Net of tax amount of the appreciation (loss) in value of unsold available-for-sale securities attributable to the parent entity. Excludes amounts related to other than temporary impairment (OTTI) losses.

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+ Details

Available-For-Sale Securities (Narrative) (Detail) (USD $) In Millions, unless otherwise specified			3 Months Ended
	Mar. 31, 2013 Power [Member]	Dec. 31, 2012 Power [Member]	Mar. 31, 2013 Rabbi Trusts [Member]	Mar. 31, 2012 Rabbi Trusts [Member]	Mar. 31, 2013 Rabbi Trusts [Member] Power [Member] Debt Securities [Member]	Mar. 31, 2013 Nuclear Decommissioning Trust (NDT) Fund [Member]	Mar. 31, 2013 Nuclear Decommissioning Trust (NDT) Fund [Member] Power [Member]	Mar. 31, 2012 Nuclear Decommissioning Trust (NDT) Fund [Member] Power [Member]	Mar. 31, 2013 Nuclear Decommissioning Trust (NDT) Fund [Member] Power [Member] Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Realized Gains			$ 0	$ 5			$ 37	$ 16
After tax amount of net unrealized gains recognized in AOCI					6				111
Amount of other-than-temporary impairments						2
Accounts Receivable	51	18	7
Accounts Payable	$ 70	$ 53	$ 6