an enhanced benefit under our defined contribution plan. In addition to the standard matching contribution by the Company, the enhanced benefit provides an automatic Company contribution for such eligible employees based on age and years of service. Also, on May 8, 2012, we announced to employees that as of January 1, 2018, Pfizer will transition its U.S. and Puerto Rico employees from its defined benefit plans to an enhanced defined contribution savings plan.

The accounting for benefit plans is highly dependent on actuarial estimates, assumptions and calculations, which result from a complex series of judgments about future events and uncertainties. The assumptions and actuarial estimates required to estimate the employee benefit obligations for the defined benefit and postretirement plans may include the discount rate; expected salary increases; certain employee-related factors, such as turnover, retirement age and mortality (life expectancy); and healthcare cost trend rates.

As of December 31, 2013, our Pension benefit obligations, net and our Postretirement benefit obligations, net declined, in the aggregate, by approximately $4.0 billion compared to December 31, 2012. The decline reflects, among other things, a significant increase in our discount rate assumptions, used in the measurement of the plan obligations, as well as the impact of a strong return on plan assets for plans with assets.

Our assumptions reflect our historical experiences and our judgment regarding future expectations that have been deemed reasonable by management. The judgments made in determining the costs of our benefit plans can materially impact our results of operations.

The following table provides the expected versus actual rate of return on plan assets and the discount rate used to measure the benefit obligations for our U.S. qualified pension plans and our international pension plans(a):

   U.S. Qualified Pension Plans

Expected annual rate of return on plan assets Actual annual rate of return on plan assets Discount rate used to measure the plan obligations

International Pension Plans

Expected annual rate of return on plan assets Actual annual rate of return on plan assets Discount rate used to measure the plan obligations

Expected Annual Rate of Return on Plan Assets

The assumptions for the expected annual rate of return on all of our plan assets reflect our actual historical return experience and our long- term assessment of forward-looking return expectations by asset classes, which is used to develop a weighted-average expected return based on the implementation of our targeted asset allocation in our respective plans (see Notes to Consolidated Financial Statements—Note 11D. Pension and Postretirement Benefit Plans and Defined Contribution Plans: Plan Assets for asset allocation ranges and actual asset allocations for 2013 and 2012).

The expected annual rate of return on plan assets for our U.S. plans and the majority of our international plans is applied to the fair value of plan assets at each year-end and the resulting amount is reflected in our net periodic benefit costs in the following year. Holding all other assumptions constant, the