Business Combinations - Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Summary of unaudited consolidated pro forma results of operations
Revenues	$ 7,695.3	$ 7,657.6	$ 22,980.8	$ 23,365.0
Net income attributable to Penske Automotive Group common stockholders	$ 213.0	$ 226.6	$ 708.0	$ 692.9
Net income per diluted common share (in dollars per share)	$ 3.23	$ 3.39	$ 10.67	$ 10.35