Open loop gain >>> closed loop gain, so the -input tracks the + input. You can derive this with feedback theory.
You can also imagine it. When the output voltage is at 1V and the open loop gain 100k, voltage between input terminals of opamp will be 10uV. therefore there is virtually no voltage across +input and -input. AC current that goes into +input will be very small, hence the input impedance will be very high.
You should think of MOhms, so the additional series resistors are only there to confuse you. An exact value can only be determined when diving fully into the opamp characteristics as actual input impedance will be determined by non-ideal behavior of the opamp.