Debt (Schedule Of General Information Of Financing Transaction) (Details) - USD ($)				12 Months Ended
		Mar. 30, 2015	Jan. 22, 2014	Dec. 31, 2019		Dec. 31, 2018
Revolving Secured Line Of Credit [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary				n/a
Debt maturity date				Jun. 22, 2022
Financing Amount				$ 340,000,000.0
Revolving Secured Line Of Credit [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				18750.00%
Revolving Secured Line Of Credit [Member] | Prime Rate [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				8750.00%
Warehouse Facility II [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			CAC Warehouse Funding Corp. II
Debt maturity date	[2]			Jul. 12, 2022
Debt financing amount				$ 400,000,000.0	[3]	$ 400,000,000.0
Warehouse Facility II [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				17500.00%
Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			CAC Warehouse Funding LLC IV
Debt maturity date	[2]			Jul. 26, 2022
Debt financing amount				$ 300,000,000.0	[3]	250,000,000.0
Warehouse Facility IV [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				20000.00%
Warehouse Facility V [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			CAC Warehouse Funding LLC V
Debt maturity date	[4]			Aug. 17, 2021
Debt financing amount				$ 100,000,000.0	[3]	100,000,000.0
Warehouse Facility V [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				19000.00%
Warehouse Facility VI [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			CAC Warehouse Funding LLC VI
Debt maturity date	[2]			Sep. 30, 2022
Debt financing amount				$ 75,000,000.0
Warehouse Facility VI [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				20000.00%
Warehouse Facility VII [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			CAC Warehouse Funding LLC VII
Debt maturity date	[5]			Dec. 16, 2021
Debt financing amount				$ 150,000,000.0	[3]	150,000,000.0
Warehouse Facility VII [Member] | Commercial Paper Offered Rate [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				20000.00%
Warehouse Facility VIII [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			CAC Warehouse Funding LLC VIII
Debt maturity date	[2]			Jul. 26, 2022
Debt financing amount	[3]			$ 200,000,000.0
Warehouse Facility VIII [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				19000.00%
Term ABS 2016-1 [Member]
Debt Instrument [Line Items]
Debt financing amount						$ 125,300,000
Term ABS 2016-3 [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			Credit Acceptance Funding LLC 2016-3
Debt maturity date	[2]			Oct. 15, 2018
Debt financing amount				$ 350,000,000.0
Term ABS 2017-1 [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			Credit Acceptance Funding LLC 2017-1
Debt maturity date	[2]			Feb. 15, 2019
Debt financing amount				$ 350,000,000.0
Term ABS 2017-2 [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			Credit Acceptance Funding LLC 2017-2
Debt maturity date	[2]			Jun. 17, 2019
Debt financing amount				$ 450,000,000.0
Term ABS 2017-3 [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			Credit Acceptance Funding LLC 2017-3
Debt maturity date	[2]			Oct. 15, 2019
Debt financing amount				$ 350,000,000.0
Term ABS 2018-1 [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			Credit Acceptance Funding LLC 2018-1
Debt maturity date	[2]			Feb. 17, 2020
Debt financing amount				$ 500,000,000.0
Term ABS 2018-2 [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			Credit Acceptance Funding LLC 2018-2
Debt maturity date	[2]			May 15, 2020
Debt financing amount				$ 450,000,000.0
Term ABS 2018-3 [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			Credit Acceptance Funding LLC 2018-3
Debt maturity date	[2]			Aug. 17, 2020
Debt financing amount				$ 398,300,000
Term ABS 2019-1 [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			Credit Acceptance Funding LLC 2019-1
Debt maturity date	[2]			Feb. 15, 2021
Debt financing amount				$ 402,500,000
Term ABS 2019-2 [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			Credit Acceptance Funding LLC 2019-2
Debt maturity date	[6]			Aug. 15, 2022
Debt financing amount				$ 500,000,000.0
Term ABS 2019-3 [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			Credit Acceptance Funding LLC 2019-3
Debt maturity date	[2]			Nov. 15, 2021
Debt financing amount				$ 351,700,000
2021 Senior Notes [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary				n/a
Debt maturity date			Feb. 15, 2021	Feb. 15, 2021	[7]
Debt financing amount			$ 300,000,000.0	$ 151,800,000
2023 Senior Notes [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary				n/a
Debt maturity date		Mar. 15, 2023		Mar. 15, 2023	[7]
Debt financing amount		$ 250,000,000.0		$ 250,000,000.0
2024 Senior Notes [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary				n/a
Debt maturity date				Dec. 31, 2024
Debt financing amount				$ 400,000,000.0
2026 Senior Notes [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary				n/a
Debt maturity date				Mar. 15, 2026
Debt financing amount				$ 400,000,000.0
Mortgage [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[2]			Chapter 4 Properties, LLC
Debt maturity date				Aug. 06, 2023
Debt financing amount				$ 12,000,000.0
Mortgage [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				15000.00%

[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 revolving maturity date based on the cash flows of the pledged assets.

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

[4] Represents the revolving maturity date. The outstanding balance will amortize after the revolving maturity date and any amounts remaining on August 17, 2023 will be due on that date.

[5] Represents the revolving maturity date. The outstanding balance will amortize after the revolving maturity date and any amounts remaining on December 16, 2023 will be due on that date.

[6] Represents the revolving maturity date. The Company has the option to redeem and retire the indebtedness after the revolving maturity date. If we do not elect this option, the outstanding balance will amortize based on the cash flows of the pledged assets.

[7] On January 17, 2020, we used a portion of the net proceeds from the 2024 senior notes to redeem the remaining $151.8 million outstanding principal amount of the 2021 senior notes. We intend to use the remaining net proceeds from the 2024 senior notes, together with borrowings under our revolving credit facility and cash on hand to the extent available, to redeem in full the $250.0 million outstanding principal amount of the 2023 senior notes on or around March 15, 2020.