Regulatory Environment (Details) $ in Millions	1 Months Ended												12 Months Ended
	Oct. 31, 2016 USD ($)	Aug. 31, 2016 USD ($) MW	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Nov. 30, 2015	Jun. 30, 2015	Apr. 30, 2015 USD ($)	Feb. 28, 2015 USD ($)	Jan. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Oct. 31, 2014 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2016 USD ($)
Regulatory environment
Percent fuel costs can vary from the rate case approved costs before deferral is required													2.00%
WE | 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%
WE | Public Service Commission of Wisconsin (PSCW) | 2016 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)										$ 0.0
WE | Public Service Commission of Wisconsin (PSCW) | 2016 Rates | Steam rates | Downtown Milwaukee (Valley) steam customers
Regulatory environment
Approved annual rate increase (decrease)										0.0
WE | Public Service Commission of Wisconsin (PSCW) | 2016 Rates | Steam rates | Milwaukee County steam customers
Regulatory environment
Approved annual rate increase (decrease)										$ 0.0
WE | 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%
WE | 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
WE | 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%
WE | 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%)
WE | 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%)
WE | 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%
WE | 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%
WE | 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%)
WE | Public Service Commission of Wisconsin (PSCW) | 2014 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)												$ 0.0
WE | 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%
WE | 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%
WE | Public Service Commission of Wisconsin (PSCW) | 2013 Rates
Regulatory environment
Approved return on equity (as a percent)												10.40%
WE | 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%
WE | 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%
WE | 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%
WE | 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%)
WE | Public Service Commission of Wisconsin (PSCW) | 2013 Rates | Natural gas rates | Bad debt expense
Regulatory environment
Approved annual rate increase (decrease)												$ (6.4)
WE | 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%
WE | 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%
WG | Public Service Commission of Wisconsin (PSCW) | 2016 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)										$ 21.4
Approved annual rate increase (decrease), percentage										3.20%
WG | Public Service Commission of Wisconsin (PSCW) | 2015 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)										$ 17.1
Approved annual rate increase (decrease), percentage										2.60%
Approved return on equity (as a percent)										10.30%
Approved common equity component average (as a percent)										49.50%
WG | Public Service Commission of Wisconsin (PSCW) | 2014 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)												$ 0.0
WG | Public Service Commission of Wisconsin (PSCW) | 2013 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)												$ (34.0)
Approved annual rate increase (decrease), percentage												(5.50%)
Approved return on equity (as a percent)												10.50%
WG | Public Service Commission of Wisconsin (PSCW) | 2013 Rates | Natural gas rates | Bad debt expense
Regulatory environment
Approved annual rate increase (decrease)												$ (43.8)
WPS | Public Service Commission of Wisconsin (PSCW) | 2016 Rates
Regulatory environment
Approved return on equity (as a percent)				10.00%
Approved common equity component average (as a percent)				51.00%
WPS | Public Service Commission of Wisconsin (PSCW) | 2016 Rates | Electric rates
Regulatory environment
Approved annual rate increase (decrease)				$ (7.9)
Approved annual rate increase (decrease), percentage				(0.80%)
Percent fuel costs can vary from the rate case approved costs before deferral is required				2.00%
Authorized revenue requirement for ReACT			$ 275.0	$ 275.0
WPS | Public Service Commission of Wisconsin (PSCW) | 2016 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)				$ (6.2)
Approved annual rate increase (decrease), percentage				(2.10%)
WPS | 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)										50.28%
WPS | Public Service Commission of Wisconsin (PSCW) | 2015 Rates | Electric rates
Regulatory environment
Approved annual rate increase (decrease)										$ 24.6
Percent fuel costs can vary from the rate case approved costs before deferral is required										2.00%
Increase in cost of fuel for electric generation										$ 42.0
Year-over-year positive (negative) change in decoupling refunded to or collected from customers										9.0
Customer recoveries (refunds) related to decoupling										(4.0)
WPS | Public Service Commission of Wisconsin (PSCW) | 2015 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)										(15.4)
Year-over-year positive (negative) change in decoupling refunded to or collected from customers										(16.0)
Customer recoveries (refunds) related to decoupling										(8.0)
WPS | Public Service Commission of Wisconsin (PSCW) | 2014 Rates | Electric rates
Regulatory environment
Customer recoveries (refunds) related to decoupling										(13.0)
WPS | Public Service Commission of Wisconsin (PSCW) | 2014 Rates | Natural gas rates
Regulatory environment
Customer recoveries (refunds) related to decoupling										$ 8.0
WPS | Michigan Public Service Commission (MPSC) | 2015 Rates | Electric rates
Regulatory environment
Approved annual rate increase (decrease)							$ 4.0
Approved return on equity (as a percent)							10.20%
Approved common equity component average (as a percent)							50.48%
Period of rate implementation							3 years
PGL and NSG | Illinois Commerce Commission (ICC) | Natural gas rates
Regulatory environment
Period of base rate freeze						2 years
PGL | Illinois Commerce Commission (ICC) | 2015 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)									$ 74.8
Approved return on equity (as a percent)									9.05%
Approved common equity component average (as a percent)									50.33%
Amended approved annual rate increase (decrease)								$ 71.1
NSG | Illinois Commerce Commission (ICC) | 2015 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)									$ 3.7
Approved return on equity (as a percent)									9.05%
Approved common equity component average (as a percent)									50.48%
Amended approved annual rate increase (decrease)								$ 3.5
MERC | Minnesota Public Utilities Commission (MPUC) | 2016 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)	$ 6.8
Approved annual rate increase (decrease), percentage	3.00%
Approved return on equity (as a percent)	9.11%
Approved common equity component average (as a percent)	50.32%
Number of years decoupling mechanism approved for	3 years
Interim rates to be refunded to customers													$ 3.0
MERC | Minnesota Public Utilities Commission (MPUC) | 2015 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)											$ 7.6
Approved return on equity (as a percent)											9.35%
Approved common equity component average (as a percent)											50.31%
Annual cap for decoupling mechanism (as a percent of rate case approved distribution revenues)											10.00%
Interim rates refunded to customers											$ 4.7
MGU | Michigan Public Service Commission (MPSC) | 2016 Rates | Natural gas rates
Regulatory environment
Approved annual rate increase (decrease)				$ 3.4
Approved annual rate increase (decrease), percentage				2.40%
Approved return on equity (as a percent)				9.90%
Approved common equity component average (as a percent)				52.00%
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%