Condensed Consolidating Financial Information - Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jan. 02, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed consolidating balance sheet
Cash and cash equivalents	$ 39.4		$ 45.7	$ 24.0	$ 62.4
Accounts receivable, net	929.1	$ 977.3	954.9
Inventories	4,040.1	3,930.7	3,944.1
Other current assets	86.6		81.8
Total current assets	5,095.2		5,026.5
Property and equipment, net	2,250.0		2,108.6
Intangible assets	2,238.2		2,134.5
Equity method investments	1,305.2		1,256.6
Other long-term assets	15.9		14.4
Total assets	10,904.5		10,540.6
Floor plan notes payable	2,362.2		2,343.2
Floor plan notes payable - non-trade	1,428.6		1,418.6
Accounts payable	598.2		641.6
Accrued expenses	566.6	523.6	523.5
Current portion of long-term debt	92.0		72.8
Liabilities held for sale	0.7		0.7
Total current liabilities	5,048.3		5,000.4
Long-term debt	2,124.7		2,090.4
Deferred tax liabilities	577.8	$ 483.8	481.5
Other long-term liabilities	519.0		540.3
Total liabilities	8,269.8		8,112.6
Total equity	2,634.7		2,428.0	$ 1,779.5	1,834.9
Total liabilities and equity	$ 10,904.5		$ 10,540.6
3.75% senior subordinated notes due 2020
Condensed consolidating balance sheet
Interest rate (as a percent)	3.75%		3.75%
5.75% senior subordinated notes due 2022
Condensed consolidating balance sheet
Interest rate (as a percent)	5.75%		5.75%
5.375% senior subordinated notes due 2024
Condensed consolidating balance sheet
Interest rate (as a percent)	5.375%		5.375%
5.50% senior subordinated notes due 2026
Condensed consolidating balance sheet
Interest rate (as a percent)	5.50%		5.50%	5.50%
Guarantor Subsidiaries
Condensed consolidating balance sheet
Domestic Subsidiaries ownership guaranteeing obligations (as a percent)	100.00%
Eliminations
Condensed consolidating balance sheet
Accounts receivable, net	$ (481.7)		$ (463.6)
Total current assets	(481.7)		(463.6)
Other long-term assets	(2,814.3)		(2,772.7)
Total assets	(3,296.0)		(3,236.3)
Accrued expenses	(481.7)		(463.6)
Total current liabilities	(481.7)		(463.6)
Long-term debt	(88.6)		(150.2)
Total liabilities	(570.3)		(613.8)
Total equity	(2,725.7)		(2,622.5)
Total liabilities and equity	(3,296.0)		(3,236.3)
Reportable legal entities | Penske Automotive Group
Condensed consolidating balance sheet
Accounts receivable, net	481.7		463.6
Other current assets	10.6		7.3
Total current assets	492.3		470.9
Property and equipment, net	3.9		3.3
Equity method investments	1,239.9		1,186.9
Other long-term assets	2,821.0		2,777.8
Total assets	4,557.1		4,438.9
Floor plan notes payable - non-trade	232.3		196.6
Accounts payable	4.9		3.9
Accrued expenses	1.4		1.0
Total current liabilities	238.6		201.5
Long-term debt	1,683.8		1,809.4
Total liabilities	1,922.4		2,010.9
Total equity	2,634.7		2,428.0
Total liabilities and equity	4,557.1		4,438.9
Reportable legal entities | Guarantor Subsidiaries
Condensed consolidating balance sheet
Cash and cash equivalents	12.9		14.8	$ 9.4
Accounts receivable, net	507.1		523.8
Inventories	1,961.6		1,935.0
Other current assets	17.8		16.8
Total current assets	2,499.4		2,490.4
Property and equipment, net	1,077.7		1,032.9
Intangible assets	1,422.6		1,334.6
Other long-term assets	2.9		4.6
Total assets	5,002.6		4,862.5
Floor plan notes payable	1,348.3		1,272.4
Floor plan notes payable - non-trade	505.9		601.9
Accounts payable	196.6		194.4
Accrued expenses	160.2		165.2
Current portion of long-term debt	6.3		5.5
Liabilities held for sale	0.7		0.7
Total current liabilities	2,218.0		2,240.1
Long-term debt	225.7		191.6
Deferred tax liabilities	570.5		480.1
Other long-term liabilities	57.6		64.7
Total liabilities	3,071.8		2,976.5
Total equity	1,930.8		1,886.0
Total liabilities and equity	5,002.6		4,862.5
Reportable legal entities | Non-Guarantor Subsidiaries
Condensed consolidating balance sheet
Cash and cash equivalents	26.5		30.9	$ 14.6	$ 62.4
Accounts receivable, net	422.0		431.1
Inventories	2,078.5		2,009.1
Other current assets	58.2		57.7
Total current assets	2,585.2		2,528.8
Property and equipment, net	1,168.4		1,072.4
Intangible assets	815.6		799.9
Equity method investments	65.3		69.7
Other long-term assets	6.3		4.7
Total assets	4,640.8		4,475.5
Floor plan notes payable	1,013.9		1,070.8
Floor plan notes payable - non-trade	690.4		620.1
Accounts payable	396.7		443.3
Accrued expenses	886.7		820.9
Current portion of long-term debt	85.7		67.3
Total current liabilities	3,073.4		3,022.4
Long-term debt	303.8		239.6
Deferred tax liabilities	7.3		1.4
Other long-term liabilities	461.4		475.6
Total liabilities	3,845.9		3,739.0
Total equity	794.9		736.5
Total liabilities and equity	$ 4,640.8		$ 4,475.5