Fair Value Disclosure Fair Value Disclosure - Other Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Recourse Fixed Rate Debt Fair Value Disclosure	$ 5,056.3	$ 4,389.3
Recourse Floating Rate Debt Fair Value Disclosure	299.9	417.5
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Recourse Fixed Rate Debt Fair Value Disclosure	5,696.9	4,644.6
Recourse Floating Rate Debt Fair Value Disclosure	$ 300.4	$ 419.0