How much less was the total margin in 2019 then in 2018?
{"Services Revenues: -- Americas": {"2019": 1576, "Actual": -5, "Constant": -3, "2018": 1654}, "Services Revenues: -- EMEA": {"2019": 1021, "Actual": -2, "Constant": 2, "2018": 1046}, "Services Revenues: -- Asia Pacific": {"2019": 643, "Actual": -7, "Constant": -4, "2018": 695}, "Services Revenues: -- Total revenues": {"2019": 3240, "Actual": -5, "Constant": -2, "2018": 3395}, "Services Revenues: -- Total Expenses (1)": {"2019": 2703, "Actual": -1, "Constant": 2, "2018": 2729}, "Services Revenues: -- Total Margin": {"2019": 537, "Actual": -19, "Constant": -18, "2018": 666}, "Services Revenues: -- Total Margin %": {"2019": 17, "Actual": "", "Constant": "", "2018": 20}, "% Revenues by Geography: -- Americas": {"2019": 49, "Actual": "", "Constant": "", "2018": 49}, "% Revenues by Geography: -- EMEA": {"2019": 31, "Actual": "", "Constant": "", "2018": 31}, "% Revenues by Geography: -- Asia Pacific": {"2019": 20, "Actual": "", "Constant": "", "2018": 20}}
total_margin_2018 = df["Services Revenues: -- Total Margin"]["2018"]
total_margin_2019 = df["Services Revenues: -- Total Margin"]["2019"]
answer = total_margin_2018 - total_margin_2019