Discontinued Operations - Reported in Consolidated Statements of Income and Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Consolidated Statements of Income
Impairments		$ 24	$ 75	$ 229
Cash Flow from Discontinued Operations
Net increase in cash and cash equivalents of discontinued operations		$ 0	$ 0	130
Canadian Business [Member]
Consolidated Statements of Income
Impairments	$ 6,600
Canadian Business [Member] | Discontinued Operations, Disposed of by Sale [Member]
Consolidated Statements of Income
Total revenue and other income				431
Net loss on disposal of assets				(43)
Total revenues and other income				388
Production				254
Depreciation, depletion and amortization				40
Impairments				6,636
Other				25
Total costs and expenses				6,955
Pretax loss from discontinued operations				(6,567)
Benefit for income taxes				(1,674)
Loss from discontinued operations				(4,893)
Cash Flow from Discontinued Operations
Operating activities				141
Investing activities				(13)
Changes in cash included in current assets held for sale				2
Net increase in cash and cash equivalents of discontinued operations				$ 130