Investments - Investment Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Investment Gains (Losses) [Abstract]
Investment gains (losses) recognized due to the change in fair value of non-redeemable preferred stock included within equity securities held	$ (46)	$ (10)	$ (55)	$ (32)
Nonredeemable Preferred Stock
Investment Gains (Losses) [Abstract]
Investment gains (losses) recognized due to the change in fair value of non-redeemable preferred stock included within equity securities held	6	1	4	12
Fixed maturity securities
Investment Gains (Losses) [Abstract]
Gross gains	5	13	18	27
Gross losses	(53)	(25)	(75)	(71)
Investment gains (losses) recognized due to the change in fair value of non-redeemable preferred stock included within equity securities held	(48)	(12)	(57)	(44)
Equity securities
Investment Gains (Losses) [Abstract]
Investment gains (losses) recognized due to the change in fair value of non-redeemable preferred stock included within equity securities held	6	1	6	12
Short-term investments and other
Investment Gains (Losses) [Abstract]
Investment gains (losses) recognized due to the change in fair value of non-redeemable preferred stock included within equity securities held	$ (4)	$ 1	$ (4)