Equity Method Investees (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity Method Investment
Equity method investments		$ 336.4	$ 352.8
Condensed income statement information
Revenues		6,770.3	6,620.1	$ 6,177.0
Gross margin		2,396.8	2,181.4	2,043.5
Net income		398.5	357.2	304.0
Equity in net income of affiliates		39.3	40.8	$ 30.7
Condensed balance sheet information
Current assets		1,069.0	1,242.0
Noncurrent assets		10,197.3	9,230.8
Total assets		11,266.3	10,472.8
Current liabilities		851.9	958.1
Noncurrent liabilities		8,105.5	7,276.8
Equity		2,308.9	2,237.9
Total liabilities and equity		$ 11,266.3	10,472.8
The Nix Group
Equity Method Investment
Ownership percentage of Equity Method Investment		50.00%
Ibericar Keldinich SL
Equity Method Investment
Ownership percentage of Equity Method Investment		50.00%
Penske Commercial Leasing Australia
Equity Method Investment
Ownership percentage of Equity Method Investment		45.00%
Penske Vehicle Services
Equity Method Investment
Ownership percentage of Equity Method Investment		31.00%
National Powersport Auctions
Equity Method Investment
Ownership percentage of Equity Method Investment		7.00%
Max Cycles
Equity Method Investment
Ownership interest sold (as a percent)	50.00%
Penske Truck Leasing Co., L.P. ("PTL")
Equity Method Investment
Equity method investments		$ 290.6	279.5
Limited partnership interest (as a percent)		9.00%
Nix Group, Ibericar Keldinich SL, Penske Commercial Leasing Australia, Penske Vehicle Services and National Powersport Auctions
Equity Method Investment
Equity method investments		$ 45.8
Jacobs Group, Nix Group, Ibericar Keldinich SL, Penske Wynn Ferrari Maserati, Penske Commercial Leasing Australia, Penske Vehicle Services and National Powersport Auctions
Equity Method Investment
Equity method investments			$ 73.3
German Automotive Dealership Group
Equity Method Investment
Ownership acquired (as a percentage)	10.00%	10.00%
Ownership interest (as a percent)		60.00%