Annual report pursuant to Section 13 and 15(d)

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

v2.4.0.8
Capitalization of Exploratory Well Costs - Schedule of Capitalized Exploratory Well Costs (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2013
Well
Dec. 31, 2012
Well
Dec. 31, 2011
Well
Projects With Exploratory Well Costs Capitalized For More Than One Year [Line Items]      
Capitalized exploratory well costs that have been capitalized for a period less than one year   $ 5.9 $ 8.0
Capitalized exploratory well costs that have been capitalized for a period greater than one year 16.7 8.1  
Total $ 16.7 $ 14.0 $ 8.0
Number of exploratory wells that have been capitalized for a period greater than one year 2 1 1