Summary of Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Data
Total revenues	$ 5,881.4	$ 5,967.6	$ 5,755.8	$ 5,564.4	$ 5,439.3	$ 5,658.6	$ 5,940.3	$ 5,746.9
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
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
Net income	101.3	116.1	118.5	99.2	97.2	130.1	135.2	107.8	435.1	470.3	612.8
Net income attributable to Penske Automotive Group common stockholders	$ 101.6	$ 116.2	$ 117.8	$ 100.2	$ 98.1	$ 130.2	$ 134.6	$ 108.1	$ 435.8	$ 471.0	$ 613.3
Diluted earnings per share attributable to Penske Automotive Group common stockholders:
Income from continuing operations per share (in dollars per share)	$ 1.25	$ 1.42	$ 1.42	$ 1.19	$ 1.15	$ 1.53	$ 1.58	$ 1.26	$ 5.28	$ 5.52	$ 7.14
Net income per share (in dollars per share)	$ 1.25	$ 1.42	$ 1.42	$ 1.19	$ 1.16	$ 1.53	$ 1.58	$ 1.26	$ 5.28	$ 5.53	$ 7.14