Agreements and Transactions with Affiliates - Transactions with Affiliates (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Related Party Transaction [Line Items]
Operating and maintenance expense	$ 146	$ 187	$ 447	$ 547
Affiliated Entity \| Phillips 66
Related Party Transaction [Line Items]
Operating and maintenance expense	4	3	10	10
Natural Gas, NGLs and Condensate [Member] \| Affiliated Entity \| Unconsolidated Affiliates
Related Party Transaction [Line Items]
Sales of natural gas, NGLs and condensate	14	9	35	27
Purchases and related costs	15	8	35	44
Natural Gas, NGLs and Condensate [Member] \| Affiliated Entity \| Phillips 66
Related Party Transaction [Line Items]
Sales of natural gas, NGLs and condensate	247	237	616	853
Purchases and related costs	15	33	52	114
Natural Gas, NGLs and Condensate [Member] \| Affiliated Entity \| Enbridge
Related Party Transaction [Line Items]
Sales of natural gas, NGLs and condensate	1	0	2	0
Purchases and related costs	2	6	2	19
Operating and maintenance expense	0	0	1	0
Transportation, Processing and Other [Member]
Related Party Transaction [Line Items]
Sales of natural gas, NGLs and condensate	109	101	330	326
Transportation, Processing and Other [Member] \| Affiliated Entity \| Unconsolidated Affiliates
Related Party Transaction [Line Items]
Sales of natural gas, NGLs and condensate	3	1	9	2
Purchases and related costs	215	201	639	585
Transportation, Processing and Other [Member] \| Affiliated Entity \| Phillips 66
Related Party Transaction [Line Items]
Purchases and related costs	26	19	70	47
Transportation, Processing and Other [Member] \| Affiliated Entity \| Enbridge
Related Party Transaction [Line Items]
Purchases and related costs	$ 1	$ 0	$ 1	$ 1

The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

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-Name Accounting Standards Codification
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

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