Segment Information - Reporting information by segment (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) segment reporting	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information
Number of reportable segments | segment	4
Revenues and segment income by reportable segment
Total revenues	$ 25,554.7	$ 20,443.9	$ 23,179.4
Floor plan interest expense	26.2	46.3	84.5
Other interest expense	68.6	111.0	124.2
Depreciation	121.5	115.5	109.6
Equity in earnings of affiliates	374.5	169.0	147.5
Adjusted segment income	1,607.7	707.6	591.5
Total assets, equity method investments, and capital expenditures by reporting segment
Total assets	13,464.6	13,247.2
Equity method investments	1,688.1	1,500.3
Capital expenditures	248.9	185.9	245.3
Intersegment Elimination
Revenues and segment income by reportable segment
Total revenues	0.0	0.0	0.0
Floor plan interest expense	0.0	0.0	0.0
Other interest expense	0.0	0.0	0.0
Depreciation	0.0	0.0	0.0
Equity in earnings of affiliates	0.0	0.0	0.0
Adjusted segment income	0.0	0.0	0.0
Total assets, equity method investments, and capital expenditures by reporting segment
Total assets	0.0	0.0
Equity method investments	0.0	0.0
Capital expenditures	$ 0.0	0.0	0.0
Retail automotive dealership
Segment Reporting Information
Number of reportable segments | segment	1
Number of operating segments | reporting	6
Revenues and segment income by reportable segment
Total revenues	$ 22,513.3	17,928.8	20,615.8
Retail automotive dealership | Operating segments
Revenues and segment income by reportable segment
Total revenues	22,513.3	17,928.8	20,615.8
Floor plan interest expense	23.9	39.6	74.9
Other interest expense	63.8	105.9	118.4
Depreciation	108.7	103.8	99.1
Equity in earnings of affiliates	8.2	4.4	5.2
Adjusted segment income	1,046.6	443.4	339.9
Total assets, equity method investments, and capital expenditures by reporting segment
Total assets	9,940.4	10,352.8
Equity method investments	40.7	77.2
Capital expenditures	239.4	175.6	231.9
Retail commercial truck dealership
Revenues and segment income by reportable segment
Total revenues	2,465.7	2,060.9	2,050.5
Retail commercial truck dealership | Operating segments
Revenues and segment income by reportable segment
Total revenues	2,465.7	2,060.9	2,050.5
Floor plan interest expense	1.9	5.6	8.0
Other interest expense	3.3	3.7	3.2
Depreciation	7.9	6.4	5.5
Equity in earnings of affiliates	0.0	0.0	0.0
Adjusted segment income	160.3	78.2	86.5
Total assets, equity method investments, and capital expenditures by reporting segment
Total assets	1,269.4	839.1
Equity method investments	0.0	0.0
Capital expenditures	6.3	7.2	9.9
Other | Operating segments
Revenues and segment income by reportable segment
Total revenues	575.7	454.2	513.1
Floor plan interest expense	0.4	1.1	1.6
Other interest expense	1.5	1.4	2.6
Depreciation	4.9	5.3	5.0
Equity in earnings of affiliates	0.0	0.0	0.0
Adjusted segment income	34.5	21.4	22.8
Total assets, equity method investments, and capital expenditures by reporting segment
Total assets	607.4	632.2
Equity method investments	0.0	0.0
Capital expenditures	3.2	3.1	3.5
Non-Automotive Investments | Operating segments
Revenues and segment income by reportable segment
Total revenues	0.0	0.0	0.0
Floor plan interest expense	0.0	0.0	0.0
Other interest expense	0.0	0.0	0.0
Depreciation	0.0	0.0	0.0
Equity in earnings of affiliates	366.3	164.6	142.3
Adjusted segment income	366.3	164.6	142.3
Total assets, equity method investments, and capital expenditures by reporting segment
Total assets	1,647.4	1,423.1
Equity method investments	1,647.4	1,423.1
Capital expenditures	$ 0.0	$ 0.0	$ 0.0