cm:Level2TextBlock: us-gaap:RevenueRecognitionPremiumsEarnedPolicy
| Revenue Recognition, Premiums Earned, Policy [Policy Text Block] |
| us-gaap:RevenueRecognitionPremiumsEarnedPolicy |
| Disclosure of accounting policy for determining revenue and timing of recognition as revenue of premiums received from policyholders, insureds and other insurance entities (the effects of ceding and assuming insurance policy risks) for the entity's insurance products. |
| cm:Level2TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:RevenueRecognitionPremiumsEarnedPolicy |