Catalyzes the oxidation of the 12-alpha-hydroxyl group of bile acids, both in their free and conjugated form. Also acts on bile alcohols. cholate + NADP(+) = 3alpha,7alpha-dihydroxy-12-oxo-5beta-cholanate + H(+) + NADPH Homotetramer. The thermostability of the enzyme is greatly increased due to NADP binding.