. the company must also maintain qualified collateral as a percent of its advances , which varies based on the collateral type , and is further adjusted by the outcome of the most recent annual collateral audit and by fhlb 2019s internal ranking of the bank 2019s creditworthiness . these advances are secured by a pool of mortgage loans and mortgage-backed securities . at december 31 , 2011 and 2010 , the company pledged loans with a lendable value of $ 5.0 billion and $ 5