Loans Receivable (Write-Offs Segmented by Year of Assignment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Financing Receivable, Originated, More than Five Years before Current Fiscal Year, Writeoff	$ 225.4
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff	277.9
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff	208.9
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff	226.9
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff	271.3
Financing Receivable, Year One, Originated, Current Fiscal Year, Writeoff	80.0
Allowance for Loan and Lease Losses, Write-offs	0.0	$ 0.0	$ 0.0
Allowance for Credit Losses [Member]
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Allowance for Loan and Lease Losses, Write-offs	1,290.4	1,333.8	1,096.5
Dealer Loans [Member]
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Financing Receivable, Originated, More than Five Years before Current Fiscal Year, Writeoff	120.6
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff	101.3
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff	107.0
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff	107.2
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff	113.3
Financing Receivable, Year One, Originated, Current Fiscal Year, Writeoff	17.2
Allowance for Loan and Lease Losses, Write-offs	0.0	0.0	0.0
Dealer Loans [Member] | Allowance for Credit Losses [Member]
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Allowance for Loan and Lease Losses, Write-offs	566.6	433.4	286.2
Purchased Loans [Member]
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Financing Receivable, Originated, More than Five Years before Current Fiscal Year, Writeoff	104.8
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff	176.6
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff	101.9
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff	119.7
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff	158.0
Financing Receivable, Year One, Originated, Current Fiscal Year, Writeoff	62.8
Allowance for Loan and Lease Losses, Write-offs	0.0	0.0	0.0
Purchased Loans [Member] | Allowance for Credit Losses [Member]
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Allowance for Loan and Lease Losses, Write-offs	$ 723.8	$ 900.4	$ 810.3