valuation techniques 2013 cash equivalents are mostly comprised of short-term money-market instruments and are valued at cost , which approximates fair value . u.s . equity securities and international equity securities categorized as level 1 are traded on active national and international exchanges and are valued at their closing prices on the last trading day of the year . for u.s . equity securities and international equity securities not traded on an active exchange , or if the closing price is not available , the trustee obtains indicative quotes from a pricing vendor , broker , or investment manager . these securities are categorized as level 2 if the custodian obtains corroborated quotes from a pricing vendor or categorized as level 3 if the custodian obtains uncorroborated quotes from a broker or investment manager . commingled equity funds are public investment vehicles valued using the net asset value ( nav ) provided by the fund manager . the nav is the total value of the fund divided by the number of shares outstanding . commingled equity funds are categorized as level 1 if traded at their nav on a nationally recognized securities exchange or categorized as level 2 if the nav is corroborated by observable market data ( e.g. , purchases or sales activity ) . fixed income securities categorized as level 2 are valued by the trustee using pricing models that use verifiable observable market data ( e.g . interest rates and yield curves observable at commonly quoted intervals ) , bids provided by brokers or dealers , or quoted prices of securities with similar characteristics . private equity funds , real estate funds , hedge funds , and fixed income securities categorized as level 3 are valued based on valuation models that include significant unobservable inputs and cannot be corroborated using verifiable observable market data . valuations for private equity funds and real estate funds are determined by the general partners , while hedge funds are valued by independent administrators . depending on the nature of the assets , the general partners or independent administrators use both the income and market approaches in their models . the market approach consists of analyzing market transactions for comparable assets while the income approach uses earnings or the net present value of estimated future cash flows adjusted for liquidity and other risk factors . commodities categorized as level 1 are traded on an active commodity exchange and are valued at their closing prices on the last trading day of the year . commodities categorized as level 2 represent shares in a commingled commodity fund valued using the nav , which is corroborated by observable market data . contributions and expected benefit payments we generally determine funding requirements for our defined benefit pension plans in a manner consistent with cas and internal revenue code rules . in 2012 , we made contributions of $ 3.6 billion related to our qualified defined benefit pension plans . we plan to make contributions of approximately $ 1.5 billion related to the qualified defined benefit pension plans in 2013 . in 2012 , we made contributions of $ 235 million related to our retiree medical and life insurance plans . we expect no required contributions related to the retiree medical and life insurance plans in 2013 . the following table presents estimated future benefit payments , which reflect expected future employee service , as of december 31 , 2012 ( in millions ) : .
what is the percentage change in common stock held by defined contribution plans from 2011 to 2012?
defined contribution plans we maintain a number of defined contribution plans , most with 401 ( k ) features , that cover substantially all of our employees . under the provisions of our 401 ( k ) plans , we match most employees 2019 eligible contributions at rates specified in the plan documents . our contributions were $ 380 million in 2012 , $ 378 million in 2011 , and $ 379 million in 2010 , the majority of which were funded in our common stock . our defined contribution plans held approximately 48.6 million and 52.1 million shares of our common stock as of december 31 , 2012 and 2011. .