cm:Concept: us-gaap:AdditionalCollateralAggregateFairValue
| Additional Collateral, Aggregate Fair Value |
| us-gaap:AdditionalCollateralAggregateFairValue |
| The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Debit |
| false |
| us-gaap:AdditionalCollateralAggregateFairValue |