Financial Instruments and Risk Management (Effect of Derivative Instruments on the Consolidated Statements of Operations Derivatives in Fair Value Hedging Relationships) (Details) - Fair value hedging relationships - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Loss Recognized in Earnings on Derivatives	$ (12.6)	$ (10.0)	$ (10.0)
Amount of Gain Recognized in Earnings on Hedging Items	12.6	10.0	10.0
Interest expense | Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Loss Recognized in Earnings on Derivatives	(12.6)	(10.0)	(10.0)
Interest expense | 2023 Senior Notes (3.125% coupon)
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain Recognized in Earnings on Hedging Items	$ 12.6	$ 10.0	$ 10.0