Income Taxes - Summary Of Earliest Tax Years Open To Examination (Details)	6 Months Ended
	Jun. 30, 2012
United States [Member]
Income Tax Examination [Line Items]
Earliest tax years open to examination by tax authorities	2007
United Kingdom [Member]
Income Tax Examination [Line Items]
Earliest tax years open to examination by tax authorities	2009
Norway [Member]
Income Tax Examination [Line Items]
Earliest tax years open to examination by tax authorities	2002
Angola [Member]
Income Tax Examination [Line Items]
Earliest tax years open to examination by tax authorities	2007
Nigeria [Member]
Income Tax Examination [Line Items]
Earliest tax years open to examination by tax authorities	2006
Brazil [Member]
Income Tax Examination [Line Items]
Earliest tax years open to examination by tax authorities	2006
Australia [Member]
Income Tax Examination [Line Items]
Earliest tax years open to examination by tax authorities	2008
Canada [Member]
Income Tax Examination [Line Items]
Earliest tax years open to examination by tax authorities	2008