Organization and Basis of Presentation, Fair Value (Details) - USD ($) $ in Millions		3 Months Ended	6 Months Ended			9 Months Ended
	Jan. 02, 2019	Sep. 30, 2019	Jun. 30, 2019	Jun. 30, 2018		Sep. 30, 2018	Jan. 01, 2019	Dec. 31, 2018
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability			$ 2	$ 0	[1]
Finance Lease, Liability			$ 13
Limited Partners' Capital Account, Units Outstanding			245,630,444			245,000,000		245,493,184
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage			64.00%			64.00%
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest						100.00%
Net Cash Provided by (Used in) Operating Activities, Continuing Operations			$ 483	547	[2]
Net Cash Provided by (Used in) Investing Activities			(265)	(748)	[2]
Debt, carrying value			5,300					$ 5,000
Debt, fair value			$ 5,400					$ 4,900
Limited Partner Units, Public
Limited Partners' Capital Account, Units Outstanding			89,457,316
Limited Partner Units, Affiliate
Limited Partners' Capital Account, Units Outstanding			156,173,128			156,000,000
Accounting Standards Update 2016-02
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 131
Finance Lease, Liability							$ 133
Predecessors
Net Cash Provided by (Used in) Operating Activities, Continuing Operations				86
Net Cash Provided by (Used in) Investing Activities				$ 422
Subsequent Event | MPLX Merger | Limited Partner Units, Public
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares		1.135
Subsequent Event | MPLX Merger | Limited Partner Units, Affiliate
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares		1.0328

[1] Adjusted to include the historical results of the Predecessors. See Note 1 for further discussion.

[2] Adjusted to include the historical results of the Predecessors. See Note 1 for further discussion.