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Income per Common Share (Tables) | 3 Months Ended
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Mar. 31, 2018
Earnings Per Share [Abstract] |
Summary of Earnings Per Common Share | 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 |
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share | 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 Tabular disclosure of securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) in the future that were not included in the computation of diluted EPS because to do so would increase EPS amounts or decrease loss per share amounts for the period presented, by antidilutive securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 + Details
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- Definition Tabular disclosure of an entity's basic and diluted earnings per share calculations, including a reconciliation of numerators and denominators of the basic and diluted per-share computations for income from continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 + Details
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