Pass the abacus

Yesterday, apparently, British banks lost 17.5 billion pounds. Now, I don't know about anyone else but I simply can't come close to imagining 17.5 billion. Which leads me to ask.......
How much money is there in the entire world??
The US bailout plan is spoken of in billions as if we're all playing Monopoly (or Zimbabwe) where money isn't real.
And what had me worried, incase someone wise actually does know how much money there is, is that there are two different definitions of billion.
I looked it up.
Great Britain and most of the world used to refer to a billion as one million with six extra noughts. In other words the prefix bi despite it's other meanings means two. So 1 000 000 is one million and 1 000 000 000 000 is a billion.
USA and the scientific community (who knows where they live) have a different system, to them a million has six zeros, a billion has nine zeros and if you have a quadrillion (not a dance) its 1000 billion.
So, pray tell, did the banks lose 17 5000000000000 or 17 5000000000. This could severley impact on my budget if I get it wrong.