Rate Matters, NSP-Wisconsin (Details) - NSP-Wisconsin - USD ($) $ in Millions		1 Months Ended
		Dec. 31, 2016	Jul. 31, 2016	Apr. 30, 2016
PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case - Electric Rates 2017
Rate Matters [Abstract]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 17.4
Public Utilities, Requested Rate Increase (Decrease), Percentage				2.40%
Public Utilities, Requested Rate Base, Amount				$ 1,188.0
Public utilities, Requested Increase Related to Rate Base Investments				11.0
Public Utilities, Requested Increase Related to Generation and Transmission Expenses	[1]			6.8
Public Utilities, Requested Increase Related to Fuel and Purchased Power Expenses				11.0
Public Utilities, Total Requested Rate Increase Excluding Refunds				28.8
Public Utilities, Requested Decrease Related to Fuel Refunds	[2]			(9.5)
Public Utilities, Requested Decrease Related to Settlement Refund				(1.9)
PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case - Gas Rates 2017
Rate Matters [Abstract]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 4.8
Public Utilities, Requested Rate Increase (Decrease), Percentage				3.90%
PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case
Rate Matters [Abstract]
Public Utilities, Requested Return on Equity, Percentage				10.00%
Percentage of excess Earnings to be Refunded due to Earnings Cap				100.00%
Public Service Commission of Wisconsin (PSCW) | PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case - Electric Rates 2017
Rate Matters [Abstract]
Public Utilities, Approved Rate Increase (Decrease), Amount		$ 22.5
Public Utilities, Approved Rate Increase (Decrease), Percentage		3.20%
Public Utilities, Approved Increase Related to Rate Base Investments		$ 7.6
Public Utilities, Approved Increase Related to Generation and Transmission Expenses	[1]	6.1
Public Utilities, Approved Increase Related to Fuel and Purchased Power Expenses		10.7
Public Utilities, Total Approved Rate Increase, Excluding Refunds		24.4
Public Utilities, Approved Decrease Related to Fuel Refunds	[2]	0.0
Public Utilities, Approved Decrease Related to Settlement Refund		(1.9)
Public Utilities, Revised Requested Rate Increase			$ 29.9
Public Utilities, Revised Requested Rate Increase, Percentage			4.20%
Public Service Commission of Wisconsin (PSCW) | PSCW Proceeding - Wisconsin 2017 Electric and Gas Rate Case - Gas Rates 2017
Rate Matters [Abstract]
Public Utilities, Approved Rate Increase (Decrease), Amount		$ 4.8
Public Utilities, Approved Rate Increase (Decrease), Percentage		3.90%

[1] Includes Interchange Agreement billings. For financial reporting purposes, these expenses are included in O&M.

[2] In July 2016, the PSCW required NSP-Wisconsin to return the 2015 fuel refund directly to customers, rather than using it to offset the proposed 2017 rate increase, as originally proposed by NSP-Wisconsin. This decision, when combined with the increase in forecasted fuel and purchased power expense, effectively increased NSP-Wisconsin’s requested electric rate increase to $29.9 million, or 4.2 percent.