Passing key/value object from AJAX POST to MVC 5 Controller action method coming as null

After searching for a few hours here it is. I have an object full of key/value pairs of questionID's and answers. This is how survey.js's onCmplete method generates their question/answers when the survey is completed. The object that I wish to pass to the MVC controller looks like this:

{18: "No", 22: "windows 7", 23: "nc programming", 24: "Server"}

Here is my AJAX POST to my controller action method:

$.ajax({
    type: 'POST',
    url: '/Assessment/CompleteAssessment',
    dataType: 'json',
    data: survey.data
  })
  .done(function() {
    alert('Success');
  })
  .fail(function(xhr) {
    alert('Failed.');
  });

On the back-end side, my action method looks like this:

[HttpPost]
    public ActionResult CompleteAssessment(Dictionary<int, string> assessmentData)
    {
        return null;
    }

I put a breakpoint on the action method and it hits after I make the AJAX POST but I'm not getting any values passed into it. Not sure what to do at this point.