cm:Concept: us-gaap:MarketRiskBenefitPeriodIncreaseDecrease
| Market Risk Benefit, Period Increase (Decrease) |
| us-gaap:MarketRiskBenefitPeriodIncreaseDecrease |
| Amount of increase (decrease) in 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. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:MarketRiskBenefitPeriodIncreaseDecrease |