Pension and Other Postretirement Plans We consider accounting for our U.S. and Canadian pension and other postretirement plans critical because management is required to make significant judgments about a number of actuarial assumptions, which include discount rates, expected return on plan assets, interest cost and mortality and retirement rates. Actuarial valuations are used in determining our benefit obligation and net periodic benefit cost. In the fourth quarter of 2020, we voluntarily changed our method of accounting for recognizing actuarial gains and losses and expected return on plan assets for our defined benefit pension and other postretirement benefit plans. Under the accounting method change, remeasurement of projected benefit obligation and plan assets are immediately recognized in earnings through net periodic benefit cost within Other Income (Expense) on the Consolidated Statements of Income (Loss), with pension and postretirement plans to be remeasured annually in the fourth quarter or on an interim basis as triggering events require remeasurement. Refer to Note 1 of the Consolidated Financial Statements in Item 8 of this report for further discussion. During 2020, we adopted the new MP-2020 mortality improvement scale in determining liability for the U.S. plans. The updated projection scale contributed to a slight decrease in the projected benefit obligation, partially offsetting the decrease in the discount rates in 2020, the net of which resulted in the increase of the projected benefit obligation as of December 31, 2020. During 2019, we adopted the new Pri-2012 mortality tables and MP-2019 mortality improvement projection scale in determining the liability for the U.S. plans. The updated mortality tables and projection scale, partially offset the decrease in the discount rates in 2019, the net of which resulted in the increase in the projected benefit obligation as of December 31, 2019. During 2018, we adopted the new MP-2018 mortality improvement projection scale in determining the liability for the U.S. plans. This updated scale, along with the change in the discount rates, contributed to a decrease in the projected benefit obligation as of December 31, 2018. Judgments and uncertainties  — We believe that the most significant assumptions related to our net periodic benefit cost are (1) the discount rate and (2) the expected return on plan assets offset by the actual return on assets, in each case as it relates to our U.S. pension plan. Our Canadian plan is not significant and the impact of changes in assumptions for that plan is not material. We determine our discount rates primarily based on high-quality, fixed-income investments and yield-to-maturity analyses specific to our estimated future benefit payments available as of the measurement date. Discount rates are reset annually on the measurement date to reflect current market conditions. To determine the discount rate for our U.S. pension and postretirement benefit plans, we use a bond matching approach to select specific bonds that would satisfy our projected benefit payments. We believe the bond matching approach reflects the process we would employ to settle our pension and postretirement benefit obligations. For our Canadian plans we use a third-party yield curve to develop our discount rates. The yield curve provides discount rates related to a dedicated high-quality bond portfolio whose cash flows extend beyond the current period, from which we choose a rate matched to the expected benefit payments required for each plan. Taking into consideration the factors noted above, our weighted-average discount rate used to determine benefit obligations was 2.56% at December 31, 2020. The weighted average expected return on plan assets for 2020 was 6.46%. The weighted average expected return on plan assets for 2021 is 4.65%. The expected return on plan assets was based on the Company's review of the asset allocation of the portfolio among various asset classes and represents an estimate of future experience for trust asset returns, reflects current and expected future market conditions along with recent changes to the asset allocations. The rate is net of investment and administrative expenses paid from the trust. In 2019, the Compensation Committee of the Board of Directors approved the termination of the Canadian pension plan. The Canadian plan was frozen effective December 31, 2020 at which date we ceased accruing benefits for all active members. The obligation is expected to be settled in 2022 with lump sum distributions and an annuity purchase. Under the new method of accounting for our pension and postretirement benefit plans, the market-related value of our assets will be equal to our fair value of plan assets and are remeasured in the fourth quarter with gains and losses recognized through the Consolidated Statements of Income. We do not expect our 2021 net periodic benefit income, which includes the effect of the market-related value of assets, to be materially different from our 2020 net periodic benefit income. See Note 9 of the Notes to the Consolidated Financial Statements in Item 8 of this report for details on changes in the pension benefit obligation and the fair value of plan assets. 56