Financial Risk Management Activities - Gross Notional Amounts of Derivative Contracts Outstanding (Detail)	Dec. 31, 2017 USD ($) MMBbls	Dec. 31, 2016 USD ($) MMBbls
Commodity, Crude Oil
Derivative [Line Items]
Outstanding gross notional amount, in millions of barrels \| MMBbls	42	0
Foreign Exchange
Derivative [Line Items]
Outstanding gross notional amount	$ 52,000,000	$ 785,000,000
Interest Rate Swaps \| Designated as Fair Value Hedges
Derivative [Line Items]
Outstanding gross notional amount	$ 450,000,000	$ 350,000,000

- Definition

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

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Namespace Prefix:	invest_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

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- Details

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- Details

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- Details

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- Details

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