residential mortgage-backed securities at december 31 , 2012 , our residential mortgage-backed securities portfolio was comprised of $ 31.4 billion fair value of us government agency-backed securities and $ 6.1 billion fair value of non-agency ( private issuer ) securities . the agency securities are generally collateralized by 1-4 family , conforming , fixed-rate residential mortgages . the non-agency securities are also generally collateralized by 1-4 family residential mortgages . the mortgage loans underlying the non-agency securities are generally non-conforming ( i.e. , original balances in excess of the amount qualifying for agency securities ) and predominately have interest rates that are fixed for a period of time , after which the rate adjusts to a floating rate based upon a contractual spread that is indexed to a market rate ( i.e. , a 201chybrid arm 201d ) , or interest rates that are fixed for the term of the loan . substantially all of the non-agency securities are senior tranches in the securitization structure and at origination had credit protection in the form of credit enhancement , over- collateralization and/or excess spread accounts . during 2012 , we recorded otti credit losses of $ 99 million on non-agency residential mortgage-backed securities . all of the losses were associated with securities rated below investment grade . as of december 31 , 2012 , the noncredit portion of impairment recorded in accumulated other comprehensive income for non-agency residential mortgage- backed securities for which we have recorded an otti credit loss totaled $ 150 million and the related securities had a fair value of $ 3.7 billion . the fair value of sub-investment grade investment securities for which we have not recorded an otti credit loss as of december 31 , 2012 totaled $ 1.9 billion , with unrealized net gains of $ 114 million . 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 . substantially all of the securities are the most senior tranches in the subordination structure . there were no otti credit losses on commercial mortgage- backed securities during 2012 . asset-backed securities the fair value of the asset-backed securities portfolio was $ 6.5 billion at december 31 , 2012 and consisted of fixed-rate and floating-rate , private-issuer securities collateralized primarily by various consumer credit products , including residential mortgage loans , credit cards , automobile loans , and student loans . substantially all of the securities are senior tranches in the securitization structure and have credit protection in the form of credit enhancement , over-collateralization and/or excess spread accounts . we recorded otti credit losses of $ 11 million on asset- backed securities during 2012 . all of the securities are collateralized by first lien and second lien residential mortgage loans and are rated below investment grade . as of december 31 , 2012 , the noncredit portion of impairment recorded in accumulated other comprehensive income for asset-backed securities for which we have recorded an otti credit loss totaled $ 52 million and the related securities had a fair value of $ 603 million . for the sub-investment grade investment securities ( available for sale and held to maturity ) for which we have not recorded an otti loss through december 31 , 2012 , the fair value was $ 47 million , with unrealized net losses of $ 3 million . the results of our security-level assessments indicate that we will recover the cost basis of these securities . note 8 investment securities in the notes to consolidated financial statements in item 8 of this report provides additional information on otti losses and further detail regarding our process for assessing otti . if current housing and economic conditions were to worsen , and if market volatility and illiquidity were to worsen , or if market interest rates were to increase appreciably , the valuation of our investment securities portfolio could be adversely affected and we could incur additional otti credit losses that would impact our consolidated income statement . loans held for sale table 15 : loans held for sale in millions december 31 december 31 .
by what percentage did total residential mortgages increase from 2011 to 2012?
we stopped originating commercial mortgage loans held for sale designated at fair value in 2008 and continue pursuing opportunities to reduce these positions at appropriate prices . at december 31 , 2012 , the balance relating to these loans was $ 772 million , compared to $ 843 million at december 31 , 2011 . we sold $ 32 million in unpaid principal balances of these commercial mortgage loans held for sale carried at fair value in 2012 and sold $ 25 million in 2011 . the pnc financial services group , inc . 2013 form 10-k 49 .