Derivative and Financial Instruments - Financial Instruments at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	$ 9,833	$ 2,991
Short-term Investments	678	3,609
Investments and long-term receivables	8,058	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	110	13
Short-term Investments	196	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	260	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	113	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	184	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	110	13
Short-term Investments	69	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	0	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	6	13
U.S. Government Agency Obligations [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	2	0
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	8	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]
Short-term Investments	10	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	3	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	2	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	$ 59	$ 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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