Java Doc - Do fields also get documented?

This is a really simple question but oddly, I'm finding it difficult to get a definite answer....

What do you do with fields? Is this valid?

/** 
 * Keeps track of all usernames in the system.
 */   
private List<String> usernames = new ArrayList<>();

Or is above ingnored by documentation tools, so would it be best to do something like:

 //Keeps track of all usernames in the system.   
private List<String> usernames = new ArrayList<>();

Since (from what I see), documentation only shows methods, constructors and classes, what do programmers usually do with fields?