Investment in Cenovus Energy - Gains and Losses Recorded in Other Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Debt and Equity Securities, FV-NI [Line Items]
Total net gain (loss) on CVE common shares			$ 743	$ (1,302)
Cenovus Energy Inc [Member]
Debt and Equity Securities, FV-NI [Line Items]
Total net gain (loss) on CVE common shares	$ 17	$ (162)	743	(1,302)
Less: Net gain on equity securities sold during the period	(50)	0	177	0
Unrealized gain (loss) on equity securities still held at the reporting date	$ 67	$ (162)	$ 566	$ (1,302)