cm:Concept: us-gaap:CashAndSecuritiesSegregatedUnderCommodityExchangeActDescription
| Cash and Securities Segregated under Commodity Exchange Act, Description (Deprecated 2019-01-31) |
| us-gaap:CashAndSecuritiesSegregatedUnderCommodityExchangeActDescription |
| Description of cash and securities deposited in a special reserve account for the exclusive benefit of customers pursuant to the Commodity Exchange Act. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:CashAndSecuritiesSegregatedUnderCommodityExchangeActDescription |