Derivative and Financial Instruments - Financial Instruments at fair value (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	$ 2,831	$ 2,991
Short-term Investments	4,104	3,609
Investments and long-term receivables	8,286	8,017
Remaining maturities within one year [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	43	13
Short-term Investments	292	289
Remaining Maturities Greater Than One Year Through Eight Years [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Schedule Of Available For Sale Securities [Line Items]
Investments and long-term receivables	217	216
Corporate Bonds [Member] \| Remaining maturities within one year [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	0	0
Short-term Investments	114	130
Corporate Bonds [Member] \| Remaining Maturities Greater Than One Year Through Eight Years [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Schedule Of Available For Sale Securities [Line Items]
Investments and long-term receivables	151	143
Commercial Paper [Member] \| Remaining maturities within one year [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	43	13
Short-term Investments	162	155
U.S. Government Obligations [Member] \| Remaining maturities within one year [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	0	0
Short-term Investments	3	4
U.S. Government Obligations [Member] \| Remaining Maturities Greater Than One Year Through Eight Years [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Schedule Of Available For Sale Securities [Line Items]
Investments and long-term receivables	7	13
U.S. Government Agency Obligations [Member] \| Remaining Maturities Greater Than One Year Through Eight Years [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Schedule Of Available For Sale Securities [Line Items]
Investments and long-term receivables	10	17
Foreign government obligations [Member] \| Remaining maturities within one year [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	43	13
Short-term Investments	13	0
Foreign government obligations [Member] \| Remaining Maturities Greater Than One Year Through Eight Years [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Schedule Of Available For Sale Securities [Line Items]
Investments and long-term receivables	0	2
Asset-backed Securities [Member] \| Remaining maturities within one year [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments	0	0
Asset-backed Securities [Member] \| Remaining Maturities Greater Than One Year Through Eight Years [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Schedule Of Available For Sale Securities [Line Items]
Investments and long-term receivables	$ 49	$ 41

Amount of investments including trading securities, held-to-maturity securities, and short-term investments classified as other and current but excluding investement in Cenovus Energy Common Shares.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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