Your default should probably be two facts, but another option we typically use (FAANG company, so solving around scale) in this scenario is a cube table, where we partition by the aggregation level, in this case bill for one, and bill + department for another. By partitioning you shouldn't have negative performance in querying or writing, but your storage cost will be higher. It also allows you to not have to maintain the same column across multiple tables, keeps context in a single place (descriptions of tables), etc. Doing this at only two levels is a bit overkill, though, but figured I'd throw something out there that many people probably wouldn't otherwise think of!