Sonic Automotive, Inc. Annual report pursuant to Section 13 and 15(d)

Business Acquisitions and Dispositions - Additional Information (Detail) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2014 Franchise	Dec. 31, 2015 USD ($) Dealerships Franchise	Dec. 31, 2014 USD ($) Dealerships Franchise	Dec. 31, 2013 Dealerships	Mar. 31, 2014 Franchise
Business Acquisition [Line Items]
Number of franchise acquired		0
Purchase price for franchise operations and underlying assets, including real estate, acquired \| $			$ 50.9
Number of dealerships held for sale		0			0
Number of franchises disposed	2	4	9	0
Cash generated from disposition \| $		$ 8.0	$ 74.8
Luxury Franchise [Member]
Business Acquisition [Line Items]
Number of franchise acquired			2
Mid-line Import Franchise [Member]
Business Acquisition [Line Items]
Number of franchise acquired			1
Domestic Franchise [Member]
Business Acquisition [Line Items]
Number of franchise acquired			1