Investment in Unconsolidated Affiliates Summarized Income Statement of Equity Method Investment (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Schedule of Equity Method Investments [Line Items]
Operating revenues	$ 626.0	$ 529.0	$ 1,292.0	$ 1,038.0
Cost of natural gas and natural gas liquids	279.0	254.0	587.0	449.0
Operating income	122.0	57.0	262.0	160.0
Net income	$ 86.2	$ 34.7	$ 197.4	$ 120.7

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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- Definition

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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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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