content_image/140089.jpg content_image/140098.jpg content_image/140097.jpg
<img src='content_image/140089.jpg'>

The pension plan discount rate assumptions are evaluated annually in consultation with our outside actuarial advisers. Long-term interest rates on high quality corporate debt instruments are used to determine the discount rate. For our lar gest plans, discount rates are developed using a discounted bond portfolio analysis, with appropriate consideration given to defined benefit payment terms and duration of the liabilities. 

The expected rate of return on plan assets was selected on the basis of our long-term view of return and risk assumptions for major asset classes. We define long-term as forecasts that span at least the next ten years. Our long-term outlook is influenced by a combination of return expectations by individual asset class, actual historical experience and our diversified investment strategy. We consult with and consider the opinions of financial professionals in developing appropriate capital market assumptions. Return projections are also validated using a simulation model that incorporates yield curves, credit spreads and risk premiums to project long-term prospective returns. The appropriateness of the expected rate of return is assessed on an annual basis and revised if necessary . We have a high percentage of total assets in fixed income securities since the benefit accruals are frozen for all of our U.S. pension plans. Based on this assessment, we have selected a 7.00% expected return on asset assumption for 2015 for our U.S. plans, the same rate we used for 2014. 

The significant weighted-average assumptions used in the measurement of OPEB obligations at December 31 of each year and the net periodic benefit cost for each year are as follows: 

<img src='content_image/140098.jpg'>

The discount rate selection process was similar to the process used for the pension plans. Assumed health care cost trend rates have a significant ef fect on the health care obligation. To determine the trend rates, consideration is given to the plan design, recent experience and health care economics. 

A one-percentage-point change in assumed health care cost trend rates would have the following ef fects for 2014: 

<img src='content_image/140097.jpg'>

Estimated future benefit payments and contributions  — Expected benefit payments by our pension and OPEB plans for each of the next five years and for the period 2020 through 2024 are as follows: 

