Shareholders' Equity - Stock Repurchase (Details) - 2015 Stock Repurchase Program - USD ($) shares in Millions, $ in Millions	1 Months Ended		9 Months Ended
	Oct. 31, 2016	Jan. 31, 2015	Sep. 30, 2016
Shareholders' Equity
Number of shares authorized to be repurchased under the current open-market stock repurchase program		10.0
Repurchase of stock program, period		2 years
Number of shares repurchased and retired			4.0
Payments for shares repurchased and retired (in dollars)			$ 229.6
Number of shares repurchased	1.0
Payments for shares repurchased (in dollars)	$ 63.3
Number of shares remaining that may be repurchased under the stock repurchase program	0.5