Condensed Consolidating Financial Information - Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed consolidating statement of income
Revenues	$ 5,746.9	$ 5,081.1
Cost of sales	4,882.5	4,306.8
Gross profit	864.4	774.3
Selling, general and administrative expenses	663.1	601.7
Depreciation	25.6	22.4
Operating income	175.7	150.2
Floor plan interest expense	(18.9)	(13.7)
Other interest expense	(29.8)	(25.0)
Equity in earnings of affiliates	17.3	13.2
Income from continuing operations before income taxes	144.3	124.7
Income taxes	(36.6)	(41.1)
Income from continuing operations	107.7	83.6
Income (loss) income from discontinued operations, net of tax	0.1	(0.6)
Net income	107.8	83.0
Other comprehensive income, net of tax	31.8	26.1
Comprehensive income	139.6	109.1
Less: Comprehensive (loss) income attributable to non-controlling interests	(0.3)	0.8
Comprehensive income attributable to Penske Automotive Group common stockholders	139.9	108.3
Eliminations
Condensed consolidating statement of income
Equity in earnings of subsidiaries	(157.9)	(135.7)
Income from continuing operations before income taxes	(157.9)	(135.7)
Income taxes	40.0	44.9
Income from continuing operations	(117.9)	(90.8)
Income (loss) income from discontinued operations, net of tax	(0.1)	0.6
Net income	(118.0)	(90.2)
Other comprehensive income, net of tax	(31.5)	(23.5)
Comprehensive income	(149.5)	(113.7)
Less: Comprehensive (loss) income attributable to non-controlling interests		(0.4)
Comprehensive income attributable to Penske Automotive Group common stockholders	(149.5)	(113.3)
Penske Automotive Group | Reportable legal entities
Condensed consolidating statement of income
Selling, general and administrative expenses	6.5	6.0
Depreciation	0.4	0.4
Operating income	(6.9)	(6.4)
Floor plan interest expense	(1.6)	(1.0)
Other interest expense	(20.8)	(16.5)
Equity in earnings of affiliates	16.0	12.5
Equity in earnings of subsidiaries	157.9	135.7
Income from continuing operations before income taxes	144.6	124.3
Income taxes	(36.6)	(41.1)
Income from continuing operations	108.0	83.2
Income (loss) income from discontinued operations, net of tax	0.1	(0.6)
Net income	108.1	82.6
Other comprehensive income, net of tax	31.8	26.1
Comprehensive income	139.9	108.7
Less: Comprehensive (loss) income attributable to non-controlling interests		0.4
Comprehensive income attributable to Penske Automotive Group common stockholders	139.9	108.3
Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of income
Revenues	2,856.5	2,667.9
Cost of sales	2,395.2	2,231.2
Gross profit	461.3	436.7
Selling, general and administrative expenses	343.0	338.4
Depreciation	13.6	12.7
Operating income	104.7	85.6
Floor plan interest expense	(11.3)	(8.4)
Other interest expense	(1.9)	(2.1)
Income from continuing operations before income taxes	91.5	75.1
Income taxes	(25.2)	(32.6)
Income from continuing operations	66.3	42.5
Income (loss) income from discontinued operations, net of tax	0.1	(0.6)
Net income	66.4	41.9
Comprehensive income	66.4	41.9
Comprehensive income attributable to Penske Automotive Group common stockholders	66.4	41.9
Non-Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of income
Revenues	2,890.4	2,413.2
Cost of sales	2,487.3	2,075.6
Gross profit	403.1	337.6
Selling, general and administrative expenses	313.6	257.3
Depreciation	11.6	9.3
Operating income	77.9	71.0
Floor plan interest expense	(6.0)	(4.3)
Other interest expense	(7.1)	(6.4)
Equity in earnings of affiliates	1.3	0.7
Income from continuing operations before income taxes	66.1	61.0
Income taxes	(14.8)	(12.3)
Income from continuing operations	51.3	48.7
Net income	51.3	48.7
Other comprehensive income, net of tax	31.5	23.5
Comprehensive income	82.8	72.2
Less: Comprehensive (loss) income attributable to non-controlling interests	(0.3)	0.8
Comprehensive income attributable to Penske Automotive Group common stockholders	$ 83.1	$ 71.4