What was the change in diluted earnings per common share between 2018 and 2019?
{"Numerator: -- Consolidated net income": {"2019": 1503.0, "2018": 1848.0, "2017": 273.0}, "Denominator: -- Denominator for basic earnings per common shareweighted-average common shares outstanding": {"2019": 767.0, "2018": 762.0, "2017": 754.0}, "Denominator: -- Effect of dilutive stock options and awards under the treasury stock method": {"2019": 4.0, "2018": 9.0, "2017": 12.0}, "Denominator: -- Denominator for diluted earnings per common shareweighted-average common shares outstanding plus dilutive common shares under the treasury stock method": {"2019": 771.0, "2018": 771.0, "2017": 766.0}, "Denominator: -- Basic earnings per common share": {"2019": 1.96, "2018": 2.43, "2017": 0.36}, "Denominator: -- Diluted earnings per common share": {"2019": 1.95, "2018": 2.4, "2017": 0.36}}
denominator_2019 = df["Denominator: -- Diluted earnings per common share"]["2019"]
denominator_2018 = df["Denominator: -- Diluted earnings per common share"]["2018"]
answer = denominator_2019 - denominator_2018