Fair Value of Financial Assets and Liabilities - Narrative (Details) - USD ($) $ in Millions |
Dec. 31, 2020 |
Dec. 31, 2019 |
|---|---|---|
| Fair Value Measurement Inputs and Valuation Techniques [Line Items] | ||
| Long-term debt | $ 7,609 | $ 7,365 |
| Level 2 | Estimate of Fair Value Measurement [Member] | ||
| Fair Value Measurement Inputs and Valuation Techniques [Line Items] | ||
| Long-term debt | $ 8,600 | $ 7,900 |