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Investments - Narrative: Equity Method Investments (Details) - USD ($)
$ in Millions
3 Months Ended
Sep. 30, 2021
Mar. 31, 2023
Mar. 31, 2022
Dec. 31, 2022
Fair Value Measured at Net Asset Value Per Share | Limited Partnership        
Net Investment Income [Line Items]        
Alternative investments   $ 268   $ 249
Unfunded additional commitments   160    
Net gains (losses) from limited partnership investments   $ 20 $ (160)  
Neumora Therapeutics, Inc.        
Net Investment Income [Line Items]        
Ownership percentage 25.90% 24.50%   24.90%
Aggregate cost $ 257      
Cash payment 100      
Noncash consideration $ 157      
Fair value of investments   $ 288   $ 335
Change in carrying value   $ 47 $ 50