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Financial Instruments - Additional Information (Details) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Carrying Value    
Derivative Instruments, Gain (Loss)    
Long term debt, fair value $ 1,520 $ 1,520
Estimated Fair Value    
Derivative Instruments, Gain (Loss)    
Long term debt, fair value $ 1,550 $ 1,580