Adding a cross-reference field within a document is easy enough, I just hit reference>cross-reference and can point to any number in a list, which will update automatically if I make changes to the list.

But how do I cross-reference a number field in an outside document?

For example, Document A is a list like this:

1. [Facts about John]
2. [Facts about Sally]
3. [Facts about Jeremy]

Document B has texts such as: "see Document A, paragraph (1) for facts about John..."

If I change my list to the following:

1. [Facts about Steve]
2. [Facts about John]
2. [Facts about Sally]
3. [Facts about Jeremy]

I want Document B to automatically update the cross-reference number to say "see Document A, paragraph (2) for facts about John..."

This is easily achieved when the list is within Document B, but how can I achieve this when dealing with 2 separate documents?