cm:Concept: us-gaap:OciLiabilityForFuturePolicyBenefitGainLossBeforeReclassificationAdjustmentAndTax
| OCI, Liability for Future Policy Benefit, Gain (Loss), before Reclassification Adjustment and Tax |
| us-gaap:OciLiabilityForFuturePolicyBenefitGainLossBeforeReclassificationAdjustmentAndTax |
| Amount, before tax and reclassification adjustment, of unrealized gain (loss) from (increase) decrease in liability for future policy benefit from change in discount rate. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:OciLiabilityForFuturePolicyBenefitGainLossBeforeReclassificationAdjustmentAndTax |