Investments (Concentrations of Credit Risk) (Details) - Foreign government - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Japan
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value, Concentration of Risk, Investments	$ 24,968	$ 24,295
Republic of Korea
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value, Concentration of Risk, Investments	6,015	5,887
MEXICO
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value, Concentration of Risk, Investments	$ 3,904	$ 3,463