Summary of Significant Accounting Policies - Contract Assets and Liabilities (Details) $ in Millions	Mar. 31, 2018 USD ($)
Schedule Of Contract Assets And Liabilities [Line Items]
Deferred customer acquisition costs	$ 85
Total accounts receivable, net	903
Unbilled revenues (included within Accounts receivable, net - Contracts with customers)	292
Deferred revenues	63
Accounts receivable, net - Contracts with customers
Schedule Of Contract Assets And Liabilities [Line Items]
Total accounts receivable, net	784
Accounts receivable, net - Leases
Schedule Of Contract Assets And Liabilities [Line Items]
Total accounts receivable, net	81
Accounts receivable, net - Derivative instruments
Schedule Of Contract Assets And Liabilities [Line Items]
Total accounts receivable, net	$ 38

[Line Items] for Schedule Of Contract Assets And Liabilities [Table]

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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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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
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- Definition

Amount, after accumulated amortization and accumulated impairment loss, of asset recognized from cost incurred to obtain or fulfill contract with customer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
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-Section 50
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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

Unbilled amounts due for services rendered or to be rendered, actions taken or to be taken, or a promise to refrain from taking certain actions in accordance with the terms of a legally binding agreement between the entity and, at a minimum, one other party. An example would be amounts associated with contracts or programs where the recognized revenue for performance thereunder exceeds the amounts billed under the terms thereof as of the date of the balance sheet.

+ References

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