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Acquisitions and Dispositions - Assets Sold - Textual (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2017
Barossa Project [Member] \| Asia Pacific Operating segment [Member] \| Operating Segments [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Before tax gain (loss) on disposition	$ 200,000,000
Barossa Project [Member] \| Asia Pacific Operating segment [Member] \| Operating Segments [Member] \| Scenario, Plan [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Proceeds from asset dispositions			$ 200,000,000
Foster Creek Christina Lake (FCCL) and western Canada gas properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Before tax gain (loss) on disposition	$ 26,000,000	$ 0
Business Combination, Contingent Consideration Arrangements, Basis for Amount	The contingent payment, calculated on a quarterly basis, is $6 million CAD for every $1 CAD by which the WCS quarterly average crude price exceeds $52 CAD per barrel. Contingent payments during the five-year period are recorded as gain on dispositions on our consolidated income statement and reflected in our Canada segment.
Foster Creek Christina Lake (FCCL) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Equity interest of ConocoPhillips				50.00%