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Variable Interest Entities (Details) bbl / d in Thousands, $ in Millions	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 01, 2017 bbl / d
Variable Interest Entity [Line Items]
Equity method investments	$ 4,817	$ 4,787
Crowley Coastal Partners
Variable Interest Entity [Line Items]
VIE, maximum loss exposure, amount	$ 487
MarkWest Utica EMG
Variable Interest Entity [Line Items]
Equity method investments, ownership percentage	56.00%
Equity method investments	$ 2,100
Ohio Gathering
Variable Interest Entity [Line Items]
Equity method investments, ownership percentage	34.00%
Sherwood Midstream
Variable Interest Entity [Line Items]
Equity method investments, ownership percentage	50.00%
Equity method investments	$ 260
Ohio Fractionation
Variable Interest Entity [Line Items]
Capacity | bbl / d			20
Sherwood Midstream Holdings
Variable Interest Entity [Line Items]
Equity method investments, ownership percentage	81.00%
Equity method investments	$ 151
Sherwood Midstream Holdings | Direct Ownership Interest
Variable Interest Entity [Line Items]
Equity method investments, ownership percentage			79.00%
Sherwood Midstream Holdings | Indirect Ownership Interest
Variable Interest Entity [Line Items]
Equity method investments, ownership percentage			10.50%

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- Definition

Capacity

+ References

No definition available.

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- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

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- Definition

This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66022249&loc=d3e33749-111570

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph b
-URI http://asc.fasb.org/extlink&oid=77990344&loc=d3e5728-111685

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=77990344&loc=d3e5747-111685

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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