Investments - Estimated Fair Values of Short and Long-Term Investments Classified by Date of Contractual Maturity (Details) $ in Millions	Mar. 31, 2024 USD ($)
Investments [Abstract]
One year or less	$ 1,743
One year through two years	437
Two years through three years	551
Three years through four years	29
Thereafter	4
Estimated Fair Value	$ 2,764