Derivative and Financial Instruments - Financial Instruments at cost plus accrued interest (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Cash and Cash Equivalents, carried at cost plus accrued interest	$ 2,788	$ 2,978
Short-term investments carried at cost plust accrued interest	3,812	3,320
Investments and long-term receivables carried at cost plus accrued interest	2	1
Cash [Member]
Schedule of Held-to-maturity Securities [Line Items]
Cash and Cash Equivalents, carried at cost plus accrued interest	636	597
Demand Deposits [Member]
Schedule of Held-to-maturity Securities [Line Items]
Cash and Cash Equivalents, carried at cost plus accrued interest	1,281	1,133
Time Deposits [Member] \| 1 to 90 days
Schedule of Held-to-maturity Securities [Line Items]
Cash and Cash Equivalents, carried at cost plus accrued interest	861	1,225
Short-term investments carried at cost plust accrued interest	3,625	2,859
Time Deposits [Member] \| 91 to 180 days
Schedule of Held-to-maturity Securities [Line Items]
Short-term investments carried at cost plust accrued interest	171	448
Time Deposits [Member] \| Within one year
Schedule of Held-to-maturity Securities [Line Items]
Short-term investments carried at cost plust accrued interest	16	13
Time Deposits [Member] \| One year through five years
Schedule of Held-to-maturity Securities [Line Items]
Investments and long-term receivables carried at cost plus accrued interest	2	1
Government obligations [Member] \| 1 to 90 days
Schedule of Held-to-maturity Securities [Line Items]
Cash and Cash Equivalents, carried at cost plus accrued interest	10	23
Short-term investments carried at cost plust accrued interest	$ 0	$ 0