Depends on what screen you saw it on and what the film's aspect ratio is.
There have only been a handful of real IMAX movies, i.e. movies with select scenes shot on IMAX 70mm cameras. These films utilize the entire screen of a real IMAX theater, which is about 70ft tall and has an AR of 1.43:1. Nolan movies, M:I Ghost Protocol, Star Trek Into Darkness, Transformers 2, Catching Fire. They are in their normal AR througout (2.35:1, 1.85:1, etc. - what you'd see in any other theater) except for the IMAX scenes which are 1.43:1. Then there are the rare films (Skyfall, Tomorrowland, maybe others) which do not have scenes filmed with IMAX cameras but extend vertically their AR for IMAX.
Then there's LIEMAX which is called IMAX but has a much shorter screen and an AR of 1.89:1. The movies with varying AR still vary, but only to the extent of the LIEMAX's screen.
Every other movie retains their original AR for both real and fake IMAX presentation. A Good Day to Die Hard has a 1.85:1 AR, so if you saw it in LIEMAX it would have just about taken up the whole screen. Furious 7 and M:I Rogue Nation are both 2.35:1, so you should have seen both letterboxed no matter what screen.