Average demand measured for a specified customer, measured in MW.

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The annual percentage change of the capacity charge specified in a power purchase, power sales, or electric sales agreement.

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Expected increase (decrease) in annual depreciation expense based on a regulatory order, if approved.

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The length of notice required to terminate a contract (in years).

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Number of Customers

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No definition available.

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- Definition

Percentage of public utility's approved equity to capital, including debt and equity.

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No definition available.

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Percentage of public utility's approved return on equity.

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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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No definition available.

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Amount of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency.

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Percentage of public utility's requested equity to capital, including debt and equity.

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Amount of public utility's amended requested rate increase (decrease) with regulatory agency.

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Amount of public utility's requested rate increase (decrease) with regulatory agency.

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Percentage of public utility's requested rate increase (decrease) with regulatory agency.

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Percentage of public utility's requested return on equity.

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The total amount of regulated operating revenues recognized during the period.

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The amount of regulated other operating revenues recognized during the period.

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Amount of increase (decrease) to previously recorded tax expense. Includes, but is not limited to, significant settlements of income tax disputes, and unusual tax positions or infrequent actions taken by the entity, including tax assessment reversal, and IRS tax settlement.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 25
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=68052875&loc=d3e28446-109314

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 25
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=68052875&loc=d3e28511-109314

