Shareholders' Equity - Share Repurchases (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Jul. 28, 2016	Oct. 29, 2015
Equity, Class of Treasury Stock [Line Items]
Shares repurchased during period (in shares)	600,000	1,500,000
Total cost of shares repurchased	$ 57.0	$ 117.7
2015 Authorization
Equity, Class of Treasury Stock [Line Items]
Shares authorized to be repurchased (in shares)				6,000,000
Shares remaining authorized for repurchase (in shares)	0
2016 Authorization
Equity, Class of Treasury Stock [Line Items]
Shares authorized to be repurchased (in shares)			6,000,000
Shares remaining authorized for repurchase (in shares)	4,200,000