Investments - Schedule of Gross Unrealized Losses by Unrealized Loss Position and Credit Quality (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Investment grade fixed income securities
Investments [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost, net	$ (331)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost, net	(22)
Total unrealized losses	(353)	$ (1,128)
Below investment grade fixed income securities
Investments [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost, net	(37)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost, net	(4)
Total unrealized losses	(41)	(102)
Fixed income securities
Investments [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost, net	(368)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost, net	(26)
Total unrealized losses	$ (394)	$ (1,230)