The money supply, ie. the amount of money in existence, fluctuates. Obviously, paper money is only a small fraction of the total amount of money "stored" in checking acccounts, etc. Money is created through debt. If nobody is in debt, the amount of money in circulation is much lower otherwise.

Does anyone know how much of the money supply is government debt?

I always get dizzy when I try to understand the monetary system. It seems insane. It really shouldn't work at all.

If you want to get a headache, too, try reading http://en.wikipedia.org/wiki/Money_supply, http://en.wikipedia.org/wiki/Fractional_reserve_banking or watching Money as Debt.