Where do input bias currents flow?

This is my answer to SE EE question AC coupled differential op amp bias current return path.

My answer

The best way to understand and explain circuits in an intuitive way is to show where currents flow and what voltages are in circuits and inside resistors.

Here the OP is interested in where the input bias currents flow. That is why I have shown in Fig. 1 only their paths on a simplified conceptual circuit diagram of a part of an internal op-amp structure.

Fig. 1. A conceptual op-amp circuit diagram with input bias currents visualized.

It can be supplemented with (thicker) loops representing the collector currents flowing in the input and output stage - Fig. 2.

Fig. 2. A conceptual op-amp circuit diagram with all currents visualized.

It is interesting to see that the input bias current I- entering the inverting op-amp input is provided by both the positive power supply V+ and negative V- (connected in series) while the input bias current I+ entering the non-inverting input is provided only by the negative power supply V-.