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Equity Securities - (Summary of Investments in Marketable Equity Securities) (Detail) - USD ($)
$ in Millions
Jun. 30, 2022
Dec. 31, 2021
Schedule Of Trading Securities And Other Trading Assets [Line Items]    
Equity securities, Cost $ 390 $ 435
Equity securities, Unrealized gains (losses) 2 222
Equity securities, Estimated fair value 392 657
Preferred Stock    
Schedule Of Trading Securities And Other Trading Assets [Line Items]    
Equity securities, Cost 16 17
Equity securities, Unrealized gains (losses) (2) 0
Equity securities, Estimated fair value 14 17
Common Stock    
Schedule Of Trading Securities And Other Trading Assets [Line Items]    
Equity securities, Cost 374 418
Equity securities, Unrealized gains (losses) 4 222
Equity securities, Estimated fair value $ 378 $ 640