Document and Entity Information - $ / shares	3 Months Ended
	Mar. 31, 2020	Apr. 30, 2020	Dec. 31, 2019
Cover [Abstract]
Document type	10-Q
Document quarterly report	true
Document period end date	Mar. 31, 2020
Document transition report	false
Commission file number	001-34568
Entity registrant name	KAR Auction Services, Inc.
Entity incorporation state	DE
Entity tax identification number	20-8744739
Entity address, address line one	11299 N. Illinois Street
Entity address, city	Carmel
Entity address, state	IN
Entity address, postal zip code	46032
City area code	800
Local phone number	923-3725
Title of 12(b) security	Common Stock, par value $0.01 per share
Trading symbol	KAR
Security exchange name	NYSE
Entity interactive data current	Yes
Entity current reporting status	Yes
Entity filer category	Large Accelerated Filer
Entity small business	false
Entity emerging growth company	false
Entity shell company	false
Entity common stock, shares outstanding		129,175,792
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01
Entity central index key	0001395942
Current fiscal year end date	--12-31
Document fiscal year focus	2020
Document fiscal period focus	Q1
Amendment flag	false