Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Information [Abstract]
Cash and cash equivalents	$ 48.7		$ 48.6
Restricted cash included in Current Assets	0.9		0.8
Total cash, cash equivalents, and restricted cash	49.6	$ 58.9	$ 49.4	$ 71.1
Accrued purchases of property and equipment	21.7	26.4
Interest payments, net of amounts capitalized and including interest on vehicle inventory financing	60.7	46.5
Income tax payments, net of income tax refunds	$ 1.2	$ 84.6