Financial Risk Management Activities (Schedule Of Reconciliation For Derivative Activity Included In Accumulated Other Comprehensive Loss) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Balance as of December 31, 2011	$ 54	$ 188
Loss Recognized in AOCI, After-Tax	17
Gain (Loss) Recognized in AOCI	28	80
Less: Gain Reclassified into Income	(70)	(214)
Balance as of September 30, 2012	12	54
Balance as of December 31, 2011	31	111
Gain Recognized in AOCI, After-Tax		47
Less: Gain Reclassified into Income, After-Tax	(41)	(127)
Balance as of September 30, 2012	$ 7	$ 31