Derivative and Hedging Activities - Narrative (Details) € in Millions, MMBoe in Millions, $ in Millions, MMBTU in Billions	1 Months Ended	3 Months Ended	9 Months Ended
	Dec. 31, 2006 USD ($) $ / €	Sep. 30, 2015 USD ($) MMBoe MMBTU counterparty Derivatives $ / €	Sep. 30, 2015 USD ($) MMBoe counterparty Derivatives $ / €	Sep. 30, 2015 EUR (€) MMBoe counterparty Derivatives $ / €	Jun. 30, 2015 USD ($)	Apr. 30, 2015 USD ($)	Dec. 31, 2014 USD ($) $ / €	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2006 EUR (€) $ / €
Derivative [Line Items]
Number of Interest Rate Derivatives Held | Derivatives		0	0	0
Derivative Assets (Liabilities), at Fair Value, Net		$ 469	$ 469				$ 652
Accumulated other comprehensive loss		119	119				143
Expected amount to be transferred of during the next 12 months		20	20
6.25% Euro-Denominated Senior Notes Due 2017 [ Member] | Senior Notes [Member]
Derivative [Line Items]
Euro-denominated debt in notes payable, adjusted value	$ 344	$ 384	$ 384				416
Multi-Counterparty Hedging Facility [Member]
Derivative [Line Items]
Number of counterparties in hedge facility | counterparty		9	9	9
Natural gas and oil proved reserves, the value of which must cover the fair value of the transactions outstanding under the facility, multiplier		1.30	1.30	1.30
Borrowing capacity		$ 7,100	$ 7,100
Multi-Counterparty Hedging Facility [Member] | Minimum [Member]
Derivative [Line Items]
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	1.65	1.65
Bilateral Hedging Agreement [Member]
Derivative [Line Items]
Borrowing capacity						$ 16,500
Line of Credit Facility, Current Borrowing Capacity		$ 7,100	$ 7,100
Cash Flow Hedging [Member]
Derivative [Line Items]
Accumulated other comprehensive loss		119	119		$ 131		143	$ 151	$ 154	$ 167
Cash Flow Hedging [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Derivative [Line Items]
Accumulated other comprehensive loss		118	$ 118
Interest Rate Contract [Member]
Derivative [Line Items]
Derivative, Amount of Hedged Item							850
Amortization Period of Deferred Gain (Loss) on Discontinuation of Fair Value Hedge			6 years
Deferred (Gain) Loss on Discontinuation of Fair Value Hedge		8	$ 8
Euro-denominated debt in notes payable, adjusted value		$ 8	$ 8				10
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net							(17)
Derivative Liability, Fair Value, Gross Liability							$ (17)
Cross Currency Interest Rate Contract [Member] | 6.25% Euro-Denominated Senior Notes Due 2017 [ Member] | Senior Notes [Member]
Derivative [Line Items]
Derivative, Forward Exchange Rate | $ / €	1.3325	1.1177	1.1177	1.1177			1.2098				1.3325
Semi Annual Interest Rate Swap Payments By Counterparty | €				€ 344							€ 11
Dollar Equivalent Interest Rate	7.491%
Short-term Debt, Refinanced, Description	$ 17	$ 459	$ 459
Foreign Exchange Contract [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net		(76)	(76)				$ (53)
Derivative Liability, Fair Value, Gross Liability		$ (76)	$ (76)				(53)
Other Contracts, A [Member]
Derivative [Line Items]
Derivative, Number of Instruments Held | Derivatives		1	1	1
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Settlements		$ 36	$ 63
Other Contracts, A [Member] | Minimum [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU		90
Credit Risk [Member]
Derivative [Line Items]
Number of counterparties in hedge facility | counterparty		17	17	17
Energy Related Derivative [Member] | Multi-Counterparty Hedging Facility [Member]
Derivative [Line Items]
Multi-counterparty hedging facility, committed to provide a trading capacity (in tcfe) | MMBoe		444.0	444.0	444.0
Price Risk Derivative [Member] | Multi-Counterparty Hedging Facility [Member]
Derivative [Line Items]
Multi-counterparty hedge facility, hedged total (in tcfe) | MMBoe		27.3	27.3	27.3
Price Risk Derivative [Member] | Bilateral Hedging Agreement [Member]
Derivative [Line Items]
Multi-counterparty hedge facility, hedged total (in tcfe) | MMBoe		87.2	87.2	87.2
Basis Derivative [Member] | Multi-Counterparty Hedging Facility [Member]
Derivative [Line Items]
Multi-counterparty hedging facility, committed to provide a trading capacity (in tcfe) | MMBoe		444.0	444.0	444.0
Multi-counterparty hedge facility, hedged total (in tcfe) | MMBoe		1.2	1.2	1.2
Basis Derivative [Member] | Bilateral Hedging Agreement [Member]
Derivative [Line Items]
Multi-counterparty hedge facility, hedged total (in tcfe) | MMBoe		12.9	12.9	12.9
Fair Value, Inputs, Level 3 [Member]
Derivative [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net		$ 214	$ 214				$ (53)
Fair Value, Inputs, Level 3 [Member] | Marketing, Gathering And Compression [Member] | Other Contracts, A [Member]
Derivative [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings		$ 70	$ 291