jQuery Ajax请求：以无处不在的方式处理JSON响应

I have a PHP script which sends me back JSON (with proper headers, confirmed by response headers in Chrome Dev Tools). When I do a POST request in jQuery, like this:

var request = $.post(formAction, formData);

I "need" to handle accessing JSON properties differently for .done() and .fail() (details being a property), thus:

request.done(function(response) {
    $('#response').text(response.details);
});

request.fail(function(response) {
    $('#response').text(response.responseJSON.details);
});

What is the recommended way of accessing JSON properties in ubiquitous manner, so I can just call a always() function ? For instance, when the fail() method fires, and I do console.log(response.details) I get errors telling me that that property is not found.