Say your source data of financial numbers is Text type. This means when they have negative values, they will be enclosed in parentheses. These parentheses prevent a direct cast to Number type as such values get evaluated to Null rather than to a negative number.
We can use a formula that will detect the presence of the parentheses, append a minus sign and then remove the parentheses prior to the casting to Number type.
Example:
If(Contains([Financial Numbers (Text Type)], "("), Number(Concat("-", Replace(Replace([Financial Numbers (Text Type)], ")", ""), "(", ""))), Number([Financial Numbers (Text Type)]))
