Regulatory Environment (Details) - Public Service Commission of Wisconsin (PSCW) $ in Millions	1 Months Ended
Nov. 30, 2015	Dec. 31, 2014 USD ($)
2016 Rates \| Electric rates
Regulatory environment
Approved annual rate increase (decrease)		$ 26.6
Approved annual rate increase (decrease), percentage		0.90%
2016 Rates \| Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)		$ 0.0
2016 Rates \| Steam rates \| Downtown Milwaukee (Valley) steam customers
Regulatory environment
Approved annual rate increase (decrease)		0.0
2016 Rates \| Steam rates \| Milwaukee County steam customers
Regulatory environment
Approved annual rate increase (decrease)		$ 0.0
2015 Rates
Regulatory environment
Approved return on equity (as a percent)		10.20%
Approved common equity component average (as a percent)		51.00%
2015 Rates \| Electric rates
Regulatory environment
Refund related to prior fuel costs and the proceeds of a Treasury Grant		$ 26.6
Percent fuel costs can vary from the rate case approved costs before deferral is required		2.00%
System Support Resource (SSR) revenues		$ 90.7
Number of other rates impacted by the Dane County Circuit Court order	0
2015 Rates \| Electric rates \| Non-fuel costs
Regulatory environment
Approved annual rate increase (decrease)		$ 2.7
Approved annual rate increase (decrease), percentage		0.10%
2015 Rates \| Electric rates \| Fuel costs
Regulatory environment
Approved annual rate increase (decrease)		$ (13.9)
Approved annual rate increase (decrease), percentage		(0.50%)
2015 Rates \| Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)		$ (10.7)
Approved annual rate increase (decrease), percentage		(2.40%)
2015 Rates \| Steam rates \| Downtown Milwaukee (Valley) steam customers
Regulatory environment
Approved annual rate increase (decrease)		$ 0.5
Approved annual rate increase (decrease), percentage		2.00%
2015 Rates \| Steam rates \| Milwaukee County steam customers
Regulatory environment
Approved annual rate increase (decrease)		$ 1.2
Approved annual rate increase (decrease), percentage		7.30%

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

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- Definition

Amount of public utility's approved rate increase (decrease) by regulatory agency.

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Percentage of public utility's approved rate increase (decrease) by regulatory agency.

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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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Number of rates, excluding the demand charge for customer-owned generation, impacted by the November 2015 Dane County Circuit Court order.

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- Definition

Represents the threshold percentage that actual fuel and purchased power costs can vary from costs charged to customers before deferral is required.

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- Definition

The amount refunded to customers for prior fuel costs and the proceeds of a Section 1603 Renewable Energy Treasury Grant.

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- Definition

The system support resource revenues received from Midcontinent Independent System Operator, Inc.

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