Financial Risk Management Activities (Schedule Of Reconciliation For Derivative Activity Included In Accumulated Other Comprehensive Loss) (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (Loss) in AOCI	$ 12	$ 17
(Gain) Loss into Income	14	(4)
Cash Flow Hedges [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Pre-Tax Balance at Beginning of Period	0	17	$ 17
Gain (Loss) in AOCI	3		3
(Gain) Loss into Income	0	(17)	(20)
Pre-Tax Balance at End of Period	3		0
After-Tax Balance at Beginning of Period	0	10	10
Gain (Loss) in AOCI	2	1	2
(Gain) Loss into Income	0	$ (10)	(12)
After-Tax Balance at End of Period	$ 2		$ 0