Available-For-Sale Securities (Fair Values And Gross Unrealized Gains And Losses For The Securities Held) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 1,471	$ 1,416
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	312	303
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(6)	(18)
Fair Value	1,777	1,701
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	644	609
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	294	290
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(2)	(2)
Fair Value	936	897
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] | Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	434	438
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	6	3
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(3)	(12)
Fair Value	437	429
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] | Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	328	285
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	12	10
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(1)	(4)
Fair Value	339	291
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] | Total Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	762	723
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	18	13
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(4)	(16)
Fair Value	776	720
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] | Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	65	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	65	84
Rabbi Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	177	172
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	12	10
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(1)	(3)
Fair Value	188	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	113	109
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	1	0
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(1)	(2)
Fair Value	113	107
Rabbi Trust [Member] | Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	49	46
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	2	1
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	0	(1)
Fair Value	51	46
Rabbi Trust [Member] | Total Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	162	155
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	3	1
Available-for-sale Securities, Gross Unrealized Loss Accumulated in Investments	(1)	(3)
Fair Value	164	153
Rabbi Trust [Member] | Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	3	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	3	3
Rabbi Trust [Member] | Power [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 44	$ 39