Available-For-Sale Securities (Proceeds From The Sales Of And The Net Realized Gains On Securities in the NDT and Rabbi Trusts) (Detail) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2016		Jun. 30, 2015		Jun. 30, 2016	Jun. 30, 2015
Rabbi Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sales	$ 36	[1]	$ 44	[1]	$ 61	$ 63	[1]
Gross Realized Gains	2		2		3	2
Gross Realized Losses	(1)		0		(2)	0
Net Realized Gains (Losses)	1		2		1	2
Power [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sales	154	[2]	232	[2]	331	822	[2]
Gross Realized Gains	10		14		25	33
Gross Realized Losses	(6)		(4)		(22)	(13)
Net Realized Gains (Losses)	$ 4		$ 10		$ 3	$ 20

[1] 2015 proceeds include activity in accounts related to the liquidation of funds being transitioned to new managers

[2] 2015 proceeds include activity in accounts related to the liquidation of funds being transitioned to new managers.