Basis of Presentation and Nature of Operations - Narrative (Details) $ in Millions		3 Months Ended
	Jun. 28, 2019 USD ($) shares	Mar. 29, 2020 USD ($) segment site	Dec. 29, 2019 USD ($)	Jun. 30, 2019 a	Mar. 31, 2019 USD ($)	Dec. 30, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of reportable segments | segment		2
Salvage vehicle auction facilities | site		200
Acres of land per site | a				8,100
Issued and outstanding shares distributed to holders of record, percentage	100.00%
Subsidiary common stock, conversion rate | shares	1
Parent common stock, conversion rate | shares	1
Reduction to cash and cash equivalents		$ (86.1)	$ (47.1)
Reduction to other accrued expenses		$ (64.7)	$ (49.3)
Reclassification Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reduction to cash and cash equivalents					$ 10.4	$ 11.7
Reduction to other accrued expenses					$ 10.4	$ 11.7
Affiliated Entity
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Dividend paid to KAR	$ 1,278.0
Payments to settle intercompany debt	456.6
Payments for certain fixed assets	40.9
Payments to settle other intercompany accounts	$ 117.8