RIDDLE:

Schwarzenegger has a big one.
Michael J. Fox has a small one.
Madonna doesn't have one.
The Pope has one but doesn't use his.
Clinton uses his all the time.
Mickey Mouse has an unusual one.
Liberace never used his on women.
Jerry Seinfeld is very, very proud of his.
Cher claims that she took on 3.
We never saw Lucy use Desi's.
What is it?