cm:Concept: us-gaap:MarketRiskBenefitChangeInFairValueGainLoss
| Market Risk Benefit, Change in Fair Value, Gain (Loss) |
| us-gaap:MarketRiskBenefitChangeInFairValueGainLoss |
| Amount of gain (loss) from (increase) decrease in fair value of contract or contract feature in long-duration contract issued by insurance entity that both protects contract holder from other-than-nominal capital market risk and exposes insurance entity to other-than-nominal capital market risk. Excludes change attributable to instrument-specific credit risk. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:MarketRiskBenefitChangeInFairValueGainLoss |