Commitments and Contingencies Environmental Requirements - Water and Waste (Details) - Federal Coal Ash Regulation [Domain]	Dec. 31, 2020
Loss Contingencies [Line Items]
Number of regulated ash units that will still be in operation by the end of 2019	6
Number of sites where statistically significant increases over established groundwater standards exist	4
Number of sites where corrective action options are being evaluated for locations with statistically significant increases above background concentrations	2
Number of sites where monitoring results indicate potential offsite impacts to groundwater	1
Number of impoundments where closure plans will be expedited	1