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Risk Management And Financial Instruments - Variable Interest Entities (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($)
Derivative [Line Items]
Outstanding principal	$ 141
Interest Rate Swap [Member] | Minimum [Member]
Derivative [Line Items]
Pay rates	0.74%
Interest Rate Swap [Member] | Maximum [Member]
Derivative [Line Items]
Pay rates	3.34%
Derivative Instrument Maturity Date [Member] | Interest Rate Swap [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Minimum [Member]
Derivative [Line Items]
Pay rates	177.00%
Length of contracts	2013-12
Derivative Instrument Maturity Date [Member] | Interest Rate Swap [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Maximum [Member]
Derivative [Line Items]
Pay rates	201.00%
Length of contracts	2018-12

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- Definition

Length of contracts.

+ References

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- Definition

Amount of the hedged item as of the balance sheet date related to the derivative. For example, the hedged balance on a debt instrument.

+ References

No definition available.

+ Details

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- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

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- 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.

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