How to help an alcoholic father?

So my dad is an alcoholic and has been for 10-20 years. We have tried to encourage him to cut down his drinking and quite smoking in the past but it's always been met with hostility. I'm a firm believer that people are entitled to make their own choices in life but i didn't realize just how bad things have got. My brother has found him unconscious on the floor twice within the last couple of weeks and he has banged his head a couple of times too. I honestly can't see him being alive much longer if he continues drinking the way he is now but but what can i do to help someone who doesn't want to be helped.