cm:Concept: us-gaap:GainLossOnDiscontinuationOfPriceRiskCashFlowHedgeDueToForecastedTransactionProbableOfNotOccurringNet
| Gain (Loss) on Discontinuation of Price Risk Cash Flow Hedge Due to Forecasted Transaction Probable of Not Occurring, Net |
| us-gaap:GainLossOnDiscontinuationOfPriceRiskCashFlowHedgeDueToForecastedTransactionProbableOfNotOccurringNet |
| The amount of net gain (loss) reclassified into earnings when price risk cash flow hedge is discontinued because it is probable that the original forecasted transactions will not occur by the end of the original period or an additional two month time period. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:GainLossOnDiscontinuationOfPriceRiskCashFlowHedgeDueToForecastedTransactionProbableOfNotOccurringNet |