Financial Risk Management Activities (Schedule Of Reconciliation For Derivative Activity Included In Accumulated Other Comprehensive Loss) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2015	Sep. 30, 2015	Sep. 30, 2014
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (Loss) in AOCI	$ (46)	$ (13)		$ (43)	$ 17
(Gain) Loss into Income	24	(13)		27	(21)
Cash Flow Hedges [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Pre-Tax Balance at Beginning of Period	1		$ 17	17
Gain (Loss) in AOCI	1		1
(Gain) Loss into Income	0	(1)	(17)	(17)	11
Pre-Tax Balance at End of Period	2		1	2
After-Tax Balance at Beginning of Period	1		10	10
Gain (Loss) in AOCI	0	2	1	1	(2)
(Gain) Loss into Income	0	$ (1)	(10)	(10)	$ 6
After-Tax Balance at End of Period	$ 1		$ 1	$ 1