Supplemental Quarterly Financial Information (Supplementary Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Selected Quarterly Financial Information [Abstract]
Revenues	$ 1,210	$ 861	$ 1,083	$ 1,289	$ 822	$ 979	$ 364	$ 753	$ 4,443	$ 2,918	$ 4,422
Impairments							484	912		1,396	6,473
Operating Income (Loss)	262	(4)	321	489	(54)	128	(912)	(1,043)	1,068	(1,881)	(6,301)
(Gain) Loss on Divestitures, net	(1)	406		(1)	(3)	395	(2)		404	390	14
Net Earnings (Loss) Before Income Tax	147	522	327	434	(251)	379	(1,068)	(680)	1,430	(1,620)	(8,010)
Income tax expense (Recovery)	376	228	(4)	3	30	62	(467)	(301)	603	(676)	(2,845)
Net Earnings (Loss)	$ (229)	$ 294	$ 331	$ 431	$ (281)	$ 317	$ (601)	$ (379)	$ 827	$ (944)	$ (5,165)
Net Earnings (Loss) per Common Share - Basic & Diluted	$ (0.24)	$ 0.30	$ 0.34	$ 0.44	$ (0.29)	$ 0.37	$ (0.71)	$ (0.45)	$ 0.85	$ (1.07)	$ (6.28)

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Amount of gain (loss) on sale or disposal of assets, including but not limited to property plant and equipment, intangible assets and equity in securities of subsidiaries or equity method investee.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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