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, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Rabbi Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sales	$ 19	[1]	$ 12	[1]
Gross Realized Gains	0		2
Gross Realized Losses	0		0
Net Realized Gains (Losses)	0		2
Power [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sales	590	[1]	245	[1]
Gross Realized Gains	19		23
Gross Realized Losses	(9)		(4)
Net Realized Gains (Losses)	$ 10		$ 19

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