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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Interest expense		$ 26.1	$ 39.5	$ 52.1	$ 85.3
Total before tax		77.5	(190.2)	143.4	(198.8)
Benefit for income taxes		(17.2)	43.9	(40.7)	45.6
Net of tax		$ 60.3	$ (146.3)	102.7	(153.2)
Reclassification out of Accumulated Other Comprehensive (Loss) Income [Member]
Income Statement [Abstract]
Net of tax				6.8	7.6
Loss on Cash Flow Hedges - Interest Rate Swaps [Member] | Reclassification out of Accumulated Other Comprehensive (Loss) Income [Member]
Income Statement [Abstract]
Interest expense				7.9	9.8
Total before tax				7.9	9.8
Benefit for income taxes				(1.9)	(3.7)
Net of tax				6.0	6.1
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]			1.0	2.4
Total before tax				1.0	2.4
Benefit for income taxes				(0.2)	(0.9)
Net of tax				$ 0.8	$ 1.5

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