cm:Concept: us-gaap:PresentValueOfFutureInsuranceProfitsUnrealizedInvestmentGains1
| Present Value of Future Insurance Profits, Unrealized Investment Gain |
| us-gaap:PresentValueOfFutureInsuranceProfitsUnrealizedInvestmentGains1 |
| Amount of unrealized investment gain which decreases present value of future profits of insurance contract acquired in business combination. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:PresentValueOfFutureInsuranceProfitsUnrealizedInvestmentGains1 |