That would be American billions?
Both - the UK has used the US '1 billion = 1,000 million' since 1974
Not a thing I shall lose sleep over

I do understand that to some it matters, I am part of the upper 50% of the world and thankful for that

but it's a very sobering thought when you consider how little money that really is these days. Unless there is 10k in the current account I am restless as you just never know what is going to pop up that needs covering and I have an aversion to borrowing money.