Property and Equipment (including Concession Assets) (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Accumulated amortization	$ 709.7	$ 709.7	$ 678.1
Concession assets, net of accumulated amortization	2,383.5	2,383.5	2,335.5
Depreciation and amortization		357.9	350.7	$ 346.7
Write-off of software development costs	$ 13.6	$ 13.6	$ 0.0	$ 0.0