cm:Concept: us-gaap:GainLossOnInvestmentsExcludingOtherThanTemporaryImpairments
| Gain (Loss) on Investments, Excluding Other than Temporary Impairments |
| us-gaap:GainLossOnInvestmentsExcludingOtherThanTemporaryImpairments |
| This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:GainLossOnInvestmentsExcludingOtherThanTemporaryImpairments |