Business Segments - Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Total operating revenues	$ 1,274		$ 1,798		$ 2,931	$ 3,997
Gross margin	300		442		811	837
Operating and maintenance expense	(148)		(182)		(301)	(360)
Depreciation and amortization expense	(93)		(101)		(192)	(204)
General and administrative expense	(51)		(68)		(107)	(135)
Asset Impairments	0		0		(746)	0
Other expense, net	(5)		(1)		(8)	(6)
Loss on sale of assets, net	0		(5)		0	(14)
Restructuring Costs	(9)		(9)		(9)	(9)
Earnings from unconsolidated affiliates	125		117		201	230
Interest expense, net	(71)		(73)		(149)	(142)
Income tax expense	0		0		1	1
Net income	48	$ (549)	120	$ 76	(501)	196
Net income attributable to noncontrolling interests	(1)		(1)		(2)	(2)
Net income attributable to partners	47		119		(503)	194
Non-cash derivative mark-to-market	(57)		39		77	(15)
Non-cash lower of cost or net realizable value adjustment	(2)		(3)		(6)	(8)
Capital expenditures	33		126		102	308
Investments in unconsolidated affiliates, net	56		139		90	270
Logistics and Marketing
Segment Reporting Information [Line Items]
Total operating revenues	1,150		1,613		2,508	3,658
Gathering and Processing
Segment Reporting Information [Line Items]
Total operating revenues	618		1,024		1,531	2,312
Operating Segments | Logistics and Marketing
Segment Reporting Information [Line Items]
Total operating revenues	1,150		1,613		2,508	2,312
Gross margin	69		88		180	691
Operating and maintenance expense	(9)		(11)		(16)	(330)
Depreciation and amortization expense	(3)		(3)		(6)	(184)
General and administrative expense	(1)		(1)		(3)	(12)
Asset Impairments					0
Other expense, net	4		1		(4)	(5)
Loss on sale of assets, net			(1)			(10)
Restructuring Costs	0		0		0	0
Earnings from unconsolidated affiliates	125		114		262	3
Interest expense, net	0		0		0	0
Income tax expense					0	0
Net income	177		185		413	332
Net income attributable to noncontrolling interests	0		0		0	(2)
Net income attributable to partners	177		185		413	332
Non-cash derivative mark-to-market	5		24		47	(21)
Non-cash lower of cost or net realizable value adjustment	(2)		(3)		(6)	(8)
Capital expenditures	0		11		1	276
Investments in unconsolidated affiliates, net	56		139		90	0
Operating Segments | Gathering and Processing
Segment Reporting Information [Line Items]
Total operating revenues	618		1,024		1,531	3,658
Gross margin	231		354		631	146
Operating and maintenance expense	(134)		(165)		(276)	(20)
Depreciation and amortization expense	(82)		(91)		(171)	(6)
General and administrative expense	(4)		(6)		(7)	(4)
Asset Impairments					(746)
Other expense, net	(1)		0		(2)	(1)
Loss on sale of assets, net			(4)			(4)
Restructuring Costs	0		0		0	0
Earnings from unconsolidated affiliates	0		3		(61)	227
Interest expense, net	0		0		0	0
Income tax expense					0	0
Net income	12		91		(632)	159
Net income attributable to noncontrolling interests	(1)		(1)		(2)	0
Net income attributable to partners	11		90		(634)	157
Non-cash derivative mark-to-market	(62)		15		30	6
Non-cash lower of cost or net realizable value adjustment	0		0		0	0
Capital expenditures	32		111		99	25
Investments in unconsolidated affiliates, net	0		0		0	270
Other
Segment Reporting Information [Line Items]
Total operating revenues	0		0		0	0
Gross margin	0		0		0	0
Operating and maintenance expense	(5)		(6)		(9)	(10)
Depreciation and amortization expense	(8)		(7)		(15)	(14)
General and administrative expense	(46)		(61)		(97)	(119)
Asset Impairments					0
Other expense, net	2		0		2	0
Loss on sale of assets, net			0			0
Restructuring Costs	(9)		(9)		(9)	(9)
Earnings from unconsolidated affiliates	0		0		0	0
Interest expense, net	(71)		(73)		(149)	(142)
Income tax expense					1	1
Net income	(141)		(156)		(282)	(295)
Net income attributable to noncontrolling interests	0		0		0	0
Net income attributable to partners	(141)		(156)		(282)	(295)
Non-cash derivative mark-to-market	0		0		0	0
Non-cash lower of cost or net realizable value adjustment	0		0		0	0
Capital expenditures	1		4		2	7
Investments in unconsolidated affiliates, net	0		0		0	0
Eliminations
Segment Reporting Information [Line Items]
Total operating revenues	(494)		(839)		(1,108)	(1,973)
Gross margin	0		0		0	0
Operating and maintenance expense	0		0			0
Depreciation and amortization expense	0		0		0	0
General and administrative expense	0		0		0	0
Other expense, net	0		0			0
Restructuring Costs	0		0		0	0
Earnings from unconsolidated affiliates	0		0		0	0
Interest expense, net	0		0		0	0
Income tax expense			0		0	0
Net income	0		0		0	0
Net income attributable to noncontrolling interests			0		0	0
Net income attributable to partners	0		0		0	0
Non-cash derivative mark-to-market	0		0			0
Non-cash lower of cost or net realizable value adjustment	0		0		0	0
Capital expenditures	0		0		0	0
Investments in unconsolidated affiliates, net	$ 0		$ 0		$ 0	$ 0