Supplementary Information for Certain Balance Sheet Accounts - Deferred Revenue and Accrued Expenses (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accounts payable, accrued liabilities and deferred income	$ 679	$ 772
Discretionary compensation	242	313
Accrued compensation	326	439
Accrued vacation	132	93
Other employee-related liabilities	86	94
Total deferred revenue and accrued expenses	$ 1,465	$ 1,711

Amount of obligations incurred classified as other, payable within one year or the normal operating cycle, if longer.

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-Name Accounting Standards Codification
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-SubTopic 10
-Section 45
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Aggregate carrying value as of the balance sheet date of the liabilities for deferred compensation arrangements payable within one year (or the normal operating cycle, if longer). Represents currently earned compensation under cash arrangements (such as a profit-sharing plan, rabbi trust, and employee contract--excluding equity-based arrangements) that is not actually paid until a later date.

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-Section 25
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Total of the carrying values as of the balance sheet date of obligations incurred through that date and payable for obligations related to services received from employees, such as accrued salaries and bonuses, payroll taxes and fringe benefits. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Amount of the liabilities, classified as other, for deferred compensation arrangements payable within one year or the operating cycle, if longer.

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Amount of obligations incurred for employer-related costs classified as other, payable within one year or the normal operating cycle, if longer.

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Deferred Revenue and Accrued Liabilities, Current

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