cm:Concept: us-gaap:GainLossFromHedgedFirmCommitmentNotQualifyingAsForeignCurrencyFairValueHedgeNet
| Gain (Loss) from Hedged Firm Commitment Not Qualifying as Foreign Currency Fair Value Hedge, Net |
| us-gaap:GainLossFromHedgedFirmCommitmentNotQualifyingAsForeignCurrencyFairValueHedgeNet |
| Amount of gain (loss) recognized in earnings for the period when a hedged firm commitment no longer qualifies as an foreign currency fair value hedge. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:GainLossFromHedgedFirmCommitmentNotQualifyingAsForeignCurrencyFairValueHedgeNet |