cm:Concept: us-gaap:GuaranteeObligationsLiquidationProceeds
| Guarantor Obligations, Liquidation Proceeds, Monetary Amount |
| us-gaap:GuaranteeObligationsLiquidationProceeds |
| Indicates, if estimable, the approximate extent to which the proceeds from liquidation of any assets held either as collateral or by third parties would be expected to cover the maximum potential amount of future payments under the guarantee or each group of similar guarantees. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:GuaranteeObligationsLiquidationProceeds |