Shareholders' Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Sep. 30, 2015	Jul. 31, 2015	May. 20, 2015	May. 19, 2015	Sep. 30, 2014
Common stock shares authorized								1,000.0	500.0
Quarterly dividend approved by Board prior to payment, per share (in dollars per share)			$ 0.10		$ 0.10					$ 0.125
Dividends paid		$ 0.0	$ 31.4	$ 77.5	$ 31.4
Dividends declared		$ 38.6	$ 31.4	$ 77.4	$ 62.8
Subsequent Event
Quarterly dividend approved by Board prior to payment, per share (in dollars per share)						$ 0.14
2015 Stock Repurchase Program
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				2.5
Payments for shares repurchased under the current open-market stock repurchase program (in dollars)				$ 143.6
2015 Stock Repurchase Program | Subsequent Event
Number of shares authorized to be repurchased under the current open-market stock repurchase program							7.5