Bill vs Willie

Bill

name

  • A diminutive of the male given name William. 

  • A nickname for the British constabulary. Often called "The Bill" or "Old Bill" 

  • A surname. 

Willie

name

  • A diminutive of the male given name William 

  • A diminutive of the female given name Wilhelmina or a feminine diminutive of William, often in the form Willie Mae. 

How often have the words Bill and Willie occurred in a corpus of books? (source: Google Ngram Viewer )