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Rate Matters (Details) - PSCW [Member] - MGE [Member] - USD ($) |  | 4 Months Ended | 12 Months Ended
--- | --- | --- | ---
Oct. 31, 2014 | Dec. 31, 2015 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Rate Proceedings [Abstract] |  |  |  |  |  |
Authorized return on equity, percentage |  |  |  | 10.20% | 10.30% | 10.30%
Fuel Rules [Abstract] |  |  |  |  |  |
Fuel rules, bandwidth |  |  |  | 2.00% |  |
Fuel rules, electric fuel costs, deferral, upper threshold |  |  |  | 102.00% |  |
Fuel rules, electric fuel costs, deferral, lower threshold |  |  |  | 98.00% |  |
Fuel Rules Credit, 2012 [Member] |  |  |  |  |  |
Fuel Rules [Abstract] |  |  |  |  |  |
Return of electric fuel credit, total |  |  |  |  | $ 6,300,000 |
Fuel Rules Credit, 2013 [Member] |  |  |  |  |  |
Fuel Rules [Abstract] |  |  |  |  |  |
Return of electric fuel credit, total | $ 6,500,000 |  |  |  |  |
Fuel Rules Credit, 2015 [Member] |  |  |  |  |  |
Fuel Rules [Abstract] |  |  |  |  |  |
Fuel rules, deferred electric cost |  |  |  | $ 9,500,000 |  |
Return of electric fuel credit, total |  |  |  | $ 2,600,000 |  |
Electric fuel credit (per kWh) |  | $ 0.00256 |  |  |  |
Approved Future Rate Matters [Member] |  |  |  |  |  |
Fuel Rules [Abstract] |  |  |  |  |  |
Electric fuel credit (per kWh) |  |  | $ 0.00256 |  |  |
Approved Future Rate Matters [Member] | Subsequent Event [Member] |  |  |  |  |  |
Fuel Rules [Abstract] |  |  |  |  |  |
Change in fuel rules monitored costs, 2016 |  |  | $ (14,800,000) |  |  |
Columbia Environmental Projects [Member] |  |  |  |  |  |
Rate Proceedings [Abstract] |  |  |  |  |  |
Authorized AFUDC rate |  |  |  | 100.00% | 100.00% | 50.00%
Electric Rate Proceeding [Member] |  |  |  |  |  |
Rate Proceedings [Abstract] |  |  |  |  |  |
Authorized rate increase (decrease), percentage |  |  |  | 3.80% | 0.00% | 3.80%
Authorized rate increase (decrease), amount |  |  |  | $ 15,400,000 | $ 0 | $ 14,900,000
Electric Rate Proceeding [Member] | Approved Future Rate Matters [Member] |  |  |  |  |  |
Rate Proceedings [Abstract] |  |  |  |  |  |
Authorized rate increase (decrease), percentage |  |  | 0.00% |  |  |
Authorized rate increase (decrease), amount |  |  | $ 0 |  |  |
Gas Rate Proceeding [Member] |  |  |  |  |  |
Rate Proceedings [Abstract] |  |  |  |  |  |
Authorized rate increase (decrease), percentage |  |  |  | (2.00%) | 0.00% | 1.00%
Authorized rate increase (decrease), amount |  |  |  | $ (3,800,000) | $ 0 | $ 1,600,000
Gas Rate Proceeding [Member] | Approved Future Rate Matters [Member] |  |  |  |  |  |
Rate Proceedings [Abstract] |  |  |  |  |  |
Authorized rate increase (decrease), percentage |  |  | 0.00% |  |  |
Authorized rate increase (decrease), amount |  |  | $ 0 |  |  |

X
- Definition This amount represents the reduction in 2016 fuel rules monitored costs which was approved by the PSCW. + References No definition available. + Details
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- Definition The approved amount ($/kWh) for an electric fuel credit to be returned to customers via a bill credit. + References No definition available. + Details
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- References No definition available. + Details
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- Definition Pursuant to the provisions of the rate order, the fuel rules bandwidth will be plus or minus this percentage. + References No definition available. + Details
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- Definition The amount of electric fuel-related costs in which an entity has deferred outside the symmetrical cost tolerance band authorized by a regulatory agency in the most recent rate order. + References No definition available. + Details
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- Definition Under fuel rules, the amount in which an entity is required to defer the benefit of lower costs if actual electric fuel costs were less than the allowed electric fuel costs in latest rate order. + References No definition available. + Details
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- Definition Under fuel rules, the amount in which an entity would defer if actual electric fuel costs exceeded allowed electric fuel costs in latest rate order. + References No definition available. + Details
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- Definition The fuel rules credit that is not required to be refunded to customers and will be amortized. The fuel credit will accrue interest at weighted cost of capital. + References No definition available. + Details
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- Definition Effective rate, including composite rate, of cost of financing additions to qualifying regulated assets, commonly called allowance for funds used during construction. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430 + Details
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- Definition Amount of public utility's approved rate increase (decrease) by regulatory agency. + References No definition available. + Details
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- Definition Percentage of public utility's approved rate increase (decrease) by regulatory agency. + References No definition available. + Details
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- Definition Percentage of public utility's approved return on equity. + References No definition available. + Details
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