Auto Loans Receivable - Components Of Receivables, Net Of Allowances For Expected Credit Losses (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024	Dec. 31, 2023
Receivables [Abstract]
Total auto loans receivable	$ 2,020.0	$ 1,103.8
Accrued interest and fees	12.8	8.2
Deferred loan origination costs	10.4	4.2
Less: unearned discounts	(0.3)	(4.3)
Less: allowances for expected credit losses	(89.0)	(54.8)	$ (46.3)
Auto loans receivable, net	$ 1,953.9	$ 1,057.1