Fair Value Disclosure Fair Value Disclosure - Other Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total	$ 11.9	$ 40.0
Short-Term Investments	0.0	148.5
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Recourse Fixed Rate Debt Fair Value Disclosure	6,553.4	6,045.1
Recourse Floating Rate Debt Fair Value Disclosure	316.3	417.8
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Recourse Fixed Rate Debt Fair Value Disclosure	5,723.7	5,309.8
Recourse Floating Rate Debt Fair Value Disclosure	$ 316.3	$ 417.0