Condensed Consolidating Financial Information - Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed consolidating balance sheet
Cash and cash equivalents	$ 45.7	$ 24.0	$ 62.4	$ 36.3
Accounts receivable, net	954.9	879.0
Inventories	3,944.1	3,408.2
Other current assets	81.8	73.9
Assets held for sale		8.4
Total current assets	5,026.5	4,393.5
Property and equipment, net	2,108.6	1,806.5
Intangible assets	2,134.5	1,711.3
Equity method investments	1,256.6	893.4
Other long-term assets	14.4	28.3
Total assets	10,540.6	8,833.0
Floor plan notes payable	2,343.2	2,084.5
Floor plan notes payable - non-trade	1,418.6	1,233.3
Accounts payable	641.6	497.4
Accrued expenses	523.5	360.0
Current portion of long-term debt	72.8	48.3
Liabilities held for sale	0.7	6.1
Total current liabilities	5,000.4	4,229.6
Long-term debt	2,090.4	1,828.8
Deferred tax liabilities	481.5	564.6
Other long-term liabilities	540.3	430.5
Total liabilities	8,112.6	7,053.5
Total equity	2,428.0	1,779.5	1,834.9	1,681.2
Total liabilities and equity	$ 10,540.6	$ 8,833.0
3.75% senior subordinated notes due 2020
Condensed consolidating balance sheet
Interest rate (as a percent)	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%
Guarantor Subsidiaries
Condensed consolidating balance sheet
Domestic Subsidiaries ownership guaranteeing obligations (as a percent)	100.00%
Eliminations
Condensed consolidating balance sheet
Accounts receivable, net	$ (463.6)	$ (447.0)
Total current assets	(463.6)	(447.0)
Other long-term assets	(2,772.7)	(2,215.0)
Total assets	(3,236.3)	(2,662.0)
Accrued expenses	(463.6)	(447.0)
Total current liabilities	(463.6)	(447.0)
Long-term debt	(150.2)	(175.8)
Total liabilities	(613.8)	(622.8)
Total equity	(2,622.5)	(2,039.2)
Total liabilities and equity	(3,236.3)	(2,662.0)
Reportable legal entities | Penske Automotive Group
Condensed consolidating balance sheet
Accounts receivable, net	463.6	447.0
Other current assets	7.3	14.3
Total current assets	470.9	461.3
Property and equipment, net	3.3	3.3
Equity method investments	1,186.9	833.7
Other long-term assets	2,777.8	2,220.6
Total assets	4,438.9	3,518.9
Floor plan notes payable - non-trade	196.6	156.0
Accounts payable	3.9	4.9
Accrued expenses	1.0	0.9
Total current liabilities	201.5	161.8
Long-term debt	1,809.4	1,577.6
Total liabilities	2,010.9	1,739.4
Total equity	2,428.0	1,779.5
Total liabilities and equity	4,438.9	3,518.9
Reportable legal entities | Guarantor Subsidiaries
Condensed consolidating balance sheet
Cash and cash equivalents	14.8	9.4
Accounts receivable, net	523.8	483.6
Inventories	1,935.0	1,830.5
Other current assets	16.8	14.6
Assets held for sale		8.4
Total current assets	2,490.4	2,346.5
Property and equipment, net	1,032.9	961.0
Intangible assets	1,334.6	1,079.6
Other long-term assets	4.6	4.1
Total assets	4,862.5	4,391.2
Floor plan notes payable	1,272.4	1,178.0
Floor plan notes payable - non-trade	601.9	623.2
Accounts payable	194.4	171.9
Accrued expenses	165.2	77.2
Current portion of long-term debt	5.5	6.0
Liabilities held for sale	0.7	6.1
Total current liabilities	2,240.1	2,062.4
Long-term debt	191.6	186.0
Deferred tax liabilities	480.1	560.9
Other long-term liabilities	64.7	65.2
Total liabilities	2,976.5	2,874.5
Total equity	1,886.0	1,516.7
Total liabilities and equity	4,862.5	4,391.2
Reportable legal entities | Non-Guarantor Subsidiaries
Condensed consolidating balance sheet
Cash and cash equivalents	30.9	14.6	$ 62.4	$ 36.3
Accounts receivable, net	431.1	395.4
Inventories	2,009.1	1,577.7
Other current assets	57.7	45.0
Total current assets	2,528.8	2,032.7
Property and equipment, net	1,072.4	842.2
Intangible assets	799.9	631.7
Equity method investments	69.7	59.7
Other long-term assets	4.7	18.6
Total assets	4,475.5	3,584.9
Floor plan notes payable	1,070.8	906.5
Floor plan notes payable - non-trade	620.1	454.1
Accounts payable	443.3	320.6
Accrued expenses	820.9	728.9
Current portion of long-term debt	67.3	42.3
Total current liabilities	3,022.4	2,452.4
Long-term debt	239.6	241.0
Deferred tax liabilities	1.4	3.7
Other long-term liabilities	475.6	365.3
Total liabilities	3,739.0	3,062.4
Total equity	736.5	522.5
Total liabilities and equity	$ 4,475.5	$ 3,584.9