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		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Rabbi Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sales	[1]	$ 20	$ 419	$ 83	$ 445
Gross Realized Gains		0	2	2	4
Gross Realized Losses		(1)	(2)	(1)	(3)
Net Realized Gains (Losses)		(1)	0	1	1
Power [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sales	[2]	215	221	1,037	779
Gross Realized Gains		14	45	47	101
Gross Realized Losses		(11)	(3)	(24)	(12)
Net Realized Gains (Losses)		$ 3	$ 42	$ 23	$ 89

[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