Exit or Disposal Cost Obligations (Details) - AutoNation Collision Parts Closure - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Liability for Exit or Disposal Costs [Rollforward]
Costs Incurred		$ 36.7
Contract Termination Charges, Other Associated Closing Costs, and Involuntary Termination Benefits
Liability for Exit or Disposal Costs [Rollforward]
Liability for exit or disposal costs, beginning balance	$ 3.4
Costs Incurred	0.0
Costs paid or otherwise settled	(3.3)
Liability for exit or disposal costs, ending balance	0.1	3.4
Contract Termination Charges
Liability for Exit or Disposal Costs [Rollforward]
Liability for exit or disposal costs, beginning balance	0.2
Costs Incurred	0.0
Costs paid or otherwise settled	(0.2)
Liability for exit or disposal costs, ending balance	0.0	0.2
Other Associated Closing Costs
Liability for Exit or Disposal Costs [Rollforward]
Liability for exit or disposal costs, beginning balance	2.4
Costs Incurred	0.0
Costs paid or otherwise settled	(2.4)
Liability for exit or disposal costs, ending balance	0.0	2.4
Involuntary Termination Benefits
Liability for Exit or Disposal Costs [Rollforward]
Liability for exit or disposal costs, beginning balance	0.8
Costs Incurred	0.0
Costs paid or otherwise settled	(0.7)
Liability for exit or disposal costs, ending balance	$ 0.1	$ 0.8