Acquisitions (Pro Forma Financial Information - Andeavor) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended																12 Months Ended
		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Sales and other operating revenues, excluding consumer excise taxes	[1],[2]																	$ 95,750
Sales and other operating revenue, including excise taxes	[2]																		$ 74,104	$ 63,277
Net income attributable to MPC		$ 951		$ 737		$ 1,055		$ 37		$ 2,016	[3]	$ 903		$ 483		$ 30		$ 2,780	$ 3,432	$ 1,174
Net income attributable to MPC per share – basic		$ 1.38	[4]	$ 1.63	[4]	$ 2.30	[4]	$ 0.08	[4]	$ 4.13	[4]	$ 1.79	[4]	$ 0.94	[4]	$ 0.06	[4]	$ 5.36	$ 6.76	$ 2.22
Net income attributable to MPC per share – diluted		$ 1.35	[4]	$ 1.62	[4]	$ 2.27	[4]	$ 0.08	[4]	$ 4.09	[4]	$ 1.77	[4]	$ 0.93	[4]	$ 0.06	[4]	$ 5.28	$ 6.70	$ 2.21
Andeavor
Business Acquisition [Line Items]
Sales and other operating revenues, excluding consumer excise taxes	[5]																	$ 131,695
Sales and other operating revenue, including excise taxes																			$ 117,549
Net income attributable to MPC																		$ 4,371	$ 4,832
Net income attributable to MPC per share – basic																		$ 8.44	$ 6.47
Net income attributable to MPC per share – diluted																		$ 8.31	$ 6.41

[1] The 2018 period reflects an election to present certain taxes on a net basis concurrent with our adoption of ASC 606.

[2] The 2018 period reflects an election to present certain taxes on a net basis concurrent with our adoption of ASU 2014-09, Revenue - Revenue from Contracts with Customers (“ASC 606”). See Notes 2 and 3 for further information.

[3] During the fourth quarter of 2017, we recorded a tax benefit of approximately $1.5 billion as a result of remeasuring certain deferred tax liabilities using the lower corporate tax rate enacted under the TCJA.

[4] The sum of the per-share amounts for the four quarters may not always equal the annual per-share amounts due to differences in the average number of shares outstanding during the respective periods.

[5] The 2018 period reflects an election to present certain taxes on a net basis concurrent with our adoption of ASC 606.