Condensed Consolidating Financial Information - Balance Sheet (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 02, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Condensed consolidating balance sheet
Cash and cash equivalents	$ 52.8		$ 45.7	$ 72.2	$ 24.0
Accounts receivable, net	1,035.4	$ 977.3	954.9
Inventories	3,972.2	3,930.7	3,944.1
Other current assets	105.0		81.8
Total current assets	5,165.4		5,026.5
Property and equipment, net	2,173.5		2,108.6
Intangible assets	2,213.2		2,134.5
Equity method investments	1,276.2		1,256.6
Other long-term assets	14.7		14.4
Total assets	10,843.0		10,540.6
Floor plan notes payable	2,355.6		2,343.2
Floor plan notes payable - non-trade	1,413.8		1,418.6
Accounts payable	720.5		641.6
Accrued expenses	563.9	523.6	523.5
Current portion of long-term debt	84.3		72.8
Liabilities held for sale	0.7		0.7
Total current liabilities	5,138.8		5,000.4
Long-term debt	2,136.9		2,090.4
Deferred tax liabilities	505.5	$ 483.8	481.5
Other long-term liabilities	567.4		540.3
Total liabilities	8,348.6		8,112.6
Total equity	2,494.4		2,428.0
Total liabilities and equity	$ 10,843.0		$ 10,540.6
3.75% senior subordinated notes due 2020
Condensed consolidating balance sheet
Interest rate (as a percent)	3.75%		3.75%
Domestic Subsidiaries ownership guaranteeing obligations (as a percent)	100.00%
5.75% senior subordinated notes due 2022
Condensed consolidating balance sheet
Interest rate (as a percent)	5.75%		5.75%
Domestic Subsidiaries ownership guaranteeing obligations (as a percent)	100.00%
5.375% senior subordinated notes due 2024
Condensed consolidating balance sheet
Interest rate (as a percent)	5.375%		5.375%
Domestic Subsidiaries ownership guaranteeing obligations (as a percent)	100.00%
5.50% senior subordinated notes due 2026
Condensed consolidating balance sheet
Interest rate (as a percent)	5.50%		5.50%
Domestic Subsidiaries ownership guaranteeing obligations (as a percent)	100.00%
Eliminations
Condensed consolidating balance sheet
Accounts receivable, net	$ (466.7)		$ (463.6)
Total current assets	(466.7)		(463.6)
Other long-term assets	(2,775.6)		(2,772.7)
Total assets	(3,242.3)		(3,236.3)
Accrued expenses	(466.7)		(463.6)
Total current liabilities	(466.7)		(463.6)
Long-term debt	(152.0)		(150.2)
Total liabilities	(618.7)		(613.8)
Total equity	(2,623.6)		(2,622.5)
Total liabilities and equity	(3,242.3)		(3,236.3)
Reportable legal entities | Penske Automotive Group
Condensed consolidating balance sheet
Accounts receivable, net	466.7		463.6
Other current assets	8.1		7.3
Total current assets	474.8		470.9
Property and equipment, net	3.0		3.3
Equity method investments	1,204.7		1,186.9
Other long-term assets	2,780.8		2,777.8
Total assets	4,463.3		4,438.9
Floor plan notes payable - non-trade	197.5		196.6
Accounts payable	4.2		3.9
Accrued expenses	1.0		1.0
Total current liabilities	202.7		201.5
Long-term debt	1,766.2		1,809.4
Total liabilities	1,968.9		2,010.9
Total equity	2,494.4		2,428.0
Total liabilities and equity	4,463.3		4,438.9
Reportable legal entities | Guarantor Subsidiaries
Condensed consolidating balance sheet
Cash and cash equivalents			14.8	1.5	9.4
Accounts receivable, net	444.0		523.8
Inventories	1,878.3		1,935.0
Other current assets	17.7		16.8
Total current assets	2,340.0		2,490.4
Property and equipment, net	997.7		1,032.9
Intangible assets	1,328.6		1,334.6
Other long-term assets	4.3		4.6
Total assets	4,670.6		4,862.5
Floor plan notes payable	1,203.1		1,272.4
Floor plan notes payable - non-trade	558.8		601.9
Accounts payable	168.2		194.4
Accrued expenses	180.5		165.2
Current portion of long-term debt	4.5		5.5
Liabilities held for sale	0.7		0.7
Total current liabilities	2,115.8		2,240.1
Long-term debt	170.6		191.6
Deferred tax liabilities	503.3		480.1
Other long-term liabilities	64.0		64.7
Total liabilities	2,853.7		2,976.5
Total equity	1,816.9		1,886.0
Total liabilities and equity	4,670.6		4,862.5
Reportable legal entities | Non-Guarantor Subsidiaries
Condensed consolidating balance sheet
Cash and cash equivalents	52.8		30.9	$ 70.7	$ 14.6
Accounts receivable, net	591.4		431.1
Inventories	2,093.9		2,009.1
Other current assets	79.2		57.7
Total current assets	2,817.3		2,528.8
Property and equipment, net	1,172.8		1,072.4
Intangible assets	884.6		799.9
Equity method investments	71.5		69.7
Other long-term assets	5.2		4.7
Total assets	4,951.4		4,475.5
Floor plan notes payable	1,152.5		1,070.8
Floor plan notes payable - non-trade	657.5		620.1
Accounts payable	548.1		443.3
Accrued expenses	849.1		820.9
Current portion of long-term debt	79.8		67.3
Total current liabilities	3,287.0		3,022.4
Long-term debt	352.1		239.6
Deferred tax liabilities	2.2		1.4
Other long-term liabilities	503.4		475.6
Total liabilities	4,144.7		3,739.0
Total equity	806.7		736.5
Total liabilities and equity	$ 4,951.4		$ 4,475.5