cm:Concept: us-gaap:ForeignReinsuranceTransactionsExpenseRecognizedAsIncome
| Foreign Reinsurance Transactions, Expense Recognized as Income |
| us-gaap:ForeignReinsuranceTransactionsExpenseRecognizedAsIncome |
| The amount of insurance policy expenses on insurance that has been ceded to companies outside the United States and for which amounts are paid or due and owing from those foreign companies. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:ForeignReinsuranceTransactionsExpenseRecognizedAsIncome |