Acquisitions and Investments	3 Months Ended
Mar. 31, 2018
Business Combinations [Abstract]
Acquisitions and Investments	Acquisitions and Investments Acquisition of Ozark Pipeline On March 1, 2017, MPLX acquired the Ozark pipeline from Enbridge Pipelines (Ozark) LLC for approximately $219 million, including purchase price adjustments made in the second quarter of 2017. Based on the fair value of assets acquired and liabilities assumed at the acquisition date, the final purchase price was primarily allocated to property, plant and equipment. The Ozark pipeline is a 433-mile, 22-inch crude oil pipeline originating in Cushing, Oklahoma, and terminating in Wood River, Illinois, capable of transporting approximately 230 mbpd. We account for the Ozark pipeline within the Midstream segment. Assuming the acquisition of the Ozark pipeline had occurred on January 1, 2016, the consolidated pro forma results would not have been materially different from reported results. Investment in Pipeline Company On February 15, 2017, MPLX acquired a partial, indirect equity interest in the Dakota Access Pipeline (“DAPL”) and Energy Transfer Crude Oil Company Pipeline (“ETCOP”) projects, collectively referred to as the Bakken Pipeline system, through a joint venture with Enbridge Energy Partners L.P. (“Enbridge Energy Partners”). The Bakken Pipeline system is capable of transporting more than 520 mbpd of crude oil from the Bakken/Three Forks production area in North Dakota to the Midwest through Patoka, Illinois and ultimately to the Gulf Coast. MPLX contributed $500 million of the $2 billion purchase price paid by the joint venture, MarEn Bakken Company LLC (“MarEn Bakken”), to acquire a 36.75 percent indirect equity interest in the Bakken Pipeline system from Energy Transfer Partners, L.P. (“ETP”) and Sunoco Logistics Partners, L.P. (“SXL”). MPLX holds, through a subsidiary, a 25 percent interest in MarEn Bakken, which equates to an approximate 9.2 percent indirect equity interest in the Bakken Pipeline system. We account for the investment in MarEn Bakken as part of our Midstream segment using the equity method of accounting. Formation of Gathering and Processing Joint Venture Effective January 1, 2017, MPLX and Antero Midstream formed a joint venture, Sherwood Midstream LLC (“Sherwood Midstream”), to support the development of Antero Resources Corporation’s Marcellus Shale acreage in West Virginia. MPLX has a 50 percent ownership interest in Sherwood Midstream. In connection with this transaction, MPLX contributed certain gas processing plants currently under construction at the Sherwood Complex with a fair value of approximately $134 million and cash of approximately $20 million. Antero Midstream made an initial capital contribution of approximately $154 million. Also effective January 1, 2017, MPLX converted all of its ownership interests in MarkWest Ohio Fractionation Company, L.L.C. (“Ohio Fractionation”), a previously wholly-owned subsidiary, to Class A Interests and amended its LLC Agreement to create Class B-3 Interests, which were sold to Sherwood Midstream for $126 million in cash. The Class B-3 Interests provide Sherwood Midstream with the right to fractionation revenue and the obligation to pay expenses related to 20 mbpd of capacity in the Hopedale 3 fractionator. Effective January 1, 2017, MPLX and Sherwood Midstream formed a joint venture, Sherwood Midstream Holdings LLC (“Sherwood Midstream Holdings”), for the purpose of owning, operating and maintaining all of the shared assets for the benefit of and use in the operation of the gas plants and other assets owned by Sherwood Midstream and the gas plants and deethanization facilities owned by MPLX. MPLX contributed certain real property, equipment and facilities with a fair value of approximately $209 million to Sherwood Midstream Holdings in exchange for a 79 percent initial ownership interest. Sherwood Midstream contributed cash of approximately $44 million to Sherwood Midstream Holdings in exchange for a 21 percent ownership interest. MPLX has a 10.5 percent indirect interest in Sherwood Midstream Holdings through its ownership in Sherwood Midstream. The net book value of the contributed assets was approximately $203 million. The contribution was determined to be an in-substance sale of real estate. As such, MPLX only recognized a gain for the portion attributable to Antero Midstream’s indirect interest of approximately $2 million. During the three months ended March 31, 2018, MarkWest Liberty Midstream sold to Sherwood Midstream 6 percent of their equity ownership in Sherwood Midstream Holdings for $15 million. We account for our direct interests in Sherwood Midstream and Sherwood Midstream Holdings as part of our Midstream segment using the equity method of accounting. We continue to consolidate Ohio Fractionation and have recognized a noncontrolling interest for Sherwood Midstream’s interest in that entity. See Note 6 for additional information related to the investments in Sherwood Midstream, Ohio Fractionation and Sherwood Midstream Holdings.

