Condensed Consolidating Financial Information - Balance Sheet (Details) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Condensed consolidating balance sheet
Cash and cash equivalents	$ 43.8			$ 39.4	$ 45.8		$ 45.7
Accounts receivable, net	944.4			929.1
Inventories	3,978.0			4,040.1
Other current assets	109.1			86.6
Total current assets	5,075.3			5,095.2
Property and equipment, net	2,308.9			2,250.0
Operating lease right-of-use assets	2,380.9		$ 2,425.6
Intangible assets	2,235.0			2,238.2
Equity method investments	1,342.2			1,305.2
Other long-term assets	18.8			15.9
Total assets	13,361.1			10,904.5
Floor plan notes payable	2,350.3			2,362.2
Floor plan notes payable - non-trade	1,435.5			1,428.6
Accounts payable	638.5			598.2
Accrued expenses and other current liabilities	651.8		636.8	566.6
Current portion of long-term debt	93.3			92.0
Liabilities held for sale	0.5			0.7
Total current liabilities	5,169.9			5,048.3
Long-term debt	2,134.2			2,124.7
Long-term operating lease liabilities	2,330.3		2,387.5
Deferred tax liabilities	604.1		578.7	577.8
Other long-term liabilities	461.6		$ 481.0	519.0
Total liabilities	10,700.1			8,269.8
Total equity	2,661.0	$ 2,660.9		2,634.7	2,525.8	$ 2,494.4	2,428.0
Total liabilities and equity	$ 13,361.1			$ 10,904.5
Domestic Subsidiaries ownership guaranteeing obligations (as a percent)	100.00%
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%
Eliminations
Condensed consolidating balance sheet
Accounts receivable, net	$ (490.9)			$ (481.7)
Total current assets	(490.9)			(481.7)
Other long-term assets	(2,830.9)			(2,814.3)
Total assets	(3,321.8)			(3,296.0)
Accrued expenses and other current liabilities	(490.9)			(481.7)
Total current liabilities	(490.9)			(481.7)
Long-term debt	(82.3)			(88.6)
Total liabilities	(573.2)			(570.3)
Total equity	(2,748.6)			(2,725.7)
Total liabilities and equity	(3,321.8)			(3,296.0)
Reportable legal entities | Penske Automotive Group
Condensed consolidating balance sheet
Accounts receivable, net	490.9			481.7
Other current assets	8.6			10.6
Total current assets	499.5			492.3
Property and equipment, net	3.8			3.9
Operating lease right-of-use assets	9.5
Equity method investments	1,276.4			1,239.9
Other long-term assets	2,838.6			2,821.0
Total assets	4,627.8			4,557.1
Floor plan notes payable - non-trade	225.9			232.3
Accounts payable	4.9			4.9
Accrued expenses and other current liabilities	1.7			1.4
Total current liabilities	232.5			238.6
Long-term debt	1,725.2			1,683.8
Long-term operating lease liabilities	9.1
Total liabilities	1,966.8			1,922.4
Total equity	2,661.0			2,634.7
Total liabilities and equity	4,627.8			4,557.1
Reportable legal entities | Guarantor Subsidiaries
Condensed consolidating balance sheet
Cash and cash equivalents	2.5			12.9	0.4		14.8
Accounts receivable, net	462.3			507.1
Inventories	1,966.1			1,961.6
Other current assets	21.8			17.8
Total current assets	2,452.7			2,499.4
Property and equipment, net	1,101.0			1,077.7
Operating lease right-of-use assets	1,600.0
Intangible assets	1,422.2			1,422.6
Other long-term assets	2.8			2.9
Total assets	6,578.7			5,002.6
Floor plan notes payable	1,350.6			1,348.3
Floor plan notes payable - non-trade	473.1			505.9
Accounts payable	177.5			196.6
Accrued expenses and other current liabilities	222.0			160.2
Current portion of long-term debt	10.4			6.3
Liabilities held for sale	0.5			0.7
Total current liabilities	2,234.1			2,218.0
Long-term debt	259.0			225.7
Long-term operating lease liabilities	1,573.0
Deferred tax liabilities	598.9			570.5
Other long-term liabilities	32.0			57.6
Total liabilities	4,697.0			3,071.8
Total equity	1,881.7			1,930.8
Total liabilities and equity	6,578.7			5,002.6
Reportable legal entities | Non-Guarantor Subsidiaries
Condensed consolidating balance sheet
Cash and cash equivalents	41.3			26.5	$ 45.4		$ 30.9
Accounts receivable, net	482.1			422.0
Inventories	2,011.9			2,078.5
Other current assets	78.7			58.2
Total current assets	2,614.0			2,585.2
Property and equipment, net	1,204.1			1,168.4
Operating lease right-of-use assets	771.4
Intangible assets	812.8			815.6
Equity method investments	65.8			65.3
Other long-term assets	8.3			6.3
Total assets	5,476.4			4,640.8
Floor plan notes payable	999.7			1,013.9
Floor plan notes payable - non-trade	736.5			690.4
Accounts payable	456.1			396.7
Accrued expenses and other current liabilities	919.0			886.7
Current portion of long-term debt	82.9			85.7
Total current liabilities	3,194.2			3,073.4
Long-term debt	232.3			303.8
Long-term operating lease liabilities	748.2
Deferred tax liabilities	5.2			7.3
Other long-term liabilities	429.6			461.4
Total liabilities	4,609.5			3,845.9
Total equity	866.9			794.9
Total liabilities and equity	$ 5,476.4			$ 4,640.8