Investments - Components of Equity Realized Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Investments, Debt and Equity Securities [Abstract]
Total net gains (losses) recognized during the period on equity securities	$ 194.3	$ (96.2)	$ 586.6	$ 214.6
Less: Net gains (losses) recognized on equity securities sold during the period	(5.4)	(16.0)	(4.8)	215.1
Net holding period gains (losses) recognized during the period on equity securities held at period end	$ 199.7	$ (80.2)	$ 591.4	$ (0.5)