cm:Concept: us-gaap:AccumulatedOtherComprehensiveIncomeLossFinancialLiabilityFairValueOptionAfterTax
| Accumulated Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, after Tax |
| us-gaap:AccumulatedOtherComprehensiveIncomeLossFinancialLiabilityFairValueOptionAfterTax |
| Amount, after tax, of accumulated gain (loss) from increase (decrease) in instrument-specific credit risk of financial liability measured under fair value option. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Credit |
| false |
| us-gaap:AccumulatedOtherComprehensiveIncomeLossFinancialLiabilityFairValueOptionAfterTax |