Benefit Obligations, Fair Value of Plan Assets and Funded Status NOTES TO CONSOLIDATED FINANCIAL STATEMENTS OF AMERICAN AIRLINES GROUP INC. The following tables provide a reconciliation of the changes in the pension and retiree medical and other postretirement benefits obligations, fair value of plan assets and a statement of funded status as of December 31, 2018 and 2017: $^{(1)}$  The December 31, 2018 and 2017 pension actuarial (gain) loss primarily relates to changes in our weighted average discount rate and mortality assumptions and, in 2018, changes to our retirement rate assumptions. $^{(2)}$  The December 31, 2018 and 2017 retiree medical and other postretirement benefits actuarial (gain) loss primarily relates to weighted average discount rate assumption changes and, in 2018, changes to our medical trend and per capita claim assumptions. $^{(3)}$  During 2018, we contributed $475 million to our defined benefit pension plans, including supplemental contributions of $433 million in addition to a $42 million minimum required contribution. During 2017, we contributed $286 million to our defined benefit pension plans, including supplemental contributions of $261 million in addition to a $25 million minimum required contribution. Pension Benefits Retiree Medical and  Other Postretirement Benefits 2018 2017 2018 2017 (In millions) Benefit obligation at beginning of period $ 18,275 $ 17,238 $ 1,011 $ 991 Service cost 3 2 5 4 Interest cost 674 721 35 39 Actuarial (gain) loss  (1) (2) (1,910) 1,016 (133) 49 Settlements (4 ) (4 ) — — Benefit payments (662) (726) (81) (80) Other 2 28 — 8 Benefit obligation at end of period $ 16,378 $ 18,275 $ 837 $ 1,011 Fair value of plan assets at beginning of period $ 11,395 $ 10,017 $ 295 $ 266 Actual return on plan assets (1,151) 1,797 (24) 37 Employer contributions  (3) 475 286 35 72 Settlements (4) (4) — — Benefit payments (662 ) (726 ) (81 ) (80 ) Other — 25 — — Fair value of plan assets at end of period $ 10,053 $ 11,395 $ 225 $ 295 Funded status at end of period $ (6,325) $ (6,880) $ (612) $ (716) 112