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Investments and Fair Value Measurement - Change In Equity Securities (Details) - USD ($)
$ in Millions
Jun. 30, 2021
Dec. 31, 2020
Fair Value Disclosures [Abstract]    
Initial cost basis $ 628 $ 6,282
Upward adjustments 0 1,984
Downward adjustments (including impairment) (36) (1,690)
Total carrying value at the end of the period $ 592 $ 6,576