Assets and Liabilities Presented in Consolidated Balance Sheet as Held for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Current Assets:
Accounts receivable	$ 1,853,364	$ 1,554,184
Total current assets	4,108,583	3,447,671
Noncurrent Assets:
Property, plant and equipment - net	13,011,606	10,475,149
Other	151,183	173,455
Current liabilities:
Accounts payable	2,803,268	1,941,008
Income taxes payable	219,847	201,784
Total current liabilities	3,409,081	2,824,928
Noncurrent liabilities:
Asset retirement obligation	724,273	615,545
U.K. exploration and production operations
Current Assets:
Accounts receivable	10,143
Inventories and other	4,976
Total current assets	15,119
Noncurrent Assets:
Property, plant and equipment - net	205,746
Other	2,422
Assets, Noncurrent, Total	208,168
Current liabilities:
Accounts payable	27,578
Income taxes payable	19,893
Total current liabilities	47,471
Noncurrent liabilities:
Deferred income taxes payable	87,893
Asset retirement obligation	53,284
Liabilities, Noncurrent, Total	$ 141,177