Common Equity (Details 4) (USD $)	1 Months Ended	12 Months Ended							1 Months Ended	8 Months Ended
	Jan. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Stock options [Member]	Dec. 31, 2011 Share Repurchases to Fulfill Exercised Stock Options and Restricted Stock Awards [Member]	Dec. 31, 2010 Share Repurchases to Fulfill Exercised Stock Options and Restricted Stock Awards [Member]	Dec. 31, 2009 Share Repurchases to Fulfill Exercised Stock Options and Restricted Stock Awards [Member]	May 31, 2011 Share Repurchase Plan, 2011 [Member]	Dec. 31, 2011 Share Repurchase Plan, 2011 [Member]
Common Equity (Textuals)
Common stock shares, Authorized		325,000,000	325,000,000
Common stock shares, Outstanding		230,486,804	233,771,194
Stock options awarded under long-term incentive compensation	938,770				458,180.0
Exercise price of non qualified stock options	$ 34.88
Intrinsic value of options exercised		$ 36,100,000	$ 62,100,000	$ 12,000,000
Exercise price of the stock option on the grant date		no less than 100% of the common stock's fair market value
Mimimum period after grant that stock options can be exercised					6 months
Option grants vesting period in years					3 years
Expiration of options from time of grant					10 years
Minimum percentage award based on performance unit		0.00
Maximum percentage award based on performance unit		1.75
Shares Purchased by agents from open market						3,000,000	5,800,000	1,400,000
Amount paid for Shares Purchased by agents from open market		193,900,000	156,600,000	29,600,000		93,900,000	156,600,000	29,600,000
Exercise of stock options		54,400,000	90,900,000	17,000,000		54,400,000	90,900,000	17,000,000
Maximum period to defer interest payments on the Junior Notes		We have the option to defer interest payments on the Junior Notes, from time to time, for one or more periods of up to 10 consecutive years per period. During any period in which we defer interest payments, we may not declare or pay any dividends or distributions on, or redeem, repurchase or acquire, our common stock.
Ability to declare common dividends limited to Percentage of Net Income by Wisconsin Electric		limited to 75% or 50%
Wisconsin Electric's common stock equity to total capitalization		is less than 25% and 20%
3.60% Serial Preferred Stock		3.60%
Maximum percentage of equity method investment		50.00%
Equity method investment		3,500,000,000
Percentage of equity method investment exceeding consolidated net assets		25.00%
Stock Repurchase Program, Authorized Amount									300,000,000
Stock Repurchased and Retired During Period, Shares										3,200,000
Treasury Stock Acquired, Average Cost Per Share										$ 30.79
Treasury Stock, Value, Acquired, Cost Method										$ 100,000,000