If you use auto ISO, the camera will just jack the ISO up till the scene is bright. There are a few things that you need to be careful of
. If you use Matrix meter, then it will average the scene out and and you have seen, blow some parts.
. Use Centre weighed when you want the meter to concentrate around the centre, and spot when you want a particular point metered - say you have the slate/display off centre and you want that properly metered, then you select the spot meter and it will expose the object under the selected focus point perfectly. Mind you the rest of the image may be either dark or blown depending on the intensity of the light with respect to the chosen spot.
. If you want any control on light, avoid auto ISO. Use fixed ISO and check the exposure speed as you adjust the aperture.
. For high contrast scenes, as a dark room with a bright window, the only way to get every thing perfectly exposed is to use HDR. The the room is properly exposed and so is the scene outside the window. Remember that the camera has a DR of 14EV of which the top 6 EV is relatively noise free. If the scene has a DR of 18EV or more, some areas are bound to be ither blown or pitch black.
One trick advocated is to expose for the brighter part of the scene and then use the D750's DR to "lift" the shadows.