I'm a little confused about the structure of your app.
As I understand it, you want an initial view that is contained in a UINavigationController. Once someone taps the "Login" UIBarButtonItem on the UINavigationBar, then you have a view come up that is not contained in a UINavigationController (probably because it is a modal view that is outside the navigation flow of your app).
The part I'm confused about is where the Detail view comes in. Is the modally presented view dismissed while the Details view is pushed onto the navigation stack from the initial view? Why does the Details view need a back button? Does going back to the initial view effectively log out the user?
At any rate, you should be able to change the UINavigationBar for every view that is pushed on to the stack (that is also contained in your UINavigationController). If you are using Storyboard, you need to make sure that you embed the views pushed on to the stack in a UINavigationController. You can do that by going to the "Editor" menu, selecting "Embed in" and then selecting "Navigation Controller".
Let me know if I didn't understand your question or if you can post more details.