Every American has an accent. Perhaps you don’t hear Kansas/Chicago and other Midwestern accents but I do. How else do actors learn to portray characters from these various locales? I have a New York accent although slightly modified unless I want to make a New York point.
Yes, Americans speak American English. I didn't include Kansas, as they have Southern inflection.
All the rest I mentioned speak properly, according to dictionary pronunciation rules. New Yorkers and New Englanders do not.
Broadcasters either have or learn the Midwestern speech pattern. I would say that despite everything I hate about Hitlary...she has no accent.