For cruise only passengers, 90kg maximum is allowed per person (with the exception of Celebrity Expedition).
Airlines also impose their own baggage allowance, which is usually much less than the cruise allowance.
If you are sailing on a transatlantic cruise and you are then meeting a flight as part of a fly/cruise package, your luggage allowance will be limited to the lower allowance as specified by the airline. (This is normally 20kg and must be made up of just one bag weighing this. Please check with the airline at the time of booking)