cm:Concept: us-gaap:InterestIncomeSecuritiesStateAndMunicipal
| Interest Income, Securities, State and Municipal |
| us-gaap:InterestIncomeSecuritiesStateAndMunicipal |
| Interest income, including any amortization and accretion (as applicable) of discounts and premiums, derived from debt securities issued by municipal governments, local taxing districts and US state government agencies. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:InterestIncomeSecuritiesStateAndMunicipal |