Debt (Schedule Of General Information Of Financing Transaction) (Details) (USD $)	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended												3 Months Ended	6 Months Ended		6 Months Ended		6 Months Ended
	Mar. 31, 2012 Revolving Secured Line Of Credit [Member]	Jun. 30, 2012 Revolving Secured Line Of Credit [Member]	Mar. 31, 2012 Warehouse Facility II [Member]	Jun. 30, 2012 Warehouse Facility II [Member]		Jun. 30, 2012 Warehouse Facility III [Member]		Jun. 30, 2012 Warehouse Facility IV [Member]		Jun. 30, 2012 Term ABS 2010-1 [Member]		Jun. 30, 2012 Term ABS 2011-1 [Member]		Jun. 30, 2012 Term ABS 2012-1 [Member]		Jun. 30, 2012 Senior Notes [Member]	Jun. 30, 2012 Senior Notes [Member]	Mar. 03, 2011 Senior Notes [Member]	Jun. 30, 2012 $250.0 Million Senior Notes [Member]	Feb. 01, 2010 $250.0 Million Senior Notes [Member]	Jun. 30, 2012 $100.0 Million Senior Notes [Member]	Mar. 03, 2011 $100.0 Million Senior Notes [Member]	Jun. 30, 2012 LIBOR [Member] Revolving Secured Line Of Credit [Member]	Mar. 31, 2012 LIBOR [Member] Revolving Secured Line Of Credit [Member]	Jun. 30, 2012 LIBOR [Member] Warehouse Facility II [Member]		Jun. 30, 2012 LIBOR [Member] Warehouse Facility III [Member]		Jun. 30, 2012 LIBOR [Member] Warehouse Facility IV [Member]		Jun. 30, 2012 Prime Rate [Member] Revolving Secured Line Of Credit [Member]	Mar. 31, 2012 Prime Rate [Member] Revolving Secured Line Of Credit [Member]	Jun. 30, 2012 Commercial Paper Rate [Member] Warehouse Facility II [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary		n/a		CAC Warehouse Funding Corp. II	[1]	CAC Warehouse Funding III, LLC	[1]	CAC Warehouse Funding LLC IV	[1]	Credit Acceptance Funding LLC 2010-1	[1]	Credit Acceptance Funding LLC 2011-1	[1]	Credit Acceptance Funding LLC 2012-1	[1]		n/a
Close Date		Jun. 15, 2012
Close date, secured financings				Jun. 17, 2011	[1]	Jun. 29, 2012	[1]	Aug. 19, 2011	[1]	Nov. 04, 2010	[1]	Oct. 06, 2011	[1]	Mar. 29, 2012	[1]				Feb. 01, 2010		Mar. 03, 2011
Maturity Date	Jun. 22, 2014	Jun. 22, 2015
Debt maturity date			Sep. 10, 2013	Jun. 17, 2014	[1],[2]	Sep. 10, 2015	[1],[3]	Feb. 19, 2014	[1],[2]	Oct. 15, 2012	[1],[2]	Sep. 16, 2013	[1],[2]	Mar. 17, 2014	[1],[2]	Feb. 01, 2017	Feb. 01, 2017
Financing Amount	$ 205.0	$ 235,000,000
Debt financing amount				$ 325,000,000	[1]	$ 75,000,000	[1]	$ 75,000,000	[1]	$ 100,500,000	[1]	$ 200,500,000	[1]	$ 201,250,000	[1]	$ 350,000,000	$ 350,000,000	$ 100,000,000		$ 250,000,000		$ 100,000,000
Basis spread on variable rate																							1.875%	2.25%	3.75%	[1],[4],[5]	1.60%	[1],[5]	2.75%	[1],[5]	0.875%	1.25%	2.75%	[1],[4],[5]

[1] Financing made available only to a specified subsidiary of the Company.

[2] Represents the revolving maturity date.  The outstanding balance will amortize after the maturity date based on the cash flows of the pledged assets.

[3] Represents the revolving maturity date.  The outstanding balance will amortize after the revolving maturity date and any amounts remaining on September 10, 2017 will be due.

[4] The LIBOR rate is used if funding is not available from the commercial paper market.

[5] Interest rate cap agreements are in place to limit the exposure to increasing interest rates.