The following table summarizes the 2¼% Notes information (in millions, except years, percentages, conversion rate, and conversion price): The Company's defined benefit pension plan future benefit accrual was discontinued in 2009. As of December 31, 2020, the assets, projected benefit obligations, and unfunded pension obligation were $957.0 million, $1,381.5 million, and $424.5 million, respectively. In 2021, the Company expects to make cash contributions of approximately $94 million to its tax-qualified defined benefit pension plan. The Company is generally able to recover contributions related to its tax-qualified defined benefit pension plan as allowable costs on its U.S. government contracts, but there are differences between when the Company contributes to its tax-qualified defined benefit pension plan under pension funding rules and when it is recoverable under Cost Accounting Standards ("CAS"). During 2020, the Company made cash contributions of $14.1 million and used $28.0 million of prepayment credits to fund its tax- qualified defined benefit pension plan. The funded status of the Company's tax-qualified pension plan may be adversely affected by the investment experience of the plan's assets, by any changes in U.S. law and by changes in the statutory interest rates used by tax-qualified pension plans in the U.S. to calculate funding requirements. Accordingly, if the performance of the plan's assets does not meet assumptions, if there are changes to income tax regulations or other applicable law, or if other actuarial assumptions are modified, future contributions to the underfunded pension plans could be higher than the Company expects. The Company provides medical and life insurance benefits to certain eligible retired employees, with varied coverage by employee group. Generally, employees hired after January 1, 1997, are not eligible for retiree medical and life insurance benefits. The medical benefit plan provides for cost sharing between the Company and its retirees in the form of retiree contributions, deductibles, and coinsurance. Medical and life insurance benefit obligations are unfunded. Medical and life insurance benefit cash payments for eligible retired employees are recoverable from the Company’s U.S. government contracts. The Company sponsors a defined contribution 401(k) plan and participation in the plan is available to all employees. The Company makes matching contributions in cash equal to 100% of the first 3% of the participants’ compensation contributed and 50% of the next 3% of the compensation contributed. The cost of the 401(k) plan was $21.8 million, $21.4 million, and $22.2 million in 2020, 2019, and 2018, respectively. The following table summarizes the balance sheet impact of the Company’s pension benefits and medical and life insurance benefits. Pension benefits include the consolidated tax-qualified plan and the unfunded non-qualified plan for benefits 63 b. Plan Results Defined Contribution 401(k) Benefits Medical and Life Insurance Benefits Pension Benefits a. Plan Descriptions Note 7. Retirement Benefits  Based on the Company's closing stock price of $52.85 on December 31, 2020, the if-converted value of the 2¼% Notes exceeded the aggregate principal amount of the 2¼% Notes by $309.8 million. The following table presents the interest expense components for the 2¼% Notes: As of December 31, 2020 2019 Carrying value, long-term $ 271.6  $ 263.0  Unamortized discount and deferred financing costs 28.4  37.0  Principal amount $ 300.0  $ 300.0  Carrying amount of equity component, net of equity issuance costs $ 54.5  $ 54.5  Remaining amortization period (years) 3.0 4.0 Effective interest rate 5.8  % 5.8  % Conversion rate (shares of common stock per $1,000 principal amount) 38.4615 38.4615 Conversion price (per share of common stock) $ 26.00  $ 26.00  Year Ended December 31, 2020 2019 2018 (In millions) Interest expense-contractual interest $ 6.8  $ 6.8  $ 6.8  Interest expense-amortization of debt discount 7.9  7.5  7.1  Interest expense-amortization of deferred financing costs 0.6  0.6  0.6 