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Financial Instruments and Fair Value Measurements, Summary of available-for-sale debt securities (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2019
Available-for-sale debt securities, additional information [Abstract]      
Allowance for credit losses related to available-for-sale debt securities $ 0   $ 0
Proceeds from maturities and sales of available-for-sale securities and the related gross realized gains and losses [Abstract]      
Proceeds from maturities of available-for-sale debt securities 0 $ 308  
Proceeds from sales of available-for-sale debt securities 0 0  
Gross realized gains 0 0  
Gross realized losses 0 $ 0  
Available-for-sale debt securities continuous unrealized loss position [Abstract]      
Unrealized loss on available-for-sale debt securities in continuous unrealized loss position for less than twelve months 0   0
Unrealized loss on available-for-sale debt securities in continuous unrealized loss position for greater than twelve months 0   0
Bonds [Member]      
Available-for-sale debt securities [Abstract]      
Cost 159   162
Gross unrealized gains 1   0
Gross unrealized losses (3)   0
Fair value $ 157   $ 162
Bonds [Member] | Minimum [Member]      
Available-for-sale debt securities, additional information [Abstract]      
Investment maturity period 10 months    
Bonds [Member] | Maximum [Member]      
Available-for-sale debt securities, additional information [Abstract]      
Investment maturity period 42 months