Sale of Norway Assets (Narrative) (Details) $ in Billions	12 Months Ended
Dec. 31, 2019 USD ($)
Sale of Norway Assets [Abstract]
Disposal Group, Including Discontinued Operation, Segment that Includes Disposal Group	upstream
Disposal Group, Not Discontinued Operation, Name	non-operated upstream assets in Norway
Agreed sales price of non-operated upstream assets	$ 4.5
Disposal Group, Including Discontinued Operation, Description and Timing of Disposal	December 10, 2019
2019 cash proceeds from divestment	$ 3.1
Estimated refund of income tax payments, due to sale	0.6
Estimated cash proceeds in future periods associated with deferred consideration	0.3
Disposal Group Disposed Of By Sale Not Discontinued Operations [Member] \| Nonoperated Upstream Assets In Norway [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
After tax gain on sale of non-operated upstream assets	3.7
Disposal Group Disposed Of By Sale Not Discontinued Operations [Member] \| Other Income Related To Norway Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Before tax gain on sale of non-operated upstream assets	2.7
Disposal Group Disposed Of By Sale Not Discontinued Operations [Member] \| Income Taxes Related To Norway Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Tax related to sale of non-operated upstream assets	$ 1.0

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