Financial Instruments and Risk Management (Impact of Cash Flow Hedges on Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification of net losses to earnings, net of taxes		$ 0.0	$ 1.3	$ 1.9
Treasury Locks [Member]
Balance at Period Start	[1]	$ 0.0	(4.0)
Reclassification of net losses to earnings, net of taxes			4.0
Balance at Period End	[1]		0.0	(4.0)
Net unamortized losses at beginning of year, tax effect			$ 2.7
Net unamortized losses at end of year, tax effect				$ 2.7

[1] Amounts above exclude taxes of $2.7 at the beginning of year in 2016