Operating Special Items, Net $^{(1)}$  Merger integration expenses included costs related to information technology, professional fees, re-branding of aircraft and airport facilities and training, and in 2016, also included costs related to alignment of labor union contracts and the launch of re-branded uniforms, both of which drove the $241 million year-over-year decrease in these expenses. $^{(3)}$  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. $^{(2)}$  Fleet restructuring expenses principally included accelerated depreciation and remaining lease payments for aircraft and related equipment grounded or expected to be grounded earlier than planned. $^{(4)}$  Bankruptcy obligations that will be settled in shares of AAG common stock are marked-to-market based on AAG’s stock price. American’s short-term investments in each period consisted of highly liquid investments that provided nominal returns. Interest income increased $111 million due to higher interest-bearing related party receivables from American’s parent company, AAG, as well as a 50 basis point increase in average yields in 2017 as compared to 2016. Interest expense, net increased $82 million in 2017 primarily due to higher outstanding debt as a result of aircraft financings associated with American’s fleet renewal program. Other nonoperating income, net in 2017 and 2016, principally included $138 million and $77 million, respectively, of non-service related pension and other postretirement benefit plan income, which reflects an increase in the expected return on pension plan assets in 2017 as compared to 2016. In 2017 and 2016, this income was offset in part by $22 million and $49 million, respectively, of net special charges associated with debt refinancings and extinguishments. American is part of the AAG consolidated income tax return. 64 Income Taxes Nonoperating Results Year Ended December 31, 2017 2016 (In millions) Merger integration expenses  (1) $ 273 $ 514 Fleet restructuring expenses  (2) 232 177 Employee 2017 Tax Act bonus expense  (3) 123 — Labor contract expenses 46 — Mark-to-market adjustments on bankruptcy obligations, net  (4) 27 25 Other operating charges (credits), net 11 (7) Total mainline operating special items, net 712 709 Regional operating special items, net 3 13 Total operating special items, net $ 715 $ 722 Year Ended December 31, Increase (Decrease) Percent Increase (Decrease) 2017 2016 (In millions, except percentage changes) Interest income $ 215 $ 104 $ 111 nm Interest expense, net (988) (906) (82) 9.1 Other income, net 123 18 105 nm Total nonoperating expense, net $ (650) $ (784) $ 134 (17.1)