cm:Concept: us-gaap:SecuritiesPurchasedUnderAgreementsToResellChangeInMethodCreditLossExpenseReversal
| Securities Purchased under Agreements to Resell, Change in Method, Credit Loss Expense (Reversal) |
| us-gaap:SecuritiesPurchasedUnderAgreementsToResellChangeInMethodCreditLossExpenseReversal |
| Amount of expense (reversal of expense) for expected credit loss on security purchased under agreement to resell, from change in methodology. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:SecuritiesPurchasedUnderAgreementsToResellChangeInMethodCreditLossExpenseReversal |