What was the increase / (decrease) in revenue from 2018 to 2019?
{"($ and shares in millions except per share amounts) -- For the year ended December 31:": {"2019": 2019.0, "2018": 2018.0, "Yr.-to-Yr. Percent/Margin Change**": "Yr.-to-Yr. Percent/Margin Change**"}, "($ and shares in millions except per share amounts) -- Revenue": {"2019": 77147.0, "2018": 79591.0, "Yr.-to-Yr. Percent/Margin Change**": -3.1}, "($ and shares in millions except per share amounts) -- Gross profit margin": {"2019": 47.3, "2018": 46.4, "Yr.-to-Yr. Percent/Margin Change**": 0.9}, "($ and shares in millions except per share amounts) -- Total expense and other (income)": {"2019": 26322.0, "2018": 25594.0, "Yr.-to-Yr. Percent/Margin Change**": 2.8}, "($ and shares in millions except per share amounts) -- Income from continuing operations before income taxes": {"2019": 10166.0, "2018": 11342.0, "Yr.-to-Yr. Percent/Margin Change**": -10.4}, "($ and shares in millions except per share amounts) -- Provision for income taxes from continuing operations": {"2019": 731.0, "2018": 2619.0, "Yr.-to-Yr. Percent/Margin Change**": -72.1}, "($ and shares in millions except per share amounts) -- Income from continuing operations": {"2019": 9435.0, "2018": 8723.0, "Yr.-to-Yr. Percent/Margin Change**": 8.2}, "($ and shares in millions except per share amounts) -- Income from continuing operations margin": {"2019": 12.2, "2018": 11.0, "Yr.-to-Yr. Percent/Margin Change**": 1.3}, "($ and shares in millions except per share amounts) -- Net income": {"2019": 9431.0, "2018": 8728.0, "Yr.-to-Yr. Percent/Margin Change**": 8.1}, "($ and shares in millions except per share amounts) -- Earnings per share from continuing operationsassuming dilution": {"2019": 10.57, "2018": 9.51, "Yr.-to-Yr. Percent/Margin Change**": 11.1}, "($ and shares in millions except per share amounts) -- Weighted-average shares outstandingassuming dilution": {"2019": 892.8, "2018": 916.3, "Yr.-to-Yr. Percent/Margin Change**": -2.6}, "($ and shares in millions except per share amounts) -- Assets++": {"2019": 152186.0, "2018": 123382.0, "Yr.-to-Yr. Percent/Margin Change**": 23.3}, "($ and shares in millions except per share amounts) -- Liabilities++": {"2019": 131202.0, "2018": 106452.0, "Yr.-to-Yr. Percent/Margin Change**": 23.2}, "($ and shares in millions except per share amounts) -- Equity++": {"2019": 20985.0, "2018": 16929.0, "Yr.-to-Yr. Percent/Margin Change**": 24.0}}
revenue_2019 = df["($ and shares in millions except per share amounts) -- Revenue"]["2019"]
revenue_2018 = df["($ and shares in millions except per share amounts) -- Revenue"]["2018"]
answer = revenue_2019 - revenue_2018