. at december 31 , 2012 and december 31 , 2011 , the unpaid principal balance outstanding of loans sold as a participant in these programs was $ 12.8 billion and $ 13.0 billion , respectively . the potential maximum exposure under the loss share arrangements was $ 3.9 billion at december 31 , 2012 and $ 4.0 billion at december 31 , 2011 . we maintain a reserve for estimated losses based upon our exposure