SLANG: Nonstandard vocabulary of a given culture or subculture. In other words, slang is typically a nonstandard word, not a phrase as is an idiom.
Slang would include words like pooped, to down a drink, boob-tube, threads, bonkers, basket case, to name a few. Slang words may or may not have alternative literal meanings. They may be "made up" words.
IDIOM: A phrase that is commonly understood in a given culture or subculture to have a meaning different from its literal meaning. A good example of this is "to bend over backwards." This phrase is commonly understood in our culture to mean "to exert an enormous effort in order to accomplish something." The literal meaning, however, is the physical act it describes, of which few may actually be capable of doing!
The following paragraph would surely go over the head of the average nonnative speaker, yet the terms and expressions are certainly common in the business:
"I don't know who blew the whistle on Bernie, the paper pusher in accounting, but he just got called on the carpet by the big wigs for calling in sick again. If he doesn't pull it together soon, he's gonna get canned, and cush jobs like his don't grow on trees!"
Sports jargon is particularly widespread in business since sports permeate American culture. This may also be related to the fact that both sports and business in the past have been predominantly influenced by men. Nothing has shaped the language of business more than sports, and not just one sport:
BASEBALL: to be home free, to come out of left field, to be in the ball park, to be out of someone's league, to pitch ideas, that's one strike against him/her.
BOATING: to be on an even keel, each man for himself, to go down with the ship, to shape up or ship out, to be smooth sailing.
BOXING: to go a few rounds with someone, to be a heavyweight, to be a lightweight, to hit below the belt....