Input Range of Differential Voltage in Op Amps
First, the number you're looking for is, in my experience, almost always found in the section labeled "Absolute Maximum Ratings", or something similar.

Second, the problem of integrator saturation is usually dealt with by using a clamp (such as a zener diode or diodes) on the feedback path. This keeps the op amp in the linear region, and differential limits simply aren't a consideration. In PID loops, in particular, paying attention to integrator saturation is often important to keep windup from playing hob with the behavior of the system when it comes out of overload.