Question: The Sorcery Mastery

I've had a question for quite some time about the "Sorcery" Mastery in the Ferocity Tree for quite some time, the wording on the Mastery is the following; > +0.4/0.8/1.2/1.6/2.0% Increased Ability Damage

So my question is, does this mean increased Ability Power Damage, or does it mean actual Ability Damage. I ask this due to Riven, and if she would use it due to her mass amount of Ability usage for damage. I would check myself, but I'm not entirely how to figure out such small ratios.