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Investments (Details) - Investment Information, Equity Securities - USD ($)
$ in Millions
9 Months Ended 12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Investment disclosure details      
Equity securities, cost $ 398   $ 387
Gross gains 116   78
Gross losses 5   12
Equity securities, at fair value 509   453
Net recognized gains (losses) on equity securities still held 45 $ (14)  
Public common stock [Member]      
Investment disclosure details      
Equity securities, cost 367   352
Gross gains 105   70
Gross losses 5   12
Equity securities, at fair value 467   410
Non-redeemable preferred stock [Member]      
Investment disclosure details      
Equity securities, cost 31   35
Gross gains 11   8
Gross losses 0   0
Equity securities, at fair value $ 42   $ 43