title: How to get the total count of unique terms on aggregations with the size set?
body: <p>When using the <a href="https://www.elastic.co/guide/en/elasticsearch/reference/5.6/search-aggregations-bucket-terms-aggregation.html" rel="nofollow noreferrer">Terms Aggregation</a> on an ElasticSearch query, the result will limit the buckets to the top 10 items or the value set on the <a href="https://www.elastic.co/guide/en/elasticsearch/reference/5.6/search-aggregations-bucket-terms-aggregation.html#_size" rel="nofollow noreferrer">size</a> parameter. For example:</p>
  
  <pre class="lang-json prettyprint-override"><code>{
    "aggs" : {
      "cities" : {
        "terms" : { 
          "field" : "city",
          "size": 20
        }
      }
    }
  }
  </code></pre>
  
  <p>This query would give me the top 20 buckets and their counts. How do I change this query to know the total count of unique <code>"city"</code> terms, so I can present something like "<em>showing the top 20 cities of 73</em>"?</p>