Common Equity (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended				12 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2010	Jan. 31, 2009	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Recorded pre-tax share-based compensation expense and related tax benefit for share-based awards made to employees and directors
Share-based compensation expense					$ 28.5	$ 35.1	$ 25.8
Related Tax Benefit					11.4	14.1	10.3
Common Equity (Textuals)
Actual tax benefit realized for the tax deductions from option exercises/settlement					14.3	24.1	4.8
Stock options [Member]
Recorded pre-tax share-based compensation expense and related tax benefit for share-based awards made to employees and directors
Share-based compensation expense					2.6	7.6	10.8
Common Equity (Textuals)
Restricted stock vesting period in years					3 years
Performance units [Member]
Recorded pre-tax share-based compensation expense and related tax benefit for share-based awards made to employees and directors
Share-based compensation expense					24.1	26.0	14.0
Restricted stock activity
Granted, Number of Shares	346,570.0	435,690.0	555,830.0	666,440.0
Common Equity (Textuals)
Unrecognized total compensation costs related share based compensation					18.3
Intrinsic Value					26.7	12.6	9.8
Actual tax benefit realized for the tax deductions from option exercises/settlement					9.7	4.3	3.4
Months, on a weighted-average basis, expected for recognizing total compensation costs related to performance units					19
Period of accrual for costs related to performance units (in years)					3 years
Restricted stock [Member]
Recorded pre-tax share-based compensation expense and related tax benefit for share-based awards made to employees and directors
Share-based compensation expense					1.8	1.5	1.0
Restricted stock activity
Outstanding	192,558.0	205,404.0			205,404.0
Granted, Number of Shares	94,959.0				74,850.0
Granted, Weighted-Average Market Price					$ 29.00
Released, Number of Shares					(83,452.0)
Released, Weighted-Average Market Price					$ 18.82
Forfeited, Number of Shares					(4,244.0)
Forfeited, Weighted-Average Market Price					$ 26.62
Outstanding					192,558.0	205,404.0
Common Equity (Textuals)
Unrecognized total compensation costs related share based compensation					2.4
Restricted stock vesting period in years	3				10
Intrinsic Value					2.5	2.3	0.9
Actual tax benefit realized for the tax deductions from option exercises/settlement					0.8	0.7	0.3
Months, on a weighted-average basis, expected for recognizing total compensation costs related to restricted stock options					20
Non-Vested Options [Member]
Common Equity (Textuals)
Unrecognized total compensation costs related share based compensation					$ 0.6
Months, on a weighted-average basis, expected for recognizing total compensation costs related to non-vested stock options					19
Maximum [Member]
Common Equity (Textuals)
Requirement to maintain common equity ratio by Wisconsin Electric		53.50%
Requirement to maintain common equity ratio by Wisconsin Gas		50.00%
Minimum [Member]
Common Equity (Textuals)
Requirement to maintain common equity ratio by Wisconsin Electric		48.50%
Requirement to maintain common equity ratio by Wisconsin Gas		45.00%