Available-For-Sale Securities (Fair Values And Gross Unrealized Gains And Losses For The Securities) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 1,416	$ 1,366
Gross Unrealized Gains	303	180
Gross Unrealized Losses	(18)	(6)
Fair Value	1,701	1,540
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	609	648
Gross Unrealized Gains	290	147
Gross Unrealized Losses	(2)	(6)
Fair Value	897	789
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] | Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	438	274
Gross Unrealized Gains	3	11
Gross Unrealized Losses	(12)	0
Fair Value	429	285
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] | Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	285	320
Gross Unrealized Gains	10	22
Gross Unrealized Losses	(4)	0
Fair Value	291	342
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] | Total Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	723	594
Gross Unrealized Gains	13	33
Gross Unrealized Losses	(16)	0
Fair Value	720	627
Nuclear Decommissioning Trust (NDT) Fund [Member] | Power [Member] | Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	84	124
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	84	124
Rabbi Trusts [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	172	175
Gross Unrealized Gains	10	10
Gross Unrealized Losses	(3)	0
Fair Value	179	185
Rabbi Trusts [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	14	13
Gross Unrealized Gains	9	5
Gross Unrealized Losses	0	0
Fair Value	23	18
Rabbi Trusts [Member] | Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	109	114
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(2)	0
Fair Value	107	117
Rabbi Trusts [Member] | Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	46	45
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(1)	0
Fair Value	46	47
Rabbi Trusts [Member] | Total Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	155	159
Gross Unrealized Gains	1	5
Gross Unrealized Losses	(3)	0
Fair Value	153	164
Rabbi Trusts [Member] | Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	3	3
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 3	$ 3