Amount of adjustment to U.S. deferred taxes due to U.S. tax rate change resulted from 2017 U.S. Tax Reform.

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The correction of an error related to prior vear valuation allowance.

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The amount of taxing authority proposed additional income tax and penalty for prior years.

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Amount of reasonable estimate for income tax expense (benefit) from effect of 2017 U.S. Tax Reform for which accounting for tax effect is incomplete.

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

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of tax benefit from exercise of stock options granted under share-based compensation arrangement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to revisions of previously reported income tax expense (benefit).

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Amount of cash outflow for pension and other postretirement benefits. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree.

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Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset.

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Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended		12 Months Ended
Income Taxes (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Estimated annual effective tax rate (as a percent)		24.00%	32.00%
Adjustment to U.S. Deferred Tax Rate change 2017 U.S. Tax Reform Amount		$ 154
U.S. 2017 tax reform estimated impact				$ 2,371
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%		35.00%
Correction of Prior Year Valuation Allowance		$ 59		$ (17)	$ (33)	$ (9)
Tax benefit for settlement of stock-based compensation awards		52	$ 45
Valuation allowance increase (decrease)		(25)
Prior year tax adjustment expense (benefit)			$ 15
Tax Year Prior Years
Income Tax Contingency
Income tax examination, proposed liability increase/(decrease)	$ 2,300	$ 2,300
Discretionary contribution
Income Tax Disclosure [Abstract]
Contributions to pension and other postretirement benefit plans	$ 1,000