[...] As a toddler I noticed her pronouncing "idea" with a trailing 'r' sound, and asked her where that 'r' came from. She got a bit touchy about it. [...]

Talk about getting touchy, a friend of mine years ago from Baltimore-way would always pronounce water as "wooter" -- not to rhyme with scooter but like wood-er.) So when I asked him why he spoke it that way and explained that "wat" is never spoken as "woot", he became annoyed and refused to discuss it (nor update his pronunciation...)

When I moved from NC to Cali in the 80s, I de-programmed most of my Southern accent before I got there. Since I was a radio DJ, once I started work in radio in CA, my on-air-personality co-workers ripped me apart, making fun of every minscule remaining shard of my old accent. Didn't bother me. Helped me finish that task. But now that I am back in NC, I can slip in and out of the two dialects easily.

A recent ex-singer for my current band hailed from Wisconsin, and while hard to describe, he also had a very distinct twang to specific words and phrases. My least favorite US accents would have to be Baltimore and Boston. John Waters worked wonders for the former, probably to the chagrin of all of Maryland, lol.

Yeah, there's a wealth of unique accents across our great land(s). US variations are more noticeable to us, I suspect, while many of the British variables sound very similar to our untrained Yank ears (although over the years, I have a better discernment for many GBR regions, just not so acutely as it is to their ears.)

In studying the British dialect, I am baffled by the rendition of the letter "r". Typically, I hear that word "saw" pronounced "soar"....

Today I traveled from Uxbridge to central London by bus and underground train and very little English was spoken on my journey both ways, so how you can tell a London accent is anyone guess

Of course, they use the New Uxbridge Dictionary there