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Regulatory Matters - Electric Rates (Details) $ in Millions			1 Months Ended			3 Months Ended		6 Months Ended		12 Months Ended
Regulatory Matters - Electric Rates (Details) $ in Millions	Jul. 13, 2017 USD ($)	Apr. 13, 2017 USD ($)	Dec. 31, 2016 USD ($)	Nov. 30, 2016 USD ($)	Jun. 30, 2016	Jun. 30, 2017 USD ($) Customers Years MW	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) Customers Years MW	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Regulatory Matters [Line Items]
Reduction in Operating Revenue due to Regulatory Outcome						$ 264.9	$ 234.9	$ 546.5	$ 487.2
PSCW [Member] \| 2012 Wisconsin General Rate Case [Member] \| SWL&P [Member] \| Retail Customers [Member]
Regulatory Matters [Line Items]
Approved Return on Common Equity								10.90%
PSCW [Member] \| 2016 Wisconsin General Rate Case [Member] \| SWL&P [Member] \| Retail Customers [Member]
Regulatory Matters [Line Items]
Requested Rate Increase (Decrease)					3.10%
Requested Return on Equity					10.90%
Requested Equity Ratio					55.00%
PSCW [Member] \| 2016 Wisconsin General Rate Case [Member] \| SWL&P [Member] \| Retail Customers [Member] \| Subsequent Event [Member]
Regulatory Matters [Line Items]
Approved Return on Common Equity	10.50%
Approved Equity Ratio	55.00%
Annual Additional Revenue Generated from Requested Final Rate Increase	$ 2.5
Electric Rates [Member] \| MPUC [Member] \| 2010 Minnesota Rate Case [Member] \| Minnesota Power [Member] \| Retail Customers [Member]
Regulatory Matters [Line Items]
Approved Return on Common Equity								10.38%
Approved Equity Ratio								54.29%
Electric Rates [Member] \| MPUC [Member] \| Minnesota Cost Recovery Riders [Member] \| Minnesota Power [Member] \| Retail Customers [Member]
Regulatory Matters [Line Items]
Revenue from Cost Recovery Riders						$ 24.4	$ 23.5	$ 48.6	$ 48.9
Electric Rates [Member] \| MPUC [Member] \| 2016 Minnesota General Rate Case [Member] \| Minnesota Power [Member] \| Retail Customers [Member]
Regulatory Matters [Line Items]
Requested Rate Increase (Decrease)				9.00%
Requested Return on Equity				10.25%
Requested Equity Ratio				53.81%
Annual Additional Revenue Generated from Requested Final Rate Increase				$ 55.0
Annual Additional Revenue Generated from Requested Interim Rate Increase		$ 32.2	$ 34.7	49.0
Annual Additional Revenue Generated from Requested Final Rate Increase, Amended								$ 49.0
Electric Rates [Member] \| MPUC [Member] \| 2016 Minnesota General Rate Case [Member] \| Minnesota Power [Member] \| Retail Customers [Member] \| Boswell Energy Center [Member]
Regulatory Matters [Line Items]
Expected Decrease in Annual Depreciation Expense				$ 25.0
Electric Rates [Member] \| MPUC [Member] \| Renewable Cost Recovery Rider [Member] \| Retail Customers [Member] \| Corporate and Other [Member]
Regulatory Matters [Line Items]
After-Tax Charge for North Dakota Investment Tax Credits Reversed										$ 8.8
Electric Rates [Member] \| MPUC [Member] \| Renewable Cost Recovery Rider [Member] \| Minnesota Power [Member] \| Retail Customers [Member]
Regulatory Matters [Line Items]
Reduction in Operating Revenue due to Regulatory Outcome										$ 15.0
Electric Rates [Member] \| FERC [Member] \| FERC-Approved Wholesale Rates [Member] \| Minnesota Power [Member] \| Municipal Customers [Member]
Regulatory Matters [Line Items]
Number of Customers \| Customers						16		16
Notice Required to Terminate (Years) \| Years						3		3
Electric Rates [Member] \| FERC [Member] \| FERC-Approved Wholesale Rates [Member] \| Minnesota Power [Member] \| Municipal Customers [Member] \| Wholesale Electric Contract (Termination Effective June 2019) [Member]
Regulatory Matters [Line Items]
Average Monthly Demand (MW) \| MW						29		29
Electric Rates [Member] \| FERC [Member] \| FERC-Approved Wholesale Rates [Member] \| Minnesota Power [Member] \| Municipal Customers [Member] \| Wholesale Electric Contract (Cost-Based Formula Methodology for Entire Term) [Member]
Regulatory Matters [Line Items]
Number of Customers \| Customers						3		3
Electric Rates [Member] \| FERC [Member] \| FERC-Approved Wholesale Rates [Member] \| Minnesota Power [Member] \| Municipal Customers [Member] \| Wholesale Electric Contracts (Expire December 2024) [Member]
Regulatory Matters [Line Items]
Number of Customers \| Customers						14		14
Electric Rates [Member] \| FERC [Member] \| FERC-Approved Wholesale Rates [Member] \| Minnesota Power [Member] \| Municipal Customers [Member] \| Wholesale Electric Contracts (Expire December 2024) [Member] \| Maximum [Member]
Regulatory Matters [Line Items]
Change in Annual Capacity Charge Per Contract, Percentage						2.00%		2.00%
Electric Rates [Member] \| FERC [Member] \| FERC-Approved Wholesale Rates [Member] \| Minnesota Power [Member] \| Municipal Customers [Member] \| Wholesale Electric Contracts (Expire December 2024) [Member] \| Minimum [Member]
Regulatory Matters [Line Items]
Change in Annual Capacity Charge Per Contract, Percentage						(1.00%)		(1.00%)
Electric Rates [Member] \| PSCW [Member] \| 2016 Wisconsin General Rate Case [Member] \| SWL&P [Member] \| Retail Customers [Member]
Regulatory Matters [Line Items]
Requested Rate Increase (Decrease)					3.50%
Natural Gas Rates [Member] \| PSCW [Member] \| 2016 Wisconsin General Rate Case [Member] \| SWL&P [Member] \| Retail Customers [Member]
Regulatory Matters [Line Items]
Requested Rate Increase (Decrease)					(1.30%)
Water Rates [Member] \| PSCW [Member] \| 2016 Wisconsin General Rate Case [Member] \| SWL&P [Member] \| Retail Customers [Member]
Regulatory Matters [Line Items]
Requested Rate Increase (Decrease)					7.80%