Property, Plant and Equipment (Schedule of Recognized Impairments) (Details) - USD ($)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Property Plant And Equipment [Line Items]
Impairment Expense		$ 0	$ 95,088,000	[1]	$ 2,493,156,000	[1]
Gulf Of Mexico [Member]
Property Plant And Equipment [Line Items]
Impairment Expense					328,982,000
Canada [Member]
Property Plant And Equipment [Line Items]
Impairment Expense			95,088,000		683,574,000
Malaysia [Member]
Property Plant And Equipment [Line Items]
Impairment Expense	[2]				1,480,600,000
Conventional [Member] | Canada [Member]
Property Plant And Equipment [Line Items]
Impairment Expense	[2]		$ 95,100,000		$ 683,600,000

[1] Reclassified to conform to current presentation (see Note A).

[2] Results exclude corporate overhead, interest and discontinued operations.