The old Fluke 8060 series had two low DC ranges (2 V and 0.2 V full scale) that had 1 Gohm guaranteed and 10 Gohm most of the time.
There was another Fluke model that I cannot remember now that had the 100 M ohm in the higher voltage scales.
All of these impedances are shunted by 100 pF of capacitance which drags the impedance down below 1 M in the audio range.
Also, using a high impedance meter is not always a good thing. When measuring power circuits you can get fooled with a high impedance meter. I once chased my tail for an hour with a wall mounted power supply. The strip extension socket measured full AC voltage, the output of the supply measured full voltage, but the battery charger it powered showed no charging of the battery. What was going on was the on-off switch on the power strip had been put to off. There was enough open circuit switch capacitance for the meter to measure full voltage. The DC supply was just a transformer-rectifier-shunt capacitor. There was enough leakage current to charge the capacitor. had I used an analog meter with a 50 microamp draw, I would not have been fooled.