REGULATORY ENVIRONMENT (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended										3 Months Ended	1 Months Ended
	Apr. 30, 2014 Public Service Commission of Wisconsin (PSCW) 2015 Rates WPS	Dec. 31, 2013 Public Service Commission of Wisconsin (PSCW) 2014 Rates WPS	Dec. 31, 2012 Public Service Commission of Wisconsin (PSCW) 2013 Rates WPS	Apr. 30, 2014 Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2015 Rates WPS	Dec. 31, 2013 Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2014 Rates WPS	Dec. 31, 2012 Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2013 Rates WPS	Apr. 30, 2014 Public Service Commission of Wisconsin (PSCW) Retail natural gas rate case 2015 Rates WPS	Dec. 31, 2013 Public Service Commission of Wisconsin (PSCW) Retail natural gas rate case 2014 Rates WPS	Dec. 31, 2012 Public Service Commission of Wisconsin (PSCW) Retail natural gas rate case 2013 Rates WPS	Jan. 31, 2013 Michigan Public Service Commission (MPSC) MGU	Jun. 30, 2013 Michigan Public Service Commission (MPSC) MGU	Dec. 31, 2013 Michigan Public Service Commission (MPSC) Retail electric rate case 2014 Rates UPPCO	Nov. 30, 2013 Michigan Public Service Commission (MPSC) Retail natural gas rate case 2014 Rates MGU	Feb. 28, 2014 Illinois Commerce Commission (ICC) Retail natural gas rate case 2015 Rates PGL	Feb. 28, 2014 Illinois Commerce Commission (ICC) Retail natural gas rate case 2015 Rates NSG	Dec. 31, 2013 Illinois Commerce Commission (ICC) Retail natural gas rate case 2013 Rates PGL	Jun. 30, 2013 Illinois Commerce Commission (ICC) Retail natural gas rate case 2013 Rates PGL	Dec. 31, 2013 Illinois Commerce Commission (ICC) Retail natural gas rate case 2013 Rates NSG	Jun. 30, 2013 Illinois Commerce Commission (ICC) Retail natural gas rate case 2013 Rates NSG	Apr. 30, 2014 Minnesota Public Utilities Commission (MPUC) Retail natural gas rate case 2014 Rates MERC	Dec. 31, 2013 Minnesota Public Utilities Commission (MPUC) Retail natural gas rate case 2014 Rates MERC	Sep. 30, 2013 Minnesota Public Utilities Commission (MPUC) Retail natural gas rate case 2014 Rates MERC	Apr. 30, 2014 Minnesota Public Utilities Commission (MPUC) Retail natural gas rate case 2014 Rates MERC Minimum	Apr. 30, 2014 Minnesota Public Utilities Commission (MPUC) Retail natural gas rate case 2014 Rates MERC Maximum	Jul. 31, 2012 Minnesota Public Utilities Commission (MPUC) Retail natural gas rate case 2011 Rates MERC	Jul. 31, 2014 Subsequent Event Retail natural gas rate case 2015 Rates PGL	Jul. 31, 2014 Subsequent Event Retail natural gas rate case 2015 Rates NSG	Aug. 31, 2014 Subsequent Event Illinois Commerce Commission (ICC) Retail natural gas rate case 2015 Rates PGL	Jul. 31, 2014 Subsequent Event Illinois Commerce Commission (ICC) Retail natural gas rate case 2015 Rates PGL	Aug. 31, 2014 Subsequent Event Illinois Commerce Commission (ICC) Retail natural gas rate case 2015 Rates NSG	Jul. 31, 2014 Subsequent Event Illinois Commerce Commission (ICC) Retail natural gas rate case 2015 Rates NSG
Regulatory Environment
Requested annual increase (decrease) in rates for customers				$ 76.8			$ (1.6)							$ 128.9	$ 7.1							$ 14.2
Requested return on common equity percent reflected in rates of customers	10.60%													10.25%	10.25%					10.75%		10.75%
Requested percent of capital structure composed of common equity	50.51%													50.31%	50.41%					50.31%		50.31%
Approved annual increase (decrease) in rates for customers					(12.8)	28.5		4.0	(3.4)			5.8	4.5				57.2		6.6						11.0
Approved return on common equity percent reflected in rates of customers		10.20%	10.30%									10.15%	10.25%				9.28%		9.28%						9.70%
Approved percent of capital structure composed of common equity		50.14%	51.61%									56.74%	48.62%				50.43%		50.32%						50.48%
Fuel refund						20.5
Deferral related to pension and other employee benefits costs						7.3			2.1
Recovery of income tax amounts previously expensed related to the Federal Health Care Reform Act			5.9
Annual cap for decoupling						14.0			8.0
Reversal of disallowance of depreciation expense associated with the retirement of certain assets										2.5
Reduction to depreciation expense											(2.5)
Adjustment to annual increase (decrease) in rates for customers																2.6		0.1
Interim annual rate increase (decrease) approved for customers																					10.5
Interim rate of return on common equity approved for customers																					9.70%
Interim percent of capital structure composed of common equity																					50.31%
Recommended rate increase (decrease) in rates for customers																							3.5	5.7		54.8	(1.0)		97.1		3.5
Recommended rate of return on common equity																										9.15%	9.15%		9.06%		9.06%
Recommended percent of capital structure composed of common equity																										50.31%	50.41%
Amended requested annual increase (decrease) in rates for customers																				$ 12.2								$ 102.3		$ 6.5
Trial basis period for decoupling mechanism																									3 years
Annual percent cap on decoupling based on distribution revenues approved in the rate case																									10.00%