Income Taxes - Summary Of Earliest Tax Years Open To Examination (Details)	6 Months Ended
	Jun. 30, 2015
United States [Member]
Income Tax Examination [Line Items]
Earliest tax years open to examination by tax authorities	2011
United Kingdom [Member]
Income Tax Examination [Line Items]
Earliest tax years open to examination by tax authorities	2011
Norway [Member]
Income Tax Examination [Line Items]
Earliest tax years open to examination by tax authorities	2006
Angola [Member]
Income Tax Examination [Line Items]
Earliest tax years open to examination by tax authorities	2010
Brazil [Member]
Income Tax Examination [Line Items]
Earliest tax years open to examination by tax authorities	2010
Australia [Member]
Income Tax Examination [Line Items]
Earliest tax years open to examination by tax authorities	2011