Condensed Consolidating Financial Information - Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed consolidating statement of income
Revenues	$ 5,439.3	$ 5,658.6	$ 5,940.3	$ 5,746.9	$ 5,398.0	$ 5,524.4	$ 5,383.4	$ 5,081.1	$ 22,785.1	$ 21,386.9	$ 20,118.5
Cost of sales									19,370.2	18,164.4	17,151.9
Gross profit	808.1	852.6	889.8	864.4	808.3	822.6	817.3	774.3	3,414.9	3,222.5	2,966.6
Selling, general and administrative expenses									2,646.3	2,516.0	2,302.0
Depreciation									103.7	95.1	89.7
Operating income									664.9	611.4	574.9
Floor plan interest expense									(80.9)	(63.4)	(50.9)
Other interest expense									(114.7)	(107.4)	(85.4)
Equity in earnings of affiliates									134.8	107.6	69.5
Income from continuing operations before income taxes									604.1	548.2	508.1
Income taxes									(134.3)	64.8	(160.7)
Income from continuing operations	96.9	130.0	135.2	107.7	328.5	94.2	106.7	83.6	469.8	613.0	347.4
Income (loss) income from discontinued operations, net of tax									0.5	(0.2)	(1.0)
Net income	$ 97.2	$ 130.1	$ 135.2	$ 107.8	$ 328.6	$ 94.3	$ 106.9	$ 83.0	470.3	612.8	346.4
Other comprehensive (loss) income, net of tax									(89.5)	107.4	(129.0)
Comprehensive income									380.8	720.2	217.4
Less: Comprehensive (loss) income attributable to non-controlling interests									(2.2)	2.7	2.7
Comprehensive income attributable to Penske Automotive Group common stockholders									383.0	717.5	214.7
Eliminations
Condensed consolidating statement of income
Equity in earnings of subsidiaries									(586.8)	(550.6)	(523.3)
Income from continuing operations before income taxes									(586.8)	(550.6)	(523.3)
Income taxes									130.3	(64.8)	166.6
Income from continuing operations									(456.5)	(615.4)	(356.7)
Income (loss) income from discontinued operations, net of tax									(0.5)	0.2	1.0
Net income									(457.0)	(615.2)	(355.7)
Other comprehensive (loss) income, net of tax									74.9	(97.5)	123.9
Comprehensive income									(382.1)	(712.7)	(231.8)
Less: Comprehensive (loss) income attributable to non-controlling interests									1.5	(3.2)	0.8
Comprehensive income attributable to Penske Automotive Group common stockholders									(383.6)	(709.5)	(232.6)
Penske Automotive Group | Reportable legal entities
Condensed consolidating statement of income
Selling, general and administrative expenses									24.9	24.5	19.2
Depreciation									1.5	1.6	1.7
Operating income									(26.4)	(26.1)	(20.9)
Floor plan interest expense									(7.2)	(4.9)	(3.0)
Other interest expense									(77.8)	(73.5)	(59.2)
Equity in earnings of affiliates									129.5	102.8	64.6
Equity in earnings of subsidiaries									586.8	550.6	523.3
Income from continuing operations before income taxes									604.9	548.9	504.8
Income taxes									(134.3)	64.8	(160.7)
Income from continuing operations									470.6	613.7	344.1
Income (loss) income from discontinued operations, net of tax									0.5	(0.2)	(1.0)
Net income									471.1	613.5	343.1
Other comprehensive (loss) income, net of tax									(89.5)	107.4	(129.0)
Comprehensive income									381.6	720.9	214.1
Less: Comprehensive (loss) income attributable to non-controlling interests									(1.5)	3.2	(0.8)
Comprehensive income attributable to Penske Automotive Group common stockholders									383.1	717.7	214.9
Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of income
Revenues									12,036.6	11,825.9	10,946.2
Cost of sales									10,130.4	9,945.0	9,251.8
Gross profit									1,906.2	1,880.9	1,694.4
Selling, general and administrative expenses									1,403.7	1,393.3	1,284.4
Depreciation									56.1	53.1	47.3
Operating income									446.4	434.5	362.7
Floor plan interest expense									(50.7)	(38.5)	(29.1)
Other interest expense									(8.8)	(8.9)	(5.1)
Income from continuing operations before income taxes									386.9	387.1	328.5
Income taxes									(88.6)	95.5	(124.4)
Income from continuing operations									298.3	482.6	204.1
Income (loss) income from discontinued operations, net of tax									0.5	(0.2)	(0.9)
Net income									298.8	482.4	203.2
Comprehensive income									298.8	482.4	203.2
Comprehensive income attributable to Penske Automotive Group common stockholders									298.8	482.4	203.2
Non-Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of income
Revenues									10,748.5	9,561.0	9,172.3
Cost of sales									9,239.8	8,219.4	7,900.1
Gross profit									1,508.7	1,341.6	1,272.2
Selling, general and administrative expenses									1,217.7	1,098.2	998.4
Depreciation									46.1	40.4	40.7
Operating income									244.9	203.0	233.1
Floor plan interest expense									(23.0)	(20.0)	(18.8)
Other interest expense									(28.1)	(25.0)	(21.1)
Equity in earnings of affiliates									5.3	4.8	4.9
Income from continuing operations before income taxes									199.1	162.8	198.1
Income taxes									(41.7)	(30.7)	(42.2)
Income from continuing operations									157.4	132.1	155.9
Income (loss) income from discontinued operations, net of tax											(0.1)
Net income									157.4	132.1	155.8
Other comprehensive (loss) income, net of tax									(74.9)	97.5	(123.9)
Comprehensive income									82.5	229.6	31.9
Less: Comprehensive (loss) income attributable to non-controlling interests									(2.2)	2.7	2.7
Comprehensive income attributable to Penske Automotive Group common stockholders									$ 84.7	$ 226.9	$ 29.2