price risk fair value hedge. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:GainLossFromHedgedFirmCommitmentNotQualifyingAsPriceRiskFairValueHedgeNet |