Restricted Securities Available for Sale (Schedule of Restricted Securities Available for Sale by Aging Category) (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Restricted Securities Available For Sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 40.4	$ 8.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.3	0.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	3.9	6.7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	0.1
Debt Securities, Available-for-sale, Unrealized Loss Position	44.3	14.7
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0.3	0.1
Corporate Bond Securities [Member]
Restricted Securities Available For Sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	15.7	1.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.1	0.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1.5	4.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	0.1
Debt Securities, Available-for-sale, Unrealized Loss Position	17.2	5.2
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0.1	0.1
US Government and Agency Securities [Member]
Restricted Securities Available For Sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	20.7	6.9
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.2	0.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1.5	1.4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	0.0
Debt Securities, Available-for-sale, Unrealized Loss Position	22.2	8.3
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0.2	0.0
Asset-backed Securities [Member]
Restricted Securities Available For Sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	4.0	0.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0.9	1.2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	0.0
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 4.9	$ 1.2

CREDIT ACCEPTANCE CORP 10-Q