Acquisitions and Dispositions (Details) $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($) franchise dealership	Dec. 31, 2019 USD ($) dealership franchise	Dec. 31, 2018 USD ($) dealership franchise
Business Acquisition [Line Items]
Aggregate consideration paid for dealerships \| $	$ 1.3	$ 143.2	$ 140.4
Cash received in acquisition \| $			5.1
Net pre-tax gain (loss) on dealership dispositions \| $	$ (3.1)	$ 5.0	$ 24.4
U.S.
Business Acquisition [Line Items]
Number of dealerships acquired		4	4
Number of franchises acquired \| franchise		6	4
Number of dealerships opened		1	1
Number of franchises awarded \| franchise		1	1
Number of dealerships disposed	2	4	2
Number of franchises disposed \| franchise	3	7	3
Number of franchises terminated		2	1
Net pre-tax gain (loss) on dealership dispositions \| $	$ 3.1		$ 25.2
U.K.
Business Acquisition [Line Items]
Number of dealerships acquired		4	5
Number of franchises acquired \| franchise		5	8
Number of dealerships opened		2	1
Number of franchises awarded \| franchise		3	1
Number of franchises added \| franchise			1
Number of dealerships disposed		3	1
Number of franchises disposed			1
Number of franchises terminated		4	1
Net pre-tax gain (loss) on dealership dispositions \| $	$ 2.2
Brazil
Business Acquisition [Line Items]
Number of dealerships acquired			1
Number of franchises acquired \| franchise			1
Number of dealerships opened			1
Number of franchises awarded \| franchise			1
Number of dealerships disposed		1
Number of franchises disposed \| franchise		1