Rate Matters Rate Matters, NSP-WI (Details) (Public Service Commission of Wisconsin (PSCW) [Member], NSP-Wisconsin, USD $) In Millions, unless otherwise specified	1 Months Ended
	May 31, 2014
NSP-WI 2015 Electric Rate Case [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Percentage	3.20%
Public Utilities, Requested Return on Equity, Percentage	10.20%
Electric Rate Case 2015 [Member]
NSP-WI 2015 Electric Rate Case [Line Items]
Public Utilities, amount requested by public utility related to production and transmission fixed charges	$ 28.1
Public Utilities, Requested Rate Increase (Decrease), Amount	20.6
Public Utilities, percentage of earnings above the authorized ROE that will be refunded to customers	100.00%
Public Utilities, amount requested by public utility related to fuel and purchased power	13.9
Public Utilities, requested base revenue increase (decrease) excluding NSP-Minnesota depreciation reserve and Monticello EPU deferral adjustments	42.0
Public Utilities, Adjustment to requested rate increase (decrease) related to the NSP-Minnesota transmission depreciation reserve	(16.2)
Public Utilities, Adjustment to requested rate increase (decrease) related to the Monticello EPU deferral	$ (5.2)