Investments (Concentrations of Credit Risk) (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
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	$ 53,529	$ 55,418
Concentrations of credit risk at fair value	41,172	44,082
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	4,346	3,912
Concentrations of credit risk at fair value	3,787	3,413
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	558	536
Concentrations of credit risk at fair value	529	510
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	1	1
Concentrations of credit risk at fair value	1	1
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	306	260
Concentrations of credit risk at fair value	306	260
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	52,952	54,863
Concentrations of credit risk at fair value	40,625	43,554
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	4,039	3,651
Concentrations of credit risk at fair value	3,480	3,152
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	19
Concentrations of credit risk at fair value	$ 18	$ 18