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		12 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (Loss) in AOCI	$ 7		$ (14)	$ 19	$ 3
(Gain) Loss into Income	10		7	24	3
Cash Flow Hedges [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Pre-Tax Balance at Beginning of Period	3	$ 0		0	17	$ 17
Gain (Loss) in AOCI	(1)	3				3
(Gain) Loss into Income	0	0	0		(17)	(20)
Pre-Tax Balance at End of Period	2	3		2		0
After-Tax Balance at Beginning of Period	2	0		0	10	10
Gain (Loss) in AOCI	(1)	2	0	1	1	2
(Gain) Loss into Income	0	0	$ 0	0	$ (10)	(12)
After-Tax Balance at End of Period	$ 1	$ 2		$ 1		$ 0