Document that min/max operate on the double representation of the data.

Relates #9545

docs/reference/aggregations/metrics/max-aggregation.asciidoc

@@ -3,6 +3,10 @@
 
 A `single-value` metrics aggregation that keeps track and returns the maximum value among the numeric values extracted from the aggregated documents. These values can be extracted either from specific numeric fields in the documents, or be generated by a provided script.
 
+NOTE: The `min` and `max` aggregation operate on the `double` representation of
+the data. As a consequence, the result may be approximate when running on longs
+whose absolute value is greater than +2^53+.
+
 Computing the max price value across all documents
 
 [source,js]

docs/reference/aggregations/metrics/min-aggregation.asciidoc

@@ -3,6 +3,10 @@
 
 A `single-value` metrics aggregation that keeps track and returns the minimum value among numeric values extracted from the aggregated documents. These values can be extracted either from specific numeric fields in the documents, or be generated by a provided script.
 
+NOTE: The `min` and `max` aggregation operate on the `double` representation of
+the data. As a consequence, the result may be approximate when running on longs
+whose absolute value is greater than +2^53+.
+
 Computing the min price value across all documents:
 
 [source,js]