Investments (Concentrations of Credit Risk) (Details) - Foreign government - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Japan
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value, Concentration of Risk, Investments	$ 21,688	$ 22,606
Republic of Korea
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value, Concentration of Risk, Investments	6,654	6,411
MEXICO
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value, Concentration of Risk, Investments	$ 3,651	$ 3,778