OP07 - Input Bias Current vs. Differential Input Voltage
It's a typo. The 'Y' axis should be mA not nA! 

The high resistance (M\$\Omega\$)applies to differential input voltages less than 1V (where the graph looks to be perfectly flat, at a scale of mA).

This is typical of this kind of bipolar super-\$\beta\$ input  op-amp. You should not generally use such an op-amp in applications with significant differential input voltage (such as a comparator or some kinds of precision rectifier).

So the resistors are more like 630\$\Omega\$ each. (14V/22mA)

From LTC's datasheet:



If they were 600M the differential input noise due to (unavoidable) Johnson-Nyquist resistor noise would be about 500x higher than the OP07 typical spec.