Condensed Consolidating Financial Information - Cash Flows (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	$ 417.0	$ 320.5
Investing activities:
Purchase of equipment and improvements	(118.8)	(113.4)
Proceeds from sale of dealerships	58.4	9.0
Proceeds from sale-leaseback transactions	5.8
Acquisitions, net	(168.6)	(431.9)
Other	(3.0)	6.0
Net cash used in continuing investing activities	(226.2)	(530.3)
Financing activities:
Net borrowings (repayments) of long-term debt	23.1	137.9
Net (repayments) borrowings of floor plan notes payable — non-trade	(92.9)	131.3
Repurchases of common stock	(55.8)	(8.5)
Dividends	(59.0)	(52.4)
Other	(6.1)	(5.8)
Net cash (used in) provided by continuing financing activities	(190.7)	202.5
Net cash provided by discontinued operations	0.2	2.5
Effect of exchange rate changes on cash and cash equivalents	(0.2)	1.5
Net change in cash and cash equivalents	0.1	(3.3)
Cash and cash equivalents, beginning of period	45.7	24.0
Cash and cash equivalents, end of period	45.8	20.7
Penske Automotive Group | Reportable legal entities
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	(24.5)	(50.5)
Investing activities:
Purchase of equipment and improvements	(0.4)	(1.4)
Other	(1.9)	6.0
Net cash used in continuing investing activities	(2.3)	4.6
Financing activities:
Net borrowings (repayments) of long-term debt	(73.0)	83.0
Net (repayments) borrowings of floor plan notes payable — non-trade	1.8	29.6
Repurchases of common stock	(55.8)	(8.5)
Dividends	(59.0)	(52.4)
Other	(0.3)	(5.8)
Distributions from (to) parent	213.1
Net cash (used in) provided by continuing financing activities	26.8	45.9
Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	357.2	252.6
Investing activities:
Purchase of equipment and improvements	(68.4)	(49.4)
Proceeds from sale of dealerships	55.9	9.0
Acquisitions, net		(316.9)
Net cash used in continuing investing activities	(12.5)	(357.3)
Financing activities:
Net borrowings (repayments) of long-term debt	(56.5)	10.8
Net (repayments) borrowings of floor plan notes payable — non-trade	(98.8)	80.2
Other	(5.8)
Distributions from (to) parent	(198.2)	3.7
Net cash (used in) provided by continuing financing activities	(359.3)	94.7
Net cash provided by discontinued operations	0.2	2.5
Net change in cash and cash equivalents	(14.4)	(7.5)
Cash and cash equivalents, beginning of period	14.8	9.4
Cash and cash equivalents, end of period	0.4	1.9
Non-Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	84.3	118.4
Investing activities:
Purchase of equipment and improvements	(50.0)	(62.6)
Proceeds from sale of dealerships	2.5
Proceeds from sale-leaseback transactions	5.8
Acquisitions, net	(168.6)	(115.0)
Other	(1.1)
Net cash used in continuing investing activities	(211.4)	(177.6)
Financing activities:
Net borrowings (repayments) of long-term debt	152.6	44.1
Net (repayments) borrowings of floor plan notes payable — non-trade	4.1	21.5
Distributions from (to) parent	(14.9)	(3.7)
Net cash (used in) provided by continuing financing activities	141.8	61.9
Effect of exchange rate changes on cash and cash equivalents	(0.2)	1.5
Net change in cash and cash equivalents	14.5	4.2
Cash and cash equivalents, beginning of period	30.9	14.6
Cash and cash equivalents, end of period	$ 45.4	$ 18.8