Leases - Schedule of components of leased cost (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Operating Leased Assets [Line Items]
Operating lease cost	$ 60.1	$ 118.4
Depreciation and amortization	0.3	0.8
Interest expense	0.2	0.4
Net lease cost	60.6	119.6
Cost of services - lease type contracts
Operating Leased Assets [Line Items]
Operating lease cost	59.1	116.1
General and administrative expenses
Operating Leased Assets [Line Items]
Operating lease cost	$ 1.0	$ 2.3