cm:Concept: us-gaap:ContractWithCustomerReceivableCreditLossExpenseReversal
| Contract with Customer, Receivable, Credit Loss Expense (Reversal) |
| us-gaap:ContractWithCustomerReceivableCreditLossExpenseReversal |
| Amount of expense (reversal of expense) for expected credit loss on right to consideration in exchange for good or service transferred to customer when right to consideration is unconditional. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:ContractWithCustomerReceivableCreditLossExpenseReversal |