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, 2014	Mar. 31, 2013
Rabbi Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sales	$ 12	$ 17
Gross Realized Gains	2	0
Gross Realized Losses	0	0
Net Realized Gains (Losses)	2	0
Power [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sales	245	241
Gross Realized Gains	23	37
Gross Realized Losses	(4)	(19)
Net Realized Gains (Losses)	$ 19	$ 18