Fair Value (Fair Value of Financial Instruments) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Carrying Amount [Member]
Available-for-sale securities		$ 3.7	$ 2.8
Debt maturing within one year	[1]	(25.7)	(18.1)
Long-term debt	[1]	(1,872.2)	(1,875.8)
Foreign exchange forward contracts		0.0	(2.4)
Fair Value [Member]
Available-for-sale securities		3.7	2.8
Debt maturing within one year		(25.7)	(18.1)
Long-term debt		(1,718.6)	(1,877.5)
Foreign exchange forward contracts		$ 0.0	$ (2.4)

[1] The carrying value of debt maturing within one year and long-term debt is presented net of debt issuance costs and includes any related discount or premium and unamortized deferred gains on terminated interest-rate swap agreements, as applicable.