Investments - Variable Interest Entity (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Variable Interest Entity
Total Assets	$ 28,675.3	$ 28,859.8
Total Liabilities	14,899.7	15,186.7
RMMC/RMBC
Variable Interest Entity
Total Assets	220.6	207.4
Total Liabilities	17.5	17.9
Other
Variable Interest Entity
Total Assets	86.2	65.3
Total Liabilities	$ 16.0	$ 20.8