Long-Term Debt and Capital Lease Obligations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Megawatt	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Long-term debt outstanding maturities and sinking fund requirements
Next year	$ 396.3
Year 2	322.4
Year 3	399.5
Year 4	27.4
Year 5	29.5
Thereafter	3,597.8
Total	4,772.9
Summary of capitalized leased facilities
Long-term power purchase commitment	140.3	140.3
Accumulated amortization	(86.8)	(81.1)
Total Leased Facilities	53.5	59.2
Future minimum lease payments under capital lease and present value of net minimum lease payments
Due next year	40.4
Due in two years	41.9
Due in three years	43.5
Due in four years	45.1
Due in five years	13.9
Thereafter	71.5
Total Minimum Lease Payments	256.3
Less: Estimated Executory Costs	(68.4)
Capital Leases Future Minimum Payments Due, Less Executory Costs	187.9
Less: Interest	(67.9)
Net Minimum Lease Payments	120.0
Less: Due Currently	(15.8)
Future minimum lease payments under our capital lease and the present value of our net minimum lease payments	104.2
Long-Term Debt and Capital Lease Obligations (Textuals) [Abstract]
Issuance of long-term debt	251.8	720.0	530.0
Number of series of tax-exempt pollution control refunding bonds	2
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
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
Total operating lease payment	32.5	31.3
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	120.0	132.4
Capital lease obligation at the end of life of contract	0
Wis Elec Debentures due December 15 2042 [Member]
Long-Term Debt and Capital Lease Obligations (Textuals) [Abstract]
Issuance of long-term debt	250.0
Debt instrument interest rate stated percentage rate	3.65%
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 2012-2030 [Member]
Long-Term Debt and Capital Lease Obligations (Textuals) [Abstract]
Issuance of long-term debt			255.0
Secured Long-term Debt, Noncurrent	238.6	245.4
Debt instrument interest rate stated percentage rate	5.209%	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%	6.09%
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%
Parent Company [Member]
Long-term debt outstanding maturities and sinking fund requirements
Next year	0
Year 2	0
Year 3	0
Year 4	0
Year 5	0
Thereafter	700.0
Total	700.0
Wisconsin Electric [Member]
Long-Term Debt and Capital Lease Obligations (Textuals) [Abstract]
Unsecured Long-term Debt, Noncurrent	$ 147.0	$ 147.0