First detent is idle reverse. Second detent is a reasonably large reverse power setting. This is set in accordance with engine life considerations. You can go beyond the second detent.
I'm afraid I can't tell you the power settings. One place you are not looking is at the engine instruments!
To give you an idea of standard practice, it is always to select idle reverse. Second detent I have not used in years. Full reverse- not at all on the 737. Reverse power is not very effective, and VERY noisy. It is also very bad for the engine, ingesting debris off the ground, shaking it badly and wearing the translation mechanism. I very occasionally pull beyond the first detent until it gets noisy enough. The autobrake is the main stopping aid. On the 747 with its much larger engine and more complicated reverse mechanism, it was not unusual to have one engine stay in idle reverse with the mechanism unable to travel. you could simply taxi in and leave it like that for the engineers to reset. It was prohibited for the pilots to operate it then in case they caused damage to the mechanism.