Commitments And Contingencies (Environmental Remediation Liability Composed) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Utility-owned natural gas compressor site near Hinkley, California	$ 227	[1]	$ 149	[1]
Utility-owned natural gas compressor site near Topock, Arizona	236		218
Utility-owned generation facilities (other than for fossil fuel-fired), other facilities, and third-party disposal sites	162		133
Former MGP sites owned by the Utility or third parties	178		154
Fossil fuel-fired generation facilities formerly owned by the Utility	87		81
Decommissioning fossil fuel-fired generation facilities and sites	23		50
Total environmental remediation liability	$ 913		$ 785

[1] See "Hinkley Natural Gas Compressor Site" below.