Can Newfoundland's be outside all winter long in below freezing temperatures?

Our Newfie is kept outdoors (sometimes although brief moments he is brought into our garage for some warmth from the woodstove in there) all the time. We live in central Minnesota. My SO does not want him inside. I just feel concerned for him out there in below 0 temps...he is alone and I personally think he's cold. He isn't shivering...and I have read that Newfie's were/are used in chilly icy waters for rescue work and such...so is he alright out there??? The other thing that concerns me is he is alone out there (no doggie friend to snuggle up to)...and dogs are pack/social animals, not loners.