Newbie Alert: Simple Subtraction Measure - Output is displaying with brackets instead of a - value

Hi All

In the visual  below

Estimate Cost and Actiual are from a data source.

The Over/Under spend is a simplea measure which takes estimated - actuals - Its juts a very simple Project Labour cost

Now I have overspent by $20K and you can see the value display with brackets

My measure looks like so:

Over/Under Spend = 
SUM('PMO'[Estimated Labour Cost - Widget Project Board]) - SUM('PMO'[Actual Labour Cost to Date - Widget Project Board])

Question: How do I get my measure output to display as a negative number?  I can then conditional format that to show red etc?

Estimated: 50,000

Actuals: 70,000

Over Spend: -20,000

Thanks

Jimmy