Debt and Interest Expense - Anadarko (Detail) (USD $)	Sep. 30, 2012 Fair Value Inputs Level 1 and Level 2 [Member] Market Approach Valuation Technique [Member]	Dec. 31, 2011 Fair Value Inputs Level 1 and Level 2 [Member] Market Approach Valuation Technique [Member]	Sep. 30, 2012 Five Billion Dollar Facility [Member]	Jun. 19, 2012 LOC Facility [Member]
Debt Instrument [Line Items]
Total borrowings, fair value	$ 17,100,000,000	$ 17,300,000,000
Line of credit, outstanding borrowings			1,000,000,000
Line of credit, interest rate			1.72%
Line of credit, available borrowing capacity			4,000,000,000
Line of credit, maximum capacity			5,000,000,000
Letter of credit facility, maximum capacity				$ 400,000,000