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Financial Instruments - Fair Value Measurements, Additional Information (Details) - USD ($)
$ in Millions
Sep. 30, 2021
Dec. 31, 2020
Carrying Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions    
Long-term debt, fair value $ 1,900 $ 1,520
Estimated Fair Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions    
Long-term debt, fair value $ 1,940 $ 1,550