Long-Term Debt and Capital Lease Obligations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 Megawatt	Dec. 31, 2010	Dec. 31, 2009
Long-term debt outstanding maturities and sinking fund requirements
2012	$ 20.3
2013	396.3
2014	322.4
2015	399.5
2016	27.4
Thereafter	3,375.5
Total	4,541.4
Summary of capitalized leased facilities
Long-term power purchase commitment	140.3	140.3
Accumulated amortization	(81.1)	(75.5)
Total Leased Facilities	59.2	64.8
Future minimum lease payments under capital lease and present value of net minimum lease payments
2012	38.9
2013	40.4
2014	41.9
2015	43.5
2016	45.1
Thereafter	85.4
Total Minimum Lease Payments	295.2
Less: Estimated Executory Costs	(74.9)
Net Minimum Lease Payments	220.3
Less: Interest	(87.9)
Present Value of Net Minimum Lease Payments	132.4
Less: Due Currently	(12.4)
Future minimum lease payments under our capital lease and the present value of our net minimum lease payments	120.0
Long-Term Debt and Capital Lease Obligations (Textuals) [Abstract]
Issuance of long-term debt	720.0	530.0	261.5
Restriction under RCC	The RCC provides that we may not redeem, defease or purchase and our subsidiaries may not purchase any Junior Notes on or before May 15, 2037, unless, subject to certain limitations described in the RCC, during the 180 days prior to the date of redemption, defeasance or purchase, we have received a specified amount of proceeds from the sale of qualifying securities.
Retirement of unsecured notes		281.5
Power capacity from a gas-fired cogeneration facility under capital lease (MW)	236
Total operating lease payment	31.3	30.2
Increase in regulatory asset due to minimum lease payment			78.5
Regulatory asset value at the end of life of contract	0
Total capital lease obligation	132.4	141.9
Capital lease obligation at the end of life of contract	0
Wis Elec Debentures due September 15 2021 [Member]
Long-Term Debt and Capital Lease Obligations (Textuals) [Abstract]
Issuance of long-term debt	300.0
Debt instrument interest rate stated percentage rate	2.95%
Series B [Member]
Long-Term Debt and Capital Lease Obligations (Textuals) [Abstract]
Issuance of long-term debt	420.0
Series B Senior Notes due January 19 2031 [Member]
Long-Term Debt and Capital Lease Obligations (Textuals) [Abstract]
Issuance of long-term debt	205.0
Debt instrument interest rate stated percentage rate	4.673%
Series B Senior Notes due January 19 2041 [Member]
Long-Term Debt and Capital Lease Obligations (Textuals) [Abstract]
Issuance of long-term debt	215.0
Debt instrument interest rate stated percentage rate	5.848%
Series A [Member]
Long-Term Debt and Capital Lease Obligations (Textuals) [Abstract]
Issuance of long-term debt		530.0
Notes (secured, nonrecourse), 5.209% due 2011-2030 [Member]
Long-Term Debt and Capital Lease Obligations (Textuals) [Abstract]
Issuance of long-term debt		255.0
Secured Long-term Debt, Noncurrent	245.4	251.9
Debt instrument interest rate stated percentage rate	5.209%	5.209%
Notes (secured, nonrecourse), 6.09% due 2030-2040 [Member]
Long-Term Debt and Capital Lease Obligations (Textuals) [Abstract]
Issuance of long-term debt		275.0
Secured Long-term Debt, Noncurrent	275.0	275.0
Debt instrument interest rate stated percentage rate	6.09%	6.09%
Debentures (unsecured), 4.25% due 2019 [Member]
Long-Term Debt and Capital Lease Obligations (Textuals) [Abstract]
Issuance of long-term debt			250.0
Unsecured Long-term Debt, Noncurrent	250.0	250.0
Debt instrument interest rate stated percentage rate	4.25%	4.25%
Notes (unsecured), 6.20% due 2033 [Member]
Long-Term Debt and Capital Lease Obligations (Textuals) [Abstract]
Unsecured Long-term Debt, Noncurrent	200.0	200.0
Debt instrument interest rate stated percentage rate	6.20%	6.20%
Wisconsin Electric [Member]
Long-Term Debt and Capital Lease Obligations (Textuals) [Abstract]
Number of series of tax-exempt pollution control refunding bonds	2
Unsecured Long-term Debt, Noncurrent	$ 147.0	$ 147.0
Period of Power purchase contract with an unaffiliated independent power producer	25
Power capacity from a gas-fired cogeneration facility under capital lease (MW)	236
Minimum energy requirement in gas-fired cogeneration facility	0
Power purchase contract expiration year	Dec. 31, 2022
Power purchase contract expected future renewable period	10