Summary of Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Data
Total 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
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
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
Net income	97.2	130.1	135.2	107.8	328.6	94.3	106.9	83.0	470.3	612.8	346.4
Net income attributable to Penske Automotive Group common stockholders	$ 98.1	$ 130.2	$ 134.6	$ 108.1	$ 330.1	$ 94.4	$ 106.2	$ 82.6	$ 471.0	$ 613.3	$ 342.9
Diluted earnings per share attributable to Penske Automotive Group common stockholders:
Income from continuing operations per share (in dollars per share)	$ 1.15	$ 1.53	$ 1.58	$ 1.26	$ 3.85	$ 1.10	$ 1.23	$ 0.97	$ 5.52	$ 7.14	$ 4.00
Net income per share (in dollars per share)	$ 1.16	$ 1.53	$ 1.58	$ 1.26	$ 3.85	$ 1.10	$ 1.23	$ 0.96	$ 5.53	$ 7.14	$ 3.99