cm:Concept: us-gaap:AociMarketRiskBenefitInstrumentSpecificCreditRiskBeforeTax
| AOCI, Market Risk Benefit, Instrument-Specific Credit Risk, before Tax |
| us-gaap:AociMarketRiskBenefitInstrumentSpecificCreditRiskBeforeTax |
| Amount, before tax, of accumulated other comprehensive income (loss) (AOCI) from (increase) decrease in instrument-specific credit risk on contract or contract feature in long-duration contract issued by insurance entity protecting contract holder from other-than-nominal capital market risk and exposing insurance entity to other-than-nominal capital market risk. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Credit |
| false |
| us-gaap:AociMarketRiskBenefitInstrumentSpecificCreditRiskBeforeTax |