Fair Value Disclosure Fair Value Disclosure - Other Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Recourse Fixed Rate Debt Fair Value Disclosure	$ 4,441.8	$ 3,933.4
Recourse Floating Rate Debt Fair Value Disclosure	419.1	522.7
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Recourse Fixed Rate Debt Fair Value Disclosure	4,631.6	3,836.0
Recourse Floating Rate Debt Fair Value Disclosure	$ 416.8	$ 515.1