Condensed Consolidating Financial Information - Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	$ 518.3	$ 614.2	$ 623.0
Investing activities:
Purchase of equipment and improvements	(245.3)	(305.6)	(247.0)
Proceeds from sale of dealerships	22.8	84.5	25.1
Proceeds from sale-leaseback transactions	18.9	10.7	22.2
Acquisition of additional ownership interest in Penske Truck Leasing			(239.1)
Acquisitions, net	(326.9)	(309.1)	(449.7)
Other	(2.2)	(5.7)	(40.2)
Net cash used in continuing investing activities	(532.7)	(525.2)	(928.7)
Financing activities:
Issuance of 3.75% senior subordinated notes			300.0
Net borrowings (repayments) of long-term debt	130.4	93.5	(26.0)
Net (repayments) borrowings of floor plan notes payable - non-trade	177.5	10.0	185.3
Payment of debt issuance costs	(0.4)	(1.9)	(4.0)
Repurchases of common stock	(169.2)	(68.9)	(18.5)
Dividends	(130.8)	(121.2)	(108.4)
Other	(4.9)	(5.8)	(5.8)
Net cash used in continuing financing activities	2.6	(94.3)	322.6
Net cash provided by discontinued operations	0.3	0.5	2.7
Effect of exchange rate changes on cash and cash equivalents	0.2	(1.5)	2.1
Net change in cash and cash equivalents	(11.3)	(6.3)	21.7
Cash and cash equivalents, beginning of period	39.4	45.7	24.0
Cash and cash equivalents, end of period	$ 28.1	$ 39.4	$ 45.7
5.50% senior subordinated notes due 2026
Condensed consolidating statement of cash flows
Interest rate (as a percent)	5.50%	5.50%	5.50%
3.75% senior subordinated notes due 2020
Condensed consolidating statement of cash flows
Interest rate (as a percent)	3.75%	3.75%	3.75%
Penske Automotive Group | Reportable legal entities
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	$ (79.2)	$ 3.4	$ (46.8)
Investing activities:
Purchase of equipment and improvements	(1.6)	(1.2)	(3.2)
Acquisition of additional ownership interest in Penske Truck Leasing			(239.1)
Other	(3.8)	(3.8)	(40.0)
Net cash used in continuing investing activities	(5.4)	(5.0)	(282.3)
Financing activities:
Issuance of 3.75% senior subordinated notes			300.0
Net borrowings (repayments) of long-term debt	84.9	(142.0)	(68.0)
Net (repayments) borrowings of floor plan notes payable - non-trade	1.6	35.6	40.6
Payment of debt issuance costs	(0.4)	(1.9)	(4.0)
Repurchases of common stock	(169.2)	(68.9)	(18.5)
Dividends	(130.8)	(121.2)	(108.4)
Other	(4.9)	(5.8)	(5.8)
Distributions from (to) parent	303.4	305.8	193.2
Net cash used in continuing financing activities	84.6	1.6	329.1
Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	554.2	535.2	643.3
Investing activities:
Purchase of equipment and improvements	(91.3)	(173.9)	(138.0)
Proceeds from sale of dealerships	16.2	82.0	9.0
Acquisitions, net	(332.7)	(140.5)	(334.5)
Other	3.4
Net cash used in continuing investing activities	(404.4)	(232.4)	(463.5)
Financing activities:
Net borrowings (repayments) of long-term debt	32.3	81.1	6.4
Net (repayments) borrowings of floor plan notes payable - non-trade	28.7	(96.0)	4.8
Distributions from (to) parent	(224.0)	(290.3)	(188.3)
Net cash used in continuing financing activities	(163.0)	(305.2)	(177.1)
Net cash provided by discontinued operations	0.3	0.5	2.7
Net change in cash and cash equivalents	(12.9)	(1.9)	5.4
Cash and cash equivalents, beginning of period	12.9	14.8	9.4
Cash and cash equivalents, end of period		12.9	14.8
Non-Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	43.3	75.6	26.5
Investing activities:
Purchase of equipment and improvements	(152.4)	(130.5)	(105.8)
Proceeds from sale of dealerships	6.6	2.5	16.1
Proceeds from sale-leaseback transactions	18.9	10.7	22.2
Acquisitions, net	5.8	(168.6)	(115.2)
Other	(1.8)	(1.9)	(0.2)
Net cash used in continuing investing activities	(122.9)	(287.8)	(182.9)
Financing activities:
Net borrowings (repayments) of long-term debt	13.2	154.4	35.6
Net (repayments) borrowings of floor plan notes payable - non-trade	147.2	70.4	139.9
Distributions from (to) parent	(79.4)	(15.5)	(4.9)
Net cash used in continuing financing activities	81.0	209.3	170.6
Effect of exchange rate changes on cash and cash equivalents	0.2	(1.5)	2.1
Net change in cash and cash equivalents	1.6	(4.4)	16.3
Cash and cash equivalents, beginning of period	26.5	30.9	14.6
Cash and cash equivalents, end of period	$ 28.1	$ 26.5	$ 30.9