Debt Debt (Schedule of Principal Debt Outstanding) (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs		$ (29.1)	$ (20.5)
Unamortized Discount		(0.8)	(1.1)
Debt Instrument, Carrying Amount		4,538.8	3,820.9
Debt Instrument, Principal Outstanding		4,568.7	3,842.5
Other Assets [Member]
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs	[1]	(3.2)	(2.9)
Revolving Secured Line Of Credit [Member]
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs	[2]	0.0	0.0
Unamortized Discount	[2]	0.0	0.0
Debt Instrument, Carrying Amount	[2]	0.0	171.9
Debt Instrument, Principal Outstanding	[2]	0.0	171.9
Secured financings [Member]
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs	[1]	(15.9)	(16.0)
Unamortized Discount	[1]	0.0	0.0
Debt Instrument, Carrying Amount	[1]	3,339.7	3,092.7
Debt Instrument, Principal Outstanding	[1]	3,355.6	3,108.7
Senior Notes [Member]
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs		(13.2)	(4.5)
Unamortized Discount		(0.8)	(1.1)
Debt Instrument, Carrying Amount		1,187.8	544.4
Debt Instrument, Principal Outstanding		1,201.8	550.0
Mortgage [Member]
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs		0.0	0.0
Unamortized Discount		0.0	0.0
Debt Instrument, Carrying Amount		11.3	11.9
Debt Instrument, Principal Outstanding		$ 11.3	$ 11.9

[1] Warehouse facilities and Term ABS.

[2] Excludes deferred debt issuance costs of $3.2 million and $2.9 million as of December 31, 2019 and December 31, 2018, respectively, which are included in other assets.