Equity-Method Eligible Investments - Carrying Values of Equity Method Eligible Investments Recorded within Other Long-Term Investments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Investments in unconsolidated affiliates
Other long-term investments	$ 1,171.2	$ 856.3
Equity method eligible private equity securities, at fair value
Investments in unconsolidated affiliates
Other long-term investments	1,087.0	761.7
Other, at fair value
Investments in unconsolidated affiliates
Other long-term investments	$ 84.2	$ 94.6