Common Share Narrative (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 23, 2012	Oct. 11, 2011	Aug. 31, 2008
Earnings Per Share [Abstract]
Weighted-average shares - basic:	92,300,000	95,500,000	89,100,000
Anti-dilutive effect on computation of diluted earnings per share	400,000	300,000	1,200,000
Common shares authorized to be repurchased						10,000,000
Increase in common share repurchase authorization				13,200,000	5,300,000
Remaining shares to be repurchased	8,700,000
Repurchase of common shares, shares	6,300,000	5,000,000	1,200,000
Purchase of common shares for treasury	$ 233.2	$ 131.6	$ 15.9
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	1,200,000	1,000,000	700,000
Weighted Average Number of Shares Outstanding, Diluted	93,500,000	96,500,000	89,800,000