Condensed Consolidating Financial Information - Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	$ 614.2	$ 623.0	$ 371.3
Investing activities:
Purchase of equipment and improvements	(305.6)	(247.0)	(203.1)
Proceeds from sale of dealerships	84.5	25.1	4.2
Proceeds from sale-leaseback transactions	10.7	22.2
Acquisition of additional ownership interest in Penske Truck Leasing		(239.1)	(498.5)
Acquisitions, net	(309.1)	(449.7)	(140.8)
Other	(5.7)	(40.2)	1.5
Net cash used in continuing investing activities	(525.2)	(928.7)	(836.7)
Financing activities:
Issuance of senior subordinated notes			500.0
Net borrowings (repayments) of long-term debt	93.5	(26.0)	122.9
Net (repayments) borrowings of floor plan notes payable — non-trade	10.0	185.3	101.0
Payment of debt issuance costs	(1.9)	(4.0)	(6.7)
Repurchases of common stock	(68.9)	(18.5)	(173.6)
Dividends	(121.2)	(108.4)	(95.1)
Other	(5.8)	(5.8)	(15.5)
Net cash (used in) provided by continuing financing activities	(94.3)	322.6	433.0
Net cash provided by discontinued operations	0.5	2.7	3.1
Effect of exchange rate changes on cash and cash equivalents	(1.5)	2.1	(9.1)
Net change in cash and cash equivalents	(6.3)	21.7	(38.4)
Cash and cash equivalents, beginning of period	45.7	24.0	62.4
Cash and cash equivalents, end of period	39.4	45.7	24.0
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		300.0	500.0
Penske Automotive Group | Reportable legal entities
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	3.4	(46.8)	(31.6)
Investing activities:
Purchase of equipment and improvements	(1.2)	(3.2)	(1.0)
Acquisition of additional ownership interest in Penske Truck Leasing		(239.1)	(498.5)
Other	(3.8)	(40.0)
Net cash used in continuing investing activities	(5.0)	(282.3)	(499.5)
Financing activities:
Issuance of senior subordinated notes			500.0
Net borrowings (repayments) of long-term debt	(142.0)	(68.0)	80.0
Net (repayments) borrowings of floor plan notes payable — non-trade	35.6	40.6	1.3
Payment of debt issuance costs	(1.9)	(4.0)	(6.7)
Repurchases of common stock	(68.9)	(18.5)	(173.6)
Dividends	(121.2)	(108.4)	(95.1)
Other	(5.8)	(5.8)	(5.8)
Distributions from (to) parent	305.8	193.2	231.0
Net cash (used in) provided by continuing financing activities	1.6	329.1	531.1
Penske Automotive Group | Reportable legal entities | 5.50% senior subordinated notes due 2026
Financing activities:
Issuance of senior subordinated notes		300.0
Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	535.2	643.3	52.1
Investing activities:
Purchase of equipment and improvements	(173.9)	(138.0)	(126.6)
Proceeds from sale of dealerships	82.0	9.0	4.2
Acquisitions, net	(140.5)	(334.5)
Other			12.8
Net cash used in continuing investing activities	(232.4)	(463.5)	(109.6)
Financing activities:
Net borrowings (repayments) of long-term debt	81.1	6.4	21.6
Net (repayments) borrowings of floor plan notes payable — non-trade	(96.0)	4.8	270.8
Distributions from (to) parent	(290.3)	(188.3)	(226.2)
Net cash (used in) provided by continuing financing activities	(305.2)	(177.1)	66.2
Net cash provided by discontinued operations	0.5	2.7	0.7
Net change in cash and cash equivalents	(1.9)	5.4	9.4
Cash and cash equivalents, beginning of period	14.8	9.4
Cash and cash equivalents, end of period	12.9	14.8	9.4
Non-Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	75.6	26.5	350.8
Investing activities:
Purchase of equipment and improvements	(130.5)	(105.8)	(75.5)
Proceeds from sale of dealerships	2.5	16.1
Proceeds from sale-leaseback transactions	10.7	22.2
Acquisitions, net	(168.6)	(115.2)	(140.8)
Other	(1.9)	(0.2)	(11.3)
Net cash used in continuing investing activities	(287.8)	(182.9)	(227.6)
Financing activities:
Net borrowings (repayments) of long-term debt	154.4	35.6	21.3
Net (repayments) borrowings of floor plan notes payable — non-trade	70.4	139.9	(171.1)
Other			(9.7)
Distributions from (to) parent	(15.5)	(4.9)	(4.8)
Net cash (used in) provided by continuing financing activities	209.3	170.6	(164.3)
Net cash provided by discontinued operations			2.4
Effect of exchange rate changes on cash and cash equivalents	(1.5)	2.1	(9.1)
Net change in cash and cash equivalents	(4.4)	16.3	(47.8)
Cash and cash equivalents, beginning of period	30.9	14.6	62.4
Cash and cash equivalents, end of period	$ 26.5	$ 30.9	$ 14.6