cm:Concept: us-gaap:SecuritiesHeldAsCollateralAtFairValue
| Securities Held as Collateral, at Fair Value |
| us-gaap:SecuritiesHeldAsCollateralAtFairValue |
| The carrying amount (fair value) as of the balance sheet date of securities held that had been pledged by counterparties under financing and lending arrangements, pursuant to which the entity has the right by agreement or custom to sell or re-pledge such securities. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Debit |
| false |
| us-gaap:SecuritiesHeldAsCollateralAtFairValue |