Condensed Consolidating Financial Information - Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Condensed consolidating statement of income
Revenues	$ 5,658.6	$ 5,524.4	$ 17,345.8	$ 15,988.9
Cost of sales	4,806.0	4,701.8	14,739.0	13,574.7
Gross profit	852.6	822.6	2,606.8	2,414.2
Selling, general and administrative expenses	662.8	646.1	2,001.3	1,869.8
Depreciation	25.9	24.3	77.2	70.0
Operating income	163.9	152.2	528.3	474.4
Floor plan interest expense	(20.2)	(16.4)	(59.0)	(45.6)
Other interest expense	(28.3)	(27.8)	(86.7)	(79.2)
Equity in earnings of affiliates	41.7	30.9	95.0	70.9
Income from continuing operations before income taxes	157.1	138.9	477.6	420.5
Income taxes	(27.1)	(44.7)	(104.7)	(136.0)
Income from continuing operations	130.0	94.2	372.9	284.5
Income (loss) income from discontinued operations, net of tax	0.1	0.1	0.2	(0.3)
Net income	130.1	94.3	373.1	284.2
Other comprehensive (loss) income, net of tax	(17.5)	35.3	(58.5)	101.9
Comprehensive income	112.6	129.6	314.6	386.1
Less: Comprehensive (loss) income attributable to non-controlling interests	(0.2)	0.6	(1.0)	3.8
Comprehensive income attributable to Penske Automotive Group common stockholders	112.8	129.0	315.6	382.3
Eliminations
Condensed consolidating statement of income
Equity in earnings of subsidiaries	(144.2)	(136.3)	(470.1)	(428.6)
Income from continuing operations before income taxes	(144.2)	(136.3)	(470.1)	(428.6)
Income taxes	24.8	43.8	104.0	139.0
Income from continuing operations	(119.4)	(92.5)	(366.1)	(289.6)
Income (loss) income from discontinued operations, net of tax	(0.1)	(0.1)	(0.2)	0.3
Net income	(119.5)	(92.6)	(366.3)	(289.3)
Other comprehensive (loss) income, net of tax	19.8	(31.9)	56.4	(93.0)
Comprehensive income	(99.7)	(124.5)	(309.9)	(382.3)
Less: Comprehensive (loss) income attributable to non-controlling interests	0.1	(0.8)	1.2	(2.8)
Comprehensive income attributable to Penske Automotive Group common stockholders	(99.8)	(123.7)	(311.1)	(379.5)
Penske Automotive Group | Reportable legal entities
Condensed consolidating statement of income
Selling, general and administrative expenses	6.3	6.3	19.1	18.5
Depreciation	0.4	0.4	1.2	1.2
Operating income	(6.7)	(6.7)	(20.3)	(19.7)
Floor plan interest expense	(1.9)	(1.3)	(5.3)	(3.4)
Other interest expense	(19.1)	(19.8)	(58.8)	(54.1)
Equity in earnings of affiliates	40.7	30.5	91.7	68.2
Equity in earnings of subsidiaries	144.2	136.3	470.1	428.6
Income from continuing operations before income taxes	157.2	139.0	477.4	419.6
Income taxes	(27.1)	(44.7)	(104.7)	(136.0)
Income from continuing operations	130.1	94.3	372.7	283.6
Income (loss) income from discontinued operations, net of tax	0.1	0.1	0.2	(0.3)
Net income	130.2	94.4	372.9	283.3
Other comprehensive (loss) income, net of tax	(17.5)	35.3	(58.5)	101.9
Comprehensive income	112.7	129.7	314.4	385.2
Less: Comprehensive (loss) income attributable to non-controlling interests	(0.1)	0.8	(1.2)	2.8
Comprehensive income attributable to Penske Automotive Group common stockholders	112.8	128.9	315.6	382.4
Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of income
Revenues	3,061.9	3,047.0	8,990.2	8,749.7
Cost of sales	2,584.1	2,570.2	7,561.6	7,351.8
Gross profit	477.8	476.8	1,428.6	1,397.9
Selling, general and administrative expenses	356.6	354.4	1,059.6	1,037.3
Depreciation	14.0	13.4	41.3	39.3
Operating income	107.2	109.0	327.7	321.3
Floor plan interest expense	(12.7)	(9.8)	(36.3)	(27.9)
Other interest expense	(2.3)	(2.3)	(6.2)	(6.6)
Income from continuing operations before income taxes	92.2	96.9	285.2	286.8
Income taxes	(14.6)	(36.0)	(67.0)	(109.8)
Income from continuing operations	77.6	60.9	218.2	177.0
Income (loss) income from discontinued operations, net of tax	0.1	0.1	0.2	(0.3)
Net income	77.7	61.0	218.4	176.7
Comprehensive income	77.7	61.0	218.4	176.7
Comprehensive income attributable to Penske Automotive Group common stockholders	77.7	61.0	218.4	176.7
Non-Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of income
Revenues	2,596.7	2,477.4	8,355.6	7,239.2
Cost of sales	2,221.9	2,131.6	7,177.4	6,222.9
Gross profit	374.8	345.8	1,178.2	1,016.3
Selling, general and administrative expenses	299.9	285.4	922.6	814.0
Depreciation	11.5	10.5	34.7	29.5
Operating income	63.4	49.9	220.9	172.8
Floor plan interest expense	(5.6)	(5.3)	(17.4)	(14.3)
Other interest expense	(6.9)	(5.7)	(21.7)	(18.5)
Equity in earnings of affiliates	1.0	0.4	3.3	2.7
Income from continuing operations before income taxes	51.9	39.3	185.1	142.7
Income taxes	(10.2)	(7.8)	(37.0)	(29.2)
Income from continuing operations	41.7	31.5	148.1	113.5
Net income	41.7	31.5	148.1	113.5
Other comprehensive (loss) income, net of tax	(19.8)	31.9	(56.4)	93.0
Comprehensive income	21.9	63.4	91.7	206.5
Less: Comprehensive (loss) income attributable to non-controlling interests	(0.2)	0.6	(1.0)	3.8
Comprehensive income attributable to Penske Automotive Group common stockholders	$ 22.1	$ 62.8	$ 92.7	$ 202.7