XML 140 R106.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2
Commitments and Contingencies Environmental Requirements - Water and Waste (Details)
$ in Millions
Dec. 31, 2019
USD ($)
Plant
Dec. 31, 2018
USD ($)
NSP Minnesota    
Loss Contingencies [Line Items]    
Number of sites where statistically significant increases over established groundwater standards exist 0  
PSCo    
Loss Contingencies [Line Items]    
Number of sites where statistically significant increases over established groundwater standards exist 4  
Federal Coal Ash Regulation [Domain]    
Loss Contingencies [Line Items]    
Number of sites where regulated ash units will still be in operation at a specified date 9  
Federal Coal Ash Regulation [Domain] | NSP Minnesota    
Loss Contingencies [Line Items]    
Number of impoundments where closure plans will be expedited 1  
Estimated cost of closure of an impoundment $ 2  
Estimated cost of construction of a new impoundment $ 9  
Federal Coal Ash Regulation [Domain] | PSCo    
Loss Contingencies [Line Items]    
Number of impoundments where closure plans will be expedited 1  
Clean Water Act Effluent Limitations Guidelines [Domain]    
Loss Contingencies [Line Items]    
Liability for estimated cost to comply with regulation $ 12  
Federal Clean Water Act Section 316 (b) | NSP Minnesota    
Loss Contingencies [Line Items]    
Minimum number of plants which could be required to make improvements to reduce entrainment | Plant 6  
Federal Clean Water Act Section 316 (b) | NSP-Wisconsin    
Loss Contingencies [Line Items]    
Minimum number of plants which could be required to make improvements to reduce entrainment | Plant 2  
Capital Addition Purchase Commitments [Member] | Federal Clean Water Act Section 316 (b)    
Loss Contingencies [Line Items]    
Liability for estimated cost to comply with regulation $ 40  
Liability for estimated cost to comply with impingement and entrainment regulation 198  
Removal Costs [Member]    
Loss Contingencies [Line Items]    
Regulatory Liabilities 1,217 $ 1,175
Removal Costs [Member] | NSP Minnesota    
Loss Contingencies [Line Items]    
Regulatory Liabilities 520 485
Removal Costs [Member] | PSCo    
Loss Contingencies [Line Items]    
Regulatory Liabilities 351 344
Removal Costs [Member] | SPS    
Loss Contingencies [Line Items]    
Regulatory Liabilities 175 188
Removal Costs [Member] | NSP-Wisconsin    
Loss Contingencies [Line Items]    
Regulatory Liabilities $ 171 $ 158