Investment in Unconsolidated Affiliate and Related Party Transactions Summarized Income Statement of Equity Method Investment (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity Method Investments and Joint Ventures [Abstract]
Total revenues	$ 3,431.0	$ 2,803.0	$ 2,272.0
Cost of natural gas and NGL	1,819.0	1,381.0	1,017.0
Operating income	648.0	528.0	385.0
Net income	$ 485.3	$ 400.3	$ 289.5

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.

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

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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.

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