Agreements and Transactions with Affiliates - Balances with Affiliates (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Related Party Transaction [Line Items]
Accounts receivable	$ 150	$ 138
Accounts payable	119	100
Cash and cash equivalents	14	1	$ 2
Unconsolidated Affiliates
Related Party Transaction [Line Items]
Accounts receivable	18	21
Accounts payable	74	78
Phillips 66
Related Party Transaction [Line Items]
Accounts receivable	132	117
Accounts payable	43	20
Related Party Transaction, Due from (to) Related Party, Noncurrent	1	0
Enbridge
Related Party Transaction [Line Items]
Accounts payable	$ 2	$ 2

Amount for accounts payable to related parties. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Amount of receivables arising from transactions with related parties due within one year or the normal operating cycle, if longer.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of receivables to be collected from related parties net of obligations owed to related parties after one year or beyond the normal operating cycle, if longer where one party can exercise control or significant influence over another party including, but not limited to, affiliates, owners or officers and their immediate families and pension trusts.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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