Acquisitions - Summary of Acquisitions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Cash paid, net of cash acquired	$ 1,503.1	$ 366.6
Contingent consideration	4.6	0.0
Debt and finance lease obligations	218.9	26.4
Total	1,726.6	393.0
Other liabilities	(8.5)	(29.3)
Goodwill	593.0	454.6	$ 434.9
2020 Acquisitions
Business Acquisition [Line Items]
Trade receivables, net	0.2
Inventories	358.9
Property and equipment	529.9
Other assets	858.4
Floor plan notes payable	(13.1)
Assets acquired and liabilities assumed, excluding goodwill	1,725.8
Goodwill	0.8
Assets acquired and liabilities assumed, net	$ 1,726.6
Acquisitions 2019
Business Acquisition [Line Items]
Trade receivables, net		0.0
Inventories		105.2
Property and equipment		124.0
Other assets		193.1
Floor plan notes payable		0.0
Assets acquired and liabilities assumed, excluding goodwill		393.0
Goodwill		0.0
Assets acquired and liabilities assumed, net		$ 393.0