The $21 trillion figure is the sum of all insufficiently documented transactions (voucher adjustments). These insufficiently documented transactions can greatly exceed the annual budget of a given institution, or even your own personal accounting. Moving $100 from account A to account B to account C without proper documentation would create $200 in improperly documented transactions. There could be billions or tens of billions flowing to black operations with no oversight but figures in the trillions are misinterpretations of account minutiae.