Shareholders' Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended		3 Months Ended		6 Months Ended
	Jul. 29, 2016	Jan. 31, 2015	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Sep. 30, 2015
Shareholders' Equity
Quarterly dividend approved by Board prior to payment, per share (in dollars per share)				$ 0.125		$ 0.125	$ 0.14
Dividends paid			$ 43.0	$ 0.0	$ 86.3	$ 77.5
Dividends declared			$ 43.2	$ 38.6	$ 86.3	$ 77.4
2015 Stock Repurchase Program
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 under the current open-market stock repurchase program					2.0
Number of shares repurchased under the current open-market stock repurchase program	0.7
Payments for shares repurchased under the current open-market stock repurchase program (in dollars)					$ 108.4
Payments for shares repurchased under the current open-market stock repurchase program (in dollars)	$ 42.2
Number of shares remaining that may be repurchased under the stock repurchase program	2.8