You generally can't disable the browser's autocomplete options for login fields:
Modern browsers implement integrated password management ... For this reason, many modern browsers do not support autocomplete="off" for login fields ... This is the behavior in Firefox (since version 38), Google Chrome (since 34), and Internet Explorer (since version 11).
It makes life slightly more complicated if you're writing a user management page. But unfortunately, too many people turned off autocomplete on login forms to try to block the browser's built-in password manager. Doing that makes your site less
secure, so browsers started ignoring it.
Don't try to make life harder for your users. Let them make the decision of whether or not to let their browser store their credentials. There is no valid reason for you to block that.