Condensed Consolidating Financial Information - Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed consolidating statement of income
Revenues	$ 5,398.0	$ 5,524.4	$ 5,383.4	$ 5,081.1	$ 4,887.8	$ 5,152.0	$ 5,254.1	$ 4,824.6	$ 21,386.9	$ 20,118.5	$ 19,284.9
Cost of sales									18,164.4	17,151.9	16,417.4
Gross profit	808.3	822.6	817.3	774.3	727.3	744.2	771.3	723.8	3,222.5	2,966.6	2,867.5
Selling, general and administrative expenses									2,516.0	2,302.0	2,223.0
Depreciation									95.1	89.7	78.0
Operating income									611.4	574.9	566.5
Floor plan interest expense									(63.4)	(50.9)	(44.5)
Other interest expense									(107.4)	(85.4)	(69.4)
Equity in earnings of affiliates									107.6	69.5	39.3
Income from continuing operations before income taxes									548.2	508.1	491.9
Income taxes									64.8	(160.7)	(158.0)
Income from continuing operations									613.0	347.4	333.9
(Loss) income from discontinued operations, net of tax									(0.2)	(1.0)	(3.5)
Net income	$ 328.6	$ 94.3	$ 106.9	$ 83.0	$ 82.7	$ 88.5	$ 95.0	$ 80.2	612.8	346.4	330.4
Other comprehensive income (loss), net of tax									107.4	(129.0)	(70.3)
Comprehensive income									720.2	217.4	260.1
Less: Comprehensive income attributable to non-controlling interests									2.7	2.7	3.2
Comprehensive income attributable to Penske Automotive Group common stockholders									717.5	214.7	256.9
Eliminations
Condensed consolidating statement of income
Equity in earnings of subsidiaries									(550.6)	(523.3)	(527.0)
Income from continuing operations before income taxes									(550.6)	(523.3)	(527.0)
Income taxes									(64.8)	166.6	170.5
Income from continuing operations									(615.4)	(356.7)	(356.5)
(Loss) income from discontinued operations, net of tax									0.2	1.0	4.0
Net income									(615.2)	(355.7)	(352.5)
Other comprehensive income (loss), net of tax									(97.5)	123.9	62.9
Comprehensive income									(712.7)	(231.8)	(289.6)
Less: Comprehensive income attributable to non-controlling interests									(3.2)	0.8	1.1
Comprehensive income attributable to Penske Automotive Group common stockholders									(709.5)	(232.6)	(290.7)
Reportable legal entities | Penske Automotive Group
Condensed consolidating statement of income
Selling, general and administrative expenses									24.5	19.2	23.6
Depreciation									1.6	1.7	1.6
Operating income									(26.1)	(20.9)	(25.2)
Floor plan interest expense									(4.9)	(3.0)	(2.8)
Other interest expense									(73.5)	(59.2)	(45.6)
Equity in earnings of affiliates									102.8	64.6	34.8
Equity in earnings of subsidiaries									550.6	523.3	527.0
Income from continuing operations before income taxes									548.9	504.8	488.2
Income taxes									64.8	(160.7)	(158.0)
Income from continuing operations									613.7	344.1	330.2
(Loss) income from discontinued operations, net of tax									(0.2)	(1.0)	(4.0)
Net income									613.5	343.1	326.2
Other comprehensive income (loss), net of tax									107.4	(129.0)	(70.3)
Comprehensive income									720.9	214.1	255.9
Less: Comprehensive income attributable to non-controlling interests									3.2	(0.8)	(1.1)
Comprehensive income attributable to Penske Automotive Group common stockholders									717.7	214.9	257.0
Reportable legal entities | Guarantor Subsidiaries
Condensed consolidating statement of income
Revenues									11,825.9	10,946.2	10,152.4
Cost of sales									9,945.0	9,251.8	8,582.4
Gross profit									1,880.9	1,694.4	1,570.0
Selling, general and administrative expenses									1,393.3	1,284.4	1,193.0
Depreciation									53.1	47.3	42.0
Operating income									434.5	362.7	335.0
Floor plan interest expense									(38.5)	(29.1)	(22.0)
Other interest expense									(8.9)	(5.1)	(5.3)
Income from continuing operations before income taxes									387.1	328.5	307.7
Income taxes									95.5	(124.4)	(117.4)
Income from continuing operations									482.6	204.1	190.3
(Loss) income from discontinued operations, net of tax									(0.2)	(0.9)	(1.4)
Net income									482.4	203.2	188.9
Comprehensive income									482.4	203.2	188.9
Comprehensive income attributable to Penske Automotive Group common stockholders									482.4	203.2	188.9
Reportable legal entities | Non-Guarantor Subsidiaries
Condensed consolidating statement of income
Revenues									9,561.0	9,172.3	9,132.5
Cost of sales									8,219.4	7,900.1	7,835.0
Gross profit									1,341.6	1,272.2	1,297.5
Selling, general and administrative expenses									1,098.2	998.4	1,006.4
Depreciation									40.4	40.7	34.4
Operating income									203.0	233.1	256.7
Floor plan interest expense									(20.0)	(18.8)	(19.7)
Other interest expense									(25.0)	(21.1)	(18.5)
Equity in earnings of affiliates									4.8	4.9	4.5
Income from continuing operations before income taxes									162.8	198.1	223.0
Income taxes									(30.7)	(42.2)	(53.1)
Income from continuing operations									132.1	155.9	169.9
(Loss) income from discontinued operations, net of tax										(0.1)	(2.1)
Net income									132.1	155.8	167.8
Other comprehensive income (loss), net of tax									97.5	(123.9)	(62.9)
Comprehensive income									229.6	31.9	104.9
Less: Comprehensive income attributable to non-controlling interests									2.7	2.7	3.2
Comprehensive income attributable to Penske Automotive Group common stockholders									$ 226.9	$ 29.2	$ 101.7