Loans Receivable - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forecast changes	$ 138.5	$ (206.5)	$ 2.6	$ (43.6)	$ 32.3
Certain Loans Acquired In Transfer Accounted For As Loans Accretable Yield Reclassifications From Nonaccretable Difference Forecast Changes, By Percentage				2.30%
Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forecast changes	39.5		(4.2)	$ (36.5)	(0.3)
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forecast changes	99.0		$ 6.8	$ (7.1)	$ 32.6
Forecast Changes [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forecast changes	(44.3)
COVID-19 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forecast changes	$ (162.2)