Shareholders' Equity - Share Repurchases (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Oct. 30, 2015	Dec. 31, 2012
Equity [Abstract]
Stock repurchased during period (in shares)	6,000,000
Repurchases of common stock	$ 523.2	$ 72.6
Subsequent Event [Line Items]
Number of shares authorized to be repurchased (in shares)				8,000,000
Subsequent event
Subsequent Event [Line Items]
Number of shares authorized to be repurchased (in shares)			6,000,000