cm:Concept: us-gaap:ForeignReinsuranceTransactionsExpenseAdditionsToUnderwritingBalances
| Foreign Reinsurance Transactions, Expense Additions to Underwriting Balances |
| us-gaap:ForeignReinsuranceTransactionsExpenseAdditionsToUnderwritingBalances |
| The amount of expenses on insured risks paid or due and owing to the ceding entity, recorded as additions to net premiums written minus net losses paid minus the sum of loss adjustment expenses and underwriting costs and expenses on insurance ceded to companies outside the United States. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:ForeignReinsuranceTransactionsExpenseAdditionsToUnderwritingBalances |