I agree that it is most likely a bullfrog. If you live within their native range and may do so legally then releasing it after metamorphosis is likely to be your best option. They do not make the best indoor captives because they are so large and nervous. If you do decide to keep it plan on a long term home that is at least six feet long and two feet wide, in a smaller cage they will often kill themselves by hitting the glass during a jump, and they will usually jump at the slightest disturbance.