Annual report pursuant to Section 13 and 15(d)

Capitalization of Exploratory Well Costs - Schedule of Capitalized Exploratory Well Costs (Detail)

v2.4.1.9
Capitalization of Exploratory Well Costs - Schedule of Capitalized Exploratory Well Costs (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Well
Dec. 31, 2013
Well
Dec. 31, 2012
Well
Extractive Industries [Abstract]      
Capitalized exploratory well costs that have been capitalized for a period less than one year     $ 5.9us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodOfOneYearOrLess
Capitalized exploratory well costs that have been capitalized for a period greater than one year 8.9us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear 16.7us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear 8.1us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear
Total $ 8.9us-gaap_CapitalizedExploratoryWellCosts $ 16.7us-gaap_CapitalizedExploratoryWellCosts $ 14.0us-gaap_CapitalizedExploratoryWellCosts
Number of exploratory wells that have been capitalized for a period greater than one year 1us-gaap_ProjectsThatHaveExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear 2us-gaap_ProjectsThatHaveExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear 1us-gaap_ProjectsThatHaveExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear