Commitments and Contingencies - Superfund-Related Matters, Southwest Power Outage and Clean Air Act (Details) - APS - Contaminated groundwater wells $ in Millions				6 Months Ended
	Apr. 05, 2018 Defendant plaintiff	Dec. 16, 2016 plaintiff	Aug. 06, 2013 Defendant	Jun. 30, 2020 USD ($)
Loss Contingencies [Line Items]
Costs related to investigation and study under Superfund site | $				$ 3
Number of defendants against whom Roosevelt Irrigation District (RID) filed lawsuit | Defendant	28		24
Number of plaintiffs		2
Settled Litigation
Loss Contingencies [Line Items]
Number of plaintiffs	2