Investments (Concentrations of Credit Risk) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Investments in Japanese government and government agency securities:
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	$ 55,561	$ 63,132
Concentrations of credit risk at fair value	50,757	62,017
Investments in Brazil government and government agency securities:
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	3,128	3,455
Concentrations of credit risk at fair value	2,806	3,419
Assets supporting experience-rated contractholder liabilities | Investments in Japanese government and government agency securities:
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	477	522
Concentrations of credit risk at fair value	460	514
Short-term investments | Investments in Brazil government and government agency securities:
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	28	0
Concentrations of credit risk at fair value	28	0
Cash equivalents | Investments in Brazil government and government agency securities:
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	232	427
Concentrations of credit risk at fair value	232	427
Fixed maturities, available-for-sale | Fixed maturities | Investments in Japanese government and government agency securities:
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	55,067	62,591
Concentrations of credit risk at fair value	50,280	61,484
Fixed maturities, available-for-sale | Fixed maturities | Investments in Brazil government and government agency securities:
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	2,825	3,028
Concentrations of credit risk at fair value	2,505	2,992
Fixed maturities, trading | Fixed maturities | Investments in Japanese government and government agency securities:
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	17	19
Concentrations of credit risk at fair value	17	19
Fixed maturities, trading | Fixed maturities | Investments in Brazil government and government agency securities:
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	43	0
Concentrations of credit risk at fair value	$ 41	$ 0