Accumulated Other Comprehensive (Loss) Income, Reclassifications out of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Interest expense		$ 26.0	$ 45.9
Total before tax		65.8	(8.6)
Income tax benefit		(23.4)	1.6
Net of tax		42.4	(7.0)
Reclassification out of Accumulated Other Comprehensive (Loss) Income [Member]
Income Statement [Abstract]
Net of tax		4.0	3.9
Loss on Cash Flow Hedges - Interest Rate Swaps [Member] | Reclassification out of Accumulated Other Comprehensive (Loss) Income [Member]
Income Statement [Abstract]
Interest expense		4.8	5.1
Total before tax		4.8	5.1
Income tax benefit		(1.2)	(1.9)
Net of tax		3.6	3.2
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	1.2
Total before tax		0.5	1.2
Income tax benefit		(0.1)	(0.5)
Net of tax		$ 0.4	$ 0.7

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