Commitments and Contingencies - Superfund-Related Matters, Southwest Power Outage and Clean Air Act (Details) - Arizona Public Service Company $ in Millions			3 Months Ended
	Aug. 06, 2013 Defendant	Sep. 08, 2011 kV Customer	Mar. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Capacity of transmission line that tripped out of service (in kV) | 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 | Customer		69,700
Contaminated groundwater wells
Loss Contingencies [Line Items]
Costs related to investigation and study under Superfund site | $			$ 2
Number of defendants against whom Roosevelt Irrigation District (RID) filed lawsuit | Defendant	24