It's actually not that much. Half the debt is such short term debt that it is already essentially cash equivalent. Most of the long term bonds have already been traded for shorter term notes. This has been the primary economic driving force of the last 5 years (ie a bond bubble). This is also why growth is struggling to hit 2%. This was the purpose behind Operation Twist. Driving down long bond rates = driving up the price = more money for bondholders to (hopefully) stimulate the economy. That didnt happen, because all they did was buy shares of AMZN, which does absolutely nothing for the economy, unless the income stream from the AMZN stock exceeds the income stream from the long bonds before their yields were driven down. Of course this cant and wont happen. Trading a stable bond yield for an uncertain (or nonexistent!) dividend yield is not a wise choice for very large pools of money. The end game of all this is Japan, where pretty much every bond is a zero yielding bond or on a trajectory to be a zero yielding bond. At that point, all the debt is monetized, it doesnt even need to be converted to cash. It essentially already is cash. Cash is simply a zero yield note with infinite duration.