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Income per Common Share | 3 Months Ended
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Mar. 31, 2018
Earnings Per Share [Abstract] |
Income per Common Share | Income per Common Share We compute basic earnings per share by dividing net income attributable to MPC by the weighted average number of shares of common stock outstanding. Diluted income per share assumes exercise of certain stock-based compensation awards, provided the effect is not anti-dilutive. MPC grants certain incentive compensation awards to employees and non-employee directors that are considered to be participating securities. Due to the presence of participating securities, we have calculated our earnings per share using the two-class method.
| Three Months Ended March 31,
(In millions, except per share data) | 2018 |  | 2017
Basic earnings per share: |  |  |
Allocation of earnings: |  |  |
Net income attributable to MPC | $ | 37 |  |  | $ | 30 |
Income allocated to participating securities | — |  |  | — |
Income available to common stockholders – basic | $ | 37 |  |  | $ | 30 |
Weighted average common shares outstanding | 476 |  |  | 525 |
Basic earnings per share | $ | 0.08 |  |  | $ | 0.06 |
Diluted earnings per share: |  |  |
Allocation of earnings: |  |  |
Net income attributable to MPC | $ | 37 |  |  | $ | 30 |
Income allocated to participating securities | — |  |  | — |
Income available to common stockholders – diluted | $ | 37 |  |  | $ | 30 |
Weighted average common shares outstanding | 476 |  |  | 525 |
Effect of dilutive securities | 4 |  |  | 5 |
Weighted average common shares, including dilutive effect | 480 |  |  | 530 |
Diluted earnings per share | $ | 0.08 |  |  | $ | 0.06 |
The following table summarizes the shares that were anti-dilutive and, therefore, were excluded from the diluted share calculation.
| Three Months Ended March 31,
(In millions) | 2018 |  | 2017
Shares issued under stock-based compensation plans | — |  |  | 2 |

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- Definition The entire disclosure for earnings per share. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -URI http://asc.fasb.org/topic&trid=2144383 + Details
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