Investments - Variable Interest Entity (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Variable Interest Entity
Total Assets	$ 26,635.3	$ 26,375.1
Total Liabilities	13,067.6	12,940.0
RMMC/RMBC
Variable Interest Entity
Total Assets	209.3	261.6
Total Liabilities	24.0	24.7
Other
Variable Interest Entity
Total Assets	3.7	2.8
Total Liabilities	$ 3.5	$ 3.3