Segment Informations (Details 3) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue from external customers by product type
Total revenues	$ 4,921.3	$ 4,960.1	$ 4,920.6	$ 4,482.9	$ 4,425.6	$ 4,396.7	$ 4,384.5	$ 4,025.2	$ 19,284.9	$ 17,232.0	$ 14,482.5
Retail Automotive | Operating segments
Revenue from external customers by product type
Total revenues									17,896.3	16,657.5	14,329.9
Retail Automotive | Operating segments | New vehicle
Revenue from external customers by product type
Total revenues									9,208.9	8,698.8	7,528.2
Retail Automotive | Operating segments | Used vehicle
Revenue from external customers by product type
Total revenues									5,425.5	4,971.1	4,201.3
Retail Automotive | Operating segments | Finance and insurance, net
Revenue from external customers by product type
Total revenues									478.3	436.0	370.4
Retail Automotive | Operating segments | Service and parts
Revenue from external customers by product type
Total revenues									1,830.7	1,716.9	1,531.7
Retail Automotive | Operating segments | Fleet and wholesale
Revenue from external customers by product type
Total revenues									952.9	834.7	$ 698.3
Retail Commercial Truck Dealership | Operating segments
Revenue from external customers by product type
Total revenues									944.1	125.6
Retail Commercial Truck Dealership | Operating segments | New vehicle
Revenue from external customers by product type
Total revenues									572.5	78.7
Retail Commercial Truck Dealership | Operating segments | Used vehicle
Revenue from external customers by product type
Total revenues									58.7	9.5
Retail Commercial Truck Dealership | Operating segments | Finance and insurance, net
Revenue from external customers by product type
Total revenues									6.7	0.9
Retail Commercial Truck Dealership | Operating segments | Service and parts
Revenue from external customers by product type
Total revenues									286.0	33.9
Retail Commercial Truck Dealership | Operating segments | Lease, rental and wholesale
Revenue from external customers by product type
Total revenues									$ 20.2	$ 2.6