Acquisitions and Investments

Acquisition of Ozark Pipeline

On March 1, 2017, MPLX acquired the Ozark pipeline from Enbridge Pipelines (Ozark) LLC for approximately $219 million, including purchase price adjustments made in the second quarter of 2017. Based on the fair value of assets acquired and liabilities assumed at the acquisition date, the final purchase price was primarily allocated to property, plant and equipment. The Ozark pipeline is a 433-mile, 22-inch crude oil pipeline originating in Cushing, Oklahoma, and terminating in Wood River, Illinois, capable of transporting approximately 230 mbpd. We account for the Ozark pipeline within the Midstream segment.

Assuming the acquisition of the Ozark pipeline had occurred on January 1, 2016, the consolidated pro forma results would not have been materially different from reported results.

Investment in Pipeline Company

On February 15, 2017, MPLX acquired a partial, indirect equity interest in the Dakota Access Pipeline (“DAPL”) and Energy Transfer Crude Oil Company Pipeline (“ETCOP”) projects, collectively referred to as the Bakken Pipeline system, through a joint venture with Enbridge Energy Partners L.P. (“Enbridge Energy Partners”). The Bakken Pipeline system is capable of transporting more than 520 mbpd of crude oil from the Bakken/Three Forks production area in North Dakota to the Midwest through Patoka, Illinois and ultimately to the Gulf Coast. MPLX contributed $500 million of the $2 billion purchase price paid by the joint venture, MarEn Bakken Company LLC (“MarEn Bakken”), to acquire a 36.75 percent indirect equity interest in the Bakken Pipeline system from Energy Transfer Partners, L.P. (“ETP”) and Sunoco Logistics Partners, L.P. (“SXL”). MPLX holds, through a subsidiary, a 25 percent interest in MarEn Bakken, which equates to an approximate 9.2 percent indirect equity interest in the Bakken Pipeline system. We account for the investment in MarEn Bakken as part of our Midstream segment using the equity method of accounting.

Formation of Gathering and Processing Joint Venture

Effective January 1, 2017, MPLX and Antero Midstream formed a joint venture, Sherwood Midstream LLC (“Sherwood Midstream”), to support the development of Antero Resources Corporation’s Marcellus Shale acreage in West Virginia. MPLX has a 50 percent ownership interest in Sherwood Midstream. In connection with this transaction, MPLX contributed certain gas processing plants currently under construction at the Sherwood Complex with a fair value of approximately $134 million and cash of approximately $20 million. Antero Midstream made an initial capital contribution of approximately $154 million.

Also effective January 1, 2017, MPLX converted all of its ownership interests in MarkWest Ohio Fractionation Company, L.L.C. (“Ohio Fractionation”), a previously wholly-owned subsidiary, to Class A Interests and amended its LLC Agreement to create Class B-3 Interests, which were sold to Sherwood Midstream for $126 million in cash. The Class B-3 Interests provide Sherwood Midstream with the right to fractionation revenue and the obligation to pay expenses related to 20 mbpd of capacity in the Hopedale 3 fractionator.

Effective January 1, 2017, MPLX and Sherwood Midstream formed a joint venture, Sherwood Midstream Holdings LLC (“Sherwood Midstream Holdings”), for the purpose of owning, operating and maintaining all of the shared assets for the benefit of and use in the operation of the gas plants and other assets owned by Sherwood Midstream and the gas plants and deethanization facilities owned by MPLX. MPLX contributed certain real property, equipment and facilities with a fair value of approximately $209 million to Sherwood Midstream Holdings in exchange for a 79 percent initial ownership interest. Sherwood Midstream contributed cash of approximately $44 million to Sherwood Midstream Holdings in exchange for a 21 percent ownership interest. MPLX has a 10.5 percent indirect interest in Sherwood Midstream Holdings through its ownership in Sherwood Midstream. The net book value of the contributed assets was approximately $203 million. The contribution was determined to be an in-substance sale of real estate. As such, MPLX only recognized a gain for the portion attributable to Antero Midstream’s indirect interest of approximately $2 million. During the three months ended March 31, 2018, MarkWest Liberty Midstream sold to Sherwood Midstream 6 percent of their equity ownership in Sherwood Midstream Holdings for $15 million.

We account for our direct interests in Sherwood Midstream and Sherwood Midstream Holdings as part of our Midstream segment using the equity method of accounting. We continue to consolidate Ohio Fractionation and have recognized a noncontrolling interest for Sherwood Midstream’s interest in that entity.

See Note 6 for additional information related to the investments in Sherwood Midstream, Ohio Fractionation and Sherwood Midstream Holdings.