cm:Level3TextBlock: us-gaap:ScheduleOfRealizedGainLossTableTextBlock
| Schedule of Realized Gain (Loss) [Table Text Block] |
| us-gaap:ScheduleOfRealizedGainLossTableTextBlock |
| Tabular disclosure of the proceeds from sales of available-for-sale securities and the gross realized gains and gross realized losses that have been included in earnings as a result of those sales. |
| cm:Level3TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:ScheduleOfRealizedGainLossTableTextBlock |
| RealizedGainLoss |