Fair Value Measurements - Reported (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 21,054	$ 18,070
SMR liability	90	92
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	19,800	18,511
SMR liability	$ 80	$ 86