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Commitments and Contingencies FERC NOPR on ROE Incentive Adders (Details) - Federal Energy Regulatory Commission (FERC) [Member] - NSP Minnesota, NSP Wisconsin and SPS	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
ROE incentive adders related to FERC NOPR	0.50%
Public Utilities, General Disclosures [Line Items]
ROE incentive adders related to FERC NOPR	0.50%

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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ROE incentive adders related to FERC NOPR

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