Investments (Concentrations of Credit Risk) (Details) - Foreign government - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Japan
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value, Concentration of Risk, Investments	$ 18,845	$ 18,886
Republic of Korea
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value, Concentration of Risk, Investments	6,323	6,078
MEXICO
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value, Concentration of Risk, Investments	$ 3,841	$ 3,468