Fair Value Disclosure (Details 3) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Carrying Amount [Member]
Liabilities
Recourse fixed rate debt	$ 3,933.4	$ 3,971.2
Recourse floating rate debt	522.7	426.0
Estimate of Fair Value Measurement [Member]
Liabilities
Recourse fixed rate debt	3,836.0	4,089.1
Recourse floating rate debt	515.1	428.7
Not Designated as Hedging Instrument [Member] \| Other Expense [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	$ (2.2)	$ 8.0	$ (2.6)

The portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(1),(2)
-URI http://asc.fasb.org/extlink&oid=109977999&loc=d3e76258-113986

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration