Debt (Schedule of Principal Debt Outstanding) - USD ($) $ in Millions		Mar. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Principal Outstanding		$ 4,762.5	$ 4,642.7
Unamortized Debt Issuance Costs		(23.5)	(26.4)
Carrying Amount		4,739.0	4,616.3
Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Principal Outstanding	[1]	104.7	2.6
Unamortized Debt Issuance Costs	[1]	0.0	0.0
Carrying Amount	[1]	104.7	2.6
Secured Financings [Member]
Debt Instrument [Line Items]
Principal Outstanding	[2]	3,848.4	3,830.4
Unamortized Debt Issuance Costs	[2]	(16.0)	(18.9)
Carrying Amount	[2]	3,832.4	3,811.5
Senior Notes [Member]
Debt Instrument [Line Items]
Principal Outstanding		800.0	800.0
Unamortized Debt Issuance Costs		(7.5)	(7.5)
Carrying Amount		792.5	792.5
Mortgages [Member]
Debt Instrument [Line Items]
Principal Outstanding		9.4	9.7
Unamortized Debt Issuance Costs		0.0	0.0
Carrying Amount		9.4	9.7
Other Assets [Member]
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs		$ (3.2)	$ (3.6)

[1] Excludes deferred debt issuance costs of $3.2 million and $3.6 million as of March 31, 2022 and December 31, 2021, respectively, which are included in other assets.

[2] Warehouse facilities and Term ABS.