What is the increase / (decrease) in the Operating (non-GAAP) expense and other (income) from 2018 to 2019?
{"($ in millions) -- For the year ended December 31:": {"2019": 2019.0, "2018": 2018.0, "Yr.-to-Yr. Percent/ Margin Change*": "Yr.-to-Yr. Percent/ Margin Change*"}, "($ in millions) -- Total consolidated expense and other (income)": {"2019": 26322.0, "2018": 25594.0, "Yr.-to-Yr. Percent/ Margin Change*": 2.8}, "Non-operating adjustments -- Amortization of acquired intangible assets": {"2019": -764.0, "2018": -437.0, "Yr.-to-Yr. Percent/ Margin Change*": 74.8}, "Non-operating adjustments -- Acquisition-related charges": {"2019": -409.0, "2018": -16.0, "Yr.-to-Yr. Percent/ Margin Change*": "NM"}, "Non-operating adjustments -- Non-operating retirement related (costs)/income": {"2019": -615.0, "2018": -1572.0, "Yr.-to-Yr. Percent/ Margin Change*": -60.9}, "Non-operating adjustments -- Operating (non-GAAP) expense and other (income)": {"2019": 24533.0, "2018": 23569.0, "Yr.-to-Yr. Percent/ Margin Change*": 4.1}, "Non-operating adjustments -- Total consolidated expense-to-revenue ratio": {"2019": 34.1, "2018": 32.2, "Yr.-to-Yr. Percent/ Margin Change*": 2.0}, "Non-operating adjustments -- Operating (non-GAAP) expense-to-revenue ratio": {"2019": 31.8, "2018": 29.6, "Yr.-to-Yr. Percent/ Margin Change*": 2.2}}
operating_expense_2019 = df["Non-operating adjustments -- Operating (non-GAAP) expense and other (income)"]["2019"]
operating_expense_2018 = df["Non-operating adjustments -- Operating (non-GAAP) expense and other (income)"]["2018"]
answer = operating_expense_2019 - operating_expense_2018