Schedule of Valuation Processes (Detail) $ in Millions	Mar. 31, 2020 USD ($) $ / gal
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Assets | $	$ 352
Level 3
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Assets | $	352
Level 3 | Market Approach Valuation Technique | Derivative Liabilities | Natural Gas Liquids
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Liabilities, fair value | $	$ (3)
Level 3 | Market Approach Valuation Technique | Derivative Liabilities | Natural Gas Liquids | Minimum
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Forward Curve Range	0.10
Level 3 | Market Approach Valuation Technique | Derivative Liabilities | Natural Gas Liquids | Maximum
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Forward Curve Range	0.53
Level 3 | Market Approach Valuation Technique | Derivative Liabilities | Natural Gas Liquids | Weighted Average [Member]
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Forward Curve Range	0.27
Level 3 | Market Approach Valuation Technique | Derivative Liabilities | Natural Gas [Member]
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Liabilities, fair value | $	$ (1)
Level 3 | Market Approach Valuation Technique | Derivative Liabilities | Natural Gas [Member] | Minimum
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Forward Curve Range	1.63
Level 3 | Market Approach Valuation Technique | Derivative Liabilities | Natural Gas [Member] | Maximum
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Forward Curve Range	2.50
Level 3 | Market Approach Valuation Technique | Derivative Liabilities | Natural Gas [Member] | Weighted Average [Member]
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Forward Curve Range	1.99
Level 3 | Market Approach Valuation Technique | Derivative Assets | Natural Gas Liquids
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Assets | $	$ 9
Level 3 | Market Approach Valuation Technique | Derivative Assets | Natural Gas Liquids | Minimum
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Forward Curve Range	0.11
Level 3 | Market Approach Valuation Technique | Derivative Assets | Natural Gas Liquids | Maximum
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Forward Curve Range	0.47
Level 3 | Market Approach Valuation Technique | Derivative Assets | Natural Gas Liquids | Weighted Average [Member]
Fair Value Inputs Assets And Liabilities Quantitative Information [Line Items]
Forward Curve Range	0.33