Common Equity Automatic Dividend Reinvestment and Stock Purchase Plan (Details) (USD $) In Millions, except Share data, unless otherwise specified	6 Months Ended		3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Automatic Dividend Reinvestment and Stock Purchase Plan [Member]	Jun. 30, 2012 Automatic Dividend Reinvestment and Stock Purchase Plan [Member]
Stock Issued During Period, Shares, Dividend Reinvestment Plan and Stock Purchase Plan			60,779	129,112
Proceeds From Issuance of Shares Under Dividend Reinvestment Plan And Stock Purchase Plan	$ 7.0	$ 7.5	$ 3.3	$ 6.9
Shares Held in Reserve Related to Dividend Reinvestment Plan and Stock Purchase Plan			2,239,931	2,239,931