Investments (Concentrations of Credit Risk) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
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	$ 63,132	$ 66,537
Concentrations of credit risk at fair value	62,017	66,396
Investments in Brazil government and government agencies securities
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	3,455	2,534
Concentrations of credit risk at fair value	3,419	2,281
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	522	613
Concentrations of credit risk at fair value	514	587
Short-term Investments | Investments in Brazil government and government agencies securities
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	0	60
Concentrations of credit risk at fair value	0	61
Cash equivalents | Investments in Brazil government and government agencies securities
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	427	210
Concentrations of credit risk at fair value	427	210
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	62,591	65,198
Concentrations of credit risk at fair value	61,484	64,959
Fixed maturities, available-for-sale | Fixed maturities | Investments in Brazil government and government agencies securities
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Concentrations of credit risk at amortized cost	3,028	2,264
Concentrations of credit risk at fair value	2,992	2,010
Fixed maturities, held-to-maturity | 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	0	706
Concentrations of credit risk at fair value	0	831
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	20
Concentrations of credit risk at fair value	$ 19	$ 19