Commitments - Extended Warranty Liability (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Deferred revenue:
Current portion	$ 11,541		$ 11,035
Noncurrent portion	3,617		$ 3,600
Extended Warranty Liability (Deferred Income)
Movement in extended warranty liability
Beginning Balance	531	$ 538
Revenue deferred for new extended warranty contracts	125	122
Amortization of deferred revenue	(137)	(134)
Other	12	9
Ending Balance	532	535
Deferred revenue:
Current portion	231	241
Noncurrent portion	$ 300	$ 294

Amount of other changes to deferred revenue during the period, including foreign currency translation adjustments.

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Amount of deferred revenue as of balance sheet date. Deferred revenue represents collections of cash or other assets related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

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Amount of deferred revenue recognized for transactions arising during the current reporting period. Deferred revenue is a liability as of the balance sheet date related to a revenue producing activity for which revenue has not yet been recognized. Generally, an Entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

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The carrying amount of consideration received or receivable as of the balance sheet date on potential earnings that were not recognized as revenue in conformity with GAAP, and which are expected to be recognized as such within one year or the normal operating cycle, if longer, including sales, license fees, and royalties, but excluding interest income.

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The noncurrent portion of deferred revenue amount as of balance sheet date. Deferred revenue is a liability related to a revenue producing activity for which revenue has not yet been recognized, and is not expected to be recognized in the next twelve months. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

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Amount of revenue recognized that was previously reported as deferred or unearned revenue.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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