Derivative Instruments (Detail Effect Of Derivative Assets And Liabilities In Statement Of Operations) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Cash Flow Hedging [Member] | Commodity Derivatives | Revenues
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	$ 0	$ 10	$ 0	$ 11
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0	6	0	6
Derivatives Not Designated In A Hedging Relationships
Derivative Instruments, Gain (Loss) Recognized in Income, Net	6	25	(11)	27
Derivatives Not Designated In A Hedging Relationships | Commodity Derivatives | Revenues
Amount of gain (loss) from designation amortized from AOCI into income	0	(2)	0	(6)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	14	17	11	19
Derivatives Not Designated In A Hedging Relationships | Embedded Derivatives | Other Income and Deductions, Net
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ (8)	$ 8	$ (22)	$ 8