Business Segments - Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Total operating revenues	$ 1,657	$ 2,199
Gross margin	511	395
Operating and maintenance expense	(153)	(178)
Depreciation and amortization expense	(99)	(103)
General and administrative expense	(56)	(67)
Asset Impairments	(746)	0
Other expense, net	(3)	(5)
Loss on sale of assets, net	0	(9)
Earnings from unconsolidated affiliates	76	113
Interest expense, net	(78)	(69)
Income tax expense	1	1
Net income	(549)	76
Net income attributable to noncontrolling interests	(1)	(1)
Net income attributable to partners	(550)	75
Non-cash derivative mark-to-market	134	(54)
Non-cash lower of cost or net realizable value adjustment	(4)	(5)
Capital expenditures	69	182
Investments in unconsolidated affiliates, net	34	131
Logistics and Marketing
Segment Reporting Information [Line Items]
Total operating revenues	1,358	2,045
Gathering and Processing
Segment Reporting Information [Line Items]
Total operating revenues	913	1,288
Operating Segments | Logistics and Marketing
Segment Reporting Information [Line Items]
Total operating revenues	1,358	1,288
Gross margin	111	337
Operating and maintenance expense	(7)	(165)
Depreciation and amortization expense	(3)	(93)
General and administrative expense	(2)	(6)
Asset Impairments	0
Other expense, net	0	(5)
Loss on sale of assets, net		(9)
Earnings from unconsolidated affiliates	137	0
Interest expense, net	0	0
Income tax expense	0	0
Net income	236	147
Net income attributable to noncontrolling interests	0	(1)
Net income attributable to partners	236	147
Non-cash derivative mark-to-market	42	(36)
Non-cash lower of cost or net realizable value adjustment	(4)	(5)
Capital expenditures	1	165
Investments in unconsolidated affiliates, net	34	0
Operating Segments | Gathering and Processing
Segment Reporting Information [Line Items]
Total operating revenues	913	2,045
Gross margin	400	58
Operating and maintenance expense	(142)	(9)
Depreciation and amortization expense	(89)	(3)
General and administrative expense	(3)	(3)
Asset Impairments	(746)
Other expense, net	(3)	0
Loss on sale of assets, net		0
Earnings from unconsolidated affiliates	(61)	113
Interest expense, net	0	0
Income tax expense	0	0
Net income	(644)	68
Net income attributable to noncontrolling interests	(1)	0
Net income attributable to partners	(645)	67
Non-cash derivative mark-to-market	92	(18)
Non-cash lower of cost or net realizable value adjustment	0	0
Capital expenditures	67	14
Investments in unconsolidated affiliates, net	0	131
Other
Segment Reporting Information [Line Items]
Total operating revenues	0	0
Gross margin	0	0
Operating and maintenance expense	(4)	(4)
Depreciation and amortization expense	(7)	(7)
General and administrative expense	(51)	(58)
Asset Impairments	0
Other expense, net	0	0
Loss on sale of assets, net		0
Earnings from unconsolidated affiliates	0	0
Interest expense, net	(78)	(69)
Income tax expense	1	1
Net income	(141)	(139)
Net income attributable to noncontrolling interests	0	0
Net income attributable to partners	(141)	(139)
Non-cash derivative mark-to-market	0	0
Non-cash lower of cost or net realizable value adjustment	0	0
Capital expenditures	1	3
Investments in unconsolidated affiliates, net	0	0
Eliminations
Segment Reporting Information [Line Items]
Total operating revenues	(614)	(1,134)
Gross margin	0	0
Operating and maintenance expense		0
Depreciation and amortization expense	0	0
General and administrative expense	0	0
Other expense, net		0
Earnings from unconsolidated affiliates	0	0
Interest expense, net	0	0
Income tax expense	0	0
Net income	0	0
Net income attributable to noncontrolling interests	0	0
Net income attributable to partners	0	0
Non-cash derivative mark-to-market		0
Non-cash lower of cost or net realizable value adjustment	0	0
Capital expenditures	0	0
Investments in unconsolidated affiliates, net	$ 0	$ 0