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, 2013	Jun. 30, 2012	Jun. 30, 2013 Automatic Dividend Reinvestment and Stock Purchase Plan [Member]	Jun. 30, 2013 Automatic Dividend Reinvestment and Stock Purchase Plan [Member]
Stock Issued During Period, Shares, Dividend Reinvestment Plan and Stock Purchase Plan			91,588	198,790
Proceeds From Issuance of Shares Under Dividend Reinvestment Plan And Stock Purchase Plan	$ 6.9	$ 7.0	$ 3.3	$ 6.4
Shares Held in Reserve Related to Dividend Reinvestment Plan and Stock Purchase Plan			4,046,198	4,046,198