Commitments and Contingencies - Environmental Requirements - Water and Waste (Details)	Sep. 30, 2020	Dec. 31, 2019
Federal Coal Ash Regulation
Site Contingency [Line Items]
Number of sites where regulated ash units will still be in operation at a specified date	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
Federal Coal Ash Regulation [Domain]
Site Contingency [Line Items]
Number of facilities where alternative storage capacity options consistent with the CCR Rule are being pursued	1