Assets and Liabilities Measured at Fair Value (Nonrecurring Fair Value Measurements) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Book Value Prior to Impairment		$ 4,033,688,000
Total Pretax (Noncash) Impairment Expense		2,493,156,000	$ 51,314,000		$ 21,587,000
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets: Impaired proved properties		1,540,532,000
United States [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Book Value Prior to Impairment		645,088,000
Total Pretax (Noncash) Impairment Expense		328,982,000	14,267,000
United States [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets: Impaired proved properties		316,106,000
Canada [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Pretax (Noncash) Impairment Expense	$ 37,047,000
Malaysia [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Book Value Prior to Impairment		2,681,500,000
Total Pretax (Noncash) Impairment Expense		1,480,600,000
Malaysia [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets: Impaired proved properties		1,200,900,000
Conventional [Member] | Canada [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Book Value Prior to Impairment		707,100,000
Total Pretax (Noncash) Impairment Expense		683,574,000	$ 37,047,000	[1]	$ 21,587,000
Conventional [Member] | Canada [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets: Impaired proved properties		$ 23,526,000

[1] This amount represented the writeoff of goodwill associated with an oil and gas company acquired in 2000.