of new issues, release of administrative guidance or the rendering of a court decision affecting a particular issue. We adjust the income tax provision in the period in which the facts that give rise to the revision become known. For additional information about income taxes, see Notes 1 and 9 of the Notes to the Consolidated Financial Statements.  

Defined Benefit Pension Plans  

     We sponsor defined benefit pension plans for our eligible employees and retirees. These plans are closed to new entrants and frozen for future benefit accruals. As of December 31, 2010, the unfunded benefit obligation for these plans recorded on our Consolidated Balance Sheet was $9.3 billion. During 2010, we contributed $728 million to these plans and recorded $367 million of expense in salaries and related costs on our Consolidated Statement of Operations. In 2011, we estimate we will contribute approximately $600 million to these plans and that our expense will be approximately $300 million. The most critical assumptions impacting our defined benefit pension plan obligations and expenses are the weighted average discount rate and the expected long-term rate of return on the assets.  

      Discount Rate. We determine our weighted average discount rate on our measurement date primarily by reference to annualized rates earned on high quality fixed income investments and yield-to-maturity analysis specific to our estimated future benefit payments. We used a weighted average discount rate of 5.69% and 5.93% at December 31, 2010 and 2009, respectively. Our weighted average discount rate for net periodic pension benefit cost in each of the past three years has varied from the rate selected on our measurement date, ranging from 5.93% to 7.19% between 2008 and 2010, due to remeasurements throughout the year.  

      Expected Long-Term Rate of Return. The expected long-term rate of return on the assets (currently approximately 9%) is based primarily on plan-specific investment studies using historical market returns and volatility data with forward looking estimates based on existing financial market conditions and forecasts. Modest excess return expectations versus some market indices are incorporated into the return projections based on the actively managed structure of the investment programs and their records of achieving such returns historically. We review our rate of return on plan asset assumptions annually. These assumptions are largely based on the asset category rate-of-return assumptions developed annually with our pension plan investment advisors; however, our annual investment performance for one particular year does not, by itself, significantly influence our evaluation. The investment strategy for our defined benefit pension plan assets is to utilize a diversified mix of global public and private equity portfolios, public and private fixed income portfolios, and private real estate and natural resource investments to earn a long-term investment return that meets or exceeds a 9% annualized return target.  

      Funding. Our funding obligations for qualified defined benefit plans are governed by the Employee Retirement Income Security Act. The