Common Equity (Details 4) (USD $)	1 Months Ended	12 Months Ended			1 Months Ended	20 Months Ended	12 Months Ended
	Jan. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	May 31, 2011 Share Repurchase Plan, 2011 [Member]	Dec. 31, 2012 Share Repurchase Plan, 2011 [Member]	Dec. 31, 2012 Share Repurchases to Fulfill Exercised Stock Options and Restricted Stock Awards [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, 2012 Share Repurchase Plan, 2011 [Member]	Dec. 31, 2011 Share Repurchase Plan, 2011 [Member]	Dec. 31, 2010 Share Repurchase Plan, 2011 [Member]	Dec. 31, 2012 Performance Units [Member]	Dec. 31, 2012 Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock Repurchased During Period, Shares		4,300,000	6,200,000	5,800,000			2,800,000	3,000,000	5,800,000	1,500,000	3,200,000	0
Common Equity (Textuals)
Common stock shares, Authorized		325,000,000	325,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Period of Accrual for Costs Related to Performance Units													3 years
Common stock shares, Outstanding		229,039,456	230,486,804
Stock options awarded under long-term incentive compensation														938,770
Exercise price of non qualified stock options	$ 37.46
Intrinsic value of options exercised		$ 47,500,000	$ 36,100,000	$ 62,100,000
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
Amount paid for Shares Purchased by agents from open market		153,200,000	193,900,000	156,600,000
Exercise of stock options		49,800,000	54,400,000	90,900,000
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		3,600,000,000
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						4,700,000
Treasury Stock Acquired, Average Cost Per Share						$ 32.63
Treasury Stock, Value, Acquired, Cost Method						151,800,000
Stock Repurchased During Period, Value		$ 153,200,000	$ 193,900,000	$ 156,600,000			$ 101,400,000	$ 93,900,000	$ 156,600,000	$ 51,800,000	$ 100,000,000	$ 0