Asset Sales, Divestitures And Discontinued Operations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Net impacts of the discontinued operations on earnings
Income from Continuing Operations	$ 512.8		$ 454.4		$ 375.7
Income from Discontinued Operations, Net of Tax	13.4		2.1		6.7
Net Income	526.2		456.5		382.4
Asset Sales, Divestitures and Discontinued Operations (Textuals) [Abstract]
Ownership percentage in Edgewater Generating Unit 5 sold	25.00%
Proceeds From Sale Of Interest In Unit	38
Edison Sault [Member]
Net impacts of the discontinued operations on earnings
Income from Discontinued Operations, Net of Tax	0		0.7		1.5
Income Statement Balance Sheet and Additional Disclosures By Disposal Groups Including Discontinued Operations (Textuals) [Abstract]
Proceeds from sale of unit of operations			63.0
Other Operations [Member]
Net impacts of the discontinued operations on earnings
Income from Discontinued Operations, Net of Tax	13.4	[1]	1.4	[1]	4.9	[1]
Water Utility Operations [Member]
Net impacts of the discontinued operations on earnings
Income from Discontinued Operations, Net of Tax	0		0		0.3
Income Statement Balance Sheet and Additional Disclosures By Disposal Groups Including Discontinued Operations (Textuals) [Abstract]
Proceeds from sale of unit of operations					$ 14.5

[1] Primarily relates to the favorable resolution of uncertain state and federal tax positions associated with our previously discontinued manufacturing business.