So General American English is exclusive by definition. Nevertheless, it is often described as “typical,” “neutral,” or some other slightly biased adjective. After reading numerous definitions of GenAm, however, I’d say the term describes a spectrum of accents rather than a single monolithic standard.
In the narrowest sense, the General American “heartland” is found in a tiny chunk of the midwest. This map, created by an astute Wikimedia Commons contributor (extrapolated from the work of renowned linguist William Labov), indicates where “classic GenAm” can be found. In this area, the accent is alleged to most closely resemble the standard phonetic description of General American: