Condensed Consolidating Financial Information - Cash Flows (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	$ 535.9	$ 466.8
Investing activities:
Purchase of equipment and improvements	(188.5)	(180.1)
Proceeds from sale of dealerships	58.4	9.0
Proceeds from sale-leaseback transactions	10.7
Acquisition of additional ownership interest in Penske Truck Leasing		(239.1)
Acquisitions, net	(168.6)	(449.7)
Other	(3.5)	4.3
Net cash used in continuing investing activities	(291.5)	(855.6)
Financing activities:
Issuance of 3.75% senior subordinated notes		300.0
Net borrowings (repayments) of long-term debt	(41.0)	50.3
Net (repayments) borrowings of floor plan notes payable — non-trade	(59.6)	155.2
Payment of debt issuance costs		(4.0)
Repurchases of common stock	(55.8)	(18.5)
Dividends	(89.7)	(80.1)
Other	(6.2)	(5.8)
Net cash (used in) provided by continuing financing activities	(252.3)	397.1
Net cash provided by discontinued operations	0.3	2.7
Effect of exchange rate changes on cash and cash equivalents	(0.5)	2.2
Net change in cash and cash equivalents	(8.1)	13.2
Cash and cash equivalents, beginning of period	45.7	24.0
Cash and cash equivalents, end of period	37.6	37.2
Penske Automotive Group | Reportable legal entities
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	16.1	(34.5)
Investing activities:
Purchase of equipment and improvements	(2.3)	(2.4)
Acquisition of additional ownership interest in Penske Truck Leasing		(239.1)
Other	(2.4)	4.6
Net cash used in continuing investing activities	(4.7)	(236.9)
Financing activities:
Issuance of 3.75% senior subordinated notes		300.0
Net borrowings (repayments) of long-term debt	(172.0)	(24.0)
Net (repayments) borrowings of floor plan notes payable — non-trade	(23.3)	63.7
Payment of debt issuance costs		(4.0)
Repurchases of common stock	(55.8)	(18.5)
Dividends	(89.7)	(80.1)
Other	(0.3)	(5.8)
Distributions from (to) parent	329.7	40.1
Net cash (used in) provided by continuing financing activities	(11.4)	271.4
Net change in cash and cash equivalents	0.0
Cash and cash equivalents, end of period	0.0
Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	356.2	359.5
Investing activities:
Purchase of equipment and improvements	(95.1)	(80.0)
Proceeds from sale of dealerships	55.9	9.0
Acquisitions, net		(316.9)
Net cash used in continuing investing activities	(39.2)	(387.9)
Financing activities:
Net borrowings (repayments) of long-term debt	41.6	8.6
Net (repayments) borrowings of floor plan notes payable — non-trade	(50.1)	43.2
Other	(5.9)
Distributions from (to) parent	(314.3)	(35.5)
Net cash (used in) provided by continuing financing activities	(328.7)	16.3
Net cash provided by discontinued operations	0.3	2.7
Net change in cash and cash equivalents	(11.4)	(9.4)
Cash and cash equivalents, beginning of period	14.8	9.4
Cash and cash equivalents, end of period	3.4
Non-Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	163.6	141.8
Investing activities:
Purchase of equipment and improvements	(91.1)	(97.7)
Proceeds from sale of dealerships	2.5
Proceeds from sale-leaseback transactions	10.7
Acquisitions, net	(168.6)	(132.8)
Other	(1.1)	(0.3)
Net cash used in continuing investing activities	(247.6)	(230.8)
Financing activities:
Net borrowings (repayments) of long-term debt	89.4	65.7
Net (repayments) borrowings of floor plan notes payable — non-trade	13.8	48.3
Distributions from (to) parent	(15.4)	(4.6)
Net cash (used in) provided by continuing financing activities	87.8	109.4
Effect of exchange rate changes on cash and cash equivalents	(0.5)	2.2
Net change in cash and cash equivalents	3.3	22.6
Cash and cash equivalents, beginning of period	30.9	14.6
Cash and cash equivalents, end of period	$ 34.2	$ 37.2