Commitments And Contingencies (Nuclear Insurance) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Diablo Canyon [Member]
Long-term Purchase Commitment [Line Items]
Amount of property damage and business interruption coverage provided by NEIL for Diablo Canyon	$ 3,200
Amount of property damage coverage provided by NEIL	2,600
Maximum public liability per nuclear incident under Price-Anderson Act	13,600
Maximum available public liability insurance for Diablo Canyon as required by Price-Anderson Act	375
Maximum public liability claims amount per nuclear event	13,600
Humboldt Bay Unit [Member]
Long-term Purchase Commitment [Line Items]
Amount of property damage coverage provided by NEIL	131
Amount of indemnification from the NRC for public liability arising from nuclear incidents	500
Amount of liability insurance for Humboldt Bay Unit 3	$ 53