Debt (Schedule of Principal Debt Outstanding) (Details) - USD ($) $ in Millions		Mar. 31, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Principal Outstanding		$ 5,652.3	$ 5,106.6
Unamortized Debt Issuance Costs		(38.6)	(36.6)
Unamortized Discount		2.2	2.5
Carrying Amount		5,611.5	5,067.5
Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Principal Outstanding	[1]	169.5	79.2
Unamortized Debt Issuance Costs	[1]	0.0	0.0
Unamortized Discount	[1]	0.0	0.0
Carrying Amount	[1]	169.5	79.2
Secured Financings [Member]
Debt Instrument [Line Items]
Principal Outstanding	[2]	4,474.5	4,019.0
Unamortized Debt Issuance Costs	[2]	(28.2)	(25.6)
Unamortized Discount	[2]	2.2	2.5
Carrying Amount	[2]	4,444.1	3,990.9
Senior Notes [Member]
Debt Instrument [Line Items]
Principal Outstanding		1,000.0	1,000.0
Unamortized Debt Issuance Costs		(10.4)	(11.0)
Unamortized Discount		0.0	0.0
Carrying Amount		989.6	989.0
Mortgages [Member]
Debt Instrument [Line Items]
Principal Outstanding		8.3	8.4
Unamortized Debt Issuance Costs		0.0	0.0
Unamortized Discount		0.0	0.0
Carrying Amount		8.3	8.4
Other Assets [Member]
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs		$ (3.8)	$ (4.2)

[1] Excludes deferred debt issuance costs of $3.8 million and $4.2 million as of March 31, 2024 and December 31, 2023, respectively, which are included in other assets.

[2] Warehouse facilities and Term ABS financings.