Question: How much detail should be given to trivial characters without overwriting?Answer:
You've pretty much answered your own question, as far as it can be answered in a general way.
It is a general rule in writing that you include the details necessary to tell the story and leave out everything else. So readers expect that the more they learn about a particular character and the more time they spend with that character, the more important that character must be. It's implicit. If the character is trivial, excessive detail is just distracting.
Of course, there are times when a character seems to be trivial when first introduced but later on plays, or is discovered to play, an important role. An example is the cliche from the mystery genre of having the butler be the murderer. It worked originally because no one in the British upper class paid close attention to butlers, so although the butler was ever present, he was overlooked as a potential suspect. But even in such stories, the reader expects to hear the butler's backstory (perhaps after the arrest) in order to make sense of the plot.
If the only reason a character exists is to contribute to the setting or atmosphere, serve as a red herring, or satisfy some point of logic (e.g. why isn't your Presidential candidate married?) a few key details may be all you need provide. The more important a character is to the story, the more details we expect to learn.
Unfortunately, I can't give an exact rule. Only you know your story. You have to decide how important a character is. And you may not know until the second or third draft. That's just how it is.
But at some point in the plannng, writing, or revising, you should develop a sense of how important a character is. Then you'll know whether to cut details that are not necessary or expand upon something that is.