pre_text: NON-GAAP FINANCIAL MEASURES Non-GAAP operating income, net income, and diluted EPS are non-GAAP financial measures which exclude the net tax impact of transfer of intangible properties, the net tax impact of the TCJA, and restructuring expenses. We believe these non-GAAP measures aid investors by providing additional insight into our operational performance and help clarify trends affecting our business. For comparability of reporting, management considers non-GAAP measures in conjunction with GAAP financial results in evaluating business performance. These non-GAAP financial measures presented should not be considered a substitute for, or superior to, the measures of financial performance prepared in accordance with GAAP. The following table reconciles our financial results reported in accordance with GAAP to non-GAAP financial results: * Not meaningful.
table: (In millions, except percentages and per share amounts) 2019 2018 2017 Percentage Change 2019 Versus 2018 Percentage Change 2018 Versus 2017
table: Operating income $42,959 $35,058 $  29,025 23% 21%
table: Net tax impact of transfer of intangible properties 0 0 0 * *
table: Net impact of the TCJA 0 0 0 * *
table: Restructuring expenses 0 0 306 * *
table: Non-GAAP operating income $42,959 $35,058 $ 29,331 23% 20%
table: Net income $39,240 $16,571 $ 25,489 137% (35)%
table: Net tax impact of transfer of intangible properties (2,567) 0 0 * *
table: Net tax impact of the TCJA 157 13,696 0
table: Restructuring expenses 0 0 243 * *
table: Non-GAAP net income $36,830 $30,267 $ 25,732 22% 18%
table: Diluted earnings per share $5.06 $2.13 $ 3.25 138% (34)%
table: Net tax impact of transfer of intangible properties (0.33) 0 0 * *
table: Net tax impact of the TCJA 0.02 1.75 0 * *
table: Restructuring expenses 0 0 0.04 * *
table: Non-GAAP diluted earnings per share $4.75 $3.88 $ 3.29 22% 18%
table: * not meaningful
question: Analyse this data from a financial earnings document. What was the average operating income for the 3 year period from 2017 to 2019?