Investments - Variable Interest Entity (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Variable Interest Entity
Total Assets	$ 27,394.2	$ 26,375.1
Total Liabilities	13,978.5	12,940.0
RMMC/RMBC
Variable Interest Entity
Total Assets	227.8	261.6
Total Liabilities	24.3	24.7
Other
Variable Interest Entity
Total Assets	3.5	2.8
Total Liabilities	$ 3.3	$ 3.3