Palo Verde (Narrative) (Details) - USD ($) $ in Millions	Jun. 01, 2015	Oct. 31, 2014	Oct. 08, 2014	Aug. 18, 2014	Dec. 19, 2012
Jointly Owned Utility Plant Interests [Line Items]
Settlement Agreement, Date				August 18, 2014
Suit Against Department of Energy for Spent Fuel
Jointly Owned Utility Plant Interests [Line Items]
Settlement Agreement, Counterparty's Name					United States Department of Energy
Lawsuit Filing Date		October 31, 2014			December 19, 2012
Suit Against Department of Energy for Spent Fuel | Palo Verde Generating Station
Jointly Owned Utility Plant Interests [Line Items]
Settlement, Amount	$ 6.6		$ 9.1
Settlement Agreement Award Received, Date	Jun. 01, 2015		Oct. 08, 2014
Suit Against Department of Energy for Spent Fuel | Palo Verde Participants
Jointly Owned Utility Plant Interests [Line Items]
Settlement, Amount		$ 42.0		$ 57.4
Minimum | Suit Against Department of Energy for Spent Fuel
Jointly Owned Utility Plant Interests [Line Items]
Litigation, Period Covered		July 1, 2011			January 1, 2007
Maximum | Suit Against Department of Energy for Spent Fuel
Jointly Owned Utility Plant Interests [Line Items]
Litigation, Period Covered		June 30, 2014			June 30, 2011