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, 2017	Mar. 31, 2016	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (Loss) in AOCI	$ 30	$ 12
(Gain) Loss into Income	(9)	14
Cash Flow Hedges [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Pre-Tax Balance at Beginning of Period	3	0	$ 0
Gain (Loss) in AOCI	0		3
(Gain) Loss into Income	0		0
Pre-Tax Balance at End of Period	3		3
After-Tax Balance at Beginning of Period	2	0	0
Gain (Loss) in AOCI	0	2	2
(Gain) Loss into Income	0	$ 0	0
After-Tax Balance at End of Period	$ 2		$ 2