Marketable Securities and Equity Investments - Available-for-Sale Debt Securities by Contractual Maturity (Details) - Total marketable available-for-sale debt securities - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Matures within one year	$ 1,338.0	$ 1,509.7
Matures after one year through five years	5,633.2	5,034.4
Matures after five years	89.6	73.5
Total	$ 7,060.8	$ 6,617.6