Accumulated Other Comprehensive (Loss) Income, Reclassifications out of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Interest expense		$ 24.4	$ 30.1	$ 76.5	$ 115.4
Total before tax		94.8	32.4	238.1	(166.3)
Benefit for income taxes		(22.6)	(4.4)	(63.2)	41.2
Net of tax		$ 72.2	$ 28.0	174.9	(125.1)
Reclassification out of Accumulated Other Comprehensive (Loss) Income [Member]
Income Statement [Abstract]
Net of tax				10.1	10.9
Loss on Cash Flow Hedges - Interest Rate Swaps [Member] | Reclassification out of Accumulated Other Comprehensive (Loss) Income [Member]
Income Statement [Abstract]
Interest expense				11.8	13.9
Total before tax				11.8	13.9
Benefit for income taxes				(2.8)	(5.3)
Net of tax				9.0	8.6
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]			1.4	3.7
Total before tax				1.4	3.7
Benefit for income taxes				(0.3)	(1.4)
Net of tax				$ 1.1	$ 2.3

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