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Fair Value Measurements - Narrative (Details) - USD ($)
$ in Millions
Sep. 30, 2020
Dec. 31, 2019
Sep. 30, 2019
Fair Value Disclosures [Abstract]      
Estimated fair value of long-term debt $ 2,980 $ 3,000 $ 2,840
Carrying value of long-term debt $ 2,900 $ 2,900 $ 2,900