Consolidated Statements of Capitalization (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Common Equity	$ 4,135.1		$ 3,963.3
Preferred Stock	30.4		30.4
Obligations under capital leases	120.0		132.4
Unamortized discount, net and other	(27.0)		(26.9)
Long-term debt due currently	(412.1)		(32.6)
Total Long-Term Debt	4,453.8		4,614.3
Total Capitalization	8,619.3		8,608.0
Debentures (unsecured), 4.50% due 2013 [Member]
Long-Term debt, Unsecured	300.0		300.0
Debentures (unsecured), 6.60% due 2013 [Member]
Long-Term debt, Unsecured	45.0		45.0
Debentures (unsecured), 6.00% due 2014 [Member]
Long-Term debt, Unsecured	300.0		300.0
Debentures (unsecured), 5.20% due 2015 [Member]
Long-Term debt, Unsecured	125.0		125.0
Debentures (unsecured), 6.25% due 2015 [Member]
Long-Term debt, Unsecured	250.0		250.0
Debentures (unsecured), 4.25% due 2019 [Member]
Long-Term debt, Unsecured	250.0		250.0
Debentures (unsecured) 2.95% due 2021 [Member]
Long-Term debt, Unsecured	300.0		300.0
Debentures (unsecured), 6-1/2% due 2028 [Member]
Long-Term debt, Unsecured	150.0		150.0
Debentures (unsecured), 5.625% due 2033 [Member]
Long-Term debt, Unsecured	335.0		335.0
Debentures (unsecured), 5.90% due 2035 [Member]
Long-Term debt, Unsecured	90.0		90.0
Debentures (unsecured), 5.70% due 2036 [Member]
Long-Term debt, Unsecured	300.0		300.0
Debentures (unsecured), 3.65% due 2042 [Member]
Long-Term debt, Unsecured	250.0		0
Debentures (unsecured), 6-7/8% due 2095 [Member]
Long-Term debt, Unsecured	100.0		100.0
Notes (secured, nonrecourse), 4.81% effective rate due 2030 [Member]
Long-Term debt, Secured	2.0		2.0
Notes (secured, nonrecourse), 4.91% due 2012-2030 [Member]
Long-Term debt, Secured	126.7		131.2
Notes (secured, nonrecourse), 5.209% due 2012-2030 [Member]
Long-Term debt, Secured	238.6		245.4
Notes (secured, nonrecourse), 4.673% due 2012-2031 [Member]
Long-Term debt, Secured	196.7		202.3
Notes (secured, nonrecourse), 6.00% due 2012-2033 [Member]
Long-Term debt, Secured	142.1		145.5
Notes (secured, nonrecourse), 6.09% due 2030-2040 [Member]
Long-Term debt, Secured	275.0		275.0
Notes (secured, nonrecourse), 5.848% due 2031-2041 [Member]
Long-Term debt, Secured	215.0		215.0
Notes (secured, nonrecourse) 6.00% due 2021 [Member]
Long-Term debt, Secured	1.8		0
Notes (unsecured), 6.51% due 2013 [Member]
Long-Term debt, Unsecured	30.0		30.0
Notes (unsecured), 6.94% due 2028 [Member]
Long-Term debt, Unsecured	50.0		50.0
Notes (unsecured), 0.504% variable rate due 2016 [Member]
Long-Term debt, Unsecured	67.0	[1]	67.0	[1]
Notes (unsecured), 0.504% variable rate due 2030 [Member]
Long-Term debt, Unsecured	80.0	[1]	80.0	[1]
Notes (unsecured), 6.20% due 2033 [Member]
Long-Term debt, Unsecured	200.0		200.0
Junior Notes (unsecured), 6.25% due 2067 [Member]
Long-Term debt, Unsecured	500.0		500.0
Wisconsin Energy Corporation [Member]
Preferred Stock	0		0
Wisconsin Electric [Member]
Long-Term debt, Unsecured	147.0		147.0
Six Per Cent. Preferred Stock [Member] | Wisconsin Electric [Member]
Preferred Stock	4.4		4.4
Serial preferred stock, 3.60% Series Redeemable [Member] | Wisconsin Electric [Member]
Preferred Stock	26.0		26.0
Serial preferred stock, $25 par value; authorized 5,000,000 shares; none outstanding [Member] | Wisconsin Electric [Member]
Preferred Stock	$ 0		$ 0

[1] Variable interest rate as of December 31, 2012.