Debt (Schedule Of General Information Of Financing Transaction) (Details) (USD $)	9 Months Ended	12 Months Ended	15 Months Ended	12 Months Ended										6 Months Ended	12 Months Ended		15 Months Ended	3 Months Ended	6 Months Ended	12 Months Ended		15 Months Ended	12 Months Ended														12 Months Ended
	Dec. 31, 2013 Revolving Secured Line Of Credit [Member]	Dec. 31, 2013 Revolving Secured Line Of Credit [Member]	Mar. 31, 2013 Revolving Secured Line Of Credit [Member]	Dec. 31, 2013 Revolving Secured Line Of Credit [Member] LIBOR [Member]	Dec. 31, 2013 Revolving Secured Line Of Credit [Member] Prime Rate [Member]	Dec. 31, 2013 Warehouse Facility II [Member]		Dec. 31, 2013 Warehouse Facility II [Member] LIBOR [Member]		Dec. 31, 2013 Warehouse Facility III [Member]		Dec. 31, 2013 Warehouse Facility III [Member] LIBOR [Member]		Sep. 30, 2013 Warehouse Facility IV [Member]	Dec. 31, 2013 Warehouse Facility IV [Member]		Mar. 31, 2013 Warehouse Facility IV [Member]	Dec. 31, 2013 Warehouse Facility IV [Member] LIBOR [Member]	Sep. 30, 2013 Warehouse Facility IV [Member] LIBOR [Member]	Dec. 31, 2013 Warehouse Facility IV [Member] LIBOR [Member]		Mar. 31, 2013 Warehouse Facility IV [Member] LIBOR [Member]	Dec. 31, 2013 Term ABS 2011-1 [Member]		Dec. 31, 2013 Term ABS 2012-1 [Member]		Dec. 31, 2013 Term ABS 2012-2 [Member]		Dec. 31, 2013 Term ABS 2013-1 [Member]		Dec. 31, 2013 Term ABS 2013-2 [Member]		Dec. 31, 2013 2017 Senior Notes [Member]	Dec. 31, 2013 $250.0 Million Senior Notes [Member]		Feb. 01, 2010 $250.0 Million Senior Notes [Member]	Dec. 31, 2013 $100.0 Million Senior Notes [Member]		Mar. 03, 2011 $100.0 Million Senior Notes [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 2011-1	[1]	Credit Acceptance Funding LLC 2012-1	[1]	Credit Acceptance Funding LLC 2012-2	[1]	Credit Acceptance Funding LLC 2013-1	[1]	Credit Acceptance Funding LLC 2013-2	[1]	n/a
Close Date		Dec. 09, 2013
Close date, secured financings						Dec. 02, 2013	[1]			Aug. 16, 2013	[1]				Dec. 04, 2013	[1]							Oct. 06, 2011	[1]	Mar. 29, 2012	[1]	Sep. 20, 2012	[1]	Apr. 25, 2013	[1]	Oct. 31, 2013	[1]	Feb. 01, 2010	Feb. 01, 2010	[2]		Mar. 03, 2011	[2]
Maturity date	Jun. 23, 2016	Jun. 23, 2016	Jun. 22, 2015
Debt maturity date						Dec. 27, 2015	[1],[3]			Sep. 10, 2015	[1],[4]			Apr. 05, 2016	Apr. 05, 2016	[1],[3]	Feb. 19, 2014						Sep. 16, 2013	[1],[3]	Mar. 17, 2014	[1],[3]	Sep. 15, 2014	[1],[3]	Apr. 15, 2015	[1],[3]	Oct. 15, 2015	[1],[3]	Feb. 01, 2017
Financing Amount	$ 235,000,000	$ 235,000,000
Debt financing amount						$ 325,000,000	[1]			$ 75,000,000	[1]				$ 75,000,000	[1]							$ 200,500,000	[1]	$ 201,300,000	[1]	$ 252,000,000	[1]	$ 140,300,000	[1]	$ 197,800,000	[1]	$ 350,000,000	$ 250,000,000		$ 250,000,000	$ 100,000,000		$ 100,000,000
Basis spread on variable rate				1.875%	0.875%			2.00%	[1],[5]			1.60%	[1],[5]					2.00%	2.25%	2.00%	[1],[5]	2.75%

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

[2] The close dates associated with the issuance of $250.0 million and $100.0 million of the senior notes were on February 1, 2010 and March 3, 2011, respectively.

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

[4] 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.

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