Investments (Concentrations of Credit Risk) (Details) - Foreign government - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Japan
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value, Concentration of Risk, Investments	$ 21,185	$ 24,295
Republic of Korea
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value, Concentration of Risk, Investments	5,460	5,887
MEXICO
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value, Concentration of Risk, Investments	$ 3,511	$ 3,463