Supplemental Cash Flow Information (Summary of Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents		$ 15	$ 77
Net cash provided by operating activities included:
Interest paid (net of amounts capitalized)		835	568	$ 263
Income taxes paid		1	1	3
Operating Lease, Payments		85	0	0
Finance Lease, Interest Expense		1	0	0
Finance Lease, Principal Payments		5	0	0
Non-cash investing and financing activities:
Net transfers of property, plant and equipment from materials and supplies inventories		2	2	6
Sales-type Lease, Selling Profit (Loss)		21	0	0
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability		26	0	0
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability		4	0	0
Contribution - fixed assets to joint venture	[1]	0	0	337
Contribution - common units issued	[2]	7,722	4,236	1,133
Acquisitions [Abstract]
Restricted Cash	[3]	0	8
Cash, cash equivalents and restricted cash at end of period		$ 15	$ 85	$ 9	$ 239

[1] Contribution of assets to Sherwood Midstream and Sherwood Midstream Holdings.

[2] For 2017, includes limited and general partner units issued to MPC as consideration in the acquisitions of the joint-interests, HST, WHC and MPLXT. For 2018, includes limited and general partner units issued to MPC as consideration in the acquisition of Refining Logistics and Fuels Distribution. For 2019, includes limited partner units issued to MPC and public unitholders as consideration in the Merger. See Note 4.

[3] The restricted cash balance is included within “Other current assets” on the Consolidated Balance Sheets.