I have a paragraph style for numbered lists with rule below set to text width. But the rule doesn't extend to the left below the numbers. Is there a way to do this automatically without having to set negative left indents for each one? There are 80+ list items and since I'm not using a monospaced font, the rule would need to be slightly different lengths throughout.
You should do it with negative values.
Make your numbered list with paragraph styles, set up the hanging intent with left inset and first line negative value.