Debt - Fair Value of Debt (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 0	$ 8,531
Liabilities subject to compromise	8,643	0
Carrying amount | Fair value, inputs, level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	0	385
Long-term debt	0	753
Liabilities subject to compromise	982	0
Carrying amount | Fair value, inputs, level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	0	8,320
Liabilities subject to compromise	6,184	0
Estimated fair value | Fair value, inputs, level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	0	360
Long-term debt	0	622
Liabilities subject to compromise	43	0
Estimated fair value | Fair value, inputs, level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	0	6,085
Liabilities subject to compromise	$ 1,694	$ 0