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Supplemental cash flow information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Condensed Cash Flow Statements, Captions [Line Items]
Interest	$ 29.3	$ 10.7
Income taxes, net	48.6	50.4
Capital Leases	27.5	23.0
Restricted cash	101.6		$ 112.6
Cash and cash equivalents	548.5		614.3
Cash, Cash Equivalents, and Restricted Cash	650.1	$ 294.8	726.9	$ 239.0
Cash from Short Term Borrowings
Condensed Cash Flow Statements, Captions [Line Items]
Restricted cash	14.6		27.0
Cash Held From Customers
Condensed Cash Flow Statements, Captions [Line Items]
Restricted cash	57.0		74.7
Deposits liability
Condensed Cash Flow Statements, Captions [Line Items]
Restricted cash	$ 30.0		$ 10.9