v3.19.3.a.u2
Cover Page - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Feb. 18, 2020
Jun. 28, 2019
Document Information [Line Items]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2019    
Document Transition Report false    
Entity File Number 001-38434    
Entity Registrant Name Dropbox, Inc.    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 26-0138832    
Entity Address, Address Line One 1800 Owens Street    
Entity Address, City or Town San Francisco    
Entity Address, State or Province CA    
Entity Address, Postal Zip Code 94158    
City Area Code 415    
Local Phone Number 857-6800    
Title of 12(b) Security Class A Common Stock, par value $0.00001 per share    
Trading Symbol DBX    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     $ 5,833.9
Documents Incorporated by Reference Portions of the registrant's definitive Proxy Statement relating to the 2020 Annual Meeting of Stockholders are incorporated herein by references in Part II and Part III of this Annual Report on Form 10-K to the extent stated herein. Such Proxy Statement will be filed with the Securities and Exchange Commission within 120 days of the registrant's fiscal year ended December 31, 2019.    
Entity Central Index Key 0001467623    
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2019    
Document Fiscal Period Focus FY    
Amendment Flag false    
Class A Common Stock      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   258,155,253  
Class B Common Stock      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   160,699,326  
Class C Common Stock      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   0