Commitments and Contingencies Removal Costs (Details) - Removal Costs [Member] - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 1,217	$ 1,175
NSP Minnesota
Regulatory Liabilities [Line Items]
Regulatory Liabilities	520	485
PSCo
Regulatory Liabilities [Line Items]
Regulatory Liabilities	351	344
SPS
Regulatory Liabilities [Line Items]
Regulatory Liabilities	175	188
NSP-Wisconsin
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 171	$ 158