Derivative and Hedging Activities Narrative (Details)			1 Months Ended							12 Months Ended										12 Months Ended			12 Months Ended
	Dec. 31, 2012 USD ($)	Dec. 31, 2010 USD ($)	Mar. 31, 2011 Six Point Two Five Percent Euro Hyphen Denominated Senior Notes Due Two Thousand Seventeen [Member] USD ($)	Mar. 31, 2011 Six Point Two Five Percent Euro Hyphen Denominated Senior Notes Due Two Thousand Seventeen [Member] EUR (€)	Dec. 31, 2012 Six Point Two Five Percent Euro Hyphen Denominated Senior Notes Due Two Thousand Seventeen [Member] USD ($)		Dec. 31, 2011 Six Point Two Five Percent Euro Hyphen Denominated Senior Notes Due Two Thousand Seventeen [Member] USD ($)		Dec. 31, 2006 Six Point Two Five Percent Euro Hyphen Denominated Senior Notes Due Two Thousand Seventeen [Member] EUR (€)	Dec. 31, 2012 Interest Expense Fair Value Derivatives Interest rate derivatives USD ($)	Dec. 31, 2011 Interest Expense Fair Value Derivatives Interest rate derivatives USD ($)	Dec. 31, 2010 Interest Expense Fair Value Derivatives Interest rate derivatives USD ($)	Dec. 31, 2012 Multi-Counterparty Hedging Facility USD ($) counterparty	Dec. 31, 2012 Multi-Counterparty Hedging Facility Credit Risk counterparty	Dec. 31, 2012 Price Derivatives Multi-Counterparty Hedging Facility Mcfe	Dec. 31, 2012 Basis Derivatives Multi-Counterparty Hedging Facility Mcfe	Dec. 31, 2012 Basis Derivatives Multi-Counterparty Hedging Facility Semi-Annual Collateral Dates	Dec. 31, 2012 Basis Derivatives Multi-Counterparty Hedging Facility Between Semi-Annual Collateral Dates	Dec. 31, 2012 Cross Currency Interest Rate Contract EUR (€)	Dec. 31, 2012 Cross Currency Interest Rate Contract Six Point Two Five Percent Euro Hyphen Denominated Senior Notes Due Two Thousand Seventeen [Member] USD ($)	Dec. 31, 2006 Cross Currency Interest Rate Contract Six Point Two Five Percent Euro Hyphen Denominated Senior Notes Due Two Thousand Seventeen [Member]	Dec. 31, 2012 Cross Currency Interest Rate Contract Scenario, Forecast EUR (€)	Dec. 31, 2012 Cross Currency Interest Rate Contract Scenario, Forecast Six Point Two Five Percent Euro Hyphen Denominated Senior Notes Due Two Thousand Seventeen [Member] USD ($)	Dec. 31, 2012 Euro-Denominated Senior Notes Scenario, Forecast USD ($)	Dec. 31, 2012 Euro-Denominated Senior Notes Scenario, Forecast Six Point Two Five Percent Euro Hyphen Denominated Senior Notes Due Two Thousand Seventeen [Member] USD ($)	Dec. 31, 2012 Balance After Tax USD ($)	Dec. 31, 2011 Balance After Tax USD ($)	Dec. 31, 2010 Balance After Tax USD ($)	Dec. 31, 2009 Balance After Tax USD ($)
Derivative [Line Items]
Number of counterparties in hedge facility													17	12
Multi-counterparty hedging facility, committed to provide a trading capacity (in tcfe)															6,400,000,000	6,400,000,000
Multi-counterparty hedge facility, committed to provide an aggregate mark-to-market capacity													$ 17,000,000,000
Multi-counterparty hedge facility, hedged total (in tcfe)															900,000,000	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
Deferred (Gain) Loss on Discontinuation of Fair Value Hedge	20,000,000
Debt Instrument, Face Amount									600,000,000
Debt Instrument Interest Rate Percentage					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																				459,000,000			17,000,000
Dollar-equivalent interest rate																							7.491%
US To Euro Exchange On Debt Ratio																								1.3193	1.3325
Derivative Liability, Fair Value, Gross Liability					20,000,000
Euro-denominated debt in notes payable, adjusted value					454,000,000	[1]	446,000,000	[1]
Derivative instruments interest expense on hedges										0	23,000,000	19,000,000
Derivative Instruments, Gain (Loss) Reclassification from AOCI to Income, Estimated Net Amount to be Transferred	(179,000,000)
Cash Flow Hedges, Accumulated OCI Balance	(189,000,000)	(181,000,000)																								(189,000,000)	(178,000,000)	(181,000,000)	84,000,000
Expected amount to be transferred of during the next 12 months	$ 20,000,000

[1] The principal amount shown is based on the exchange rate of $1.3193 to €1.00 and $1.2973 to €1.00 as of December 31, 2012 and 2011, respectively. See Note 9 for information on our related foreign currency derivatives.