This is a big brown bat, Eptesicus fuscus. They're very similar to many Myotis species, but they're larger. They also have a keeled calcar, which the very similar Myotis lucifugus, the little brown bat, lacks.
This was shot a year ago in Maryland, actually, not at Christmas. I always have Christmas lights in my bathroom. I got a call for a bat removal from some guy's dorm room, caught the little bugger, let her loose in my bathroom for photographing, then let her go outside.