cm:Concept: us-gaap:BusinessCombinationSeparatelyRecognizedTransactionsNetGainsAndLosses
| Business Combination, Separately Recognized Transactions, Net Gains and Losses |
| us-gaap:BusinessCombinationSeparatelyRecognizedTransactionsNetGainsAndLosses |
| The net gains or losses recognized for each transaction with the acquiree that was recognized separately from the acquisition of assets and assumptions of liabilities in the business combination. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:BusinessCombinationSeparatelyRecognizedTransactionsNetGainsAndLosses |