cm:Level3TextBlock: us-gaap:SecuritiesPurchasedUnderAgreementsToResellAllowanceForCreditLossTableTextBlock
| Securities Purchased under Agreements to Resell, Allowance for Credit Loss [Table Text Block] |
| us-gaap:SecuritiesPurchasedUnderAgreementsToResellAllowanceForCreditLossTableTextBlock |
| Tabular disclosure of allowance for credit loss on securities purchased under agreement to resell. |
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| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
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| us-gaap:SecuritiesPurchasedUnderAgreementsToResellAllowanceForCreditLossTableTextBlock |