Accumulated Other Comprehensive (Loss) Income, Reclassifications out of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Interest expense		$ 22.4	$ 26.0
Total before tax		59.1	65.8
Income tax benefit		(12.0)	(23.4)
Net of tax		47.1	42.4
Reclassification out of Accumulated Other Comprehensive (Loss) Income [Member]
Income Statement [Abstract]
Net of tax		3.2	4.0
Loss on Cash Flow Hedges - Interest Rate Swaps [Member] | Reclassification out of Accumulated Other Comprehensive (Loss) Income [Member]
Income Statement [Abstract]
Interest expense		3.7	4.8
Total before tax		3.7	4.8
Income tax benefit		(0.9)	(1.2)
Net of tax		2.8	3.6
Amortization of Defined Benefit Pension and Other Postretirement Benefit Items [Member] | Reclassification out of Accumulated Other Comprehensive (Loss) Income [Member]
Income Statement [Abstract]
Net periodic benefit cost	[1]	0.5	0.5
Total before tax		0.5	0.5
Income tax benefit		(0.1)	(0.1)
Net of tax		$ 0.4	$ 0.4

[1] These components are included in the computation of net periodic benefit cost. See Note 7 "Pension and Other Postretirement Benefits" for additional details.