Fair Value Measurements - Schedule of Fair Value of Investment Assets (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized cost basis	$ 705	$ 95
Fair Value \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments fair value disclosure	706	95
Fair Value \| Level 2 \| Certificates of Deposit and Commercial Paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments fair value disclosure	610	0
Fair Value \| Level 2 \| Corporate Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments fair value disclosure	56	61
Fair Value \| Level 2 \| Government Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments fair value disclosure	$ 40	$ 34

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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- Definition

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.

+ References

No definition available.

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- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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