Basis of Presentation - Narrative (Details) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
	Jun. 28, 2019 USD ($) shares	Dec. 29, 2019 segment	Sep. 29, 2019 segment	Dec. 29, 2019 USD ($) segment	Dec. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of reportable segments | segment		2	1	2
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
Dividend paid to KAR				$ 1,278.0	$ 0.0	$ 0.0
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