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, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2015
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (Loss) in AOCI	$ 27	$ (46)		$ 46	$ (43)
(Gain) Loss into Income	7	24		31	27
Cash Flow Hedges [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Pre-Tax Balance at Beginning of Period	2		$ 0	0
Gain (Loss) in AOCI	1		2
(Gain) Loss into Income	0	0	0		(17)
Pre-Tax Balance at End of Period	3		2	3
After-Tax Balance at Beginning of Period	1		0	0
Gain (Loss) in AOCI	1	0	1	2	1
(Gain) Loss into Income	0	$ 0	0	0	$ (10)
After-Tax Balance at End of Period	$ 2		$ 1	$ 2