. commercial mortgage-backed securities the fair value of the non-agency commercial mortgage- backed securities portfolio was $ 5.9 billion at december 31 , 2012 and consisted of fixed-rate , private-issuer securities collateralized by non-residential properties , primarily retail properties , office buildings , and multi-family housing . the agency commercial mortgage-backed securities portfolio was $ 2.0 billion fair value at december 31 , 2012 consisting of multi-family housing