Discontinued Operations - Assets and Liabilities Presented in Consolidated Balance Sheets as Held for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accounts receivable	$ 999,872	$ 1,853,364
Held for sale assets of U.K. oil and gas operations	943,732	15,119
Property, plant and equipment	13,481,055	13,011,606
Other	98,123	151,183
Total non-current assets held for sale	381,404	208,168
Accounts payable	2,158,485	2,803,268
Income taxes payable	222,930	219,847
Total current liabilities associated with assets held for sale	639,140	47,471
Deferred income taxes payable	1,466,100	1,544,336
Deferred credits and other liabilities	339,028	516,540
Asset retirement obligations	852,488	724,273
Total non-current liabilities associated with assets held for sale	95,544	141,177
U.K. downstream operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash	301,302	0
Accounts receivable	302,059	0
Inventories	254,240	0
Other	86,131	0
Property, plant and equipment	360,347	0
Other	21,057	0
Accounts payable	637,432	0
Other	1,708	0
Deferred income taxes payable	68,096	0
Deferred credits and other liabilities	27,448	0
U.K. oil and gas operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Held for sale assets of U.K. oil and gas operations	0	15,119
Property, plant and equipment	0	205,746
Other	0	2,422
Accounts payable	0	27,578
Income taxes payable	0	19,893
Deferred income taxes payable	0	87,893
Asset retirement obligations	$ 0	$ 53,284