Business Segments - Segment Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Segment Reporting, Asset Reconciling Item [Line Items]
Segment long-term assets	$ 12,048	$ 13,047
Current assets	866	1,080
Total assets	12,914	14,127
Operating Segments | Logistics and Marketing
Segment Reporting, Asset Reconciling Item [Line Items]
Segment long-term assets	3,968	3,848
Operating Segments | Gathering and Processing
Segment Reporting, Asset Reconciling Item [Line Items]
Segment long-term assets	7,851	8,904
Other
Segment Reporting, Asset Reconciling Item [Line Items]
Segment long-term assets	$ 229	$ 295