as LAITHKHRESHEH said, it depends on the CPU, but id say almost 0ºC is a nice temperature lol... some have the cold bug which is a rediculous thing to exist lol. with this i mean to say keep it as cool as you can... over 70 as he said is way to much, but id say around 30-40 is a nice idle temperature... if you can keep it even cooler, your CPU will only thank you by working a few more years 😉