- Fair Value of Debt Table (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	$ 10,161	$ 7,787
Quoted Prices in Active Markets (Level 1) | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt, fair value	0	381
Long-term debt, fair value	3,321	3,495
Quoted Prices in Active Markets (Level 1) | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt, fair value	0	379
Long-term debt, fair value	3,126	3,173
Significant Other Observable Inputs (Level 2) | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	6,380	3,846
Significant Other Observable Inputs (Level 2) | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	$ 6,060	$ 3,644