pre_text: 2016 Collective Bargaining Negotiations During 2016, we adopted changes to our defined benefit pension plans and other postretirement benefit plans to reflect the agreed upon terms and conditions of the collective bargaining agreements ratified in June 2016. The impact includes a net increase to Accumulated other comprehensive income of $2.9 billion (net of taxes of $1.8 billion). The amount recorded in Accumulated other comprehensive income will be reclassified to net periodic benefit cost on a straight-line basis over the average remaining service period of the respective plans’ participants, which, on a weighted-average basis, is 12.2 years for defined benefit pension plans and 7.8 years for other postretirement benefit plans. The above-noted reclassification resulted in a decrease to net periodic benefit cost and increase to pre-tax income of approximately $658 million during 2019, 2018 and 2017, respectively. Information for pension plans with an accumulated benefit obligation in excess of plan assets follows: Information for pension plans with an accumulated benefit obligation in excess of plan assets follows:
table: (dollars in millions)
table: At December 31, 2019 2018
table: Projected benefit obligation $ 21,190 $ 19,510
table: Accumulated benefit obligation 21,134 19,461
table: Fair value of plan assets 19,388 17,757
question: Analyse this data from a financial earnings document. What was the average accumulated benefit obligation for 2018 and 2019?