Derivative Financial Instruments (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments and Hedges, Assets [Abstract]
Gain on cash flow hedges		$ 25.3
Loss on cash flow hedges			$ (10.3)	$ (9.0)
Cash flow hedges of forecasted transactions, net of tax, AOCI	$ 28.5	28.5	$ 126.5
Cash flow hedge gain (loss) to be reclassified within twelve months		$ 23.0
Total derivative contracts, maturity year	2020