Debt (Schedule of Principal Debt Outstanding) (Details) - USD ($) $ in Millions		Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Principal Outstanding		$ 4,865.4	$ 4,568.7
Unamortized Debt Issuance Costs		(27.6)	(29.1)
Unamortized Discount		0.0	(0.8)
Carrying Amount		4,837.8	4,538.8
Other Assets [Member]
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs		(2.8)	(3.2)
Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Principal Outstanding	[1]	79.9	0.0
Unamortized Debt Issuance Costs	[1]	0.0	0.0
Unamortized Discount	[1]	0.0	0.0
Carrying Amount	[1]	79.9	0.0
Secured financings [Member]
Debt Instrument [Line Items]
Principal Outstanding	[2]	3,974.4	3,355.6
Unamortized Debt Issuance Costs	[2]	(16.8)	(15.9)
Unamortized Discount	[2]	0.0	0.0
Carrying Amount	[2]	3,957.6	3,339.7
Senior Notes [Member]
Debt Instrument [Line Items]
Principal Outstanding		800.0	1,201.8
Unamortized Debt Issuance Costs		(10.8)	(13.2)
Unamortized Discount		0.0	(0.8)
Carrying Amount		789.2	1,187.8
Mortgages [Member]
Debt Instrument [Line Items]
Principal Outstanding		11.1	11.3
Unamortized Debt Issuance Costs		0.0	0.0
Unamortized Discount		0.0	0.0
Carrying Amount		$ 11.1	$ 11.3

[1] Excludes deferred debt issuance costs of $2.8 million and $3.2 million as of March 31, 2020 and December 31, 2019, respectively, which are included in other assets.

[2] Warehouse facilities and Term ABS.