NOTES TO CONSOLIDATED FINANCIAL STATEMENTS OF AMERICAN AIRLINES, INC. Benefit Obligations, Fair Value of Plan Assets and Funded Status 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, 2019 and 2018: $^{(1)}$  The 2019 and 2018 pension actuarial (gain) loss primarily relates to changes in American’s weighted average discount rate and mortality assumption and, in 2018, changes to American’s retirement rate assumptions. $^{(2)}$  The 2019 retiree medical and other postretirement benefits actuarial loss primarily relates to changes in American’s weighted average discount rate assumption and plan experience adjustments. The 2018 retiree medical and other postretirement benefits actuarial gain primarily relates to changes in American’s weighted average discount rate, medical trend and per capita claims assumptions. $^{(3)}$  During 2019, American contributed $1.2 billion to its defined benefit pension plans, including supplemental contributions of $444 million and a $780 million minimum required contribution. During 2018, American contributed $472 million to its defined benefit pension plans, including supplemental contributions of $433 million and a $39 million minimum required contribution. 142 Pension Benefits Retiree Medical and Other Postretirement Benefits 2019 2018 2019 2018 (In millions) Benefit obligation at beginning of period $ 16,282 $ 18,175 $ 837 $ 1,010 Service cost 2 2 3 5 Interest cost 699 670 33 35 Actuarial (gain) loss  (1), (2) 1,951 (1,905) 20 (132) Settlements (2 ) (4 ) — — Benefit payments (686) (659) (74) (81) Other — 3 5 — Benefit obligation at end of period $ 18,246 $ 16,282 $ 824 $ 837 Pension Benefits Retiree Medical and Other Postretirement Benefits 2019 2018 2019 2018 (In millions) Fair value of plan assets at beginning of period $ 10,001 $ 11,340 $ 225 $ 295 Actual return (loss) on plan assets 2,292 (1,148) 41 (24) Employer contributions  (3) 1,224 472 12 35 Settlements (2) (4) — — Benefit payments (686 ) (659 ) (74 ) (81 ) Fair value of plan assets at end of period $ 12,829 $ 10,001 $ 204 $ 225 Funded status at end of period $ (5,417 ) $ (6,281 ) $ (620 ) $ (612 )