Accumulated Other Comprehensive (Loss) Income, Reclassifications out of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Interest expense		$ 22.4	$ 26.1	$ 44.8	$ 52.1
Total before tax		53.2	77.5	112.4	143.4
Income tax benefit		(8.3)	(17.2)	(20.3)	(40.7)
Net of tax		$ 44.9	$ 60.3	92.1	102.7
Reclassification out of Accumulated Other Comprehensive (Loss) Income [Member]
Income Statement [Abstract]
Net of tax				6.7	6.8
Loss on Cash Flow Hedges - Interest Rate Swaps [Member] | Reclassification out of Accumulated Other Comprehensive (Loss) Income [Member]
Income Statement [Abstract]
Interest expense				7.6	7.9
Total before tax				7.6	7.9
Income tax benefit				(1.8)	(1.9)
Net of tax				5.8	6.0
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]			1.2	1.0
Total before tax				1.2	1.0
Income tax benefit				(0.3)	(0.2)
Net of tax				$ 0.9	$ 0.8

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