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Income Taxes - Tax Years Subject to Examination by Tax Authorities (Detail)	12 Months Ended
	Dec. 31, 2017
Brazil | Earliest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2012
Brazil | Latest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2017
Canada | Earliest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2010
Canada | Latest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2017
Ecuador | Earliest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2014
Ecuador | Latest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2017
Mexico | Earliest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2011
Mexico | Latest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2017
Norway | Earliest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2013
Norway | Latest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2017
Russia | Earliest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2014
Russia | Latest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2017
Saudi Arabia | Earliest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2004
Saudi Arabia | Latest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2017
United Kingdom | Earliest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2015
United Kingdom | Latest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2017
United States | Earliest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2014
United States | Latest Tax Year
Income Tax Examination [Line Items]
Income tax examination, year(s) under examination	2017

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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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- Definition

Tax year being audited in the income tax examination, in CCYY format.

+ References

No definition available.

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