Detect duplicates of _id

[Hiroki_Otsuka (Hiroki)]

I use two indexes.

The two indexes contain the same _id by the program.
For example, IndexA has "_id 777", and also indexB has "_id 777".

I want to output the same _id in something nested form like collapse, when I search in all indexes.
like this
https://www.elastic.co/guide/en/elasticsearch/reference/current/search-request-collapse.html

[dadoonet (David Pilato)]

You can't join indices.