Investment in Unconsolidated Affiliate and Related Party Transactions Summarized Income Statement of Equity Method Investment (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity Method Investments and Joint Ventures [Abstract]
Operating revenues	$ 2,272.0	$ 2,418.0	$ 3,367.0
Cost of natural gas and natural gas liquids	1,017.0	1,097.0	1,914.0
Operating income (loss)	385.0	(712.0)	586.0
Net income (loss)	$ 289.5	$ (752.0)	$ 530.0

Equity Method Investment, Summarized Financial Information, Operating Income

No definition available.

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- Definition

The amount of the cost of sales reported by an equity method investment of the entity.

+ 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 (c)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
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- Definition

The amount of net income (loss) reported by an equity method investment of the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
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- Definition

The amount of revenue from sale of goods and services reduced by sales returns, allowances, and discounts reported by an equity method investment of the entity.

+ References

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