Investments (Concentrations of Credit Risk) (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
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	$ 61,259	$ 56,947
Concentrations of credit risk at fair value	52,001	51,657
Investments in Brazilian government and government agency securities:
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	3,753	3,027
Concentrations of credit risk at fair value	3,307	2,521
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	562	472
Concentrations of credit risk at fair value	548	462
Short-term investments \| Investments in Brazilian government and government agency securities:
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	2	2
Concentrations of credit risk at fair value	2	2
Cash equivalents \| Investments in Brazilian government and government agency securities:
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	109	228
Concentrations of credit risk at fair value	109	228
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	60,678	56,457
Concentrations of credit risk at fair value	51,434	51,177
Fixed maturities, available-for-sale \| Fixed maturities \| Investments in Brazilian government and government agency securities:
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	3,568	2,753
Concentrations of credit risk at fair value	3,125	2,251
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	19	18
Concentrations of credit risk at fair value	19	18
Fixed maturities, trading \| Fixed maturities \| Investments in Brazilian government and government agency securities:
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	74	44
Concentrations of credit risk at fair value	$ 71	$ 40