cm:Concept: us-gaap:OtherComprehensiveLossHeldToMaturitySecurityOttiAfterTaxAndAdjustmentsAttributableToNoncontrollingInterest
| Other Comprehensive Loss, Held-to-maturity Security, OTTI, after Tax and Adjustments, Attributable to Noncontrolling Interest |
| us-gaap:OtherComprehensiveLossHeldToMaturitySecurityOttiAfterTaxAndAdjustmentsAttributableToNoncontrollingInterest |
| Amount, after tax and adjustments, of increase (decrease) in other than temporary impairment (OTTI) on investment in held-to-maturity security, recognized in other comprehensive loss and attributable to noncontrolling interest. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:OtherComprehensiveLossHeldToMaturitySecurityOttiAfterTaxAndAdjustmentsAttributableToNoncontrollingInterest |