What was the change in Pension Plans in 2019 from 2018?
{"Pension plans": {"2019": 9.8, "2018": 11.3, "2017": 45.8}, "Other postretirement plans": {"2019": 1.8, "2018": 2.9, "2017": 2.6}, "Net periodic benefit costs": {"2019": 11.6, "2018": 14.2, "2017": 48.4}}
pension_plans_2019 = df["Pension plans"]["2019"]
pension_plans_2018 = df["Pension plans"]["2018"]
answer = pension_plans_2019 - pension_plans_2018