Rate Matters, NSP-Wisconsin (Details) (Public Service Commission of Wisconsin (PSCW) [Member], NSP-Wisconsin, USD $) In Millions, unless otherwise specified	1 Months Ended
	May 31, 2013
Electric and Gas Rate Case 2014, Electric Rates [Member]
Rate Matters [Abstract]
Entity's requested rate increase (decrease)	$ 40.0
Percentage increase in entity's requested rate increase (in hundredths)	6.50%
Electric and Gas Rate Case 2014, Gas Rates [Member]
Rate Matters [Abstract]
Entity's requested rate increase (decrease)	4.7
Percentage increase in entity's requested rate increase (in hundredths)	3.80%
Electric and Gas Rate Case 2014 [Member]
Rate Matters [Abstract]
Entity's requested return on equity (in hundredths)	10.40%
Entity's requested equity ratio percent (in hundredths)	52.50%
Forecasted Average Net Investment Rate Base, Electric Utility	895.3
Forecasted Average Net Investment Rate Base, Natural Gas Utility	$ 89.8