Changes in Accumulated Other Comprehensive Income by Component - Summary of Reclassifications Out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassifications out of Accumulated Other Comprehensive Income [Line Items]
Cost of operations	$ (1,506.1)	$ (1,469.8)
Interest expense	(100.4)	(94.8)
Tax expense	(77.9)	(72.7)
Total gains reclassified into earnings	0.1	0.2
Gains (Losses) on Cash Flow Hedges
Reclassifications out of Accumulated Other Comprehensive Income [Line Items]
Total gains reclassified into earnings	0.1
Amount Reclassified from Accumulated Other Comprehensive Income | Gains (Losses) on Cash Flow Hedges
Reclassifications out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	0.1	0.3
Tax expense	0.0	(0.1)
Amount Reclassified from Accumulated Other Comprehensive Income | Gains (Losses) on Cash Flow Hedges | Fuel hedges
Reclassifications out of Accumulated Other Comprehensive Income [Line Items]
Cost of operations	0.0	0.8
Amount Reclassified from Accumulated Other Comprehensive Income | Gains (Losses) on Cash Flow Hedges | Terminated interest rate locks
Reclassifications out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	$ 0.1	$ (0.5)