Reporting by top-level tasks from master document of multiple sub-projects

[Guest]

I maintain a master document that organizes 3 inserted sub-projects
each with its own owner. The sub-projects all have a structure of
Top-level Task A, B, C. I need to produce a report from the master on
the fly that shows all tasks for the 3 sub-projects broken under A, B,
and C. Is there a way to directly do this in MS Project? Or do I need
to write a Macro/VBA to add an implementation button (it needs to be
easy and transparent for a limited-knowedge MSP person to use).

This seems to be a straightforward use of Project, but I can't seem to
find any info. And it seems that breaking tasks away from a subproject
is not encouraged by MSP. Thanks for any help anyone may provide.

 

[Guest]

To clarify, current setup:
Master
Sub-doc1
A, B, C
Sub-doc2
A, B, C
Sub-doc3
A, B, C

Desired report:

A
Sub-doc1 tasks, Sub-doc2 tasks, Sub-doc3 tasks
B
Sub-doc1 tasks, Sub-doc2 tasks, Sub-doc3 tasks
C
Sub-doc1 tasks, Sub-doc2 tasks, Sub-doc3 tasks