Tax Matters - Deferred Taxes - Footnotes (Details) - USD ($) $ in Millions |
12 Months Ended | |||||
|---|---|---|---|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
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| Income Tax Examination [Line Items] | ||||||
| Reduction for unrecognized tax benefit | $ 3,000 | $ 2,900 | ||||
| Net deferred tax liability | [1],[2] | 3,123 | 4,961 | |||
| Noncurrent Deferred Tax Assets And Other Noncurrent Tax Assets [Member] | ||||||
| Income Tax Examination [Line Items] | ||||||
| Net deferred tax liability | 900 | 700 | ||||
| Noncurrent Deferred Tax Liabilities [Member] | ||||||
| Income Tax Examination [Line Items] | ||||||
| Net deferred tax liability | $ 4,100 | $ 5,700 | ||||
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