Financial Instruments - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Long-term debt [Member] - USD ($) $ in Millions |
Dec. 31, 2020 |
Dec. 31, 2019 |
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|---|---|---|---|---|
| Derivative [Line Items] | ||||
| Carrying Amount of Hedged Assets Liabilities | [1] | $ 2,016 | $ 7,092 | |
| Cumulative Amount of Fair Value Hedging Adjustment Increase/(Decrease) to Carrying Amount, Active Hedging Relationships, Liability | 117 | 266 | ||
| Cumulative Amount of Fair Value Hedging Adjustment Increase/(Decrease) to Carrying Amount, Discontinued Hedging Relationships, Liability | $ 1,149 | $ 690 | ||
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