The table below shows the maximum availability under revolving credit facilities, all of which were undrawn, as of December 31, 2018 (in millions): 146 NOTES TO CONSOLIDATED FINANCIAL STATEMENTS OF AMERICAN AIRLINES, INC. $^{(1)}$  Fleet restructuring expenses principally included accelerated depreciation and rent expense for aircraft and related equipment grounded or expected to be grounded earlier than planned. $^{(2)}$  Merger integration expenses included costs associated with integration projects, principally American's flight attendant, human resources and payroll, and technical operations systems. $^{(3)}$  Severance expenses primarily included costs associated with reductions of management and support staff team members. $^{(4)}$  Settlement of a private party antitrust lawsuit. See Note 10(e) - “ Private Party Antitrust Action Related to Passenger Capacity ” for further discussion. $^{(5)}$  Intangible asset impairment includes a non-cash charge to write-off American’s Brazil route authority as a result of the U.S.-Brazil open skies agreement. $^{(6)}$  Bankruptcy obligations that will be settled in shares of AAG common stock are marked-to-market based on AAG’s stock price. $^{(7)}$  Employee bonus expense included costs related to the $1,000 cash bonus and associated payroll taxes granted to mainline employees as of December 31, 2017 in recognition of the 2017 Tax Act. $^{(8)}$  Mark-to-market adjustments on equity investments relate to net unrealized losses primarily associated with American’s equity investments in China Southern Airlines and Mesa Air Group, Inc. $^{(9)}$  Income tax special items for 2018 included an $18 million charge related to an international income tax matter. $^{(10)}$  Impact of the 2017 Tax Act includes a $924 million non-cash charge to income tax expense to reflect the impact of lower corporate income tax rates on the Company’s deferred tax asset and liabilities resulting from the 2017 Tax Act, which reduced the federal corporate income tax rate from 35% to 21%. Long-term debt included in the consolidated balance sheets consisted of (in millions): 3. Debt December 31, 2018 2017 Secured 2013 Credit Facilities, variable interest rate of 4.26%, installments through 2025  (a) $ 1,825 $ 1,825 2014 Credit Facilities, variable interest rate of 4.39%, installments through 2021  (a) 1,215 728 April 2016 Credit Facilities, variable interest rate of 4.52%, installments through 2023  (a) 980 990 December 2016 Credit Facilities, variable interest rate of 4.46%, installments through 2023  (a) 1,225 1,238 Aircraft enhanced equipment trust certificates (EETCs), fixed interest rates ranging from 3.00% to 9.01%, averaging 4.21%, maturing from 2019 to 2029  (b) 11,648 11,881 Equipment loans and other notes payable, fixed and variable interest rates ranging from 2.34% to 8.48%, averaging 4.26%, maturing from 2019 to 2030  (c) 5,060 5,259 Special facility revenue bonds, fixed interest rates of 5.00%, maturing from 2019 to 2031 769 828 Other secured obligations — 1 Total long-term debt 22,722 22,750 Less: Total unamortized debt discount, premium and issuance costs 219 227 Less: Current maturities 2,466 1,980 Long-term debt, net of current maturities $ 20,037 $ 20,543