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Fair Value Measurements - Carrying Value and Fair Value of Other Financial Instruments (Details) - USD ($)
$ in Millions
Sep. 30, 2019
Dec. 31, 2018
Carrying Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, including current maturities $ 4,098 $ 3,435
Level 2 [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, including current maturities 4,239 3,301
Level 2 [Member] | Valuation, Market Approach [Member] | Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, including current maturities $ 4,041 $ 2,826