On the datasheet, there are some formulas to calculate the input leakage current (7.5 Electrical Characteristics, page 6).
The datasheet claims that the unit for the result value on the leakage current formula is in µA.
Considering Rin = 1MΩ, input range, 2.5xVref, Vin = 0V, we would have: -2.5/1000000 = -0.0000025 µA = -2.5 pA.
Should the leakage current be on the level of some pA or is it too low?