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Investments (Equity Investments Without Readily Determinable Fair Values Assessed Under the Measurement Alternative) (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2020
Dec. 31, 2019
Other Investment Not Readily Marketable [Line Items]    
Equity investments without readily determinable fair values: $ 520 $ 514
Various Equity Investments Without Readily Determinable Fair Values    
Other Investment Not Readily Marketable [Line Items]    
Equity investments without readily determinable fair values: 6  
Equity securities without readily determinable fair value, increase (decrease) $ 9