Investment Securities - Investment Gains (Losses) for Level 3 (Details) - Other long-term investments - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Gain (Loss) on Securities [Line Items]
Total net unrealized investment gains recognized during the period on Level 3 investments held at the end of period	$ 39.6	$ 49.2	$ 126.6	$ 89.9
Level 3
Gain (Loss) on Securities [Line Items]
Total net unrealized investment gains recognized during the period on Level 3 investments held at the end of period	$ 42.0	$ 31.3	$ 103.6	$ 82.6