There was a mini-debate about this a while back. Even though the name he utters sounds very much like 'Corleone', and the line reads 'Corleone' in the GF transcript found on the Trilogy website...Vito is actually saying 'Cuneo'. Brando mumbles this name so badly that if you're not paying attention, it really does sound like Corleone. But to listen carefully it does come across as the correct name.

Apple