"Shuttered" seems to me to be normal US usage, but I'd never heard "idled" used like that. It seems especially inapt for auto workers, given that it's car engines that are usually idled.

We use both "let go" and "fire," but they mean different things -- if you have your job taken away due to some specific reason you supposedly weren't doing it right, that's being fired, while being "let go" implies they couldn't afford to keep you on, nothing personal. (Anyone else remember Dustin Hoffman in Kramer vs. Kramer protesting indignantly that he was not fired, he was let go?)