I currently have a custom format that shows a number over 1000 as a $1K -
$999K and over 1,000,000 as $1M, etc. This works for positive numbers but I
can not figure out how to also have it work for negative numbers. The format
I currently use is the following:

[=1000000]$0,,"M";[=1000]$0,"K";$0

Any suggestions about how to have this same formatting apply to negative
numbers so that they show up as -$1K, -$1M, etc.?

Thanks.