cm:Concept: us-gaap:CashAndSecuritiesSegregatedUnderFederalAndOtherRegulationsDescription
| Cash and Securities Segregated under Federal and Other Regulations, Description (Deprecated 2019-01-31) |
| us-gaap:CashAndSecuritiesSegregatedUnderFederalAndOtherRegulationsDescription |
| Disclosure of cash subject to withdrawal restrictions, restricted deposits held as compensating balances, and cash and securities segregated in compliance with regulations (such as cash deposited in a special reserve account for the exclusive benefit of customers). |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:CashAndSecuritiesSegregatedUnderFederalAndOtherRegulationsDescription |