Consolidated Balance Sheets (Parenthetical) - shares shares in Millions	Dec. 31, 2019	Dec. 31, 2018
Limited Partners Common Units \| Public
Units issued	392.0	289.0
Units outstanding	392.0	289.0
Limited Partners Common Units \| MPC
Units issued	666.0	505.0
Units outstanding	666.0	505.0
Series B Preferred Stock [Member]
Units issued	0.6	0.0
Units outstanding	0.6	0.0

The number of limited partner units outstanding.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB Topic 4.F)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70434-108055

Name:	us-gaap_LimitedPartnersCapitalAccountUnitsOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant