Investment in Unconsolidated Affiliates Summarized Income Statement of Equity Method Investment (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Schedule of Equity Method Investments [Line Items]
Operating revenues	$ 705.0	$ 620.0	$ 1,997.0	$ 1,658.0
Cost of natural gas and NGLs	349.0	268.0	936.0	717.0
Operating income	137.0	139.0	399.0	299.0
Net income	$ 104.0	$ 110.1	$ 301.0	$ 230.8

Equity Method Investment, Summarized Financial Information, Operating Income

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- Definition

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
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-Publisher FASB
-Name Accounting Standards Codification
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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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- Definition

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.

+ References

No definition available.

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