Debt Debt (Schedule of Principal Debt Outstanding) (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Principal Outstanding		$ 2,622.1	$ 2,086.3
Unamortized Debt Issuance Costs		16.8	16.8
Unamortized Discount		(1.6)	(1.7)
Debt Instrument, Carrying Amount		2,603.7	2,067.8
Other Assets [Member]
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs	[1]	2.4	2.2	[2]
Revolving Secured Line Of Credit [Member]
Debt Instrument [Line Items]
Principal Outstanding	[3]	0.0	57.7
Unamortized Debt Issuance Costs	[3]	0.0	0.0
Unamortized Discount	[3]	0.0	0.0
Debt Instrument, Carrying Amount	[3]	0.0	57.7
Secured financings [Member]
Debt Instrument [Line Items]
Principal Outstanding	[1]	2,072.1	1,478.6	[2]
Unamortized Debt Issuance Costs	[1]	9.7	8.5	[2]
Unamortized Discount	[1]	0.0	0.0	[2]
Debt Instrument, Carrying Amount	[1]	2,062.4	1,470.1	[2]
Senior Notes [Member]
Debt Instrument [Line Items]
Principal Outstanding		550.0	550.0	[2]
Unamortized Debt Issuance Costs		7.1	8.3	[2]
Unamortized Discount		(1.6)	(1.7)	[2]
Debt Instrument, Carrying Amount		$ 541.3	$ 540.0	[2]

[1] Warehouse facilities and Term ABS financings.

[2] Prior year amounts have been reclassified to reflect the adoption of ASU 2015-03, as amended by ASU No. 2015-15, which resulted in a reclassification of certain deferred debt issuance costs from other assets to secured financing and senior notes.

[3] Excludes deferred debt issuance costs of $2.4 million and $2.2 million as of December 31, 2016 and December 31, 2015, respectively, which are included in other assets.