cm:Concept: us-gaap:OciMarketRiskBenefitInstrumentSpecificCreditRiskGainLossBeforeAdjustmentsAndTax
| OCI, Market Risk Benefit, Instrument-Specific Credit Risk, Gain (Loss), before Adjustments and Tax |
| us-gaap:OciMarketRiskBenefitInstrumentSpecificCreditRiskGainLossBeforeAdjustmentsAndTax |
| Amount, before tax and adjustments, of unrealized gain (loss) from (increase) decrease in instrument-specific credit risk on 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) |
| Credit |
| false |
| us-gaap:OciMarketRiskBenefitInstrumentSpecificCreditRiskGainLossBeforeAdjustmentsAndTax |