Earnings Per Common Share (Earnings Per Share Computation) (Details) (USD $) Share data in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Earnings Per Common Share [Abstract]
Net income attributable to common shareholders	$ 130,100,000	$ 127,500,000	$ 214,200,000	$ 373,000,000
Less: Income allocated to participating securities	2,300,000	1,300,000	4,000,000	4,100,000
Net income available to common shareholders	$ 127,800,000	$ 126,200,000	$ 210,200,000	$ 368,900,000
Weighted average common shares outstanding	86.6	93.3	86.0	94.4
Dilutive common share equivalents from share-based compensation plans	1.2	1.0	1.7	1.1
Weighted average common and common equivalent shares outstanding, assuming dilution	87.8	94.3	87.7	95.5