Derivative Financial Instruments (Schedule Of Derivative Instruments) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivative Assets, Current	$ 156	$ 14
Derivative Assets, Noncurrent	29	0
Derivative Liabilities, Current	3	77
Derivative Liabilities, Noncurrent	1	7
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Net	185	14
Derivative Liability, Fair Value, Net	4	84
Not Designated as Hedging Instrument [Member] | Commodity Price Derivatives [Member] | Derivatives - Current [Member]
Derivative [Line Items]
Total derivatives, Asset, Gross	153	33
Derivative Liability, Fair Value, Gross Liability	5	102
Derivative Assets Offset In Balance Sheet	(2)	(25)
Derivative Liabilities Offset In Balance Sheet	(2)	(25)
Derivative Assets, Current	151	8
Derivative Liabilities, Current	3	77
Not Designated as Hedging Instrument [Member] | Commodity Price Derivatives [Member] | Derivatives - Noncurrent [Member]
Derivative [Line Items]
Total derivatives, Asset, Gross	30
Derivative Liability, Fair Value, Gross Liability	2	7
Derivative Assets Offset In Balance Sheet	(1)
Derivative Liabilities Offset In Balance Sheet	(1)	0
Derivative Assets, Noncurrent	29
Derivative Liabilities, Noncurrent	1	7
Not Designated as Hedging Instrument [Member] | Interest Rate Derivatives [Member] | Derivatives - Current [Member]
Derivative [Line Items]
Total derivatives, Asset, Gross	5	6
Derivative Assets Offset In Balance Sheet	0	0
Derivative Assets, Current	$ 5	$ 6