Question on Including/Excluding Work Places

Hi, I'm not sure if this is the correct newsgroup for this question.

Suppose you have worked for 15 years in companies A through E.
However, you want to concentrate your resume on companies B, C and E.
The other companies (A and D) are important corporations that you still
want to include, but with less detail since they don't match the
positions of companies C and E. How would you go about doing this if
you currently have a resume written in chronological order?

Hahnemann