Summary of Quarterly Financial Data (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Data
Total revenues	$ 4,410.1	$ 4,381.4	$ 4,370.5	$ 4,015.2	$ 3,793.3	$ 3,724.6	$ 3,599.2	$ 3,326.8	$ 17,177.2	$ 14,443.9	$ 12,902.6
Gross profit	658.7	646.2	654.8	614.0	571.0	558.4	547.8	519.8	2,573.7	2,197.0	1,975.6
Net income	73.2	75.1	73.9	67.9	59.7	65.5	62.5	58.0	290.1	245.7	187.2
Net income attributable to Penske Automotive Group common stockholders	$ 71.8	$ 74.5	$ 72.9	$ 67.5	$ 59.2	$ 65.3	$ 62.0	$ 57.7	$ 286.7	$ 244.2	$ 185.5
Diluted earnings per share attributable to Penske Automotive Group common stockholders (in dollars per share)	$ 0.80	$ 0.83	$ 0.81	$ 0.75	$ 0.66	$ 0.72	$ 0.69	$ 0.64	$ 3.17	$ 2.70	$ 2.05