Condensed Consolidating Financial Information - Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Condensed consolidating statement of income
Revenues	$ 5,940.3	$ 5,383.4	$ 11,687.2	$ 10,464.5
Cost of sales	5,050.5	4,566.1	9,933.0	8,872.9
Gross profit	889.8	817.3	1,754.2	1,591.6
Selling, general and administrative expenses	675.4	622.0	1,338.5	1,223.7
Depreciation	25.7	23.3	51.3	45.7
Operating income	188.7	172.0	364.4	322.2
Floor plan interest expense	(19.9)	(15.5)	(38.8)	(29.2)
Other interest expense	(28.6)	(26.4)	(58.4)	(51.4)
Equity in earnings of affiliates	36.0	26.8	53.3	40.0
Income from continuing operations before income taxes	176.2	156.9	320.5	281.6
Income taxes	(41.0)	(50.2)	(77.6)	(91.3)
Income from continuing operations	135.2	106.7	242.9	190.3
Income (loss) income from discontinued operations, net of tax		0.2	0.1	(0.4)
Net income	135.2	106.9	243.0	189.9
Other comprehensive (loss) income, net of tax	(72.8)	40.5	(41.0)	66.6
Comprehensive income	62.4	147.4	202.0	256.5
Less: Comprehensive (loss) income attributable to non-controlling interests	(0.5)	2.4	(0.8)	3.2
Comprehensive income attributable to Penske Automotive Group common stockholders	62.9	145.0	202.8	253.3
Eliminations
Condensed consolidating statement of income
Equity in earnings of subsidiaries	(168.3)	(156.6)	(325.9)	(292.3)
Income from continuing operations before income taxes	(168.3)	(156.6)	(325.9)	(292.3)
Income taxes	39.4	50.3	79.2	95.2
Income from continuing operations	(128.9)	(106.3)	(246.7)	(197.1)
Income (loss) income from discontinued operations, net of tax		(0.2)	(0.1)	0.4
Net income	(128.9)	(106.5)	(246.8)	(196.7)
Other comprehensive (loss) income, net of tax	68.1	(37.6)	36.6	(61.1)
Comprehensive income	(60.8)	(144.1)	(210.2)	(257.8)
Less: Comprehensive (loss) income attributable to non-controlling interests	1.1	(1.6)	1.1	(2.0)
Comprehensive income attributable to Penske Automotive Group common stockholders	(61.9)	(142.5)	(211.3)	(255.8)
Penske Automotive Group | Reportable legal entities
Condensed consolidating statement of income
Selling, general and administrative expenses	6.6	6.2	12.8	12.2
Depreciation	0.4	0.4	0.8	0.8
Operating income	(7.0)	(6.6)	(13.6)	(13.0)
Floor plan interest expense	(1.8)	(1.1)	(3.4)	(2.1)
Other interest expense	(18.9)	(17.8)	(39.7)	(34.3)
Equity in earnings of affiliates	35.0	25.2	51.0	37.7
Equity in earnings of subsidiaries	168.3	156.6	325.9	292.3
Income from continuing operations before income taxes	175.6	156.3	320.2	280.6
Income taxes	(41.0)	(50.2)	(77.6)	(91.3)
Income from continuing operations	134.6	106.1	242.6	189.3
Income (loss) income from discontinued operations, net of tax		0.2	0.1	(0.4)
Net income	134.6	106.3	242.7	188.9
Other comprehensive (loss) income, net of tax	(72.8)	40.5	(41.0)	66.6
Comprehensive income	61.8	146.8	201.7	255.5
Less: Comprehensive (loss) income attributable to non-controlling interests	(1.1)	1.6	(1.1)	2.0
Comprehensive income attributable to Penske Automotive Group common stockholders	62.9	145.2	202.8	253.5
Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of income
Revenues	3,071.8	3,034.8	5,928.3	5,702.7
Cost of sales	2,582.3	2,550.4	4,977.5	4,781.6
Gross profit	489.5	484.4	950.8	921.1
Selling, general and administrative expenses	359.7	344.5	703.0	682.9
Depreciation	13.7	13.2	27.3	25.9
Operating income	116.1	126.7	220.5	212.3
Floor plan interest expense	(12.3)	(9.7)	(23.6)	(18.1)
Other interest expense	(2.0)	(2.2)	(3.9)	(4.3)
Income from continuing operations before income taxes	101.8	114.8	193.0	189.9
Income taxes	(27.4)	(41.2)	(52.4)	(73.8)
Income from continuing operations	74.4	73.6	140.6	116.1
Income (loss) income from discontinued operations, net of tax		0.2	0.1	(0.4)
Net income	74.4	73.8	140.7	115.7
Comprehensive income	74.4	73.8	140.7	115.7
Comprehensive income attributable to Penske Automotive Group common stockholders	74.4	73.8	140.7	115.7
Non-Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of income
Revenues	2,868.5	2,348.6	5,758.9	4,761.8
Cost of sales	2,468.2	2,015.7	4,955.5	4,091.3
Gross profit	400.3	332.9	803.4	670.5
Selling, general and administrative expenses	309.1	271.3	622.7	528.6
Depreciation	11.6	9.7	23.2	19.0
Operating income	79.6	51.9	157.5	122.9
Floor plan interest expense	(5.8)	(4.7)	(11.8)	(9.0)
Other interest expense	(7.7)	(6.4)	(14.8)	(12.8)
Equity in earnings of affiliates	1.0	1.6	2.3	2.3
Income from continuing operations before income taxes	67.1	42.4	133.2	103.4
Income taxes	(12.0)	(9.1)	(26.8)	(21.4)
Income from continuing operations	55.1	33.3	106.4	82.0
Net income	55.1	33.3	106.4	82.0
Other comprehensive (loss) income, net of tax	(68.1)	37.6	(36.6)	61.1
Comprehensive income	(13.0)	70.9	69.8	143.1
Less: Comprehensive (loss) income attributable to non-controlling interests	(0.5)	2.4	(0.8)	3.2
Comprehensive income attributable to Penske Automotive Group common stockholders	$ (12.5)	$ 68.5	$ 70.6	$ 139.9