Derivative and Hedging Activities - Additional Information (Detail)			1 Months Ended							3 Months Ended		9 Months Ended									9 Months Ended			9 Months Ended
	Sep. 30, 2012 USD ($)	Dec. 31, 2011 USD ($)	Mar. 31, 2011 6.25% Euro-Denominated Senior Notes Due 2017 USD ($)	Mar. 31, 2011 6.25% Euro-Denominated Senior Notes Due 2017 EUR (€)	Sep. 30, 2012 6.25% Euro-Denominated Senior Notes Due 2017 USD ($)		Dec. 31, 2011 6.25% Euro-Denominated Senior Notes Due 2017 USD ($)		Dec. 31, 2006 6.25% Euro-Denominated Senior Notes Due 2017 EUR (€)	Sep. 30, 2012 Interest Expense Fair Value Derivatives Interest rate derivatives USD ($)	Sep. 30, 2011 Interest Expense Fair Value Derivatives Interest rate derivatives USD ($)	Sep. 30, 2012 Interest Expense Fair Value Derivatives Interest rate derivatives USD ($)	Sep. 30, 2011 Interest Expense Fair Value Derivatives Interest rate derivatives USD ($)	Sep. 30, 2012 Multi-Counterparty Hedging Facility USD ($) counterparty	Sep. 30, 2012 Multi-Counterparty Hedging Facility Credit Risk counterparty	Sep. 30, 2012 Price Derivatives Multi-Counterparty Hedging Facility Mcfe	Sep. 30, 2012 Basis Derivatives Multi-Counterparty Hedging Facility Mcfe	Sep. 30, 2012 Basis Derivatives Multi-Counterparty Hedging Facility Semi-Annual Collateral Dates	Sep. 30, 2012 Basis Derivatives Multi-Counterparty Hedging Facility Between Semi-Annual Collateral Dates	Sep. 30, 2012 Cross Currency Interest Rate Contract EUR (€)	Sep. 30, 2012 Cross Currency Interest Rate Contract 6.25% Euro-Denominated Senior Notes Due 2017 USD ($)	Dec. 31, 2006 Cross Currency Interest Rate Contract 6.25% Euro-Denominated Senior Notes Due 2017	Sep. 30, 2012 Cross Currency Interest Rate Contract Scenario, Forecast EUR (€)	Sep. 30, 2012 Cross Currency Interest Rate Contract Scenario, Forecast 6.25% Euro-Denominated Senior Notes Due 2017 USD ($)	Sep. 30, 2012 Euro-Denominated Senior Notes Scenario, Forecast USD ($)	Sep. 30, 2012 Euro-Denominated Senior Notes Scenario, Forecast 6.25% Euro-Denominated Senior Notes Due 2017 USD ($)
Derivative [Line Items]
Number of counterparties in hedge facility														18	16
Multi-counterparty hedging facility, committed to provide a trading capacity (in tcfe)																6,500,000,000	6,500,000,000
Multi-counterparty hedge facility, committed to provide an aggregate mark-to-market capacity														$ 17,500,000,000
Multi-counterparty hedge facility, hedged total (in tcfe)																1,400,000,000	100,000,000
Natural gas and oil proved reserves, the value of which must cover the fair value of the transactions outstanding under the facility, multiplier																		1.65	1.30
Duration gains will be recognized on terminated qualifying interest rate derivative transactions, years	8 years
Amount realized over the next nine years for gains and losses related to terminated qualifying interest rate derivative transactions are amortized as an adjustment to interest expense	21,000,000
Debt Instrument, Face Amount									600,000,000
Interest rate					6.25%																	6.25%
Debt instrument, increase (decrease) for period, net				256,000,000
Debt instrument reclassification of accumulated other comprehensive income			(38,000,000)
Loss on redemption of debt			(20,000,000)
Loss included in interest expense			(18,000,000)
Semi-annual interest rate swaps proceeds																				11,000,000			344,000,000
Semi-annual interest rate swaps payments																					17,000,000			459,000,000
Dollar-equivalent interest rate																								7.491%
US To Euro Exchange On Debt Ratio																									1.2856	1.3325
Derivative Liability, Fair Value, Gross Liability					37,000,000
Euro-denominated debt in notes payable, adjusted value	16,218,000,000	10,626,000,000			442,000,000	[1]	446,000,000	[1]
Derivative instruments interest expense on hedges										0	2,000,000	0	23,000,000
Expected amount to be transferred of during the next 12 months	$ 13,000,000

[1] The principal amount shown is based on the exchange rate of $1.2856 to €1.00 and $1.2973 to €1.00 as of September 30, 2012 and December 31, 2011, respectively. See Note 7 for information on our related foreign currency derivatives.