Investments (Concentrations of Credit Risk) (Details) - Foreign government - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Japan
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value, Concentration of Risk, Investments	$ 20,960	$ 22,606
Republic of Korea
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value, Concentration of Risk, Investments	6,007	6,411
MEXICO
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value, Concentration of Risk, Investments	$ 3,765	$ 3,778