Description of Business and Significant Accounting Policies - Summary of Amounts Capitalized and Amortized (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Capitalized deferred commission costs	$ 8	$ 24
Amortized deferred commission costs	$ 2	$ 3

Amount of amortization expense for asset recognized from cost incurred to obtain or fulfill contract with customer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131252-203054

Name:	us-gaap_CapitalizedContractCostAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration