XML 79 R67.htm IDEA: XBRL DOCUMENT v3.21.2
Commitments and Contingencies Environmental Requirements - Water and Waste (Details) - Federal Coal Ash Regulation
$ in Millions
 3 Months Ended
Sep. 30, 2021
USD ($)
Site Contingency [Line Items]  
Number of sites where regulated ash units will still be in operation at a specified date 8
NSP-Minnesota  
Site Contingency [Line Items]  
Number of sites where statistically significant increases over established groundwater standards exist 0
Cost of construction of a new impoundment $ 9
Estimated cost of closure of an impoundment $ 4
Time period of existing ash pond closure completion in accordance with the CCR rule 5 years
PSCo  
Site Contingency [Line Items]  
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
Estimated cost to remediate groundwater sampling results $ 35
Estimated cost of construction of an alternative collection and treatment system 25
Estimated cost to close Comanche station bottom ash pond $ 3
NSP-Minnesota and PSCo  
Site Contingency [Line Items]  
Number of impoundments where closure plans will be expedited 2