Palo Verde (Narrative) (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended			3 Months Ended	0 Months Ended									6 Months Ended
	May 16, 2014	Apr. 21, 2014	May 17, 2012	Sep. 30, 2014	Apr. 21, 2014 Suit Against Department of Energy for Spent Fuel	May 17, 2012 Suit Against Department of Energy for Spent Fuel	Apr. 21, 2014 Suit Against Department of Energy for Spent Fuel APS and Palo Verde Participants	Oct. 31, 2014 Subsequent Event	Oct. 08, 2014 Subsequent Event	Oct. 31, 2014 Subsequent Event Suit Against Department of Energy for Spent Fuel	Oct. 31, 2014 Subsequent Event Suit Against Department of Energy for Spent Fuel APS and Palo Verde Participants	Oct. 31, 2014 Subsequent Event Suit Against Department of Energy for Spent Fuel Palo Verde Generating Station	Oct. 08, 2014 Subsequent Event Suit Against Department of Energy for Spent Fuel Palo Verde Generating Station	Jun. 30, 2015 Minimum Scenario, Forecast	Jun. 30, 2015 Maximum Scenario, Forecast
Jointly Owned Utility Plant Interests [Line Items]
Reimbursement anticipated to be received, date														Jan. 01, 2015	Jun. 30, 2015
Settlement Agreement, Counterparty's Name					United States Department of Energy
Lawsuit Filing Date			May 17, 2012					October 31, 2014
Settlement Agreement, Date					April 21, 2014
Name of Federal Authority or Agency		Department of Justice
Settlement, Amount							$ 57.0						$ 9.1
Litigation Covered Period Start Date						Jan. 01, 2007				Jul. 01, 2011
Litigation Covered Period End Date						Jun. 30, 2011				Jun. 30, 2014
Reimbursement requested, Amount											$ 42.5	$ 6.7
Settlement Agreement Award Received, Date									Oct. 08, 2014
DOE award refunded to customers, date				Sep. 30, 2014
Spent Nuclear Fuel Disposal Fee, per kWh				0.001
Period to Conduct an Adequacy Assessment Analysis				6 months
One-Mill Fee Suspended, Date	May 16, 2014