Derivative And Hedging Activities (Narrative) (Details)	6 Months Ended						6 Months Ended				6 Months Ended	12 Months Ended	1 Months Ended		6 Months Ended					6 Months Ended
	Jun. 30, 2011 USD ($)	Dec. 31, 2017 EUR (€)	Apr. 30, 2011 USD ($)	Apr. 30, 2011 EUR (€)	Dec. 31, 2010 USD ($)	Jun. 30, 2010	Jun. 30, 2011 Multi Counterparty Hedge Facility [Member] USD ($)	Jun. 30, 2011 Multi Counterparty Hedge Facility [Member] Cross Currency Interest Rate Contract [Member] EUR (€)	Jun. 30, 2011 Multi Counterparty Hedge Facility [Member] Price Derivative [Member]	Jun. 30, 2011 Multi Counterparty Hedge Facility [Member] Basis Derivative [Member]	Jun. 30, 2011 Cross Currency Interest Rate Contract [Member] 6.25% Euro-Denominated Senior Notes Due 2017 [Member] USD ($)	Dec. 31, 2017 Cross Currency Interest Rate Contract [Member] 6.25% Euro-Denominated Senior Notes Due 2017 [Member] USD ($)	May 31, 2011 6.25% Euro-Denominated Senior Notes Due 2017 [Member] USD ($)	May 31, 2011 6.25% Euro-Denominated Senior Notes Due 2017 [Member] EUR (€)	Jun. 30, 2011 6.25% Euro-Denominated Senior Notes Due 2017 [Member] USD ($)		Dec. 31, 2010 6.25% Euro-Denominated Senior Notes Due 2017 [Member] USD ($)		Dec. 31, 2006 6.25% Euro-Denominated Senior Notes Due 2017 [Member] EUR (€)	Jun. 30, 2011 Euro Denominated Senior Notes [Member]
Derivative instrument maximum effectiveness	100.00%
Expected amount (net of income taxes) to be transferred of the loss included in the balance in accumulated other comprehensive income to net income (loss) during the next 12 months	$ 75,000,000
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)
Number of counterparties in hedge facility	17
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
Amount realized over the next ten years for gains and losses related to terminated qualifying interest rate derivative transactions are amortized as an adjustment to interest expense	30,000,000
Multi-counterparty hedge facility, committed to provide a trading capacity (in tcfe)							6.5
Multi-counterparty hedge facility, committed to provide an aggregate mark-to-market capacity							17,300,000,000
Multi-counterparty hedge facility, hedged total (in tcfe)									2.5	0.1
Issued 6.25% Euro-denominated Senior Notes due 2017																			600,000,000
Interest rate						2.25%									6.25%				6.25%
Semi-annual interest rate swap proceeds		344,000,000						11,000,000
Semi-annual interest rate swap payments											17,000,000	459,000,000
Dollar-equivalent interest rate											7.491%
Euro-denominated debt in notes payable, adjusted value	10,047,000,000				12,640,000,000										500,000,000	[1]	796,000,000	[1]
Euro-denominated debt in notes payable, adjusted value, based on exchange rate															$ 1.4821					$ 1.4523
Retired amount of euro-denominated senior notes through tender offer			380,000,000	256,000,000
Terms of the cross currency swap															1.3325
Fair value of the cross currency swap liability															$ 7,000,000
Counterparties	14						11

[1] The principal amount shown is based on the exchange rate of $1.4523 to € 1.00 and $1.3269 to € 1.00 as of June 30, 2011 and December 31, 2010, respectively. See Note 2 for information on our related foreign currency derivatives.