Condensed Consolidating Financial Information - Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed consolidating statement of income
Revenues									$ 23,179.4	$ 22,785.1	$ 21,386.9
Cost of sales									19,723.9	19,370.2	18,164.4
Gross profit	$ 866.5	$ 869.7	$ 867.8	$ 851.5	$ 808.1	$ 852.6	$ 889.8	$ 864.4	3,455.5	3,414.9	3,222.5
Selling, general and administrative expenses									2,693.2	2,646.3	2,516.0
Depreciation									109.6	103.7	95.1
Operating income									652.7	664.9	611.4
Floor plan interest expense									(84.5)	(80.9)	(63.4)
Other interest expense									(124.2)	(114.7)	(107.4)
Equity in earnings of affiliates									147.5	134.8	107.6
Income from continuing operations before income taxes									591.5	604.1	548.2
Income taxes									(156.7)	(134.3)	64.8
Income from continuing operations	101.3	116.0	118.4	99.1	96.9	130.0	135.2	107.7	434.8	469.8	613.0
Income (loss) from discontinued operations, net of tax									0.3	0.5	(0.2)
Net income	$ 101.3	$ 116.1	$ 118.5	$ 99.2	$ 97.2	$ 130.1	$ 135.2	$ 107.8	435.1	470.3	612.8
Other comprehensive income (loss), net of tax									31.4	(89.5)	107.4
Comprehensive income									466.5	380.8	720.2
Less: Comprehensive loss attributable to non-controlling interests									(1.0)	(2.2)	2.7
Comprehensive income attributable to Penske Automotive Group common stockholders									467.5	383.0	717.5
Eliminations
Condensed consolidating statement of income
Equity in earnings of subsidiaries									(568.6)	(586.8)	(550.6)
Income from continuing operations before income taxes									(568.6)	(586.8)	(550.6)
Income taxes									150.5	130.3	(64.8)
Income from continuing operations									(418.1)	(456.5)	(615.4)
Income (loss) from discontinued operations, net of tax									(0.3)	(0.5)	0.2
Net income									(418.4)	(457.0)	(615.2)
Other comprehensive income (loss), net of tax									(20.1)	74.9	(97.5)
Comprehensive income									(438.5)	(382.1)	(712.7)
Less: Comprehensive loss attributable to non-controlling interests									0.3	1.5	(3.2)
Comprehensive income attributable to Penske Automotive Group common stockholders									(438.8)	(383.6)	(709.5)
Penske Automotive Group | Reportable legal entities
Condensed consolidating statement of income
Selling, general and administrative expenses									25.9	24.9	24.5
Depreciation									1.4	1.5	1.6
Operating income									(27.3)	(26.4)	(26.1)
Floor plan interest expense									(8.0)	(7.2)	(4.9)
Other interest expense									(83.4)	(77.8)	(73.5)
Equity in earnings of affiliates									142.3	129.5	102.8
Equity in earnings of subsidiaries									568.6	586.8	550.6
Income from continuing operations before income taxes									592.2	604.9	548.9
Income taxes									(156.7)	(134.3)	64.8
Income from continuing operations									435.5	470.6	613.7
Income (loss) from discontinued operations, net of tax									0.3	0.5	(0.2)
Net income									435.8	471.1	613.5
Other comprehensive income (loss), net of tax									31.4	(89.5)	107.4
Comprehensive income									467.2	381.6	720.9
Less: Comprehensive loss attributable to non-controlling interests									(0.3)	(1.5)	3.2
Comprehensive income attributable to Penske Automotive Group common stockholders									467.5	383.1	717.7
Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of income
Revenues									12,928.7	12,036.6	11,825.9
Cost of sales									10,909.5	10,130.4	9,945.0
Gross profit									2,019.2	1,906.2	1,880.9
Selling, general and administrative expenses									1,471.2	1,403.7	1,393.3
Depreciation									59.9	56.1	53.1
Operating income									488.1	446.4	434.5
Floor plan interest expense									(57.1)	(50.7)	(38.5)
Other interest expense									(12.6)	(8.8)	(8.9)
Income from continuing operations before income taxes									418.4	386.9	387.1
Income taxes									(116.9)	(88.6)	95.5
Income from continuing operations									301.5	298.3	482.6
Income (loss) from discontinued operations, net of tax									0.3	0.5	(0.2)
Net income									301.8	298.8	482.4
Comprehensive income									301.8	298.8	482.4
Comprehensive income attributable to Penske Automotive Group common stockholders									301.8	298.8	482.4
Non-Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of income
Revenues									10,250.7	10,748.5	9,561.0
Cost of sales									8,814.4	9,239.8	8,219.4
Gross profit									1,436.3	1,508.7	1,341.6
Selling, general and administrative expenses									1,196.1	1,217.7	1,098.2
Depreciation									48.3	46.1	40.4
Operating income									191.9	244.9	203.0
Floor plan interest expense									(19.4)	(23.0)	(20.0)
Other interest expense									(28.2)	(28.1)	(25.0)
Equity in earnings of affiliates									5.2	5.3	4.8
Income from continuing operations before income taxes									149.5	199.1	162.8
Income taxes									(33.6)	(41.7)	(30.7)
Income from continuing operations									115.9	157.4	132.1
Net income									115.9	157.4	132.1
Other comprehensive income (loss), net of tax									20.1	(74.9)	97.5
Comprehensive income									136.0	82.5	229.6
Less: Comprehensive loss attributable to non-controlling interests									(1.0)	(2.2)	2.7
Comprehensive income attributable to Penske Automotive Group common stockholders									$ 137.0	$ 84.7	$ 226.9