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, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Rabbi Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sales	[1]	$ 44	$ 14	$ 63	$ 26
Gross Realized Gains		2	0	2	2
Gross Realized Losses		0	(1)	0	(1)
Net Realized Gains (Losses)		2	(1)	2	1
Power [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sales	[2]	232	313	822	558
Gross Realized Gains		14	33	33	56
Gross Realized Losses		(4)	(5)	(13)	(9)
Net Realized Gains (Losses)		$ 10	$ 28	$ 20	$ 47

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

[2] Includes activity in accounts related to the liquidation of funds being transitioned to new managers