cm:Level3TextBlock: us-gaap:FDICIndemnificationAssetRollForwardTableTextBlock
| FDIC Indemnification Asset Roll Forward [Table Text Block] |
| us-gaap:FDICIndemnificationAssetRollForwardTableTextBlock |
| Tabular disclosure of the change in the indemnification asset relating to loss sharing agreements with the Federal Deposit Insurance Corporation (FDIC). |
| cm:Level3TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:FDICIndemnificationAssetRollForwardTableTextBlock |