Revenue Recognition - Practical Expedient (Details) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($)
Revenue Recognition
Practical expedient, disclosure of performance obligation	true
Contract with Customer, Asset and Liability
Revenue recognized included in deferred revenue	$ 327

Indicates (true false) whether optional exemption was applied not to disclose amount of transaction price allocated to and explanation of expected timing of revenue recognition for remaining performance obligation, when contract has expected duration of one year or less or right to consideration corresponds directly to performance completed.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130558-203045

Name:	us-gaap_RevenuePracticalExpedientRemainingPerformanceObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:booleanItemType
Balance Type:	na
Period Type:	duration