Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended
	Apr. 15, 2016	Feb. 25, 2016	Mar. 31, 2016	Mar. 31, 2015	Feb. 24, 2016
Common stock dividends paid			$ 53.1	$ 39.4
Dividends declared per common share (in US$ per share)		$ 0.55	$ 0.55	$ 0.55
Repurchases of common stock			$ 100.3	$ 7.6
Shares of common stock repurchased			1,987,187
Stock Repurchase Program, Authorized Amount		$ 200.0			$ 150.0
Subsequent Event
Common stock dividends paid	$ 51.9