Condensed Consolidating Financial Information - Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	$ 623.0	$ 371.3	$ 397.8
Investing activities:
Purchase of equipment and improvements	(247.0)	(203.1)	(199.5)
Proceeds from sale-leaseback transactions	22.2
Acquisition of additional ownership interest in Penske Truck Leasing	(239.1)	(498.5)
Acquisitions, net	(449.7)	(140.8)	(156.9)
Other	(15.1)	5.7	4.7
Net cash used in continuing investing activities	(928.7)	(836.7)	(351.7)
Financing activities:
Net borrowings (repayments) of long-term debt	(26.0)	122.9	(62.1)
Net borrowings (repayments) of floor plan notes payable — non-trade	185.3	101.0	154.2
Payment of debt issuance costs	(4.0)	(6.7)	(1.8)
Repurchases of common stock	(18.5)	(173.6)	(48.9)
Dividends	(108.4)	(95.1)	(84.8)
Other	(5.8)	(15.5)	(12.2)
Net cash provided by (used in) continuing financing activities	322.6	433.0	(55.6)
Net cash provided by discontinued operations	2.7	3.1	37.0
Effect of exchange rate changes on cash and cash equivalents	2.1	(9.1)	(1.4)
Net change in cash and cash equivalents	21.7	(38.4)	26.1
Cash and cash equivalents, beginning of period	24.0	62.4	36.3
Cash and cash equivalents, end of period	45.7	24.0	62.4
3.75% senior subordinated notes due 2020
Financing activities:
Issuance of senior subordinated notes	300.0
5.50% senior subordinated notes due 2026
Financing activities:
Issuance of senior subordinated notes		500.0
Reportable legal entities | Penske Automotive Group
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	(46.8)	(31.6)	1.4
Investing activities:
Purchase of equipment and improvements	(3.2)	(1.0)	(1.3)
Acquisition of additional ownership interest in Penske Truck Leasing	(239.1)	(498.5)
Other	(40.0)
Net cash used in continuing investing activities	(282.3)	(499.5)	(1.3)
Financing activities:
Net borrowings (repayments) of long-term debt	(68.0)	80.0	72.0
Net borrowings (repayments) of floor plan notes payable — non-trade	40.6	1.3	67.9
Payment of debt issuance costs	(4.0)	(6.7)
Repurchases of common stock	(18.5)	(173.6)	(48.9)
Dividends	(108.4)	(95.1)	(84.8)
Other	(5.8)	(5.8)	(6.3)
Distributions from (to) parent	193.2	231.0
Net cash provided by (used in) continuing financing activities	329.1	531.1	(0.1)
Reportable legal entities | Penske Automotive Group | 3.75% senior subordinated notes due 2020
Financing activities:
Issuance of senior subordinated notes	300.0
Reportable legal entities | Penske Automotive Group | 5.50% senior subordinated notes due 2026
Financing activities:
Issuance of senior subordinated notes		500.0
Reportable legal entities | Guarantor Subsidiaries
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	643.3	52.1	230.3
Investing activities:
Purchase of equipment and improvements	(138.0)	(126.6)	(119.7)
Acquisitions, net	(334.5)		(93.2)
Other	9.0	17.0
Net cash used in continuing investing activities	(463.5)	(109.6)	(212.9)
Financing activities:
Net borrowings (repayments) of long-term debt	6.4	21.6	(4.9)
Net borrowings (repayments) of floor plan notes payable — non-trade	4.8	270.8	(58.3)
Distributions from (to) parent	(188.3)	(226.2)	8.8
Net cash provided by (used in) continuing financing activities	(177.1)	66.2	(54.4)
Net cash provided by discontinued operations	2.7	0.7	37.0
Net change in cash and cash equivalents	5.4	9.4
Cash and cash equivalents, beginning of period	9.4
Cash and cash equivalents, end of period	14.8	9.4
Reportable legal entities | Non-Guarantor Subsidiaries
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	26.5	350.8	166.1
Investing activities:
Purchase of equipment and improvements	(105.8)	(75.5)	(78.5)
Proceeds from sale-leaseback transactions	22.2
Acquisitions, net	(115.2)	(140.8)	(63.7)
Other	15.9	(11.3)	4.7
Net cash used in continuing investing activities	(182.9)	(227.6)	(137.5)
Financing activities:
Net borrowings (repayments) of long-term debt	35.6	21.3	(129.2)
Net borrowings (repayments) of floor plan notes payable — non-trade	139.9	(171.1)	144.6
Payment of debt issuance costs			(1.8)
Other		(9.7)	(5.9)
Distributions from (to) parent	(4.9)	(4.8)	(8.8)
Net cash provided by (used in) continuing financing activities	170.6	(164.3)	(1.1)
Net cash provided by discontinued operations		2.4
Effect of exchange rate changes on cash and cash equivalents	2.1	(9.1)	(1.4)
Net change in cash and cash equivalents	16.3	(47.8)	26.1
Cash and cash equivalents, beginning of period	14.6	62.4	36.3
Cash and cash equivalents, end of period	$ 30.9	$ 14.6	$ 62.4