Investments - Variable Interest Entity (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Variable Interest Entity
Total Assets	$ 26,568.4	$ 25,868.3
Total Liabilities	13,080.4	12,953.1
RMMC/RMBC
Variable Interest Entity
Total Assets	250.3	228.2
Total Liabilities	20.4	21.2
Other
Variable Interest Entity
Total Assets	5.2	43.3
Total Liabilities	$ 3.0	$ 16.1