Description of the Business and Basis of Presentation	9 Months Ended
Sep. 30, 2015
Accounting Policies [Abstract]
Description of the Business and Basis of Presentation	Description of the Business and Basis of Presentation Description of the Business—MPLX LP is a fee-based, growth-oriented master limited partnership formed to own, operate, develop and acquire pipelines and other midstream assets related to the transportation and storage of crude oil, refined products and other hydrocarbon-based products. As of September 30, 2015, our assets consisted of a 99.5 percent indirect interest in a network of common carrier crude oil and product pipeline systems and associated storage assets in the Midwest and Gulf Coast regions of the United States. We also own a 100 percent interest in a butane cavern in Neal, West Virginia with approximately one million barrels of natural gas liquids storage capacity. Our operations consist of one reportable segment. Basis of Presentation—Our financial position, results of operations and cash flows consist of consolidated MPLX LP activities and balances. All significant intercompany transactions and accounts have been eliminated. The accompanying interim consolidated financial statements are unaudited; however, in the opinion of our management, these statements reflect all adjustments necessary for a fair statement of the results for the periods reported. All such adjustments are of a normal, recurring nature unless otherwise disclosed. These interim consolidated financial statements, including the notes, have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission(“SEC”) applicable to interim period financial statements and do not include all of the information and disclosures required by accounting principles generally accepted in the United States (“U.S. GAAP”) for complete financial statements. These interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2014. The results of operations for the three months and nine months ended September 30, 2015 are not necessarily indicative of the results to be expected for the full year. In preparing our consolidated statements of equity, net income attributable to MPLX LP is allocated to unitholders in accordance with their respective ownership percentages. However, when distributions related to the incentive distribution rights are made, earnings equal to the amount of those distributions are first allocated to the general partner before the remaining earnings are allocated to the unitholders based on their respective ownership percentages. The allocation of net income attributable to MPLX LP for purposes of calculating net income per limited partner unit is described in Note 5.

Description of the Business and Basis of Presentation

Description of the Business—MPLX LP is a fee-based, growth-oriented master limited partnership formed to own, operate, develop and acquire pipelines and other midstream assets related to the transportation and storage of crude oil, refined products and other hydrocarbon-based products. As of September 30, 2015, our assets consisted of a 99.5 percent indirect interest in a network of common carrier crude oil and product pipeline systems and associated storage assets in the Midwest and Gulf Coast regions of the United States. We also own a 100 percent interest in a butane cavern in Neal, West Virginia with approximately one million barrels of natural gas liquids storage capacity.

Our operations consist of one reportable segment.

Basis of Presentation—Our financial position, results of operations and cash flows consist of consolidated MPLX LP activities and balances. All significant intercompany transactions and accounts have been eliminated.

The accompanying interim consolidated financial statements are unaudited; however, in the opinion of our management, these statements reflect all adjustments necessary for a fair statement of the results for the periods reported. All such adjustments are of a normal, recurring nature unless otherwise disclosed. These interim consolidated financial statements, including the notes, have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission(“SEC”) applicable to interim period financial statements and do not include all of the information and disclosures required by accounting principles generally accepted in the United States (“U.S. GAAP”) for complete financial statements.

These interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2014. The results of operations for the three months and nine months ended September 30, 2015 are not necessarily indicative of the results to be expected for the full year.

In preparing our consolidated statements of equity, net income attributable to MPLX LP is allocated to unitholders in accordance with their respective ownership percentages. However, when distributions related to the incentive distribution rights are made, earnings equal to the amount of those distributions are first allocated to the general partner before the remaining earnings are allocated to the unitholders based on their respective ownership percentages. The allocation of net income attributable to MPLX LP for purposes of calculating net income per limited partner unit is described in Note 5.