In financial reports, you may want to display negative numbers using parenthesis. For this format, cut-and-paste the following in the Properties of a field.
¤ #,##0.00;(¤ #,##0.00)
|Formatting a Field with a Custom Pattern|
If you designate a field as numeric (Double, Integer, etc.) you may want to add additional formatting. For example, the scientific notation -- which is the default -- is not used for financial statements. Add in a currency formatting.