Summary of Principal Accounting Policies DDA (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Office furniture, equipment and computer hardwareWells and Related Equipment and Facilities [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	1 year
Office furniture, equipment and computer hardwareWells and Related Equipment and Facilities [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		15 years
Pipelines [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Pipelines [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		40 years
Plants, facilities, mine equipment and infrastructure [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	16 years
Plants, facilities, mine equipment and infrastructure [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life		40 years