Shareholders' Equity - Share Repurchases (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jul. 28, 2016	Oct. 29, 2015	Dec. 12, 2012
Equity, Class of Treasury Stock [Line Items]
Repurchases of common stock	$ 290.5	$ 168.7
Common Stock Repurchase 2012 Authorization
Equity, Class of Treasury Stock [Line Items]
Number of shares authorized to be repurchased (in shares)					8,000,000
Stock repurchased during period (in shares)		2,000,000
Repurchases of common stock		$ 168.7
Remaining authorized repurchase amount (shares)	0
Common Stock Repurchase 2015 Authorization
Equity, Class of Treasury Stock [Line Items]
Number of shares authorized to be repurchased (in shares)				6,000,000
Stock repurchased during period (in shares)	3,800,000
Repurchases of common stock	$ 290.5
Remaining authorized repurchase amount (shares)	1,500,000
Subsequent Event
Equity, Class of Treasury Stock [Line Items]
Number of shares authorized to be repurchased (in shares)			6,000,000