It would be fun to calculate the total debt of public + private worldwide. Do you know if anyone who has done the calculation?
The nominal aggregate derivative number is bullshit because it represents both sides of counter trades as if they were all one way. The real risk is not such a big deal as it is hedged and otherwise collateralized. If you want to read about aggregate debt of both private and public...you could go to the St. Louis fed and total up the public debt with the aggregate bank private asset debt...you could also look in up in Rhinehart and Rogoff's book, "This Time it is Different." Understand that public debt and private debt have dramatically different impacts on the real economy so I think when you aggregate the two you learn less about what is going on, not more.
http://www.usdebtclock.org/ http://www.usdebtclock.org/world-debt-clock.html Might help you get started.