Condensed Consolidating Financial Information - Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2019	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Condensed consolidating balance sheet
Cash and cash equivalents	$ 77.5			$ 39.4	$ 37.6		$ 45.7
Accounts receivable, net	967.3			929.1
Inventories	4,043.9			4,040.1
Other current assets	98.8			86.6
Total current assets	5,187.5			5,095.2
Property and equipment, net	2,309.3			2,250.0
Operating lease right-of-use assets	2,384.4		$ 2,425.6
Intangible assets	2,423.9			2,238.2
Equity method investments	1,362.8			1,305.2
Other long-term assets	21.6			15.9
Total assets	13,689.5			10,904.5
Floor plan notes payable	2,444.1			2,362.2
Floor plan notes payable - non-trade	1,410.6			1,428.6
Accounts payable	672.3			598.2
Accrued expenses and other current liabilities	722.2		636.8	566.6
Current portion of long-term debt	96.8			92.0
Liabilities held for sale	0.5			0.7
Total current liabilities	5,346.5			5,048.3
Long-term debt	2,282.5			2,124.7
Long-term operating lease liabilities	2,334.7		2,387.5
Deferred tax liabilities	620.7		578.7	577.8
Other long-term liabilities	446.0		$ 481.0	519.0
Total liabilities	11,030.4			8,269.8
Total equity	2,659.1	$ 2,661.0		2,634.7	2,612.0	$ 2,525.8	2,428.0
Total liabilities and equity	$ 13,689.5			$ 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	$ (493.6)			$ (481.7)
Total current assets	(493.6)			(481.7)
Other long-term assets	(2,911.0)			(2,814.3)
Total assets	(3,404.6)			(3,296.0)
Accrued expenses and other current liabilities	(493.6)			(481.7)
Total current liabilities	(493.6)			(481.7)
Long-term debt	(82.5)			(88.6)
Total liabilities	(576.1)			(570.3)
Total equity	(2,828.5)			(2,725.7)
Total liabilities and equity	(3,404.6)			(3,296.0)
Reportable legal entities | Penske Automotive Group
Condensed consolidating balance sheet
Accounts receivable, net	493.6			481.7
Other current assets	7.7			10.6
Total current assets	501.3			492.3
Property and equipment, net	3.6			3.9
Operating lease right-of-use assets	9.3
Equity method investments	1,298.2			1,239.9
Other long-term assets	2,920.2			2,821.0
Total assets	4,732.6			4,557.1
Floor plan notes payable - non-trade	227.2			232.3
Accounts payable	5.1			4.9
Accrued expenses and other current liabilities	1.6			1.4
Current portion of long-term debt	13.0
Total current liabilities	246.9			238.6
Long-term debt	1,817.6			1,683.8
Long-term operating lease liabilities	9.0
Total liabilities	2,073.5			1,922.4
Total equity	2,659.1			2,634.7
Total liabilities and equity	4,732.6			4,557.1
Reportable legal entities | Guarantor Subsidiaries
Condensed consolidating balance sheet
Cash and cash equivalents	0.0			12.9	3.4		14.8
Accounts receivable, net	467.9			507.1
Inventories	2,156.7			1,961.6
Other current assets	21.6			17.8
Total current assets	2,646.2			2,499.4
Property and equipment, net	1,110.9			1,077.7
Operating lease right-of-use assets	1,632.9
Intangible assets	1,635.8			1,422.6
Other long-term assets	3.1			2.9
Total assets	7,028.9			5,002.6
Floor plan notes payable	1,447.0			1,348.3
Floor plan notes payable - non-trade	515.4			505.9
Accounts payable	213.1			196.6
Accrued expenses and other current liabilities	296.0			160.2
Current portion of long-term debt	10.6			6.3
Liabilities held for sale	0.5			0.7
Total current liabilities	2,482.6			2,218.0
Long-term debt	256.4			225.7
Long-term operating lease liabilities	1,603.7
Deferred tax liabilities	615.8			570.5
Other long-term liabilities	36.6			57.6
Total liabilities	4,995.1			3,071.8
Total equity	2,033.8			1,930.8
Total liabilities and equity	7,028.9			5,002.6
Reportable legal entities | Non-Guarantor Subsidiaries
Condensed consolidating balance sheet
Cash and cash equivalents	77.5			26.5	$ 34.2		$ 30.9
Accounts receivable, net	499.4			422.0
Inventories	1,887.2			2,078.5
Other current assets	69.5			58.2
Total current assets	2,533.6			2,585.2
Property and equipment, net	1,194.8			1,168.4
Operating lease right-of-use assets	742.2
Intangible assets	788.1			815.6
Equity method investments	64.6			65.3
Other long-term assets	9.3			6.3
Total assets	5,332.6			4,640.8
Floor plan notes payable	997.1			1,013.9
Floor plan notes payable - non-trade	668.0			690.4
Accounts payable	454.1			396.7
Accrued expenses and other current liabilities	918.2			886.7
Current portion of long-term debt	73.2			85.7
Total current liabilities	3,110.6			3,073.4
Long-term debt	291.0			303.8
Long-term operating lease liabilities	722.0
Deferred tax liabilities	4.9			7.3
Other long-term liabilities	409.4			461.4
Total liabilities	4,537.9			3,845.9
Total equity	794.7			794.9
Total liabilities and equity	$ 5,332.6			$ 4,640.8