cm:Concept: us-gaap:FinancingReceivableUnamortizedLoanCommitmentOriginationFeeAndPremiumDiscount
| Financing Receivable, Unamortized Loan Commitment, Origination Fee, and Premium (Discount) |
| us-gaap:FinancingReceivableUnamortizedLoanCommitmentOriginationFeeAndPremiumDiscount |
| Amount of commitment, origination, and other fee and cost and purchase premium (discount) on financing receivable. Excludes financing receivable covered under loss sharing agreement. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Debit |
| false |
| us-gaap:FinancingReceivableUnamortizedLoanCommitmentOriginationFeeAndPremiumDiscount |