Summary of Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Data
Total 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
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
Net income	328.6	94.3	106.9	83.0	82.7	88.5	95.0	80.2	612.8	346.4	330.4
Net income attributable to Penske Automotive Group common stockholders	$ 330.1	$ 94.4	$ 106.2	$ 82.6	$ 82.6	$ 87.5	$ 93.5	$ 79.3	$ 613.3	$ 342.9	$ 326.1
Diluted earnings per share attributable to Penske Automotive Group common stockholders (in dollars per share)	$ 3.85	$ 1.10	$ 1.23	$ 0.96	$ 0.97	$ 1.03	$ 1.10	$ 0.90	$ 7.14	$ 3.99	$ 3.63