Investments - Concentrations of Credit Risk - Industry Concentrations (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Insurance	16.00%
Electric utilities	10.00%
Banks	7.00%
Oil and natural gas pipelines	6.00%
Chemicals	5.00%
Transportation	4.00%
Real estate investment trusts	4.00%
Food	4.00%
Oil and natural gas exploration and production	4.00%
Telecommunications	3.00%
Percentage of invested assets rated below investment grade	3.00%
Par value of investments rated below investment grade	$ 795
Amortized cost of investments rated below investment grade	702
Fair value of investments rated below investment grade	783
Securities, cash, and short-term investments, amortized cost	969	$ 892
Securities, cash, and short-term investments, fair value	$ 1,100	$ 1,100