Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Number of days from period end	2 days
Long-term debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 11,608	$ 10,767
Carrying value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, Long-term and Short-term, Combined Amount	10,329	10,348
Level 1 | Long-term debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	8,219	6,726
Level 2 | Long-term debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	3,389	4,041
Level 3 | Long-term debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 0	$ 0