Additional information related to pension plans was as follows: Weighted-average assumptions used to determine defined benefit pension plan obligations were as follows: Weighted-average actuarial assumptions used to determine defined benefit pension plan net periodic benefit cost/(credit) were as follows: The yield on high quality corporate bonds matching the duration of the benefit obligations is used in determining the discount rate. The Citi Pension Discount curve is used in developing the discount rate for the U.S. plans. The expected return on plan assets assumption for each plan is based on management's expectations of long-term average rates of return to be achieved by the underlying investment portfolio. Several factors are considered in developing the expected return on plan assets, including long- term historical returns and input from external advisors. Individual asset class return forecasts were developed based upon market conditions, for example, price-earnings levels and yields and long-term growth expectations. The expected long-term rate of return is the weighted-average of the target asset allocation of each individual asset class. Actuarial gains and losses resulted from changes in actuarial assumptions (such as changes in the discount rate and revised mortality rates) and from differences between assumed and actual experience (such as differences between actual and expected return on plan assets). Actuarial losses in 2019 related to plan benefit obligations were primarily the result of decreases in discount rates. Actuarial gains in 2018 related to plan benefit obligations were primarily the result of increases in discount `rates. Gains and losses are amortized over the life expectancy of the plan participants for U.S. plans (26 years in 2020) and expected remaining service periods for most other plans to the extent they exceed 10% of the higher of the market-related value or the projected benefit obligation for each respective plan. Comprehensive medical and group life benefits are provided for substantially all legacy BMS U.S. retirees electing to participate in comprehensive medical and group life plans and to a lesser extent certain benefits for non-U.S. employees. The medical plan is contributory. Contributions are adjusted periodically and vary by date of retirement. The life insurance plan is noncontributory. Plan assets consist principally of fixed-income securities. Postretirement benefit plan obligations were $255 million and $253 million at December 31, 2019 and 2018, respectively, and the fair value of plan assets were $398 million and $331 million at December 31, 2019 and 2018, respectively. The weighted-average discount rate used to determine benefit obligations was 2.9% and 3.9% at December 31, 2019 and 2018, respectively. The net periodic benefit credits were not material. 96 Postretirement Benefit Plans Actuarial Assumptions December 31, Dollars in Millions 2019 2018 Pension plans with projected benefit obligations in excess of plan assets: Projected benefit obligation $ 1,652 $ 1,275 Fair value of plan assets 1,056 817 Pension plans with accumulated benefit obligations in excess of plan assets : Accumulated benefit obligation 1,417 1,181 Fair value of plan assets 875 757 December 31, 2019 2018 Discount rate 1.6 % 3.5 % Rate of compensation increase 1.3% 0.5% Year Ended December 31, 2019 2018 2017 Discount rate 3.2 % 3.1 % 3.5 % Expected long-term return on plan assets 4.5% 6.2% 7.0% Rate of compensation increase 0.5 % 0.5 % 0.5 %