you can make a new column and multiple all the amounts by -1 

E.g. if col C has the amounts, then in D1 formula is =C1*-1 which takes the amount from C1 and flips it. Then copy that all the way down column D and all of col C is flipped. Then copy all of col D and paste values into Col E. Then delete cols C and D and zappa do. Way easier than splitting out the negs and positives