Revenue Recognition - Contract with Customer, Asset and Liability (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jan. 01, 2018
Revenue from Contract with Customer [Abstract]
Customer receivables	$ 2,436	$ 2,504
Contract liabilities	716	623
Contract assets	352	255
Accounts receivable, gross	2,600	2,700
Allowance for doubtful accounts receivable	$ 153	$ 155

For unclassified balance sheet, amounts due from customers or clients for goods or services that have been delivered or sold in the normal course of business.

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- Definition

For an unclassified balance sheet, the amount due from customers or clients for goods or services that have been delivered or sold in the normal course of business, reduced to their estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

+ References

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For an unclassified balance sheet, a valuation allowance for receivables due a company that are expected to be uncollectible.

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- Definition

Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

+ References

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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as noncurrent.

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