Loans Receivable (Schedule of Loans Receivable) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 5,780.1	$ 5,498.1	$ 5,049.0	$ 4,637.7	$ 4,474.0	$ 4,207.0
Allowance for credit losses	(435.7)	(448.4)	(429.4)	(354.1)	(338.0)	(320.4)
Loans receivable, net	5,344.4		4,619.6
Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	3,918.4	3,773.5	3,518.1	3,385.3	3,326.5	3,209.0
Allowance for credit losses	(365.9)	(379.3)	(366.0)	(336.9)	(323.8)	(309.3)
Loans receivable, net	3,552.5		3,152.1
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	1,861.7	1,724.6	1,530.9	1,252.4	1,147.5	998.0
Allowance for credit losses	(69.8)	$ (69.1)	(63.4)	$ (17.2)	$ (14.2)	$ (11.1)
Loans receivable, net	$ 1,791.9		$ 1,467.5

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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