Restructuring and Other Charges - Schedule of Restructuring and Other Charges (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring And Related Activities [Abstract]
Settlements and/or curtailments related to retirement benefits			$ 331	$ 8	$ 17
Allowance on value-added tax credits			107
Power contract payments – non-recurring			62	244
Asset impairments			18	40	155
Asset retirement obligations			5	10	97
Environmental remediation			2	8	26
Layoff costs			2	15	15
Legal matter in Italy				(22)
Other			48	49	44
Reversals of previously recorded layoff and other costs			(48)	(43)	(36)
Restructuring and other charges	$ 138	$ 297	$ 527	$ 309	$ 318

Power contract expenses, non-recurring.

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Restructuring charges legal settlement.

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Reversals of previously recorded layoff and other costs.

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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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Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

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Amount of gain (loss) recognized in net periodic benefit (cost) credit from event reducing expected years of future service of present employees or eliminating accrual of defined benefits for some or all future services of present employees.

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A credit or adjustment for government or taxing authority authorized decrease in taxes owed as a result of meeting certain tax policy conditions.

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Amount of other expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses associated with a discontinued operation or an asset retirement obligation.

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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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Amount of expenses for special or contractual termination benefits provided to current employees involuntarily terminated under a benefit arrangement associated exit or disposal activities pursuant to an authorized plan. Excludes expenses related to one-time termination benefits, a discontinued operation or an asset retirement obligation.

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