Investments - Other Investments Carrying Values (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Equity Securities at Modified Cost	$ 32.6	$ 38.4
Convertible Securities at Fair Value	0.0	43.3
Real Estate at Depreciated Cost	94.7	93.6
Mortgage Loans	99.8	91.1
Other	14.8	3.5
Total Investments	$ 241.9	$ 269.9	[1]

[1] As of January 1, 2023, the Company adopted ASU 2018-12 using the modified retrospective method applied as of the transition date of January 1, 2021. Prior period amounts in the financial statements have been recast to reflect application of the new guidance. See Note 2 to the Consolidated Financial Statements for additional information.