Derivative Financial Instruments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Loss on discontinuation of cash flow hedge due to forecasted transaction probable of not occurring	$ 1.2		$ 5.1
Gain on discontinuation of cash flow hedge due to forecasted transaction probable of not occurring		$ 18.9		$ 16.1
Cash flow hedges of forecasted transactions, net of tax, in accumulated OCI gain (loss)	$ (7.8)		(7.8)		$ 28.5
Cash flow hedge gain (loss) expected to be reclassified within 12 months			$ 8.3