Derivative Financial Instruments (Schedule Of Derivative Instruments) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Derivative [Line Items]
Derivative Assets, Current	$ 172	$ 694
Derivative Assets, Noncurrent	8	64
Derivative Liabilities, Current	7	0
Derivative Liabilities, Noncurrent	20	1
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Net	180	758
Derivative Liability, Fair Value, Net	27	1
Not Designated as Hedging Instrument [Member] | Commodity Price Derivatives [Member] | Derivatives - Current [Member]
Derivative [Line Items]
Total derivatives, Asset, Gross	190	695
Derivative Liability, Fair Value, Gross Liability	25	1
Derivative Assets Offset In Balance Sheet	(18)	(1)
Derivative Liabilities Offset In Balance Sheet	(18)	(1)
Derivative Assets, Current	172	694
Derivative Liabilities, Current	7	0
Not Designated as Hedging Instrument [Member] | Commodity Price Derivatives [Member] | Derivatives - Noncurrent [Member]
Derivative [Line Items]
Total derivatives, Asset, Gross	11	64
Derivative Liability, Fair Value, Gross Liability	15	1
Derivative Assets Offset In Balance Sheet	(3)	0
Derivative Liabilities Offset In Balance Sheet	(3)	0
Derivative Assets, Noncurrent	8	64
Derivative Liabilities, Noncurrent	12	$ 1
Not Designated as Hedging Instrument [Member] | Interest Rate Derivatives [Member] | Derivatives - Noncurrent [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	8
Derivative Liabilities Offset In Balance Sheet	0
Derivative Liabilities, Noncurrent	$ 8