Available-For-Sale Securities (Fair Values And Gross Unrealized Gains And Losses For The Securities Held) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 1,444	$ 1,416
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	302	303
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(12)	(18)
Fair Value	1,734	1,701
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	619	609
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	288	290
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(3)	(2)
Fair Value	904	897
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] | Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	464	438
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	3	3
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(7)	(12)
Fair Value	460	429
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] | Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	306	285
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	11	10
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(2)	(4)
Fair Value	315	291
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] | Total Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	770	723
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	14	13
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(9)	(16)
Fair Value	775	720
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] | Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	55	84
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	0	0
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	0	0
Fair Value	55	84
Rabbi Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	175	172
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	10	10
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(2)	(3)
Fair Value	183	179
Rabbi Trust [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	12	14
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	9	9
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	0	0
Fair Value	21	23
Rabbi Trust [Member] | Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	110	109
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	0	0
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(1)	(2)
Fair Value	109	107
Rabbi Trust [Member] | Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	46	46
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	1	1
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(1)	(1)
Fair Value	46	46
Rabbi Trust [Member] | Total Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	156	155
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	1	1
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(2)	(3)
Fair Value	155	153
Rabbi Trust [Member] | Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	7	3
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	0	0
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	0	0
Fair Value	7	3
Rabbi Trust [Member] | Power [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 43	$ 39