Common Shareholders' Equity (Narrative) (Details) (USD $) In Millions, except Share data	1 Months Ended		3 Months Ended			6 Months Ended	12 Months Ended
	Jun. 30, 2011	Oct. 27, 2010	Jun. 30, 2011	Dec. 31, 2010	Mar. 31, 2010	Jun. 30, 2011	Dec. 31, 2009
Common Shareholders' Equity
Common stock, shares authorized	250,000,000		250,000,000	250,000,000		250,000,000
Common stock, shares outstanding	117,712,910		117,712,910	116,924,844		117,712,910
Amount authorized to be repurchased		$ 200
Stock repurchased, shares				2,040,000	145,915	0
Shares repurchase average per share price				$ 25.75	$ 26.71
Amount available to be used to repurchase stock			147.5
Amount of stock repurchase							3.9
Warrants exercised	700,000
Proceeds from exercise of warrants	$ 14.7					$ 14.7
Repurchase of warrants outstanding	1,000,000		1,000,000			1,000,000
Common shares exercise price	$ 130		$ 130			$ 130