Is the shorthand electron configuration of Br- just [Kr]?
You could render bromide ion that way.  But the outermost electrons in the "krypton core" are potentially reactive, valence electrons; therefore $\text{[Kr]}$ is not an accurate description of how the electrons really act.  Only the argon core acts like a noble gas, so you are better off rendering the bromide ion as $\text{[Ar]3d}^{10}\text{4s}^2\text{4p}^6$.

Cations stripped to the noble gas core, however, really are stripped to unreactive electrons, so calcium ion can accurately be rendered as $\text{[Ar]}$.