Commitments and Contingencies (Details) $ in Millions	Dec. 31, 2017 USD ($)
Minimum rental commitments under non-cancelable leases
Minimum lease payments, 2018	$ 72.6
Minimum lease payments, 2019	72.3
Minimum lease payments, 2020	68.4
Minimum lease payments, 2021	66.9
Minimum lease payments, 2022	65.7
Minimum lease payments, Thereafter	271.1
Minimum lease payments, Total	617.0
Less: income from subleases, 2018	(24.3)	[1]
Less: income from subleases, 2019	(24.7)	[1]
Less: income from subleases, 2020	(23.9)	[1]
Less: income from subleases, 2021	(22.3)	[1]
Less: income from subleases, 2022	(22.0)	[1]
Less: income from subleases, Thereafter	(71.3)	[1]
Less: income from subleases, Total	(188.5)	[1]
Net minimum lease payments, 2018	48.3
Net minimum lease payments, 2019	47.6
Net minimum lease payments, 2020	44.5
Net minimum lease payments, 2021	44.6
Net minimum lease payments, 2022	43.7
Net minimum lease payments, Thereafter	199.8
Net minimum lease payments, Total	$ 428.5

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