by the SOA, except that we project that the mortality rate improvements will normalize to an ultimate improvement rate of 0.75%, which is more closely aligned with the scale used by the United States Social Security Administration, and that the rate will normalize over a ten-year period. The projected benefit obligation (for defined benefit pension plans), and the accumulated postretirement benefit obligation (for postretirement plans), increased by approximately $580 million as a result of the revised mortality assumptions.

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 weighted-average 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

         (a) For detailed assumptions associated with our benefit plans, see Notes to Consolidated Financial Statements—Note 11B. Pension and Postretirement Benefit Plans and Defined Contribution Plans: Actuarial Assumptions.

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.

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. In January 2015, Pfizer made a voluntary contribution of approximately $1.0 billion to plan assets. In 2015, this contribution will be included in the plan asset balance for purposes of determining the expected rate of return on plan assets.

The following table illustrates the sensitivity of net periodic benefit costs to a 50 basis point decline in our assumption for the expected annual rate of return on plan assets, holding all other assumptions constant (in millions, pre-tax):

Increase in 2015 Net Periodic Benefit Change Costs

Assumption

Expected annual rate of return on plan assets 50 basis point decline $109

The actual return on plan assets resulted in an increase in our aggregate plan assets of approximately $1.9 billion during 2014.

Discount Rate Used to Measure Plan Obligations

The weighted-average discount rate used to measure the plan obligations for our U.S. defined benefit plans