Regulatory Environment (Details) $ in Millions	1 Months Ended
	Aug. 31, 2016 USD ($) MW	Nov. 30, 2015	Dec. 31, 2014 USD ($)	Dec. 31, 2012 USD ($)
Public Service Commission of Wisconsin (PSCW) | 2016 Rates | Electric rates
Regulatory environment
Approved annual rate increase (decrease)			$ 26.6
Approved annual rate increase (decrease), percentage			0.90%
Public Service Commission of Wisconsin (PSCW) | 2016 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)			$ 0.0
Public Service Commission of Wisconsin (PSCW) | 2016 Rates | Steam rates | Downtown Milwaukee (Valley) steam customers
Regulatory environment
Approved annual rate increase (decrease)			0.0
Public Service Commission of Wisconsin (PSCW) | 2016 Rates | Steam rates | Milwaukee County steam customers
Regulatory environment
Approved annual rate increase (decrease)			$ 0.0
Public Service Commission of Wisconsin (PSCW) | 2015 Rates
Regulatory environment
Approved return on equity (as a percent)			10.20%
Approved common equity component average (as a percent)			51.00%
Public Service Commission of Wisconsin (PSCW) | 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%
SSR revenues			$ 90.7
Number of other rates impacted by the Dane County Circuit Court order		0
Public Service Commission of Wisconsin (PSCW) | 2015 Rates | Electric rates | Non-fuel costs
Regulatory environment
Approved annual rate increase (decrease)			$ 2.7
Approved annual rate increase (decrease), percentage			0.10%
Public Service Commission of Wisconsin (PSCW) | 2015 Rates | Electric rates | Fuel costs
Regulatory environment
Approved annual rate increase (decrease)			$ (13.9)
Approved annual rate increase (decrease), percentage			(0.50%)
Public Service Commission of Wisconsin (PSCW) | 2015 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)			$ (10.7)
Approved annual rate increase (decrease), percentage			(2.40%)
Public Service Commission of Wisconsin (PSCW) | 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%
Public Service Commission of Wisconsin (PSCW) | 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%
Public Service Commission of Wisconsin (PSCW) | 2014 Rates | Electric rates
Regulatory environment
Approved annual rate increase (decrease)				$ 28.0
Approved annual rate increase (decrease), percentage				1.00%
Approved reduction in bill credits				$ 45.0
Approved reduction in bill credits, percentage				(1.60%)
Public Service Commission of Wisconsin (PSCW) | 2014 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)				$ 0.0
Public Service Commission of Wisconsin (PSCW) | 2014 Rates | Steam rates | Downtown Milwaukee (Valley) steam customers
Regulatory environment
Approved annual rate increase (decrease)				$ 1.3
Approved annual rate increase (decrease), percentage				6.00%
Public Service Commission of Wisconsin (PSCW) | 2014 Rates | Steam rates | Milwaukee County steam customers
Regulatory environment
Approved annual rate increase (decrease)				$ 1.0
Approved annual rate increase (decrease), percentage				6.00%
Public Service Commission of Wisconsin (PSCW) | 2013 Rates
Regulatory environment
Approved return on equity (as a percent)				10.40%
Public Service Commission of Wisconsin (PSCW) | 2013 Rates | Electric rates
Regulatory environment
Refund related to proceeds of a Treasury Grant				$ 63.0
Refund related to proceeds of a Treasury Grant, percentage				2.30%
Public Service Commission of Wisconsin (PSCW) | 2013 Rates | Electric rates | Non-fuel costs
Regulatory environment
Approved annual rate increase (decrease)				$ 70.0
Approved annual rate increase (decrease), percentage				2.60%
Approved annual rate increase, excluding Treasury Grant				$ 133.0
Approved annural rate increase percentage, excluding Treasury Grant				4.80%
Public Service Commission of Wisconsin (PSCW) | 2013 Rates | Electric rates | Fuel costs
Regulatory environment
Approved annual rate increase (decrease)				$ 44.0
Approved annual rate increase (decrease), percentage				1.60%
Public Service Commission of Wisconsin (PSCW) | 2013 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)				$ (8.0)
Approved annual rate increase (decrease), percentage				(1.90%)
Public Service Commission of Wisconsin (PSCW) | 2013 Rates | Natural gas rates | Bad debt expense
Regulatory environment
Approved annual rate increase (decrease)				$ (6.4)
Public Service Commission of Wisconsin (PSCW) | 2013 Rates | Steam rates | Downtown Milwaukee (Valley) steam customers
Regulatory environment
Approved annual rate increase (decrease)				$ 1.3
Approved annual rate increase (decrease), percentage				6.00%
Public Service Commission of Wisconsin (PSCW) | 2013 Rates | Steam rates | Milwaukee County steam customers
Regulatory environment
Approved annual rate increase (decrease)				$ 1.0
Approved annual rate increase (decrease), percentage				7.00%
UMERC
Regulatory environment
Term of Electric Power Purchase Agreement	20 years
Capacity of Natural Gas Generating Facility | MW	180
Cost to construct power plant	$ 265.0
Cost to construct power plant with AFUDC	$ 275.0
Estimated portion of power plant cost recovery from Tilden Mines	50.00%
Estimated portion of power plant cost recovery from utility customers	50.00%