Full frame Nikon d750 and 18-55mm?

How will an 18-55mm lens work on a Full Frame Nikon D750

The sensor automatically crops.

Image quality might suffer because you'll be producing an image of 18x24mm instead of 24x36mm.

It's not recommended since the 18-55mm is DX lens designed and optimized to work with DX bodies.
The same goes for FX lenses on DX bodies.

You can do it with the D750 in crop mode. But you're wasting the power of the FF sensor by using such a low-end lens.

It will work as the D750 will automatically crop if set up to do so. The 18-55 is a sub par lens on a D750, so don't expect the best quality.