Idiom? Definition of idiom: "an expression whose meaning is not predictable from the usual meanings of its constituent elements." The meaning of "ways and means" can be ascertained from its components. I think it's just a compound and not an idiom.
Google «define "ways and means"» & google «idiom "ways and means"».
By the way, shame on you. You're asking other people to do your research for you. If you were in my class, that would be an automatic fail.
I hope this puts you on the right track.