Fair Value Measurement - Schedule of Valuation Processes (Detail) - Level 3 - Market Approach Valuation Technique - Natural Gas Liquids $ in Millions	Dec. 31, 2016 USD ($) $ / Gallon
Derivative Financial Instruments, Liabilities
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Fair Value, Liabilities \| $	$ 23
Derivative Financial Instruments, Liabilities \| Minimum
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Forward Curve Range	0.25
Derivative Financial Instruments, Liabilities \| Maximum
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Forward Curve Range	1.23
Derivative Financial Instruments, Assets
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Fair Value, Assets \| $	$ 14
Derivative Financial Instruments, Assets \| Minimum
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Forward Curve Range	0.25
Derivative Financial Instruments, Assets \| Maximum
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Forward Curve Range	1.20

Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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- Definition

The forward price on the price risk forward or futures contract, such as a gas futures contract.

+ References

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- Definition

Fair value of financial and nonfinancial obligations.

+ References

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