Fair Value Measurements - Reported (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 20,560	$ 19,800
SMR liability	79	80
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	18,352	21,054
SMR liability	$ 77	$ 90