Debt (Schedule of Principal Debt Outstanding) (Details) - USD ($) $ in Millions		Sep. 30, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Principal Outstanding		$ 4,968.5	$ 4,616.5
Unamortized Debt Issuance Costs		(25.0)	(22.4)
Unamortized Discount		2.7	3.4
Carrying Amount		4,940.8	4,590.7
Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Principal Outstanding	[1]	102.1	30.9
Unamortized Debt Issuance Costs	[1]	0.0	0.0
Unamortized Discount	[1]	0.0	0.0
Carrying Amount	[1]	102.1	30.9
Secured Financings [Member]
Debt Instrument [Line Items]
Principal Outstanding	[2]	4,057.9	3,776.7
Unamortized Debt Issuance Costs	[2]	(21.0)	(16.9)
Unamortized Discount	[2]	2.7	3.4
Carrying Amount	[2]	4,034.2	3,756.4
Senior Notes [Member]
Debt Instrument [Line Items]
Principal Outstanding		800.0	800.0
Unamortized Debt Issuance Costs		(4.0)	(5.5)
Unamortized Discount		0.0	0.0
Carrying Amount		796.0	794.5
Mortgages [Member]
Debt Instrument [Line Items]
Principal Outstanding		8.5	8.9
Unamortized Debt Issuance Costs		0.0	0.0
Unamortized Discount		0.0	0.0
Carrying Amount		8.5	8.9
Other Assets [Member]
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs		$ (4.6)	$ (3.9)

[1] Excludes deferred debt issuance costs of $4.6 million and $3.9 million as of September 30, 2023 and December 31, 2022, respectively, which are included in other assets.

[2] Warehouse facilities and Term ABS financings.