How to display 2 different classes (activities) in a fragment in ANDROID?

I have an already working android app, but I need to update it for better layout on tablets. I can rewrite it no-problem, but what I want to ask is;

I will have 2 fragments on screen (one for list, and one for details). When I select a customer from list, details will update itself (I have already done this without a problem). BUT, when I select an item from details fragment, it must change itself (it must be opened on details fragment, but of course it will be a different class). For example first details will be a list of details, but when I select an item from details list, it will be a different layout, maybe WebView or so..

To better represent the idea,

LLLLLL DDDDDDDDDDDDDDDDDDDDDDDDDD

LLLLLL DDDDDDDDDDDDDDDDDDDDDDDDDD

LLLLLL DDDDDDDDDDDDDDDDDDDDDDDDDD

LLLLLL DDDDDDDDDDDDDDDDDDDDDDDDDD

LLLLLL DDDDDDDDDDDDDDDDDDDDDDDDDD

LLLLLL DDDDDDDDDDDDDDDDDDDDDDDDDD

Where "L" is list fragment, and "D" is details fragment. But I want to show 2 (or more) different classes (activities) (Not at the same time btw) in the details fragment. How do I do that? I was searching this for 2 full days, there is nice tutorials but I couldn't find any example for this behaviour.

Thanks in advance.