Condensed Consolidating Financial Information - Balance Sheet (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Condensed consolidating balance sheet
Cash and cash equivalents	$ 43.5		$ 39.4	$ 52.8	$ 45.7
Accounts receivable, net	1,034.1		929.1
Inventories	4,104.1		4,040.1
Other current assets	101.5		86.6
Total current assets	5,283.2		5,095.2
Property and equipment, net	2,276.1		2,250.0
Operating lease right-of-use assets	2,416.4	$ 2,425.6
Intangible assets	2,247.9		2,238.2
Equity method investments	1,332.4		1,305.2
Other long-term assets	18.9		15.9
Total assets	13,574.9		10,904.5
Floor plan notes payable	2,419.2		2,362.2
Floor plan notes payable - non-trade	1,488.7		1,428.6
Accounts payable	668.5		598.2
Accrued expenses and other current liabilities	704.7	636.8	566.6
Current portion of long-term debt	94.5		92.0
Liabilities held for sale	0.5		0.7
Total current liabilities	5,376.1		5,048.3
Long-term debt	2,118.3		2,124.7
Long-term operating lease liabilities	2,378.2	2,387.5
Deferred tax liabilities	591.4	578.7	577.8
Other long-term liabilities	450.0	$ 481.0	519.0
Total liabilities	10,914.0		8,269.8
Total equity	2,660.9		2,634.7	2,494.4	2,428.0
Total liabilities and equity	$ 13,574.9		$ 10,904.5
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%
Guarantor Subsidiaries
Condensed consolidating balance sheet
Domestic Subsidiaries ownership guaranteeing obligations (as a percent)	100.00%
Eliminations
Condensed consolidating balance sheet
Accounts receivable, net	$ (481.1)		$ (481.7)
Total current assets	(481.1)		(481.7)
Other long-term assets	(2,826.7)		(2,814.3)
Total assets	(3,307.8)		(3,296.0)
Accrued expenses and other current liabilities	(481.1)		(481.7)
Total current liabilities	(481.1)		(481.7)
Long-term debt	(84.0)		(88.6)
Total liabilities	(565.1)		(570.3)
Total equity	(2,742.7)		(2,725.7)
Total liabilities and equity	(3,307.8)		(3,296.0)
Reportable legal entities | Penske Automotive Group
Condensed consolidating balance sheet
Accounts receivable, net	481.1		481.7
Other current assets	8.6		10.6
Total current assets	489.7		492.3
Property and equipment, net	3.9		3.9
Operating lease right-of-use assets	9.5
Equity method investments	1,267.3		1,239.9
Other long-term assets	2,834.0		2,821.0
Total assets	4,604.4		4,557.1
Floor plan notes payable - non-trade	219.9		232.3
Accounts payable	3.4		4.9
Accrued expenses and other current liabilities	1.5		1.4
Total current liabilities	224.8		238.6
Long-term debt	1,709.6		1,683.8
Long-term operating lease liabilities	9.2
Total liabilities	1,943.6		1,922.4
Total equity	2,660.8		2,634.7
Total liabilities and equity	4,604.4		4,557.1
Reportable legal entities | Guarantor Subsidiaries
Condensed consolidating balance sheet
Cash and cash equivalents			12.9		14.8
Accounts receivable, net	473.5		507.1
Inventories	1,945.8		1,961.6
Other current assets	17.8		17.8
Total current assets	2,437.1		2,499.4
Property and equipment, net	1,086.8		1,077.7
Operating lease right-of-use assets	1,627.9
Intangible assets	1,422.2		1,422.6
Other long-term assets	2.9		2.9
Total assets	6,576.9		5,002.6
Floor plan notes payable	1,306.4		1,348.3
Floor plan notes payable - non-trade	503.1		505.9
Accounts payable	187.4		196.6
Accrued expenses and other current liabilities	228.8		160.2
Current portion of long-term debt	9.6		6.3
Liabilities held for sale	0.5		0.7
Total current liabilities	2,235.8		2,218.0
Long-term debt	219.9		225.7
Long-term operating lease liabilities	1,613.3
Deferred tax liabilities	583.5		570.5
Other long-term liabilities	33.8		57.6
Total liabilities	4,686.3		3,071.8
Total equity	1,890.6		1,930.8
Total liabilities and equity	6,576.9		5,002.6
Reportable legal entities | Non-Guarantor Subsidiaries
Condensed consolidating balance sheet
Cash and cash equivalents	43.5		26.5	$ 52.8	$ 30.9
Accounts receivable, net	560.6		422.0
Inventories	2,158.3		2,078.5
Other current assets	75.1		58.2
Total current assets	2,837.5		2,585.2
Property and equipment, net	1,185.4		1,168.4
Operating lease right-of-use assets	779.0
Intangible assets	825.7		815.6
Equity method investments	65.1		65.3
Other long-term assets	8.7		6.3
Total assets	5,701.4		4,640.8
Floor plan notes payable	1,112.8		1,013.9
Floor plan notes payable - non-trade	765.7		690.4
Accounts payable	477.7		396.7
Accrued expenses and other current liabilities	955.5		886.7
Current portion of long-term debt	84.9		85.7
Total current liabilities	3,396.6		3,073.4
Long-term debt	272.8		303.8
Long-term operating lease liabilities	755.7
Deferred tax liabilities	7.9		7.3
Other long-term liabilities	416.2		461.4
Total liabilities	4,849.2		3,845.9
Total equity	852.2		794.9
Total liabilities and equity	$ 5,701.4		$ 4,640.8