Commitments and Contingencies - Superfund-Related Matters and Southwest Power Outage (Details) (Arizona Public Service Company, USD $) In Millions, unless otherwise specified	0 Months Ended			9 Months Ended	0 Months Ended
	Jul. 07, 2014 Requirement	Jan. 22, 2014 Entity Requirement	Sep. 08, 2011 item MW kV Customer	Sep. 30, 2014	Aug. 06, 2013 Contaminated groundwater wells Defendant
Superfund-Related Matters
Costs related to investigation and study under Superfund site				$ 2
Number of defendants against whom Roosevelt Irrigation District (RID) filed lawsuit					24
Southwest Power Outage
Capacity of transmission line that tripped out of service (in kV)			500
Period, after the transmission line went off-line, over which generation and transmission resources for the Yuma area were lost			10 minutes
Number of customers losing service in Yuma area			69,700
Capacity of firm load that were reported to have been affected due to outages affecting portions of southern Arizona, southern California and northern Mexico (in MW)			7,900
Number of customers that were reported to have been affected due to outages			2,700,000
Number of alleged entities		6
Number of reliability standard requirements violations		7
Number of reliability standard requirements neither admitted nor denied violations in settlement	4
Amount of civil penalty agreed in settlement	3.25
Civil penalty amount required to be paid in equal parts	2
Civil penalty amount offset in exchange for completing certain reliability enhancements	$ 1.25