Investments - Concentrations of Credit Risk - Industry Concentrations (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Insurance	16.00%
Electric utilities	10.00%
Banks	9.00%
Oil and natural gas pipelines	6.00%
Chemicals	5.00%
Transportation	4.00%
Telecommunications	4.00%
Food	3.00%
Diversified financial services	3.00%
Real estate investment trusts	3.00%
Percentage of invested assets rated below investment grade	2.00%
Par value of investments rated below investment grade	$ 646
Amortized cost of investments rated below investment grade	530
Fair value of investments rated below investment grade	459
Securities, cash, and short-term investments, amortized cost	1,000	$ 975
Securities, cash, and short-term investments, fair value	$ 983	$ 889