I just checked all of the department style income statements & all of them drill down to detail fine. Did you check to see if you get the same result in a different datafolder ie Sample Company?

Drill down works fine in my 20.5 Sample Company.

Sometimes drill down gets weird when there's a problem with the report that drill down pulls up - in this case 2-4-0-51. Can you run 2-4-0-51 from the 2-4 menu? Is there a default report form or other default print settings for 2-4-0-51 that may be problematic? Try clearing print defaults for 2-4-0-51 and then run a departmental income statement and test drill down again.

Yes, this worked! Thank you! I had no issues running the 2-4-0-51 subsidiary ledger on it's own, but I went ahead and deleted the print defaults and then reset them. This took care of the departmental income statement drill-down issue.